22 - Early Embryogenesis & Endocrinology of Gestation

Question 1

Four steps in pre-attachment embryonic development

Answer 1

1. Development within the zona pellucida
2. Hatching from the zona pellucida
3. Maternal recognition of pregnancy
4. Extra-embryonic membranes

Question 2

What is an ootid

Answer 2

Oocyte after the 1st meiotic division in which the 1st polar body is present

Question 3

What is syngamy

Answer 3

Fusion of the male and female pronuclei within the cytoplasm of a newly fertilized oocyte, giving rise to a zygote

Question 4

What is a zygote

Answer 4

Diploid cell resulting from fusion of the male and female pronuclei

Question 5

What is an embryo

Answer 5

Animal in the early stages of development that has not taken on an anatomical form that is recognizable as a member of a species

Question 6

What is a fetus

Answer 6

Unborn young that possesses identifiable features of a given species

Question 7

What is conceptus

Answer 7

A product of conception including:
- embryo in early development (preimplantation)
- fetus and placenta (postimplantation)

Question 8

During fertilization, syngamy…

Answer 8

occurs to produce a zygote that begins to go cleave (mitotic division) to give rise to blastomeres

Question 9

Cleavage step in pre-attachment embryonic development

Answer 9

Cleavage of the blastomeres continues (2-celled -> 4-celled -> 8-celled embryo) until a ball of cells within the zona pellucida is formed referred to as a morula

Question 10

Two groups of cells that form the morula? Through the process of…

Answer 10

1. outer cells (adhesions create tight junctions between cells)
2. inner cells (connected by gap junctions between cells)

Through compaction

Question 11

What happens during blastcoele development

Answer 11

• Two groups of cells form in the morula
• sodium pumped into the intracellular spaces and water follows osmotically (fluid accumulates in morula)
• fluid accumulation causes outer cells to flatten & blastocoele forms
• two separate cellular components (ICM and trophoblast) merge

Question 12

What happens during blastocyst hatching in pre-attachment embryonic development

Answer 12

blastocyst eventually “hatches” from the zona pellucida

Question 13

Three main factors causing hatching of blastocyst

Answer 13

1. growth and accumulation of liquid within the blastocyst
2. enzymes from the trophoblast that degrade the ZP
3. contractions of the blastocysts

Question 14

Slides 7-13

Answer 14

Pre-attachment embyronic development **

Question 15

Successful pregnancy maintenance requires… Why?

Answer 15

High blood progesterone concentrations

Prostaglandin F2a induced luteolysis must be prevented

Question 16

Maternal recognition of pregnancy in cow & ewe? Sow?

Answer 16

Cow & ewe: blastocyst(s) produce interferon to prevent luteolysis

sow: blastocysts produce estradiol to prevent lutoelysis. Number of conceptus is important

Question 17

Maternal recognition of pregnancy in the mare? Bitch & queen?

Answer 17

Mare: proteins/estradiol synthesis and contact of the conceptus with endometrium prevents luteolysis

Bitch & queen: does not require a signal from the conceptus (lifespan of the CL is longer than the gestation period)

Slide 17**

Question 18

Luteolysis depends on… (3)

Answer 18

• presence of oxytocin receptors on uterine endometrium
• oxytocin production by the large luteal cells
• PGF2a synthesis by uterine endometrium

Question 19

Role of interferon (IFN) in cow/ewe

Answer 19

Produced by blastocyst and inhibits the oxytocin-receptor development so that oxytocin cannot stimulate PGF2a production by the uterine endometrium

Question 20

Role of estradiol in the sow

Answer 20

Produced by the blastocyst (trophoblast cells) and causes PGF2a production by the uterine endometrium to be rerouted into the uterine lumen where it is destroyed

Question 21

Maternal recognition of pregnancy in the mare more in depth

Answer 21

Migration of the conceptus over the uterine endometrium distributes factors that significantly reduce the production of PGF2a

Slide 21

Question 22

Hormones of pregnancy/parturition

Answer 22

Pregnancy:
- early pregnancy factor (EPF)
- progesterone
- equine chorionic gonadotropin (eCG in mares only)

Parturition:
- adrenal corticotropin
- estrogens
- PGF2a
- relaxin
- oxytocin

Question 23

What is early pregnancy factor (EPF)**

Answer 23

• protein (chaperonin 10) expressed into the maternal circulation prior to embryonic attachment
• shown to have immunosuppressive properties (inhibits female immune system during critical stage of embryonic dev)
• produced in endometrial cups

Question 24

EPF found in what species? has been used to develop…

Answer 24

Human, cattle, sheep and pigs

Early pregnancy test based on EPF has been developed

Question 25

Describe progesterone. Provides...

Answer 25

- dominant hormone of pregnancy - essential for embryonic/fetal dev to prevent return to estrus and produce uterine env appropriate for implantation Provides "progesterone block" that inhibits myometrial contractions during pregnancy

Question 26

Describe progesterone production

Answer 26

- levels of P4 vary with species (up to 40ng in pigs) - produced by CL in early pregnancy - placenta eventually takes over production

Question 27

How does the role of CL & placenta in P4 production vary among species

Answer 27

- ewe & mare: placenta takes over in early gestation - cow: placenta takes over in late gestation - sow, bitch and queen: CL is source of P4 throughout gestation (NOT placenta) CL continues to produce P4 throughout pregnancy in all these species (stops = abortion)

Question 28

Slide 27-29

Answer 28

Timing of placental takeover for P4 production Progesterone profiles

Question 29

Describe equine chorionic gonadotropin (what makes it, when)

Answer 29

- Gonadotropin produced by endometrial cups of the placenta - cups begin to form & express eCG at the time of attachment - cup dev & eCG secretion peaks midway through first trimester - cups regress & eCG secretion bottoms out by ~100 days of gestation (placenta takes over) Slide 31

Question 30

What is the role of eCG

Answer 30

- maintains CL production of P4 during the first trimester (maintains the primary CL and as eCG increases mare will ovulate (d40-70) to create an accessory CL which takes over P4 production) - placenta assumes major P4 producing role ~100d gestation

Question 31

Effects of eCG injected into other species

Answer 31

Strong FSH-like effects and often used as part of superovulation protocoles

Question 32

Slide 33

Answer 32

CL P4 output in the mare

Question 33

Uterine endometrium produces various...

Answer 33

growth factors and cytokines that stimulate growth and development of the fetus in utero