Early Embryonic Development II Flashcards
3 Functions of Zona Pellucida?
- Protect the pre-implantation embryo from muscular contracitons of the oviduct
- Aid in eventual breakdown of itself by storing proteases
- Protection from infection
Why cant Bovine Viral Diarrhea affect early embryo?
Most likely due to the blocking of zona pellucida
What is required to break down zona pellucida?
Proteases
e.g. strypsin
What are the 3 axes
Anteror-posterior (craniocaudal)
Dorsoventral
Right-left
What is the hypoblast?
Flattened cells facing blastocyst cavity
Form a cell sheet that lines epiblast
Epithelium
Eventually forms part of yolk sac
What is essential for hypoblast development?
GATA-6 Expression
What is epiblast?
Remaining cells of the ICM that are multilayered
Eventually form embryo
What is essential for epiblast development?
Nanog expression
What is Rauber’s layer?
Trophectoderm cells overlying the epiblast
Formation of embryonic disc
THe Rauber’s layer disintegrates and leaves the epiblast exposed
Epiblast becomes ovoid structure
What are the 2 groups of mammals in terms of development within the uterus and implantation
Pre-attachment period within the uterus is long (several weeks) - domestic animals
Blastocyst implants quickly after entering uterus (primates)
How do horses, carnivores and primates differ from ruminants and pigs durring expansion?
Ruminants and pig the blastocyst becomes tubular then filamentous
In horses, carnivores and primates, the blastocyst remains spherical and does not elongate
What is histotrophe?
Secretory products of the endometrial glands
- Enzymes
- Growth Factor
What occurs to allow for maximum production of histotrophe?
Endometrial glands undergo substantial hyperplasia and hypertrophy during gestation to increase surface area for maximum production of histotrophe
What does histotophe do?
Nourish the embryo during pre-implantataion period
What must be prevented in order for the early events of embryogenesis to continue into an established pregnancy?
Luteolysis must be prevented
What is luteolysis?
Breakdown or loss of the corpus luteum
What are the two forms that recognition signalling from conceptus to maternal system?
Luteotrophic
Anti-luteolytic
What is luteotrophic?
A hormone(s) to act on the corpus luteum to maintain luteal function
What is anti-luteolytic
A hormone(s) to prevent utereine release of luteolytic-promoting substances such as prostaglandin (F2-alpha)
Two function of IFN Tau?
Acts on endometrial cells of uterus and inhibits oxytocin receptor production - Oxytocin cannot now stimulate PGF2alpha synthesis
Increases secretion of proteins from endometrial glands which enter lumen and nourish the embryo
What is function of estradiol in pregnant sow?
Re-routes PGF2alpha to uterine lumen where it is destroyed - preventing luteolysis
What is trans-uterine migration of equine conceptus?
During pre-attachment phase, horse conceptus is moved over the endometrial surface by uterine contractions
PGF2alpha is significantly reduced
5 phases of implantation
Phase 1 - Shedding of ZP
Phase 2 - Pre-contact period when blastocysts can migrate and undergo orientation without contact with epithelia, initiate pregnancy recognition signalling
Phase 3 - Trophectoderm associates with endometrial epithelium for unstable adhesion. In ruminants initial development of microvilli begins
Phase 4 - Trophectoderm firmly adheres to luminal epithelium and in some species superficial glandular epithelium
Phase 5 - Unique to species with invasive implantation of blastocyst through uterine luminal epithelium into uterine stroma that becomes decidualized
Which phase does initiation of pregnancy signal occur?
Phase 2
What occurs for ruminants in phase 3?
Initial development of microvilli begins
What species stop at phase 4?
Domestic animals
Cows and so on
What species undergo phase 5 of implantation?
Primates
Carnivores
Which species has longest time from ovulation does implantation occur?
Horse 17-56
Which species has shortest time from ovulation of implantation?
Rodents
Four forms of implantation?
Antimesometrium implantation
Mesometrium Implantation
Eccentric Implantation
Centric Implantation
What occurs durring antimesometrium and mesometrium implantation
Blastocyst invades the uterine epithelium and into the unterine stroma where the embryo will develop
- Primates and Guineapigs
What occurs in ecentric implantation?
Blastocyst gets lodged in a uterine fold or cleft and the uterine mucosa around it proliferates
- Rodents
What occurs in centric implantation?
The fluid filled sacs around the embryo become tightly associated or apposed to the uterine epithelium and attach
- Horse , cattle , sheep , pigs , dogs . cats . rabbits
What is Diapause?
Blastocyst can enter a period of decreased cell division and metabolic inactivity and ususally delayed blastocyst implantation
Benefit of seasonal delayed implantation?
Increase probability that offspring are born at a favorable time of yr for optimal survival
Two types of Diapause?
Seasonal delayed implantation
Falculative or Lactational dely implantation
Benifit of faculative or lactational delayed implantation?
Since rodents can become pregnant during post-partum estrus while still feeding pups, implantation can be delayed until weaning is complete to prevent the mother from having to support two litters at the same time
