Fertilization, implantation development

Question 1

Mating

Answer 1

Union of male and female gametes
-requires mating behaviour
-accomplishes delivery of sperm containing semen to a mature ova or egg

Question 2

When does mating occur?

Answer 2

Occurs at peak of female fertility
**estrus in most mammals

Question 3

Semen deposition types

Answer 3

1.Vaginal semen deposition (cows, rabbits, humans, carnivores;cervix open)

2.Uterine semen deposition (llamas, horse, pig, AI)

3. Copulatory plugs/gels (canine penis=plug, coagulation of semen)

Question 4

Sperm transport through uterus rodents and pig

Answer 4

Sperm reach oviducts within 30min of mating

Question 5

Sperm transport through uterus large and small ruminants

Answer 5

8-10hr are needed after mating for sufficient sperm numbers in oviduct
-strong uterine contraction activity during estrus

Question 6

Sperm transport through uterus in primates

Answer 6

Sperm can reach oviducts within 10min
>uterus has waves of smooth muscle contraction in late follicular phase

Question 7

Capacitation

Answer 7

The process of physiological alterations of the sperm so they are competent to fertilize the oocyte
**required female reproductive tract

Question 8

What happens to sperm during capacitation?

Answer 8

-removal of membrane cholesterol to improve oocyte binding
-increase in intracellular Ca2+ (flagella motion/energy) and pH (activate calcium channels)
-protein phosphorylation (tyrosine residues)
-hyperactivated motility (eg. asymmetrical beating)

Question 9

What does capacitation allow the sperm to do?

Answer 9

-Penetrate cumulus cell matrix..if uncapacitated the sperm adheres to outer edge of oocyte
-Adherence to zona pellucida of oocyte
-undergo zona-stimulated acrosome rxn

Question 10

Uterotubal junction (UTJ)

Answer 10

-The second major selective barrier with lots of folds (after the cervix) where sperm is concentrated after ejaculation

Question 11

What is selected for at uterotubal junction?

Answer 11

**Select for life, motility, morphology, acrosome intact, uncapacitated

Question 12

What occurs to the sperm at the isthmus?

Answer 12

Sperm binds to ciliated Oviduct epithelial cells (OECs) that have specific glycoproteins
**Attached sperm can be stored for 2-4 days and are considered the sperm of highest quality, ready for ovulation

Question 13

Pre-ovulatory period and sperm

Answer 13

-Estradiol levels in circulation and oviductal fluid are high, which promotes short term sperm storage

Question 14

Post-ovulation period and sperm

Answer 14

-Progesterone levels rise in circulation and in oviductal fluid which acts as a chemotactic signal for sperm to move to ampulla and undergo capacitation.

Question 15

Stages of fertilization

Answer 15

1.Sperm contact and penetration through cumulus cell layer (corona radiata)

2. Zona pellucida binding and acrosome reaction
3. Zona penetration
4. Sperm fusion with oocyte membrane and ooplasm
5. Cortical granule release from oocyte= zona rxn and vitelline block
6. Pronuclear fusion and metabolism initiation

Question 16

Acrosome reaction receptors that bind to initiate acrosome rxn

Answer 16

1. Zona binding region-ZBR on sperm which binds Zona pellucida-3 glycoprotein on oocyte zona (ZP3)
2. Acrosome reaction promoting region (ARPR) of zona pellucida- binds ZP3 starting rxn

Question 17

Acrosome Reaction

Answer 17

-During the rxn, overlying plasma membrane fuses with outer acrosomal membrane.
**Results in contents (acrosin) being released and digest zona proteins and increase in sperm binding to zona

Question 18

Post-acrosome rxn

Answer 18

1. Sperm penetrates zona and perivitelline space
2. Oocyte and sperm fuse at equatorial region
3. Oocyte has cortical granules accumulating at periphery which will release contents
4. Contents cause a change in zona pellucida to prevent polyspermy=zona block, AND/OR also change oocyte membrane to prevent sperm attachment=vitelline block
5. Sperm nuclear contents decondense

Question 19

What is released by cortical granules of oocyte?

Answer 19

• mucopolysaccharides, proteases, plasminogen activator, acid phosphatases, peroxidases

Question 20

Pronuclear fusion

Answer 20

1.Sperm nucleus forms male pronucleus (haploid)
2. Pronuclei (male and female) fuse and a zygote is created= diploid
3.DNA replication takes place, chromosomes condense and first mitotic divisions occur
4. Male mitochondria (and mtDNA) are degraded leaving only maternal mitochondria= reason why we only have mothers mitochondrial DNA

Question 21

Cleavage divisions

Answer 21

-mitotic divisions in early embryos.
Each cell in the division=blastomeres

Question 22

Cleavage deviations during implantation which are different than normal cell division

Answer 22

-rapid multi cellularity
-no growth
-shape maintained
-asynchronous in mammals

Question 23

Holoblastic

Answer 23

-division completely cuts through the embryo. This occurs in embryos with moderate to little/no yolk (mammals) and can be equal or unequal
**blastomeres will produce blastomeres at right angles to each other BUT often asynchronous

Question 24

Pre implantation/pre attachment period

Answer 24

The period of embryonic development from fertilization to just prior to implantation or uterine attachment
-implantation in uterus must occur for further development

Question 25

Activation of embryonic genome

Answer 25

-Need maternal transcripts and proteins from the oocyte to start early development
*when embryonic genome is activated, the maternal transcripts and proteins are degraded

Question 26

Morphogenetic Event I- Compaction

Answer 26

-Starts after 3rd cleavage
-cells huddle close together and form a compact ball at 8-cell stage

1. Blastomeres become polarized=attached so borders are less visible
   2.Results in tight permeability seal with tight junctions, desmosomes and adherens junctions. Gap junctions allow for connection/communication.
2. Results in Morula

Question 27

What are the cells of the morula destined to be?

Answer 27

Outside cells=trophectoderm and trophoblast

Inner cells= inner cell mass which will become the embryo

**both regions are distinct and synthesize different proteins

Question 28

Morphogenetic event II- Cavitation

Answer 28

1.Fluid accumulates in morula forming small vesicles
2. Vesicles will eventually fuse together into blastocoel; embryo becomes mammalian blastula= blastocyst

Question 29

What drives cavitation?

Answer 29

The enzyme Na-K ATPase

Will pump 3 Na into developing cavity, 2 K into the cell resulting in osmotic gradient for water to flow into the blastocoel. Helps for expansion

Question 30

Morphogenetic event III- Blastocyst expansion disruption

Answer 30

**driven by Na-K ATPase
can be disrupted by drugs that break down actin cytoskeleton or Ca2+ required for adhesion molecules

Question 31

Morphogenetic event III- Blastocyst expansion

Answer 31

-continued expansion of blastocyst
-Culminates in first differentiation event: ICM and trophectoderm (first epithelium)

ICM will become hypoblast and epiblast which are known as bilaminar disk, and then embryo proper; trophectoderm will become extra-embryonic lineages

Question 32

Preparation for hatching

Answer 32

-Need release of proteases to break down matrices that make up the zona pellucida

Question 33

What 3 forces are needed for hatching?

Answer 33

1. growth and fluid accumulation within the blastocyst
2. production of enzymes by the trophectoderm cells to break down the matrices comprising the zona pellucida
3. Contraction of the blastocyst

Question 34

What does hatching result in?

Answer 34

Results in the blastocyst being a free-floating embryo within the lumen of the uterus
**The blastocyst depends on the uterine environment for survival

Question 35

Equine Zona Pellucida

Answer 35

No hatching!!
-the zona pellucida will disintegrate around d7-d8 post-ovulation AND at day ~6.5, the trophectoderm of the blastocyst begins to secrete glycoprotein containing capsule.
-Capsule will remain until day 22 of pregnancy