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REPRO > Fertilisation and embryo development > Flashcards

Fertilisation and embryo development Flashcards

1
Q

What are the steps in fertilisation in mammals?

A
  • Sperm capacitation
  • Sperm binding
  • Acrosome reaction
  • Sperm membrane fusion
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2
Q

Describe sperm capacitation

A
  • Removal of glycoprotein coat and alteration of sperm mitochondria
  • Hyperacitve motility occurs
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3
Q

What receptor is required is required for sperm binding?

A

ZP3 on the zona pellucida

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4
Q

Describe the acrosome reaction

A
  • Loss of acrosome contents (enzymes)
  • Digests ZP
  • Exposed sperm surface proteins bind to ZP3
  • Once bound, sperm and egg can fuse
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5
Q

Describe sperm membrane fusion

A
  • Causes depolarisation of egg membrane
  • Sperm completely invaginated into egg
  • Stimulates cortical reaction (release of cortical granules)
  • Blocks polyspermy
  • Membrane depolarised
  • Oocyte activation
  • Formation of ootid
  • Tail of sperm lost
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6
Q

How does sperm membrane fusion depolarise the oocyte membrane?

A
  • Granules induce calcium influx into egg from extracelular space
  • Induces more calcium release from endoplasmic reticulum
  • Wave of depolarising calcium
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7
Q

What is the function of membrane depolarisation in sperm membrane fusion?

A
  • Blocks polyspermy

- Once depolarised, ZP impermeable to other spem

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8
Q

What occurs in oocyte activation following sperm membrane fusion?

A
  • Completion of meiosis

- Extrusion of hte second polar body

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9
Q

Where does membrane fusion begine?

A

The equatorial segment of the sperm

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10
Q

Describe the chromosomal events that occur during sperm membrane fusion

A
  • Immediately after fusion, chromatin of sperm completely decondensed (nucleus of sperm loses shape)
  • Nucleus appears larger and fluffier
  • 2 pro-nuclei now present in cell = ootid
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11
Q

What is syngamy?

A

Fusion of the 2 pro-nuclei to form a zygote

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12
Q

Where does fertilisation take place?

A

In the oviduct

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13
Q

What is the zygote?

A

Single celled embryo formed following syngamy

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14
Q

What is formed from the first cleavage division of the zygote?

A
  • 2 cell embryo
  • Each cell within is called blastomere
  • ZP still present
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15
Q

Describe cleavage of the zygote

A
  • No cytoplasm synthesis, only DNA replication
  • So individual blastomere volume increases
  • Eary stages, each blastomere has potential to develop into separate offspring
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16
Q

What happens to the blastomeres following the first cleavage division of the zygote?

A
  • Further divisons resulting in 4, 8 and tehn 16 cell embryos
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17
Q

What is the morula?

A

Last point in the embryo where all cells are identical (16 cells)
(Is the last point at which a cell can be used for genetic analysis)

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18
Q

Define totipotent

A

Having the ability to form all cell necessary for normal development

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19
Q

In what stages of development are all cells in the embryo totipotent?

A

Up to and including the morula, not demonstrated beyond 16 cell stage

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20
Q

Describe the formation of the blastocyst

A
  • Outer cells within morula more squashed than inner
  • Outer cells form cell-cell adhesions (tight junctions, expression of proteins)
  • Inner cells have gap-junctions
  • Outer cells pump sodium into morula
  • Increases ionic concentration, water in through ZP = fluid accummulation causing increased pressure
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21
Q

Define blastocyst

A

The embryological stage where there is a distinct cavity formed

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22
Q

What do the outer cells of the blastocyst become?

A

Trophoblasts

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23
Q

What do the inner cells of the blastocyst become?

A

Inner cell mass

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24
Q

What do the trophoblasts give rise to?

A

Chorion and placenta

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25
Q

What does the inner cell mass give rise to?

A

The embryo

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26
Q

Describe the hatching of the blastocyst

A
  • Continues to undergo mitosis and fluid accumulation
  • Proteolytic enzymes produced by trophoblast
  • ZP weakens (increased pressure, enzymes)
  • ZP splits, blastocyst emerges (hatches)
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27
Q

What happens to the blastocyst following hatching?

A

Ready to implant (following formation of germ layers), does not occur in same way in all species, some fast, some slow

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28
Q

Describe the formation of the 3 germ layers

A
  • Cells of ICM flatten to form embryonic disc
  • Outer ectoderm and inner endoderm formed
  • Mesoderm produced
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29
Q

What are the nutritional requirements of the pre-implantation embryo?

A
  • Carbohydrate, proteins and lipids
  • Supplied by endometrial glands via uterine milk/histiotroph
  • Required for massive growth during this period
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30
Q

What are the different types of embryo progression?

A
  • Slow, continuous
  • Discontinuous
  • Fertilised
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31
Q

What species have slow, continuous embryo progression?

A

Rabbit and sow

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32
Q

What species have discontinuous embryo progression?

A

Cow, ewe, human

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33
Q

Describe discontinuous embryo progression

A
  • Prolonged stay in uterine tube
  • Anti-peristaltic contractions maitain egg for 2-3 days
  • Stronger, peristaltic contractions then transport egg onwards
  • Regardless of egg being fertilised or not
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34
Q

Why do ruminants use discontinuous progression of the embryo?

A
  • Foetus needs to grow to large size

- More time needed for embryo to develop before implantation

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35
Q

What species use fertilised embryo pregression?

A

Horses, rats, hamsters

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36
Q

Describe fertilised embryo progression in the mare

A

Only fertilsied eggs pass into uterus

  • Embryo secretes progstaglandins E and F
  • These promote embryo migration through oviduct as well as uterus
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37
Q

Describe fertilsied embryo progression in rats and hamsters

A
  • Ferrtilised eggs pas more rapidly and synchronously

- May secrete motility regulatory factors

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38
Q

Outline the process of ovulation

A
  • Spike in plasma LH
  • Spontaneous or induced
  • Follicular wall bursts, oocyte and granulsa cells released from grnaulosa cell anchor point
  • Oocyte carried with follicular fluid to peritoneal cavity, captured by fimbriae of infundibulum
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39
Q

What is the fertilisation period?

A

The period following ovulation during which the oocytes can be fertilised
- In most species is immediately after ovulation for up to a few hours (days in bitch)

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40
Q

What is the fertile period?

A
  • The period of time in which mating can result in a pregnancy
  • Longer than fertilisation period due to sperm storage in female following mating
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41
Q

At what stage in oocyte development are the oocytes ovulated in most species?

A

Metaphase of meiosis II

42
Q

Describe the oocytes ovulated in bitches

A
  • Metaphase of meiosis I
  • Completion of meiosis II and formation of the second polar body occurs after fertilisation
  • Immature oocytes ovulated that can be penetrated by not fertilised
43
Q

When is the fertile and fertilisation period in the bitch?

A
  • Fertilisation period: day 2 to day 5 after ovulation

- Fertile period: between 5 days before and 5 days after ovulation

44
Q

Describe gastrulation

A
  • Begins at posterior end of embryo where node arises
  • Cells from epiblast migrate thorugh primitive streak, differentiate into ecto, endo and mesoderm
  • During migration, position and become 3 germ layers
45
Q

In general terms, what features are formed from the ectederm?

A

Head and spine (nervous system, skin, hair)

46
Q

In general terms, what features are formed from the mesoderm?

A

Appendages (muscle, skeleton, cardiovascular, reproductive, kidney, liver)

47
Q

In general terms, what features are formed from the endoderm?

A

Intestines (digestive system, lungs, endocrine system)

48
Q

What mediates the differentiation into the germ layers?

A

Cytokines and growth factors

49
Q

What does the ICM give rise to before gastrulation?

A

Epiblast and hypoblast (the cells that form the embryo)

50
Q

What do the epiblast cells form?

A

The amionic ectoderm (amnion)

- Epiblast cells form from cells in the middle being “squashed”

51
Q

What do the hypoblast cells form?

A

Extraembryonic or primitive endoderm (primitive endoderm will go on to form the yolk sac)

52
Q

What is formed from the primitive endoderm?

A
  • Lining of blastocoel
  • When complete results in cavity called yolk sac
  • This is following implantation but before formaiton of placenta and will provide nutrients for developing embryo
53
Q

How are the extraembryonic membranes formed?

A

Embryonic mesoderm forms sac around yolk sac

54
Q

How are the amniotic folds formed?

A
  • Extra-embryonic mesoderm folds dorsally around the embryo
  • Amniotic folds form the amnion (ectoderm is the amnion)
  • Mesoderm closes around the amnion to form the placenta
55
Q

How is the chorioallantois formed?

A
  • Outpouching of hindgut is allantois

- Makes contact with chorion

56
Q

What is the function of the chorioallantois?

A

Analogous to the waste bag of the foetus

57
Q

Describe the chorion?

A
  • Membranes between developing foetus and mother
  • Formed by extra-embryonic mesoderm and 2 layers of trophoblast
  • Surrounds the embryo and other membranes
58
Q

Define maternal recognition of pregnancy

A
  • Adaptation of the maternal endocrine system to the presence of the conceptus
  • I.e. maintian CL and progesterone production
59
Q

Where does the signal for maternal recognition of pregnancy come from?

A

Must come from embryo before luteolysis

60
Q

Define pseudopregnancy

A

Being in the same endocrinological state as would be in pregnancy without actually being pregnant

61
Q

In what species does pseudopregnancy commonly occur?

A
  • Monooestrus

- E.g. rodents, rabbits, dogs

62
Q

Other than normal physiological processes, what may cause pseudopregnancy to occur?

A
  • Sterile mating

- Induced ovulation

63
Q

What are the 2 types of pseudopregnancy found in dogs?

A
  • Overt (show signs)

- Covert (no signs)

64
Q

Outline pseudopregnancy in the bitch

A
  • Increased prolactin
  • Develop mammary gland, lactate, build nests, mothering behaviour
  • Will occur with every cycle due to the extended luteal phase
65
Q

What is diapause?

A

Embryological state of dormancy, where the embryo does not immediately implant

66
Q

What species commonly have embryonic diapause?

A

Bagers, roe dear, marsupials

67
Q

What are the 2 types of embryonic diapause?

A
  • Facultative

- Obligate

68
Q

Describe facultative embryonic diapause

A
  • Occurs in times of metabolic stress e.g. lactation

- Commonly in marsupials, some insectivores

69
Q

Describe facultative diapause in marsupials specifically

A
  • Forms embryo soon after parturition
  • While lactating embryo remains dormant
  • Once suckling has finished, embryo implants
  • Therefore marsupails are always lactating or pregnant at all times
70
Q

Describe obligate embryonic diapause

A
  • Mustelids, roe deer, armadillo

- Time birth for favourable conditions

71
Q

List the maternal recognition hormones in common domestic animals

A
  • Early conception factor
  • interferon tau (ruminants)
  • Oestradiol (pigs)
  • Chorionic gonadotrophin (primates)
  • Prolactin and placental lactogen in rodents
72
Q

Describe luteolysis in non-pregnant animals

A
  • occurs in absence of embryo
  • Induced by decline in progesterone and increase in PGF2a from uterus
  • CL regression occurs allowing return to oestrus
73
Q

How is PGF2a produced?

A
  • From arachidonic acid via conversion by cyclo-oxygenase 1/2
  • Uterine derived
74
Q

What is the function of PGE2?

A

Luteotrophic, supports the CL

75
Q

Describe the role of the endometrial oxytocin receptors in luteolysis in ruminants

A
  • OXTR absent in luteal phase, suppressed by high P4
  • Reappear before P4 falls, stimulated by decreasing P4 levels
  • Oxytocin produced by CL binds to OCTR
  • Stimulates pulsatile PGF2a release
  • Increases oestradiol as well which increases OXTR expression (positive feedback)
76
Q

Describe the countercurrent system used for PGF2a

A
  • PGF2a released from endometrium
  • Into uterine vein
  • From vein to ovarian artery to go to ovary and stimulate oestradiol production
77
Q

Describe the oxytocin-PGF2a postivie feedback loop

A
  • PGF2a acts on CL to reduce progesterone and increase oxytocin
  • Acts on uterus to make more PGF2a
78
Q

Describe the early conception factor in maternal recognition of pregnancy

A
  • Maternal response within hours of fertilisation
  • Produces early conception factor
  • protexts embryo by binding to T-lymphocytes
  • Presence does not indicate whether the pregnancy will be estbalished or maintained, only that conception has taken place
79
Q

In what species is the early conception factor present?

A
  • Mice
  • Sheep
  • Cattle
  • Pigs
  • Human
80
Q

What is the function of progesterone during pregnancy?

A
  • Maintains uterine gland secretory function
  • Suppresses myometrial contractions and luteolytic mechanisms
  • Suppresses FSH and LH secretion (reduces follicular development and suppresses ovulation directly)
  • Inadequate leads to embryo mortality
81
Q

What is the maternal recognition factor in ruminants?

A

Interferon tau (cytokines, typically cantivirals)

82
Q

Describe the expression of interferon tau

A
  • Initiated during trophoblast elongation
  • Expressed in trophoectoderm
  • Stimulated by uterine growth factors
  • Tight window of expression (days 12-24 of pregnancy)
  • Production related to embryo size
83
Q

Why is interferon tau expressed in days 12-24 of pregnancy?

A
  • Normally would have luteolysis occuring in this period

- IFNT prevents luteolysis

84
Q

Describe the actions of interferon tau

A
  • Acts on endometrium to suppress OXTR expression
  • stimulates protein synthesis critical for embyro
  • Antiviral action
  • Suppresses PGF2a pulsatile secretion
  • Indirectly maintains progesterone
85
Q

Describe the role of oestradiol in maternal recognition of pregnancy in pigs

A
  • Secreted before implantation
  • Re-direct flow of PGF2a away from uterine vein but does not prevent PGF2a secretion
  • Some interferon present but not anti0luteolytic
86
Q

Describe PGF2a redirection in pigs

A
  • Excreted through uterine glands into lumen rather than being absorbed into veins then to CL
  • Embryo in lumen is secreting enzymes that metabolise PGF2a
87
Q

Describe maternal recognition of pregnancy in horses

A
  • Oxytocin stimulates luteolytic PGF2a
  • Embryo suppresses OXTR
  • No blastocyst interferon
  • But signal unknown
  • Pregnant mare serum gonadotrophin (eCG) is NOT the signal (production after luteolysis)
88
Q

Describe the blastocyst migration in horses

A
  • Blastocyst does not elongate, remains spherical and unattached
  • Migrates through whole of uterus and horns before implantation
  • Critical for MRP and establishment of pregnancy
  • Distributes MRP signal
  • Stimulated by prostaglandins
  • Blastocyst produces oestradiol
  • 3 low MW proteins that suppress PGF2a prod.
89
Q

What is the maternal recognition of pregnancy factor in primates?

A

Chorionic gonadotrophin (hCG in humans)

90
Q

Describe PGF2a in primates

A
  • Luteolytic
  • Produced by CL
  • CL stimualtes own regression (need signal from embryo to stimulate this)
91
Q

Describe the action of chorionic gonadotrophin

A
  • hCG produced by syncytiotrophoblast cells
  • Acts on LH receptor on CL
  • Suppresses PGF2a
  • Absorbed by venous supply, acts directly on CL
92
Q

Describe the role of prolactin and placental lactogen in maternal recognition of pregnancy in rodents

A
  • Oestrous cycle~4 days
  • Mating leads to (psuedo)pregnancy
  • Prolactin secretion, extends luteal phase 10-14 days
  • Can be caused by sterile mating
  • Placental lactogen is later MRP (takes over once prolactin secretion finished)
93
Q

In what species does MRP occur before implantation?

A
  • Ruminants
  • Pigs
  • Mare
94
Q

What species have no MRP?

A
  • Dogs
  • Ferrets
  • Roe deer
95
Q

In what species does MRP occur mid-gestation?

A
  • Rabbits

- Rodents

96
Q

When does MRP occur in the cow?
(days)
And the ewe?

A

Cow: Day 16-1
Ewe: day 13-14

97
Q

When does MRP occur in the mare?

A

Day 14

98
Q

When does MRP occur in sows?

A

Day 12-13

99
Q

When does MRP occur in goats?

A

Day 17

100
Q

When does MRP occur in humans?

A

Day 7-12

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