Fertilization and Early Embryonic Development Flashcards
(77 cards)
1
Q
when does metaphase 2 begin?
A
when follicle is recruited for further development
arrested in Metaphase 2
1
Q
oocyte development
A
- oocytes (2n) begin meiosis 1 during fetal development
- arrested in Prophase 1 and remain dormant until after puberty
- meiosis 1 resumes when an individual follicle is recruited in adult life
- paired chromosomes divide and one polar body extruded
2
Q
the follicle gets arrested in
A
meiosis II
3
Q
what phase is the follicle in at ovulation?
A
Metaphase II
4
Q
for a follicle arrested in Metaphase II, meiosis resumes only if
A
the oocyte is fertilized by a sperm
5
Q
what is unique about the dog oocyte?
A
it is IMMATURE: still in Prophase of Meiosis 1 at ovulatioN!!
6
Q
what phase is a dog oocyte in at ovulation?
A
Prophase of Meiosis 1: the oocyte is immature!! has to mature before it is fertilized
7
Q
in most animals, the oocyte is arrested in
A
Metaphase II
8
Q
where are sperm reservoirs established?
A
established within the cervix, or utero-tubular junction, or distal isthmus. somewhere near the oviduct. these reservoirs could harbor sperm for days or weeks
8
Q
how is the oocyte transported after ovulation?
A
- cumulus-oocyte complex released from the follicle at ovulation
- picked up by the infundibulum of the oviduct
- transported distally to the ampulla region
9
Q
where do sperm attach in the female repro tract?
A
attach to the epithelium of the female repro tract by burying their heads in the crypts. eventually are released and travel proximally up oviduct
10
Q
what is sperm capacitation?
A
when sperm gain the capacity to fertilize an egg
11
Q
what are the events of capacitation?
A
- changes in glycoproteins on the surface of the sperm plasma membrane
- alteration of the lipid structure of the sperm plasma membrane
- hyperactivated motility
sperm go thru these changes to be able to penetrate and fertilize an egg
12
Q
how does fertilization work?
A
- sperm penetrate thru the cumulus cells surrounding oocyte
- sperm binds to the zona pellucida (ZP3) of the oocyte (species specific binding)
- an influx of calcium triggers acrosome rxn
- outer acrosomal membrane fuses with the sperm plasma membrane
- acrosomal enzymes are released and digest a pathway thru the zona pollucida
- hyperactivated, acrosomally reacted sperm burrows its way thru the ZP and the spermatozoon enters the perivitelline space between the ZP and the oocyte plasma membrane
13
Q
once the sperm penetrates thru the cumulus cells, where does it bind?
A
the zona pellucida (ZP3) of the oocyte (species specific binding)
14
Q
once a sperm binds to the zona pellucida, the ________ reaction occurs
A
acrosome reaction
15
Q
how does the sperm get inside the egg?
A
- binds to and fuses with the oocyte plasma membrane
- binding site on sperm is only exposed after the acrosome reaction
- sperm is subsequently internalized/engulfed into the cytoplasm of the oocyte
15
Q
what is the acrosome reaction?
A
a release of enzymes that allows the sperm to digest its way thru to get to the egg
- outer acrosomal membrane fuses with the sperm plasma membrane
- acrosomal enzymes are released and digest a pathway thru the zona
15
Q
what triggers the acrosome reaction?
A
an influx of calcium
16
Q
when the sperm enters into the cytoplasm of the oocyte, what reaction gets triggered? how?
A
- phospholipase zeta from sperm triggers a calcium release
- calcium spike causes the release of cortical granules into the perivitelline space
- these granules cause the ZP to harden so a 2nd sperm cannot get in!
17
Q
what prevents a 2nd sperm from getting into the oocyte?
A
cortical reaction
- phospholipase zeta from the sperm triggers calcium release
- calcium spike causes release of cortical granules into perivitelline space
- these granules cause the ZP to harden so that a 2nd sperm cannot get in
18
Q
how does the body prevent polyspermy (multiple sperm entering an egg)
A
- limitation of # of sperm entering oviduct
- limitation of # of sperm in sperm reservoir
- limitation of # of sperm arriving at site of fertilization
- limitation of # of sperm penetrating cumulus
- plasma membrane block
- zona pellucida block “zona hardening”f
19
Q
zygote formation
A
- after the zperm has entered the egg, meiosis II resumes
- male and female pronuclei form and fuse
- now mitosis starts (chromosomes duplicated) and the cell cleaves into 2 blastomeres
= ^ this is when it is now recognized as an embryo
20
Q
when does the oocyte become recognized as an embryo?
A
once cell division starts
21
how often do blastomere cells divide?
every 12-24 hours
each division results in smaller individual cells.
22
what is the developing embryo called when it reaches 16-32 cells?
morula
23
what cells form the placenta?
trophoblast
outer layer of the blastocele in the center of the embryo
24
what cells form the fetus?
inner cell mass (inner layer of the blastocele)
25
where does fertilization occur?
near the ampulla-isthmus junction
- developing embryo is transported distally thru the isthmus and into the uterus by oviductal smooth muscle contractions and ciliary movement
26
when does the embryo enter the uterus in the pig?
3.5 days
27
when does the embryo enter the uterus in the cow?
4-7 days
28
when does the embryo enter the uterus in the mare?
5.5-6.5 days
29
when can you get an embryo out of a mare?
5.5-6.5 days after ovulation
30
what is unique about equine embryos compared to other species like cows?
only VIABLE embryos are transported distally thru the isthmus and pass thru the UTJ into the uterus
- equine embryos must produce prostaglandin E2 (PGE2) which relaxes the inner circular smooth muscle of the oviduct and allows embryo passage
31
what do equine embryos have to make to allow passage into the uterus?
prostaglandin E2 (PGE2): relaxes the inner circular smooth muscle of the oviduct and allows embryo passage
32
what type of equine embryos get passed into the uterus?
viable embryos
33
why do only viable equine embryos get passed into the uterus?
because viable embryos make prostaglandin E2, which relaxes the inner circular smooth muscle of the oviduct and allows embryo passage. non-viable embryos and un-fertilized eggs don't make PGE2
34
what is zona hatching?
- embryonic development creates pressure
- a small crack eventually occurs in the zona pellucida
- the blastocyst stage embryo squeezes out thru this crack = "hatching"
- mice and ruminant embryos
35
what species embryos undergo "hatching"?
ruminants and mice
36
T/F: mice, ruminants and horse embryos under go zona pellucida "hatching"
false- only mice and ruminants. equine embryos "thins" and get "shed"
37
what is the equine version of zona hatching?
thinning: equine embryos expand and the zona "thins" and is subsequently "shed"
38
what happens to equine zona pellucida?
it gets "shed" off
39
what is the equine embryonic capsule?
- in vivo produced equine embryos develop a unique glycoprotein "capsule" between the trophoblast cells and the zona pellucida
40
what are the 2 membranes around an equine embryo?
1. zona pellucida
2. equine embryonic glycoprotein capsule
41
T/F: both in vivo and in vitro equine embryos make a glycoprotein capsule
false. only natural in vivo embryos will have the glycoprotein capsule because there is a maternal component involved in making the capsule
42
what is the purpose of the equine embryonic capsule?
capsule protects the embryo after the zona is shed. keeps it spherical. protects it while the embryo is migrating around the uterus
43
what is the hormone that is required by all female mammals to maintain pregnancy?
progesterone: have to have it to develop
44
what is the initial source of progesterone?
corpus luteum of the ovary
in some species, progesterone and other progestins are eventually produced by the placenta
45
if an animal does not have or does not produce enough progesterone, what happens
the embryo cannot survive
46
47
hormonal supplementation in horses?
- little clinical evidence to support routine use of supplemental exogenous progesterone in order to maintain pregnancy
- but when horse embryo is 10k- often used in mares in the equine world.
- Regu-Mate: synthetic progestin
48
how do large animal embryos prevent luteolysis?
- LA embryos must signal the uterus to prevent secretion of prostaglandins and subsequent luteolysis
- a decrease in progesterone production would result in pregnancy failure
- embryo signals to the uterus- receiving end is the endometrium!
49
what do bovine and ovine embryos secrete?
interferon tau (IFN-t)
50
what does interferon tau do in ruminants?
inhibits production of oxytocin receptors in the endometrium so that oxytocin cannot stimulate prostaglandin F2a synthesis
51
what species' embryos secrete IFN-t?
bovine and ovine
52
what do pig embryos produce?
estradiol (E2): re-routes PGF secretion into the uterine lumen
53
why do pig embryos secrete estradiol (E2)?
it re-routes PGF secretion into the uterine lumen
54
pig embryos secrete E2, and ovine and bovine embryos secrete _________
IFN-t (interferon tau)
55
what is the maternal recognition of pregnancy in horses?
we don't know. MRP signal, but don't know how it works
56
bovine and ovine embryos __________ to fill the uterine horn ipsilateral (same side) to the corpus luteum
elongate
the elongated embryo produces IFN-t and is secreted and detected in all parts of the uterine horn as the same side that she ovulated from
57
if a cow ovulates from the R side, the R uterine horn must
recognize its pregnancy, and the elongation of the embryo and production of IFN tau tells the uterine horn: you're pregnant, don't release prostaglandins
58
why do bovine and ovine embryos elongate?
elongation allows IFN-t produced by the trophoblast cells to contact the entire ipsilateral endometrium to signal MRP. important relative to the mechanism by which prostaglandins travel to the ovary in the ruminant female: counter-current transport system
59
how do prostaglandins travel to the ovary in the ruminant female?
counter-current transport system
60
how does maternal recognition of pregnancy occur in bovine and ovine embryos?
- bovine and ovine embryos elongate to fill the uterine horn ipsilateral (same side) to the corpus luteum
- elongation allows IFN-t produced by the trophoblast cells to contact the entire ipsilateral endometrium to signal MRP. important relative to the mechanism by which prostaglandins travel to the ovary in the ruminant female: counter-current transport system
61
when do pig embryos enter the uterus after ovulation?
approx 48 hours
62
pigs are litter-bearing species. how do the embryos not end up squished together in the uterus?
- pig embryos "migrate" thruout the uterus beginning on day 8-9 and spread apart
- cross-horn migration occurs: ones from L can go to R, etc
- migration stops at day 12
63
how many embryos are required in a pig uterus for MRP?
a total of at least 4 embryos are required for MRP
at least 1 embryo has to be in each uterine horn
64
what is the MRP signal in pigs?
estrogen
65
equine embryos remain spherical and ______ throughout the entire uterine lumen (horns and body) multiple times each day
migrate
migration facilitates the embryo signaling the entire endometrium for MRP. actual signal for MRP is unknown
66
why is migration of pig and horse embryos important?
migration allows the entire uterus to recognize that it is pregnant by the embryo signaling to the entire endometrium for MRP. actual signal for MRP is unknown in the horse
67
how do prostaglandins travel to the ovary in the mare?
systemic circulation
uterine contractions rhythmically move the embryo up and down all thruout the uterus
68
what are dizygotic twins?
- non identical twins
- arised from 2 ovulations: each releasing 1 egg, and each egg fertilized by 1 sperm per egg. not identical twins
69
monozygotic twins?
- identical twins
- arise from fertilization of 1 oocyte
- single embryo splits into 2, and they are identical
70
identical twins are _________
monozygotic
71
non identical twins are _________
dizygotic
72
in what species are twins and triplets advantageous?
goats and sheep: common, survival rate is good, and multiple offspring are economic benefit
73
twins in horses?
often do not survive to term or early neonatal loss occurs. 97% lost before they are born, and some born alive: tiny fraction will survive
- reduce 1 embryo: rupture capsule and embryo itself allows the other one to develop and be fine. if not, 1 fetus will have more room and be better developed and neither will survive
