Pregnancy recognition Flashcards
Interrupting the estrus cycle
Luteolysis is what normally triggers the end of the luteal phase and new follicular phase Pregnancy interrupts the normal estrus cycle by preventing luteolysis (the default)
Maternal recognition of pregnancy, what hormones are increased, which are for ruminants, mares, sow, Bitch/queen.
For pregnancy to succeed, the embryo(s) must biochemically signal to the maternal environment prior to luteolysis, a molecular interaction known as maternal recognition of pregnancy Signalling varies across species: (all keep P4 high during pregnancy)
- ruminants = IFNT
- mare = mechanical? PGF2a inhibition?
- Sow = estradiol
- Bitch/queen = no signal (default is no luteolysis)
Pregnancy recognition - Ruminants (4)
- IFNT secreted
- IFNT blocks oxytocin receptors in uterine epithelium = no production of PGF2a
- No signal for luteolysis = Corpus Luteum is maintained
- IFNt promotes uterine gland secretion + immune system
Critical time = d13-14 (ewe) or d15-16 (cow) Recognition cascade:
- Conceptus secretes interferon tau (IFNT) aka trophoblastic protein 1
- IFNt blocks expression of oxytocin receptors in uterine epithelium
- Lack of OTR blocks production of PGF2a
- No signal for luteolysis = CL is maintained
IFNt also promotes uterine gland secretion to support developing conceptus, and can influence maternal immune system
IFNt is not directly luteotropic (doesn’t enhance CL function), just prevents luteolysis
Pregnancy recognition - horse (4)
Critical time = d12-14 Recognition cascade:
- molecular signal still not identified
- Physical migration of the conceptus through the uterus
is required (substitute for elongation)
- PGF2a concs are decreased/stay low (somehow)
- No signal for luteolysis = CL is maintained.
Pregnancy recognition - Pig (3)
Critical time = d11-12 Recognition cascade:
Conceptus secretes estradiol (E2)
PHF2a is still produced in response to oxytocin from PP, CL and endometrium
E2 causes rerouting of PGF2a into uterine lumen (Exocrine) instead of uterine vein (endocrine)
PGF2a breaks down in lumen
No signal for luteolysis = CLs are maintained
E2 also drives myometrial contractions to evenly distribute conceptuses
A minimum of 2 conceptuses in each horn is required to generate enough local signal to prevent luteolysis in the sow.
Pregnancy recognition – bitch/queen
Carnivores are unique:
- Bitch = CLs last for length of gestation, whether there is a pregnancy or not
- Queen = no CLs formed unless mating occurs (induced ov), CLs last length of gestation
No specific signal is required for maternal recognition of pregnancy
Maintaining P4 throughout pregnancy
Maternal recognition of pregnancy prevents luteolysis, which has one critical outcome – maintaining high concentrations of progesterone
- In most species, the placenta will eventually take over P4 production – CL may still contribute
What would happen if we gave recombinant IFNt to a cycling (non-pregnant) ewe?
Prolong luteal phase, can help with synchronising estrus
Prevent luteolysis.
Gestation
Need to know gestation lengths in months.
Cattle, Sheep, Horse, Sow, Bitch/Queen
Following implantation, key organ systems differentiate during oncogenesis (gastrulation to birth)
- Many early processes happen at the same time, regardless of total gestation length (i.e. heartbeat present)
- Body systems are differentiated by ~ half way through gestation
- Often, species w/ larger fetus = longer gestation
- Elephants have 22 month gestation!
Growth rate
When body systems stop forming (mostly differentiated), then mostly growth is happening. As pregnancy progresses, foetal size increases exponentially.
Fetal size through pregnancy, based on a cattle
Most relevant in cattle – you can use fetal size to estimate gestational age by rectal palpation
Sexual differentiation during fetal development
Biological sex (not gender) is determined genetically by sex chromosomes (X & Y) Mammals = male XY, female XX
- Only males can carry Y, so offspring sex is determined by sperm (sperm can either be X or Y bearing sperm ~ sex sorting)
Y chromosome contains the SRY gene (sex determining region), which produces the testis determining factor protein
Fetal gonad starts as indifferent – ovary is not the “default” pathway
Migration of primordial germ cells
In very early embryo (15%) gestation, primordial germ cells (PGCs) differentiate
- PGCs develop in hindgut (in yolk sac)
- PGCs are precursor that become spermatogonia stem cells
and early oocytes
- Migrate to the genital (gonadal) ridge and undergo massive mitosis
- Gonadal ridge forms a bipotential gonad (can
develop into a testis or ovary)
Sexual differentiation during fetal development
Two duct systems form alongside the intermediate (mesonephros) and final (metanephros) kidneys:
- Paramesonephric duct (aka Mullerian duct)
- Mesonephric duct (aka wolffian duct)
At this stage (early in dev), embryo is phenotypically sexually indifferent – due to effects of SRY
- Male = regression of paramesophenric duct to anti-mullerian hormone (AMH) Female = regression of mesonephric duct
Gonad differentiation - male
Gonad differentiation - female
