Wk9 pregnancy recognition and foetal development Flashcards
- Recall species timing of implantation in relation to blastocyst hatching (days)
- In order to pregnancy to keep going, we need maternal recognition of pregnancy…
- Mare = 16-18 days NOT 36-38**
- Cow = 18-22 for implantation
- ewe = 15-18
- sow = 14-18
- bitch = 18-20
1) Describe the process of maternal recognition of pregnancy in different species and how this ensures ongoing pregnancy
- Luteolysis usually occurs which ends luteal phase and starts a new follicular phase
- But if pregnancy, pregnancy interrupts the normal oestrous cycle by preventing luteolysis (the default)
- Progesterone levels remain high as a result
- For pregnancy to proceed, embryo must biochemically signal to the maternal environment prior to luteolysis - molecular interaction known as maternal recognition of pregnancy.
2) Recall gestation length across species
- Horses pregnant for almost a year
- Pigs have weird amount (3.8months)
- Dog and cat 2 month
- We can see that many early processes happen at the same time between species, regardless of total gestation length: e.g heartbeat present occurs on 25 day approximately for all species
- Body systems are differentiated by about half way through gestation.
Signalling hormones vary for animals:
- Ruminants
- Mare
- Sow
Bitch/queen
- Ruminants: IFNt
- Mare: mechanical? PGF2a inhibition
- Sow: estradiol
Bitch/queen: no signal (default is no luteolysis)
Pregnancy recognition - ruminants
IFNt role
- Critical time = d13-14 (ewe) or d15-16 (cow)
- Conceptus secretes interferon tau (IFNt) aka trophoblast protein 1
- It just prevents luteolysis*
IFNt also promotes uterine gland secretion to support developing conceptus, and can influence maternal immune response
- It just prevents luteolysis*
Pregnancy recognition - horses
We don’t know molecular signal, but describe physical migration of conceptus in mares
- Critical time: d12-14
- Conceptus: stays spherical, we don’t get elongation in mares
- So we get physical migration of the conceptus through the uterus is required - which substitutes for elongation that occurs in other species
Eventually though, PGF2a concentrations are decreased - so we escape luteolysis
Pregnancy recognition - pigs (sow)
- Critical time
Recognition cascade of pigs (in relation to PGF2a and E2)
- Critical time: d11-12
- Recognition cascade:
- Conceptus secretes estradiol E2
- PGF2a is still produced in response to oxytocin from PP and CL and endometrium
- E2 causing rerouting of PGF2a into uterine lumen (Exocrine) instead of uterine vein (endocrine)
- PGF2a breaks down in lumen
- No signal for luteolysis = CL maintained
NOTE: minimum of 2 conceptuses in each horn is required to generate enough local signal to prevent luteolysis in the sow
Pregnancy recognition - carnivores
- No specific signal required for maternal recognition of pregnancy
CL last for length of gestation, whether there is a pregnancy or not..
Maintaining P4 throughout pregnancy
- Maternal recognition of pregnancy prevents luteolysis which has one critical outcome:
- Maintaining high concentrations of progesterone
Note: important for insemination as if you miss this time period, the body will resort back to follicular phase
- Maintaining high concentrations of progesterone
What would happen if we gave recombinant IFNT to a cycling (non-pregnant) ewe?
- Prevent luteolysis from occurring
We don’t use this in practice though.
Foetal size/growth rate through pregnancy
- Most relevant in cattle - use foetal size to estimate gestational age by rectal palpation for pregnancy diagnosis
Stage of pregnancy relevant to the size
Sexual differentiation during foetal development
- Male and female chromosomes
What does the Y chromosome contain
- Mammals: X and Y chromosomes
- Male: XY and female XX
- Only males can carry Y, so offspring sex is determined by sperm
- Y chromosomes contains SRY gene (sex determining region)
Produces the testis determining factor protein
Migration of primordial germ cells (PGC’s)
The yolk sac - why is this important feature?
- Yolk sac: this is the source of the primordial germ cells *
- PGCs develop in the hindgut
- Migrate to genital (gonadal) ridge and undergo MASSIVE mitosis - building up reservoir of stem cells
Gonadal ridge forms a bipotential gonad (can develop into a testis or ovary)
Sexual differentiation during foetal development:
The 2 duct systems that form alongside intermediate and final kidneys are..
- Paramesonephric duct (aka Mullerian duct)
Mesonephric duct (aka Wolffian duct)
Why are the 2 duct systems that form alongside the kidneys important for sex development?
At this stage embryo is phenotypically sexually indifferent - due to effects of SRY (sex determining region)
- Male = regression of paramesonephric duct due to anti-mullerian hormone (AMH)
Female = regression of mesonephric duct
