Jones Flashcards
(274 cards)
1
Q
What does viviparous mean, what organisms are?
A
- prod smaller eggs that dev in vivo and give birth to live young
- mammals
2
Q
What does the HPG axis inc?
A
- multiple endocrine glands working together as a system to reg dev, reproduction and ageing in animals
- inc hypothalamus, anterior pituitary and testes/ovaries
3
Q
Where is the hypothalamus?
A
- component of forebrain, part of diencephalon
4
Q
What is the role of the hypothalamus?
A
- reg many of core body functions (homeostatic) –> eg. metabolism, growth, reprod, stress (lots of these things can influence on each other)
5
Q
How is the hypothalamus in contact w/ the anterior pituitary gland?
A
- joined by infundibulum
6
Q
Importantly, what does the hypothalamus gland secrete?
A
- the peptide hormone, gonadotropin releasing hormone (GnRH)
7
Q
What are the 2 distinct lobes of pituitary gland and how do they arise?
A
- anterior and posterior
- derived from sep cell types during embryogenesis, diff functions
8
Q
What hormones made in body are synthesised by the anterior pituitary?
A
- gonadotrophs: FSH (follicle-stimulating hormone) and LH (luteinising hormone)
- also others: thyrotropes, somatotropes, corticotrophs, lactotropes
9
Q
How and where does GnRH travel from the hypothalamus?
A
- in portal blood (= blood ds of hypothalamus) to anterior pituitary where it acts on gonadotrophs
10
Q
How is GnRH reg?
A
- +vely reg by GnRH signalling through GPCR (GnRHr)
11
Q
How big is GnRH?
A
- 10AA short polypeptide
12
Q
What do gonadotrophs secrete?
A
- FSH and LH
13
Q
What are FSH and LH?
A
- both heterodimeric glycoprotein hormones
14
Q
What is the 1°androgen in males?
A
- testosteron
15
Q
What are the roles of inhibin/activin?
A
- have inhibitory/activatory roles on hormone prod respectively
16
Q
What are the 3 main types of sex steroids?
A
- progestogens, androgens and oestrogens
17
Q
What are all sex steroids derived from?
A
- common precursor = cholesterol
18
Q
How does interconversion of sex steroids occur?
A
- via biosynthetic network, enz defects at single point in network can have far reaching effects (ie. if defect in A –> B get less B and more A than want, and both can cause problems)
19
Q
What can determine the effects of sex hormones?
A
- levels in blood
- rate of breakdown
- levels of binding to binding partners
- levels of receptors –> may not have to change levels of hormones to have effects, instead having more receptors on certain cell types can increase effects
20
Q
What happens once sex hormones inside cell?
A
- steroid receptor complexes bind to steroid response elements on DNA and impact on transcrip
21
Q
What happens in gonadotroph cell when oestrogen binds receptor (ER)?
A
- hormone receptor complex translocates to nucleus and mediates -ve transcrip control of target genes through oestrogen response elements (EREs)
- some control at level of pituitary and some at level of hypothalamus, even some at testes/ovaries level
- male and female gonadal cells express inhibins and activins
- bind to inhibin and activin receptors on gonadotroph cell and act to reg FSH/LH expression
22
Q
What fam are inhibins and activins members of?
A
- TGF-β fam
23
Q
How is the HPG axis reg in females?
A
- DIAG*
- FSH/LH predom reg by secretory products from ovary (feedback control mech to stop levels of LH and FSH getting too high)
- -> -ve feedback: oestrogens, progestogens and inhibins exert depressant effect on gonadotropin output
- -> +ve feedback: activin, oestradiol causes LH surge
- low concs oestradiol acts to -vely reg LH exp, but at high levels +vely regs exp
- progesterone also has 2 effects:
- -> high conc seen in luteal phase of menstrual cycle (after ovulation) enhances -ve feedback of oestradiol
- -> at certain levels, +ve feedback effect blocked
- inhibins selectively -vely reg FSH secretion
24
Q
When does the LH surge occur, and why?
A
- immed before fertilisation, so essential for ovulation
25
How does the hypothalamus reg HPG axis?
- by changing amplitude or freq of GnRH
26
How are gonadotropins reg in males?
* DIAG*
- v similar mechanisms to females in relation to hypothalamic and pituitary reg
- but absence of signif +ve feedback --> as don’t need cycle, just continuous prod
- Leydig cells secrete androgens
- exerts -ve feedback response which causes decrease in GnRH
- as in females, inhibin acts at level of pituitary to suppress FSH secretion
27
How is GnRH secreted?
- pulsatile release (approx 1 per hr), begins at puberty, pulse generator resides in hypothalamus
28
How is it known that GnRH is essential for gonadal function?
- destruction of GnRH neurons, gen of genetically null GnRH mico, or immunisation against GnRH peptide all result in gonadal atrophy
29
How are anterior pituitary hormones released?
- also released in pulsatile manner on post-pubertal humans
| - v little released before puberty
30
How are alts in output of LH and FSH achieved?
- increasing or decreasing amplitude or freq of GnRH pulses
| - modulating response of gonadotrophs to pulses
31
What is the role of kisspeptin?
- master player in control of reprod
| - binds GPR54 receptor (or KISS1R) found in GcRH neurons --> potent GnRH stim
32
What is the structure of kisspeptin 1 and what encodes it?
- 54 AA neuropeptide
| - encoded by KISS1
33
What is leptin, and what cells prod it?
- peptide hormone
| - prod by adipocytes
34
What is the role of leptin?
- key role in activating HPG axis at puberty --> may be via KISS1 or by alternative route
- good marker of metabolic state
35
How can weight affect puberty?
- lean female athletes can have delayed puberty onset or lack of menstrual cycle
- obesity can cause early onset of puberty
36
Can weight affect fertility?
- yes, relationship between fertility and both ends of weight spectrum
37
In what way is puberty metabolically gated?
- many peripheral hormones and central transmitters involved in sensing metabolic state
38
How do leptins and kisspeptins interplay in controlling puberty onset?
- kisspeptins are essential upstreams regulators of GnRH neurons
- leptin necessary for puberty to proceed --> but not sole req
- leptin acts on GnRH neurons indirectly (via other neurons)
- some evidence suggests leptin acts via kiss1 neurons
- other evidence suggests kisspeptin indep signalling
- during puberty hypothalamic kiss1 system undergoes extensive and complex activation --> essential for correct timing of puberty
39
What is spermatogenesis?
- prod of spermatozoa (mature male gametes) from spermatogonial stem cells
40
What do the testes house?
- seminiferous tubules (highly coiled) --> site of spermatogenesis
41
What is the role of epididymis?
- sperm storage and maturation
42
What is the role of the vas deferens?
- transport of sperm from epididymis to urethra during ejaculation
43
What is the role of the seminal vesicle?
- prod mucus secretion which aids mobility of sperm
44
What is the role of the prostate gland?
- prod alkaline secretion that neutralises acidity of any urine in urethra and aids mobility of sperm
45
What is the role of the urethra?
- tube carrying urine and sperm out of body
46
What are the 2 main (overlapping) functions of the testes?
- prod androgens and other hormones for sexual differentiation and 2° sexual characteristics
- prod spermatozoa for sexual reprod, occurs in seminiferous tubules w/ maturation in epididymis
47
What is the structure of testes?
- in each lobe highly coiled network of tubules, lined w/ seminiferous epithelium --> site of spermatogenesis
- stroma consisting of blood vessels, lymph and leydig cells
48
What is the role of Leydig cells?
- synthesise and secrete steroid hormones
49
What are PGCs (primordial germ cells)?
- gamete precursors (become eggs or sperm dep on which way differentiation goes) --> 1st identifiable at about 3 wks gestation
50
How does pop of PGCs dev?
- by mitosis and migrates to genital ridge primordium (part of dev embryo) by 6 wks gestation
- 2nd set of cells also migrates in (play critical role in supporting maturation of germ cells): the germinal epithelium which will eventually become Sertoli cells (male) and Granulosa cells (female)
51
How is no. sertoli cells determined, and what does a low no. ?
- in utero
| - low no. could lead to low sperm count
52
How does spertagonium dev in spermatogenesis?
* DIAG*
- diploid cell
- divides by mitosis, then divides to become 1° spermatocytes in meiosis I
- then 2° spermatocytes in meiosis II
53
What is the final differentiation step in spermatogenesis?
- spermiogenesis = spermatids to spermatocytes
54
Are 4 mature spermatozoa gen by spermatogenesis identical?
- identical in size but not genetically
55
What are the fates of spermatogonial stem cells (SSCs)?
- self regen pool, undergoes rounds of mitosis (so large no. prod)
- at intervals groups of morphologically distinct cells emerge = type A spermatogonia
- prod clone of 16 cells which enter rounds of mitosis w/ some differentiation in between
- eventually prods type B spermatogonia --> go on to become 1° spermatocytes
- karyokinesis step happens normally, but cytokinesis doesn’t, so all cells stay connected by cytoplasmic bridges
56
What determines whether cells divide of differentiate?
- presence of growth factors locally
57
What direction does dev occur in spermatogenesis?
- in centripetal direction = from outside towards lumen
58
What happens at spermiation?
- all cytoplasmic bridges broken and fully differentiated sperm washed down lumen into ducts downstream
59
What happens to cells attached to sertoli cells as spermatogenesis proceeds?
- as dev move inwards --> so find mature sperm right next to lumen
60
What is the morphology of sperm?
- acrosome cap goes round outside of head = important for fertilisation
- tail req for mobility
- midpiece section contains mt
- central axoneme made up of bundles of fibres --> req for tail movement
61
How does sperm change at spermiogenesis?
- undergoes huge remodelling
- nucleus changes shape to fit into sperm head --> DNA repackaged
- golgi apparatus forms acrosome cap
- 1 of centrioles of spermatid elongates to become the tail
- remaining cyto and organelles (residual body) removed by sertoli cells via phagocytosis
62
What chromatin remodelling occurs during spermatogenesis?
- X and Y chromosome transcrip stops before meiotic divisions --> surge after meiosis
- autosomal transcrip activity ceases later, during spermiogenesis
- massive repackaging of DNA, histones are replaced by protamines, tightly compressed chromatin w/ no gene expression
63
Why are dev sperm cells always attached to 1 or multiple sertoli cells?
- important for movement of germ cells and transfer of nutrients
64
How do sertoli cells maintain close contact w/ each other?
- via ‘tight junctional complexes’ --> form barrier to macromols and cells, called blood-testis barrier (sep testes into basal and adluminal compartments)
65
What is the purpose of ectoplasmic specialisations in sertoli cells?
- connections between germ and sertoli cells
66
What is the role of indented tubulobulbar complexes in sertoli cells?
- important role in spermiation and phagocytosis, need to strip off excess cyto before final maturation
67
When and how do spermatogonia become spermatocytes?
- once enter meiosis and move away from basement membrane, cross into adluminal compartment where they receive all nutrients from Sertoli cells --> no blood vessel connection to this compartment, hence importance of sertoli cells
68
What is the role of adluminal compartment in sertoli cells?
- ‘immune-privileged site’ protecting haploid cells from pot immune rejection (or could lead to subfertility)
69
How is a constant prod of sperm ensured?
- pools of cells at diff points in testes entering cycle at diff times
- in humans takes 64 days for completion of spermatogenesis
- at any given time there are 4 clones of dev sperm cells (w/in region of seminiferous epithelium) at diff stages of maturation --> so every section of seminiferous tubule prod sperm every 16 days
70
How do sertoli cells reg spermatogenesis?
- set lag time between dev of SSC fams
- gap junctions between adj sertoli cells provide means for communication --> high degree of spatial and temporal organisation of spermatogenesis
- sertoli cells play role in dictating length of time it takes for sperm cells to dev
71
What happened when rat SSCs transplanted into mouse seminiferous tubules?
- imposed rat timing on spermatogenesis --> thus must be cross communication between germ and sertoli cells
- communication must go both ways
72
What are the 3 main functions of testosterone in sertoli cells?
- maintains integrity of blood-testis barrier
- req for sertoli-spermatid adhesion
- essential for spermiation
73
How do androgens act on Leydig cells?
- act autocrinologically in -ve feedback loop
74
What is testosterone converted to in sertoli cells?
- dihydrotestosterone and oestrogen
75
Where does testosterone travel after sertolic ells?
- to tubule lumen where it binds androgen binding prots (ABP) secreted by sertoli cells --> testosterone-ABP travels to and stim ducts (epididymis and other ds ducts)
76
What happens if levels of testosterone too low (or too high)?
- can interfere w/ spermatogenesis
77
What does steroid conversion in testes involve?
- androgen dev in leydig cells on LH stimulation
- some testosterone and androstenedione from leydig cells enter sertoli cells
- here may bind androgen receptors directly or after conversion to more potent dihydrotestosterone
- androgens may also be converted to oestrogens
78
Are testosterone and oestrogen only important in males and females respectively?
- no, important roles in both sexes
79
How are sperm stored and matured?
- 90% fluid is absorbed in vasa efferentia, dep on oestrogen
- passage through epididymis takes 5-11 days --> sperm continue maturing and acquire pot to swim and fertilise oocyte, dep on androgens
- mature sperm stored in tail end of epididymis ready for ejaculation via vas deferens
80
What is oogenesis?
- prod of oocytes (mature female gametes) from primordial germ lines
81
What are the diff (important) parts of the female reproductive system?
- uterus
- ovaries
- ovarian stroma
- uterine (fallopian) tube
82
What is the role of the uterus?
- supports pregnancy and dev embryo
83
What is the role of the ovaries?
- prod oocytes and secrete hormones
84
What makes up the ovarian stroma?
- connective tissue, smooth muscle, stromal cells, dev follicles, interstitial glands
85
What is the role of the uterine tube?
- connects ovary and uterus, important for transport of oocyte/embryo to uterus for implantation (if fertilised)
86
What are the 2 main functions of the female genital tract?
- gamete prod and transportation
| - site of implantation, support foetal dev
87
How does the episodic nature of the menstrual cycle facilitates the 2 functions of the female genital tract?
- during 1st (follicular/oestrogenic) half, a mature oocyte is prod and made ready for fertilisation, ovulation occurs at end of this part of cycle
- in 2nd (luteal/progestogenic) half the uterus is made ready to allow implantation and to support pregnancy
88
Why is there 2 stages of the female reproductive cycle?
- both req diff hormonal roles
89
What happens at puberty, relating to oogenesis?
- ovary becomes active endocrine gland and starts to prod mature oocytes
90
When does oogenesis begin?
- at fetal dev
91
How does adult ovarian function differ from testicular function?
- timings of diff mitotic and meiotic divisions
- far fewer oocytes are prod (around 400 in lifetime vs millions each day) --> translates to diff in no. of mitotic divisions (lots of rounds in spermatogenesis, but in females all occur in foetal dev and then enter into meiosis)
- ovulation occurs episodically rather cont prod (1/2 eggs prod per mo)
- ovulation stops at menopause, sperm prod declines w/ age but continues into old age
92
How do the levels of oestrogen, FSH, LH and progesterone change t/o the menstrual cycle?
- *DIAG*
93
What is the follicular phase in oogenesis?
- when eggs and follicles dev
94
What day does ovulation gen occur?
- around day 14
95
What is an outline of oogenesis, from fetus to after puberty?
- mitotic divisions all occur during foetal dev
- oogonia undergo mitosis to self renew, then onset of meiosis I
- girls born w/ 1° oocytes arrested at prophase I (has full complement of oocytes)
- resumption of meiosis and dev of oocyte occurs after puberty --> this is when follicles recruited to dev further, few recruited each mo
- asymmetric divs in meiosis II prod only 1 mature oocyte and 2 polar bodies that contain chroms but v little cytoplasmic material
96
Why are the divisions in meiosis II of oogenesis considered asymmetric?
- oocyte has half genetic material but most of cyto, polar body is half genetic material but small prop of cyto
97
What is the purpose of the polar body in oogenesis?
- for loss of half genetic material, then they are lost
98
Why does the oocyte req large amount of resources?
- largest cell in body
| - this is why have asymmetric divisions
99
What are the diff stages of follicle dev, and how long can it stay in each stage?
- primordial follicle (stays in this stage up to 50 yrs, ie. till menopause)
- preantral (1°) follicle (77-85 days) --> once recruited, follicle starts to grow, but not yet getting full stim from pituitary
- antral (2°) follicle (8-12 days)
- preovulatory (3°) follicle (30-36 hrs)
100
What is the equivalent to the follicle in terms of role in sperm dev?
- seminiferous tubules
| - both provide approp supportive env for dev
101
How does dev from primordial to preantral follicle occur?
- growth of follicle and massive expansion of cells that make up follicle
- 1° oocyte finishes growth to 60-120µm --> still arrested in prophase I of meiosis
- large amounts of mRNA and rRNA prod to build organelles and gen prot stores
- oocyte secretes glycoprots which condense to form zona pellucida
- granulosa cells prolif to form thick layer around oocyte --> contact between granulosa cells and oocyte is maintained through cytoplasmic processes (similarly to sertoli cell dev cell connection)
- ovarian stromal cells condense to form thecal layer, sep from granulosa layer by membrana propria --> forms barrier, and inside barrier is avascular
102
What is the zona pellucida?
- protective layer outside of oocyte, w/ important role in fertilisation
103
What does avascular mean?
- no connections to blood
104
How does the antral follicle dev?
- thecal layer expands and further dev to form 2 layers: theca interna and theca externa
- granulosa cells secrete fluid --> start to get pockets of fluid building up, fluid coallesces together to form antrum --> this stage characterised by increasing follicle size (due to antrum)
- also still prolif of surrounding cells contrib to increasing size
- oocyte surrounded by granulosa layer ‘cumulus oophorus’ and suspended in follicular fluid by thin stalk which connects to ‘mural’ granulosa cells
- oocyte continues to synthesise RNA and make prots --> lots of resources req
105
What is the antrum?
- fluid filled cavity
106
What is the cumulus oophorus?
- layer of granulosa cells that immed surround oocyte
107
How do primordial, preantral and antral follicle differ, ie. in their structure?
- primordial: surrounded by thin layer of granulosa cells
- preantral: larger oocyte w/ zona pellucida, expanding granulosa cell layer
- antral: oocyte w/ zona pellucida, surrounded by cumulus cells, vast no. of granulosa cells, antrum filled w/ follicular fluid
108
How do oocyte and granulosa cells communicate?
- granulosa cells connected to oocyte through cytoplasmic processes
- gap junctions form between adj granulosa cells and at oocyte surface
- extensive network of communication which allows transfer of AAs and nts to growing oocyte
109
What in spermatogenesis does the granulosa-oocyte complex resemble?
- sertoli cell spermatogenic complex
110
How is follicle dev reg?
- v early primordial follicle dev is stim locally via GFs and cytokines (local microenv, not to do w/ pituitary)
- further follicle dev is dep on pituitary --> absence of pituitary input results in atresia (stop dev, in this way lose follicles each month
- need FSH and LH for full dev
- only cells in theca interna bind LH, only granulosa cells bind FSH (<< true of only this point in dev)
111
What happens in FSH KO mice?
- arrest follicular dev at prenatal stage
112
What happens in LH KO mice?
- stop at antral phase
113
What does the HPG axis involve in females, ie. what hormones are released?
- in response to FSH and LH stim, follicles grow and eggs mature
- antral follicles prod and release increasing amounts of steroid hormones as they grow
- thecal cells prod androgens: androstenedione and testosterone as result of LH stim
- granulosa cells convert androgens (from thecal cells) to oestrigens oestradiol 17beta and oestrone upon FSH stim
114
What occur during steroid conversion in the antral follicle?
- antral follicles release increasing amounts of steroids as they grow
- thecal cells synthesise androgens from acetate and cholesterol --> also gen low levels of oestrogen
- granulosa cells convert exogenous androgens (from thecal cells) to oestrogens
- androgens stim aromatase activity and therefore promote oestrogen synthesis
- later in menstrual cycle granulosa cells express LH receptors; LH stimulation results in synthesis of progesterone
115
How is the LH surge stim during the female HPG axis?
- increase in androgens causes granulosa cell prolif and increase in oestrogen prod
- oestrogens also promote granulosa prolif
- causes oestrogen surge which then exerts +ve feedback to stim LH surge
116
What does increase in oestrogen cause?
- b ig surge in LH
| - small surge FS
117
If LH surge doesn't occur what happens to antral follicles?
- die
118
What does LH surge coincide w/?
- exp of LH receptors on outer granulosa cells
119
What are the effects of LH surge in ovulation?
- entry into preovulatory phase of growth
- nuclear mem breaks down and meiosis resumes up to metaphase II, half of chroms but majority of cyto to 2° oocyte, rest is 1st polar body (dies)
- cytoplasmic maturation occurs (synthesis of specific set of prots, reorg of microtubules)
- w/in 2 hrs of start of LH surge there is transient rise (then decline) in output of follicular oestrogens and androgens
- follicle ruptures (cytoplasmic connections broken) and oocyte carried out in follicular fluid
120
How does LH stim alt granulosa cells in ovulation, and what is the result of this?
- switch from oestrogen prod to progesterone prod
- forms +ve feedback loop where granulosa cells then stim by own progesterone resulting in exponential increase in progesterone release
121
What are the effects of progesterone increase in ovulation
- essential for ovulation
- depresses growth of less mature follicles
- promotes transition to progestagenic phase of ovarian cycle
- levels of progesterone maintained if pregnant
122
What is the corpus luteum?
- following ovulation empty follicle collapses and becomes highly vascularised = corpus luteum
123
What is the corpus luteum made up of?
- large lutein cells (granulosa cells) which synthesise progestogens and small lutein cells (thecal cells) which prod progesterone and androgens
124
What does the corpus luteum secrete?
- inhibin A and oxytocin
125
How is LH req for luteinisation?
- prolactin, oestrogen and progesterone are req to maintain corpus luteum
126
Why does the corpus luteum undergo luteolysis?
- life ranges from 12-14 days in humans
| - needs limited life span, or don’t get dev of new follicles
127
What are the similarities between spermatogenesis and oogenesis?
- involve mitotic and meiotic divisions
- result in the prod of haploid gametes from diploid stem cells
- depend on effective germ cell-somatic cell interactions, there is no vascular connection to oocytes or spermatocytes
- Leydig cells are equivalent to Thecal cells
- Sertoli cells are equivalent to Granulosa cells
- req stim by pituitary hormones FSH and LH
- rely on approp prod of sex steroids by gonadal cells
128
What are the diff between spermatogenesis and oogenesis?
- in females, all mitotic divisions during foetal development; in males, rounds of mitosis at the start of post-pubertal sperm production, means all pot gametes are prod before birth in females but not in males
- oogenesis begins in the foetus; spermatogenesis begins at puberty
- eggs reach prophase of meiosis I during foetal development; meiosis only starts post-pubertally in males
- meiotic divisions unequal in females; equal in males
- result is 1 mature oocyte (and 2 polar bodies) from a 1° oocyte; vs 4 identically sized spermatozoa from a 1° spermatocyte
- mature oocytes much larger than the 1° oocyte; mature spermatozoa are smaller than 1° spermatocytes
→ in females, long stages of meiotic arrest, meiosis II not completed until after fertilisation; in males, divisions continuous so the dev of mature sperm from spermatogonial stem cells takes only around 64 days;
- only 1 egg (or sometimes 2) released each mo adding up to around 400 in lifetime; prod of sperm continuous w/ about 100 mil prod each day
- ovulation and reproduction naturally end during menopause in females; spermatogenesis continues throughout life
129
What is sperm activation referred to as?
- capacitation
130
What is sperm-egg fusion referred to as?
- fertilisation
131
What is an overview of what happens in fertilisation?
- oviduct(/uterine tube) connects ovary to uterus
- when mature egg ovulated initially attached to epithelium in uterine tube, then begins to move down oviduct to uterus
- sperm enter through cervix, through uterus, go up tube to meet egg
- many sperm prod as so many get lost
132
How are sperm lost?
- caught in epithelia, go to wrong ovary, don't make it through cervix etc.
133
Why do sperm need to be able to swim strongly?
- in order to swim and meet egg
134
Where do sperm undergo maturation?
- in epididymis (under stim by androgens)
135
What happens during sperm maturation?
- further fluid absorption (100x), to concentrate sperm/secretions --> secretions inc fructose, prots and glycoprots
- results in transfer of prots into and onto sperm pm = increase in mem fluidity
- acquire ability to swim progressively (= gain motility)
136
How do sperm gain motility?
- more rigid flagellum
| - cAMP content of tail increases
137
Where do steps of sperm maturation occur?
- most in male tract
| - then final step in female tract (activation)
138
What does sperm need for capacitation?
- proteolytic enzs, cholesterol ‘sinks’ and higher ionic strength
139
What are the 2 main characteristic of fully capacitated sperm?
- hyperactivated motility
| - changes in mem properties that subsequently allow the acrosome reaction to happen
140
Why does capacitation need to happen?
- so more responsive to signals from oocyte
- able to swim better
- able to undergo acrosome reaction (essential for fertilisation)
141
What happens during capacitation?
- stripping or mod of surface glycoprots
| - changes in surface charge: reduction in mem stability through loss of cholesterol and form of lipid rafts
142
How does capacitation happen, ie. the mech?
- mechs not fully understood (this is suggested seq of events)
- sperm cyto becomes more alkaline
- higher pH increases Ca permeability and thus ic Ca conc
- results in increased adenylate cyclase activity and thus cAMP prod
- activation of spermatozoal PKA
- ds phos (inc flagellum prots), signalling pathways
143
Why does just because capacitation happens, does it not necessarily mean acrosome reaction will happen?
- for acrosome reaction, sperm has to have undergone capacitation
- but also has to make contact w/ oocyte
144
What is hyperactivated sperm motility, and why is it beneficial?
- involves high amp, asymmetric beating of flagellum, rather than more regular wave like movement
- so move in v erratic ways, rather than in fairly straight manner --> allows them to escape epithelium or to make contact w/ egg
- helps sperm meet its target
- aids sperm penetration of zona pellucida
145
Do sperm usually enter cervix?
- no, in humans over 99% spermatozoa do not enter cervix
146
What are the survival time of oocytes and sperm?
- oocytes 6-24 hrs after ovulation
| - sperm 24-48 hrs in female tract
147
How do sperm find the oocyte?
- swim through uterus and into oviduct, cilia may help
- oocyte and cumulus cells release chemoattractants to aid sperm
- oocyte moves down oviduct by muscular contractions and beating cilia
148
When does the acrosome reaction occur?
- after sperm head binds to zona pellucida, zona prots responsible for inducing reaction
149
What happens as a result of the acrosome reaction?
- sperm acrosome swells, acrosome mem fuses w/ sperm pm
- acrosomal vesicle undergoes exocytosis
- release of hyaluronidase --> as digests cumulus cells (made up of a lot of hyaluron) and exposes acrosin
150
What occurs during the acrosome reaction?
- sperm makes contact w/ egg
- acrosome reacts w/ zona pellucida and release of hydrolytic enz
- acrosome reacts w/ perivitelline space
- pm of sperm and egg fuse
- sperm nucleus enters egg
- cortical granules fuse w/ egg pm which renders vitelline layer impenetrable to sperm
151
What is the perivitelline space?
- space between zona pellucida and oocyte pm
152
What is the zona pellucida primarily composed of?
- 4 glycoprots: ZP1, ZP2, ZP3, ZP4
153
What are the roles of each glycoprot in the zona pellucida?
- ZP1 = structural prot, cross links others
- ZP2 = contains sperm binding dom necessary for oocyte recognition and penetration of zona pellucida, also responsible for 1° block to polyspermy
- ZP3 complexed w/ ZP4 = involved in 1° sperm-egg binding
154
What occurs during the process of gamete binding?
- hyaluronidase from acrosome digests cumulus cells and exposes acrosin (a protease on inner mem of sperm
- 1° binding = sperm mem binds zona pellucida via ZP3 (complexed to ZP4) and a species specific complementary binding partner on sperm
- 2° binding = sperm inner acrosomal mem binds to zona pellucida via ZP2 and acrosin on sperm
- acrosin digests zona pellucida and oocyte pm
- adhesion of sperm equatorial region and oocyte mem
- penetration of sperm head into oocyte (only sperm head enters, midpiece and tail left outside)
155
What is the main step that prevents cross species fertilisation, and how can this be overcome?
- in 1° gamete binding, when sperm mem binds zona pellucida and species specific complementary binding partner on sperm
- overcome if strip zona from eggs
156
How is oocyte activated, following fusion w/ sperm?
- sperm releases PLCζ (phospholipase C ζ) into cyto of oocyte
- causes cleavage (by hydrolysis) of mem bound PIP2 to DAG and IP3
- IP3 binds to receptors on ER --> triggering Ca2+ induced Ca2+ release and oocyte activation
- results in Ca oscillations, following wave like pattern from site of sperm entry
- stimulates cortical granule release (inv ovastacin)
- PKC stim phos of other prots essential for dev of conceptus
157
What is polyspermy?
- multiple sperm binding successfully to egg
158
Why is it important to block polyspermy?
- so have right no. chroms
159
How is polyspermy blocked?
- Ca2+ stim fusion of zygotic cortical granules w/ oocyte pm and release of contents into perivitelline space
- enzs inc ovastatin act on zona pellucida which hardens, inactivation of sperm receptors through ZP2 cleavage
- Ca pulses stim resumption of meiosis, 2nd polar body extruded and female pronucleus forms
- sperm nucleus decondenses, protamines replaced by histones, male pronucleus forms
- pronuclei come together, DNA rep occurs, pronuclear mems break down and rep chroms align on mitotic spindle ready for 1st cleavage division
160
What is syngamy?
- combo of 2 genomes
161
When is it referred to as a zygote?
- after syngamy has occurred
162
How does size of zygote change w/ each cleavage division?
- not much increase in size overall and decrease in size of each cell
163
When do cell divisions of zygote stop being synchronous?
- after about 8 cell, divisions not necessarily synchronous, so doesn’t just double
164
What is the morula stage?
- approx 32 cells onwards --> just a ball of cells undergoing increasing cell divisions
165
When does the embryo become a blastocyst?
- when adopts specific shape, w/ blastocoel cavity, so cavity on inside and ICM (inner cell mass) near top (= where derive ESC from)
166
How does implantation into the uterus occur?
- at some point sheds zona pellucida, hatches through this (much softer at this point)
167
When does hatching of zygote occur?
- day 6/7
168
When does implantation of zygote occur?
- day 8/9 --> corpus luteum degen and placenta takes over hormone prod (make HCG, which is basis of most pregnancy tests)
169
Why are no new follicles dev during pregnancy?
- pregnancy hormones override monthly cycle
170
How long is the gestation period?
- 40 wks (38 of actual dev +2) --> as count from last day of last period
171
Why have oestrogen and progestins in oral contraceptives been alt since initial introd?
- started as synthetic versions in high doses
- but raised health concerns w/ high cardiovascular
health risks
172
Why was progestin derived from progesterone and spironolactone dev to use in oral contraceptives?
- bind more selectively to
progesterone receptors
- avoids androgenic effect --> caused oily skin, acne and hair growth etc.
- also avoids estrogenic and glucocorticoid side effects
173
But, what was the problem w/ progestin derived from progesterone and spironolactone dev for use in oral contraceptives, so what was done instead?
- worsened safety profile in terms of venous risk
| - so type of oestrogen changed to overcome metabolic effects and decrease risk of thrombotic problems
174
What additional effects can result from exposure to progesterone?
- endometrial atrophy (loss of hormonal support causing wasting away of the endometrium = common disease linked to post-menopausal bleeding or over-exposure to hormone contraception)
- cervical mucus thickening
- decreased tubal motility
175
What is the role of both progestogens and oestrogens in oral contraception?
- progestogens provide the dominant contraceptive benefit
- oestrogen req to stabilise the endometrium (minimising breakthrough bleeding) and promote action of progestogens (allows for lower doses for contraception protection)
176
How does combined hormonal oral contraception (COC) work?
- used correctly and consistently aims to interrupt HPG axis by suppressing the secretion of LH (progestogen) and FSH (oestrogen)
- prevents ovulation --> as LH stimulates ovulation
- antral follicles req LH surge
- no LH surge means = no entry into pre-ovulatory phase of growth
- inhibition of the maturation of dominant follicle and follicular growth due to presence of progesterone
177
What did a study measuring inhibition of ovulation by grading of ovarian activity w/ the COC find?
- no ovulation cycles seen t/ treatment, but some subjects showed signs of some ovarian activity
- enhanced follicular activity noted in some patients as well as increase in follicle-like structures (some women more prone to develop them)
- introduces the pot that could ovulate while taking the contraceptive
- but in order for this to be classed as failure of oral contraceptive, there would be additional requirements of timed changes in cervical penetrability and endometrial receptivity --> based on results this not likely
178
What is the most common emergency contraception (EC) drug?
- levonorgestrel --> progesterone based and given as single dose
179
How do EC drugs work?
- uses same hormones as normal contraceptive pill
- delays ovulation and follicle development until later stage, w/ aim to prevent egg release until sperm all cleared
- Levonorgestrel specifically targets LH release from the pituitary and prevents LH surge (needed for ovulation) --> has no effects on implantation or sperm function, affects only ovulation
180
When does EC need to be taken in order to be effective?
- works best earlier its taken
- only effective if taken before ovulation begins --> at the latest 1 day before LH surge
- at later point unlikely to be effective as follicle already reached size where will follow t/ rest of ovulation process
181
Is it poss to still become pregnant t/ unprotected sex at later point during the same cycle after taking EC, why?
- yes, as only delays ovulation during 1 cycle and doesn’t prevent it completely
182
What happens if EC is taken while already pregnant?
- doesn't harm dev embryo
183
Can obesity affect EC?
- some studies have shown it may reduce effectiveness
184
How can IUD be used as EC?
- can be inserted up to 5 days after unprotected sex and still be effective
185
How does the copper IUD work?
- small piece of flexible plastic in a T shape, wrapped in copper
- causes inflam reaction localised in the uterus, which reaches concs of luminal fluids that are toxic to sperm and embryos
- copper release changes the way sperm cells move so they can’t swim to an egg and fertilise it
186
How does the hormonal IUD work?
- thickens cervical mucus so more difficult for sperm to move through cervix
- thins lining of womb, so egg less likely to implant itself, and also causes inflam response
- can also stop eggs from leaving your ovaries so there is no egg for the sperm to fertilise
187
How have IUDs been assoc w/ pelvic inflam disease (PID)
- some IUDs removed from market due to assoc risk
| - risk inversely assoc w/ age, - PID rates most strongly assoc w/ insertion process and background risk of STDs
188
How can the zona pellucida be used as a target for immunocontraception?
- immunise patients against ZP3 glycoprot epitopes found on the Zona Pellucida glycoprot layer that protect mature oocyte
- resultant Abs gen would coat ZP3 ligands and prevent sperm heads forming a ligand-receptor complex (necessary to induce the acrosome reaction)
- currently, only tested in animal models, eg. Marmots
189
What are advs of targeting the zona pellucida through immunocontraception?
- doesn't rely on the addition of female hormones which can have adverse effects on mood, weight and other metabolic processes
190
What are disadvs of targeting the zona pellucida through immunocontraception?
- may be permanent
- vaccines req injection and medical staff to administer it, would increase costs (oral more favourable)
- in humans shown to cause oophoritis (inflam of ovary)
191
How does the dual purpose Dapivirine-Levonorgestrel Vaginal Ring work?
- contains combo of dapivirine (anti-HIV drug) and Levonorgestrel (contraceptive)
- Levonorgestrel can prevent pregnancy in 3 ways:
- -> by affecting natural mucus in cervix, so more difficult for sperm to cross vagina into uterus
- -> can change quality of the womb lining, preventing fertilised eggs from successful implantation onto wall of womb
- -> may prevent release of egg from ovaries (but may not occur in all women)
- Dapivirine prevents sexual transmission of HIV
- req replacing every 3 mo
192
In what cases might the dual purpose Dapivirine-Levonorgestrel Vaginal Ring be a good option?
- in less-developed countries, where HIV transmission higher and high rates of complications during pregnancy/childbirth, often resulting in maternal and newborn death
193
What were the results of the 1st trial of dual purpose Dapivirine-Levonorgestrel Vaginal Ring?
- well-tolerated w/ no safety concerns
- plasma concs of Levonorgestrel consistent w/ those required for contraception t/o study
- plasma concentrations of dapivirine comparatively higher than prev studies
- 70% women had an adverse event, mostly classified as mild
194
What is the future for the dual purpose Dapivirine-Levonorgestrel Vaginal Ring?
- trial now underway to assess the safety, pharmacokinetics, and bleeding patterns assoc with 90-day usage
195
How could synthetic androgens be used as a hormonal male contraceptive?
- Dimethandrolone undecanoate (DMAU) orally administered in healthy men
- activity at both androgen and progesterone receptors showed strong suppression of gonadotropins and suppression of sperm w/ complete reversibility
- as well as reversible suppression of testosterone prod
196
What problems are assoc w/ using synthetic androgens as a male contraceptive method?
- incomplete suppression of gonadotropins may allow for ongoing stimulation of spermatogenesis
197
How could 11-βmntdc work as a hormonal male contraceptive?
- binds human androgen and progesterone receptors --> binds 10x tighter to the androgen receptor than dihydrotestosterone does, and comparable binding affinity to progesterone for the progesterone receptor
- reduces av testosterone conc in blood
- reversible --> serum hormone concs returned to normal after stopping dosage
- appears to suppress LH, FSH and T production
- combo of progestin w/ androgen enhances suppression of spermatogenesis
198
What problems have been assoc w/ 11-βmntdc as a male contraceptive?
- side effects = weight gain
- needs to be converted to active form to be functional, but low conversion of prodrug to active compound
- needs to be taken w/ food to improve PK
- no suppression of FSH
199
How could Vasalgel be used as a non-hormonal male contraceptive?
- injection to reversibly block vas deferens
- forms hydrogel which prevents passage of sperm
- reduced forward progression and the lack of normal acrosomes strongly suggest impaired sperm function
- reversal of the process, shown by: spermatozoa present in all subject ejaculates after the reversal procedure, sperm concentration and motility similar to baseline levels
200
How is infertility defined?
- unable to conceive in 1 yr of trying if under 35 or 6 mo if over 35
201
How common is infertility?
- 15% couples can’t conceive after 1 yr of trying
202
What can cause male infertility?
- problems w/ sperm --> oligozoospermia, asthenozoospermia, teratozoospermia, azoospermia
- other problems --> eg. hormone imbalance (could lead to eg. oligozoospermia), tumours, tube blockages, chromosome defects, undescended testicles, infection, neurological problems (and many more)
203
What is oligozoospermia, and how common is it?
- low sperm count
| - 1/20 men, ⅓ couples have trouble conceiving due to this
204
What is asthenozoospermia?
- low sperm mobility, sperm movement impeded so can’t reach egg
205
What is teratozoospermia?
- abnormal sperm, may have unusual shape, making it harder to move and fertilise egg
206
What is azoospermia?
- no sperm
| - 1/100 men
207
What can cause female infertility?
- ovulation problems
- -> age (most signif factor: oocytes age, endometriosis risk increases)
- -> hormone imbalance (problems w/ HPG axis)
- -> PCOS (polycystic ovarian syndrome) = 30% infertile women,
- -> thyroid problems (over and underactive)
- -> premature ovarian failure
- uterus or uterine tube damage
208
What is PCOS, how does it affect fertility?
- lots of tiny cysts on ovaries
- doesn’t stop conceiving, but makes it harder
- arises from hormone imbalance
209
What is premature ovarian failure?
- when ovaries stop working before age 40 (early menopause)
210
What can cause uterus/uterine tube damage (leading to infertility)?
- infection
- pelvic inflam disease
- birth defect
- prev tubal pregnancy
- endometriosis
- fibroids
211
What is endometriosis?
- prolif of cells that line uterus, grow w/in uterine tube and ovaries, impeding transport of eggs
212
What is IVF?
- process in which mature eggs removed from woman's body and fertilised in vitro, before inserted into uterus
213
How successful is IVF?
- success rate approx 1 in 4 per cycle
214
What are the stages of IVF?
- ovarian hyperstim
- egg retrieval - before ovulation
- sperm prep --> must be matured by addition of approp factors that can stim capacitation
- co-incubation --> eggs fertilised, monitored to ensure dev normally
- embryo transfer --> healthiest 2 at blastocyst stage inserted into uterus (if more than 2 healthy then others can be cryopreserved)
- pregnancy
215
What happens during in vitro maturation (IVM?
- oocytes collected before final maturation (when follicles at antral phase)
- cultured in vitro in presence of FSH and other factors prior to fertilisation using IVF or ICSI
216
When can IVM be a better alt to IVF?
- if vulnerable to ovarian hyperstim syndrome (eg. PCOS) --> as can avoid use of drugs to stim ovaries
217
What is a more extreme version of IVM?
- artificial gametes
218
What occurs during intra-cytoplasmic sperm injection (ICSI?
- single sperm injected directly into egg cyto (or spermatids --> has been successfully performed if can’t dev into mature spermatozoa, but don’t know LT implications of this)
- bypasses normal fertilisation --> don’t need capacitation, acrosome reaction etc. as directly inserted
- so allows use of non-motile sperm (good if eg. low sperm count, or non motile)
219
How does ICSI success comp to eg. IVF?
- success rates higher than IVF
220
What concerns are there surrounding ICSI?
- relatively new dev, so unsure about LT implications, take a while to become evident
221
How does gamete intra-fallopian transfer
| (GIFT) work?
- eggs and sperm combined in vitro, then immediately inserted into fallopian tubes through small incision in abdomen
- fertilisation occurs inside body and embryo implants naturally
222
In what instances might GIFT be a good option?
- eg. if religious objections and couple want fertilisation to occur in body
223
How does zygote intra-fallopian transfer (ZIFT) work?
- eggs and sperm combined in vitro, but wait till fertilisation occurred before transferring embryos to fallopian tubes (as opposed to uterus in IVF)
224
What is cryopreservation?
- freezing of gametes or embryos to stop all biological activity and preserve them for future use
225
How has method of cryopreservation changed over time?
- used to freeze slowly to stop ice crystals forming and damaging cells
- now freeze rapidly (vitrification) so frozen before ice crystals can form
226
When can cryopreservation be esp useful?
- before undergo chemotherapy --> as this can destroy gametes
227
What is a potential ethical issue w/ cryopreservation?
- if frozen embryos and couple no longer together, who has the right to them?
228
How was cytoplasmic transfer used as ART and what happened?
- transfer of cyto from donor egg to egg from infertile woman
- 1st cases of ‘3 parent babies’
- then banned as dev abnormalities detected in some of children (only carried out in low no. patients)
- some analysed and found heteroplasmic children (mt from 2 sources)
229
Who is mt transfer aimed at as an option?
- parents w/ high risk of passing on debilitating and even fatal genetic diseases to their children
230
What 2 techniques can be used for mt transfer?
- spindle transfer (ST)
| - or pronuclear transfer (PNT)
231
How is spindle transfer carried out?
- start w/ unfertilised patients egg w/ abnormal mt and unfertilised donor egg w/ normal mt
- at fert eggs arrested at metaphase 2 (don’t complete meiosis till after fert) --> so all chroms clustered on metaphase spindle
- spindle and assoc chroms removed as karyoplast from both eggs --> discarded from donor egg and patients spindle fused into “enucleated” donor egg (so have donor ooplasm and mtDNA w/ patients chromosomes)
- reconstituted egg fertilised w/ sperm
232
How is pronuclear transfer carried out?
- patients and donors egg fertilised and form zygote
| - take out pronuclei from donor egg and insert pronuclei from patient egg
233
Will mutated mtDNA persist in offspring after mt transfer?
- don't know, may be some levels of heteroplasmy, as unlikely could transfer w/o any occurring
234
What does somatic cell nuclear transfer (SCNT) involve?
- take somatic cell, insert into enucleated egg, allow to form blastocyst and implant and form offspring
235
How has mammalian cloning progressed over time?
- started w/ embryo splitting of (what happens naturally when form twins) --> technically prod clone
- then cloned w/ embryonic cells --> if newly gen embryo cleaves to 2, 4, then 8 cell, then 1 cell taken out and transferred to enucleated oocyte and allowed to dev
- then done w/ somatic cells
236
How is therapeutic cloning carried out?
- embryo created using SCNT
- pluripotent ESCs harvested from inner cell mass of blastocyst
- ESCs can differentiate in vitro into specific lineage
- successful animal studies so far inc cardiac muscle cells, neurons, islet cells, bone, cornea, cochlear hair cell regrowth
237
What is an alt to embryonic SCs?
- can use adult SCs (less ethical issues) --> by inducing pluripotent state in them
238
What is an artificial gamete?
- oocytes or sperm gen by manipulation of progenitors or of somatic cells (dev at least partly in vitro)
239
What multiple diff routes are there for both oocytes and sperm in the creation of artificial gametes?
- GSCs (germline stem cells), eg. SSCs (spermatogonial stem cells)
- ESCs
- iPSCs (induced pluripotent stem cells)
- somatic cells
- in vitro differentiation w/ or w/o autotransplantation
240
What diff animal models have there been for artificial gametes over the years?
- 2007: in vitro differentiation of male mouse ESCs into both sperm and eggs
- 2011: mouse sperm grown in lab from testicular tissue
- 2012: immature egg cells created from PGCs, made from mouse skin
- 2016: immature sperm grown from ESCs, fertile egg cells grown from mouse skin cells, live births achieved
- 2018: gen of bimaternal and bipaternal mice from haploid ESCs w/ imprinting region deletions --> took stem cells, got some to dev into egg and some into sperm then fertilise them
241
What progress has there been w/ artificial gametes in humans in recent years?
- 2014: immature human eggs grown from stem cells in lab
- 2018: complete in vitro dev of human oocytes from primordial follicles taken from adult women
- but to date no human live birth has resulted from artificial gametes
242
What perinatal outcomes have been suggested to be more likely in babies gen by ART?
- lower birth weight
- small for gestational age
- lower mobility
- more freq delivered prematurely
- birth defects
243
What evidence is there for lower birth weight in ART babies?
- study of 20,000 ART births)
- single infants conceived with ART seen to have increased risk for low/v low birth weight when comp to the general pop
- did account for other factors, but were other influences, eg. increased risk if 1st child or ART procedure
244
What evidence is there for birth defects in ART babies?
- some defects seen to be signif more common in IVF babies: inc upper limb defects, atrial and ventricular septal defects and anotia/microtia
- also stated male IVF children appeared to be at higher risk of birth defects than females
- overall, the study found signif (but small) increase in the risk of major birth defects in children conceived by IVF
245
What were the problems w/ some early studies showing IVF was safe?
- no. of problems inc small sizes of the studies and flawed methods for identifying birth defects
246
What diff LT outcome effects have been obs in ART children?
- growth and gonadal dev
- physical health
- cerebral palsy
- cardiometabolic diffs
- childhood cancer
247
What evidence is there for diff growth and gonadal development in ART children?
- limited evidence suggests children born by ART are taller, concerns could lead to later health problems
- linked to weight gain between 1-3 years, linked to higher blood pressure levels
- male offspring can inherit impaired testicular function from fathers
248
What evidence is there for effects on physical health in ART children?
- some studies found no noticeable diffs
- other studies found ART children more prone to childhood diseases, needing medical/surgical care
- ART children found to need increase in urogenital surgeries due to undescended testicles
249
What evidence is there for increased cases of cerebral palsy in ART children?
- 2.8 times more likely
| - based on study of 19,000 ART children
250
What evidence is there for cardiometabolic diffs in children born by ART?
- 225 IVF children matched w/ control child of same gender/similar age
- IVF children approx 2x more likely to be in highest systolic and diastolic blood pressure quartile
- higher fasting glucose levels
- no signif diffs in insulin concs and resistance
- early activation of the HPG axis may inappropriately cause higher prostaglandin levels
- increased BP levels mostly indep of birth weight, suggesting underlying mechs can mod cardiovascular system w/o affecting birth size
- can’t be explained by current risk indicators, early life factors, parental
characteristics or subfertility cause
251
What evidence is there for increased incidence of childhood cancers in children born by ART?
- study of approx 27,000 IVF children)
- slightly increased risk (not signif) --> and still low risk
- incidence of langerhans histiocytosis 6x greater than expected
- results may not be due to IVF procedure --> unidentified confounding variables poss
252
What evidence is there for chrom abnormalities in ART children?
- 1000 prenatal tests on babies conceived by ICSI
- signif increase in sex-chrom abnormalities
- signif increase in structural de novo aberrations
253
Why might male children born via ICSI have increased infertility?
- in vivo sperm usually undergo selection for fittest and most adapted to fertilise oocyte, this process removed w/ ICSI
254
What have animal model studies shown about the assoc of ART w/ imprinting?
- large offspring syndrome (LOS) seen more freq in cattle born from in vitro cultured embryos --> assoc w/ exp of IGF2R
- study of mouse 2-cell embryos dev in vitro signif higher meth levels than those dev in vivo, also higher degree of demeth of male pronuclei after fertilisation in vivo than in vitro (female pronuclei showed no diff)
255
What links have been shown between ART and diff imprinting disorders?
- link between BWS and ART suggested in no. of studies --> due to DNA meth errors, rather than UPD (as often seen in normal children)
- PWS --> increased risk, but may be assoc w/ increased maternal age
- AS --> no assoc
SRS --> 9x higher risk (most)
- these increased risks may occur after fertilisation as a result of IVF/ICSI techniques
256
Is ART itself likely to be causing the diffs seen in these studies?
- often suggested risk isn’t from technique itself but instead caused by fertility problem which lead to the parents using ART
- significance isn't that reliable as still such small numbers w/ imprinting and rare childhood cancers, so hard to conclude a genuine difference and not chance
257
Why is comparing IVF over 20 years w/ natural conceptions not a well controlled comparison?
- technologies have changed and dev signif, so have medications used etc.
258
Why are results from diff studies looking at assoc of ART w/ diff outcomes at odds w/ one another?
- dep on underlying infertility/subfertility
- multiple births, increases risk of birth defects and low birth weight (linked to lots of other things --> but studies usually on singletons
- confounding variables, eg. maternal age, follow-up (closer scrutiny following ART), genetic origin, sample size
- diffs in procedures over time and in diff places (eg. types of medication, day of transfer, oocyte/sperm selection criteria/culture media) --> difficult to say whether prevalence differs naturally or as a result of differences in the quality and safety of the ART techniques used due to more or less stringent safety regulations
- risk behaviours (obesity, smoking, alcohol)
- importance of LT follow up
Ineffective controls
- diff standards of major malformations
259
Is ICSI as safe as IVF?
- evidence that it is
| - but may be due to smaller sample size
260
What methods are used to create 3-parent babies?
- cytoplasmic (ooplasmic) transfer
- MRT via ST or PNT
- could also consider standard NT
261
In studies of 3 parent babies if heteroplasmy present, is it always detected?
- no, assays only sensitive to certain level of heteroplasmy --> so may be there but just not detected
262
What are the benefits of 3 parent babies?
- couples able to conceive via CT despite poor-quality oocytes
- couples able to conceive via ST and PNT despite maternal mtDNA disease
263
What problems can arise in offspring/future gens from 3 parent babies?
- mtDNA heteroplasmy/persistence of donor or mutant mtDNA --> reported small amounts of a patient’s mtDNA can be co-transferred during ST, causing heteroplasmy
- reversion of mtDNA pop due to genetic drift
- dev abnormalities
- need to consider nuclear mutations as can also impact on mtDNA
- lots of evidence for preferential rep --> donor mtDNA can be diluted out and mutant DNA become dominant again, likely due to mtDNA replication efficiency (impacted by compatibility between donor and patient eggs)
- even if don’t dev disease, could pass onto their offspring
264
What did an experiment in monkeys show about 3 parent babies and a bottleneck?
- gen heteroplasmic oocytes w/ equal mix of 2 WT mtDNA haplotypes and dev them
- analysed somatic and germ cells gen from these oocytes --> saw rapid segregation of mtDNA variants, some showed reversion to almost homoplasmy
- results imply bottleneck at v early stages in epiblast dev and that only few cells w/in epiblast actually give rise to somatic cells w/in embryo (could have implications for dev of bottleneck)
- in the dev of 3 parent babies likely offspring will not be 100% homoplasmic, so bottleneck at such early stage could cause high levels of mutant mtDNA
- mechs that pref select for 1 mtDNA pop are apparent and there is a poss mutant mtDNA could be selected for --> so offspring could still dev mt disease
265
What was the limitation of a study on monkeys about 3 parent babies?
- seg patterns may differ in human embryos
266
What did a study into cytoplasmic transfer find about the implications of 3 parent babies?
- proposed that resulting offspring are recipients of 2 nDNA genomes from mother and father and 2 mtDNA genomes from mother and donor
- can alt normal inheritance of mtDNA, resulting in heteroplasmy
- results so far suggest no reason to think mixing 2 mt pops is harmful
267
What is the diff between synchronous and asynchronous transfer in cytoplasmic transfer?
- synchronous transfer = replacement of cytoplasm from donor oocyte to recipient oocyte at same developmental stage
- asynchronous transfer = replacement of cytoplasm from 1 developmental stage to a different stage
- during synchronous ooplasmic transfer, donor mitochondria become mixed with recipient mt of the oocyte --> may be because donor and recipient mitochondria are indistinguishable except at mtDNA level
- however, procedures that result in a mix of asynchronous cytoplasm, may actually lead to donor mt being recognized as foreign, similar to sperm mt, and thus being eliminated
268
What is the flaw of a study which suggested there were no reported health consequences assoc w/ 3 parent babies?
- we cannot analyse mt in the heart or brain tissues and this is where faulty mtDNA would be likely to cause the most issues
269
Why do some say only male embryos should be brought to term for 3 parent babies?
- as would be unable to pass on remaining faulty mtDNA to next gen
270
What is the pot impact on offspring and offspring phenotype of 3 parent babies largely dep on?
- technique used
- the 3 parents involved/their demographic history
- other events offspring exposed to during pregnancy
271
What parents might be more/less likely to take risk on 3 parent babies?
- some families predicted to be, or who have previously conceived offspring severely afflicted by mtDNA diseases more likely to be prepared to take the risk
- others whose children expected to suffer less detrimental symptoms, cognition problems or infertility, may wish to wait for further empirical clarification of the risks involved
272
How are male contraceptives similar to female ones?
- also utilise HPG -ve feedback to suppress spermatogenesis, w/o causing symptoms of hypogonadism
273
What are the 2 major challenges to the dev of a male contraceptive?
- lack of consistent efficacy amongst all users
- req for multiple agents via multiple delivery methods (ie. pills plus injections, transdermal gels plus injections etc.)
274
How could exogenous testosterone be used as a male contraceptive, and what were the problems?
- reduces sperm conc
- in 1 of 1st trials in area: 65% dev azoospermia after 4 mo treatment
- no pregnancies in those who dev azoospermia
- low no. pregnancies in those who dev oligospermia
- reversible --> regained normal spermatogenesis after cessation
- weekly injection --> pain at site, may reduce LT compliance
