Fertilization and Maternal Recognition of Pregnancy

What is fertilization?

Fusion of haploid gametes to form a diploid zygote

Where does fertilization occur?

Ampulla of the fallopian tube

What do most species ovulate?

Secondary oocyte

What does the dog ovulate?

Primary oocyte

Describe what happens during fertilization?

Ciliar move egg to site of fertilization and block it at the ampulla/ishtmus jct or the

Why does the oocyte get blocked during fertilization?

The uterus is hostile to the embryo until progesterone is higher

How does sperm get to the egg?

Deposited in vagina or uterus and uterine contractions move sperm to the oviduct

What species have sperm deposited in the vagina?

Cattle and dog

What species have sperm deposited in uterus?

Horse and pig

How many sperm make it to the site of fertilization/

Few hundred 1%

What are some barriers to reaching the uterine tube?

Vagina is hostile and the cervix has mucus-filled crypts

When is it easier for sperm to get past the cervix?

When estrogen is high

What happens in the epididymis?

Develop ability for sustained progressive motility

Modify membrane

Increase stability of chromatin in sperm head

What is capacitation?

Chemicals in female tract change sperm so it can fertilize an egg

What happens during capacitation/

Develop hyperactive motility

Prepare membrane for acrosome reaction

T/F during in vitro fertilization sperm is artificially capacitated?

True

Where does the acrosome reaction occur?

Zona pellucida initiated by ZP receptors

T/F a sperm cell with an intact acrosome cannot penetrate the egg?

True

What enzymes are in the acrosome?

Hyaluronidase

Acrosin

Corona penetrating enzyme

What is hyaluronidase?

Enzyme that breaks down ECM

What is acrosin?

Trypsin-like enzyme that digests zona pellucida

What is corona penetrating enzyme?

Aids in penetrating the layers of corona cells surrounding the egg

Where is the binding site of sperm?

Mid-region of sperm head

What is sperm binding dependent on?

Ca2+

What triggers the acrosome reaction?

Sperm binding to the ZP receptor

What does fusion of sperm and egg membranes trigger?

Release of cortical granules from egg to block ZP penetration by other sperm

Decondensation of the sperm nucleus

Egg cortex engulfs from of the sperm head

Formation of the secondary polar body

How is polyspermic fertilization blocked?

Receptors from sperm are removed from the ZP surface after 1 sperm fuses (zona block)

Vitelline block changes electrostatic character of vitelline membrane

What is early pregnancy factor?

Immunosuppressive factor made by early embryo to prevent the dam from rejecting the embryo

In sheep and cows, what is released by the early embryo to prevent CL regression and PGF2alpha release from uterus?

INFtau

In the mare, what prevents the uterus from releasing PGF2a?

The conceptus moves around the and endometrial contact inhibits PGF2a production

What happens in humans to prevent CL regression?

Blastocyst produces hCG

In pigs, how is CL regression prevented?

Estrogen redirects PGF2alpha to only circulate locally and not cause CL lysis

In dogs and cats what is done to prevent CL regression?

Nothing because the CL will be there no matter what

What is embryonic diapause?

Embryonic development arrests in the blastocyst stage and implantation is delayed until conditions are favorable

What are the phases of embryonic diapause?

Onset

Maintenance

Reactivation

What can cause the onset of embryonic diapause?

External cues like photoperiod or internal signals like lactation

What is facultative diapuase?

Induced by physiological stressors such as lactation or poor nutrition

What animals have a facultative diapause?

Rodents and marsupials

What mediates facultative diapause?

Increase in suckling causing increase in prolactin and decreased P4

What is obligate diapause?

Seasonally programmed to occur in every pregnancy of the species

What triggers obligate diapause?

Photoperiod via melatonin-prolactin signaling

What animals are obligate diapause?

Minks skunks, bears, seals

How long in diapause in minks?

14 days

How long is diapause in skunks?

200 days

What is the benefit of diapause?

Uncouples mating and parturition for increased reproductive success