10 – Fertilization and Pre-Implantation Development Flashcards
1
Q
Mating
A
- Union of male and female gametes
- Occurs at PEAK of female fertility (in most vertebrates)
2
Q
Capacitation
A
- Process of physiological alterations of sperm so they are COMPENENT to fertilize the oocyte
- Requires the female reproductive tract
3
Q
Sperm undergo (capacitation)
A
- Removal of membrane cholesterol to improve oocyte binding
- Increase intracellular Ca2+ concentration
- Increase in intracellular pH
- Protein phosphorylation
- Hyperactivated motility (ex. asymmetrical beating)
4
Q
Functional affects (capacitation)
A
- Penetrate cumulus cell matrix
- Adherence to zona pellucida of oocyte
- Undergo zona-stimulated acrosome reaction
5
Q
Uterus and Uterotubal Junction (UTJ)
A
- Sperm maintained at HIGH numbers at UTJ after ejaculation
- Beyond cervix, UTJ is second major barrier with lots of FOLDS
6
Q
Isthmus as a reservoir
A
- Sperm bind ciliated oviduct epithelial cells (OECs) that have SPECIFIC GLYCOPROTEINS
- Can be bound for 2-4 days=HIGH quality
7
Q
Pre-ovulatory period
A
- E2 elevated in circulation and oviductal fluid
- *promote SHORT TERM SPERM STORAGE
8
Q
Post-ovulation
A
- P4 rise in circulation and oviductal fluid
- *chemotactic signal for sperm to MOVE TO AMPULLA and undergo CAPACITATION in ampulla
9
Q
Fertilization ‘steps’
A
- Sperm contact and penetration (through cumulus cell layer)
- Zona pellucida (ZP) binding and acrosome reaction
- Zona penetration
- Sperm fusion with oocyte membrane and ooplasm
- Cortical granule release from oocyte
- Pronuclear fusion and initiation of metabolism
10
Q
Sperm plasma membrane covering acrosome: 2 receptor regions
A
- Zona binding region (ZBR)
- Acrosome reaction promoting region (ABPR)
11
Q
Zona binding region (ZBR)
A
- Binds zona pellucida-3 glycoproteins on oocyte zona (ZP3)
o Attaches sperm to zona
12
Q
Acrosome reaction promoting region (ABPR)
A
- Binds ZP3 and starts acrosome reaction (ex. fusion of membranes)
13
Q
Acrosome reaction
A
- Overlying plasma membrane FUSES with OUTER ACROSOMAL membrane
- *contents released (eg. ACROSIN) and digest zona proteins and increase sperm biding to zona
14
Q
What is left after acrosomal reaction?
A
- Inner acrosomal membrane and equatorial portion of sperm head
- *increase binding to oocyte membrane
15
Q
Post-acrosome reaction
A
- Sperm penetrates zona and into perivitelline space
- Oocyte produced CORITCAL GRANULES accumulate at periphery
- Oocyte and sperm fuse at equatorial region
- Granules RELEASE CONTENTS
- Sperm nuclear contents decondense
16
Q
Cortical granules release contents (2 mechanism to prevent polyspermy)
A
- Change zona to PREVENT polyspermy (zona block/reaction)
AND/OR - Change oocyte membrane to PREVENT sperm attachment (vitelline block)
Ex. mucopolysacchardies, proteases, plasminogen activator, phosphatases
17
Q
Pronuclei
A
- Fuse=diploid
- DNA replication
- Male mitochondria including mtDNA are DEGRADED
- *only maternal mitochondria remain
18
Q
Cleavage division during preimplantation development deviations from normal cell division
A
- rapid multi-cellularity
- no growth
- shape is maintained
- asynchronous in mammals (can appear as 3-5 cell under microscope)
19
Q
Holoblastic (cleavage division)
A
- Division completely cuts through the embryo
- Occurs in embryos with moderate (ex. amphibians) to LITTLE/NO YOLK (ex. mammals)
- Equal or unequal
- *ROTATIONAL in mammals
20
Q
Rotational holoblastic division in mammals
A
- Cleavage produces blastomeres at RIGHT ANGLES to one another
21
Q
Pre-implantation/pre-attachment development in mammals
A
- Period of embryonic development from FERTILZATION to JUST PRIOR TO IMPLANTAION or uterine attachment
- Timing/stage varies among species
22
Q
Activation of embryonic genome
A
- During oocyte development lots of maternal mRNA has been stored and proteins made=*important for oocyte to survive
- MUST OCCUR to survive!
- Varies in species
23
Q
Morphogenic events
A
- Compaction
- Cavitation
- Blastocyst expansion
24
Q
Morphogenetic event I: compaction
A
- After 3rd cleavage
- Outside cells: Individual blastomeres start to tightly attach to one another (NO fusion, future trophectoderm ->trophoblast=extraembryonic lineage)
- Cells on inside: connected by gap junctions
o Derive the embryo by forming ICM - MORULA (16-cell stage)
- *2 regions synthesize different proteins
25
Morphogenetic event II: cavitation
* Fluid accumulates in compacted morulae forming SMALL vesicles
* Vesicles coalesce into blastocoel=blastocyst
* *Na,K-ATPase appears to be primary driver (3 Na into developing cavity, 2 K into cell)
26
Morphogenetic event III: blastocyst expansion
* *Na,K-ATPase=primary driver
* Requires a very efficient permeability seal that can be disrupted by drugs and break down the actin cytoskeleton or Ca2+ requiring adhesion molecules
* *culminates in first differentiative event
27
Blastocyst expansion: culminates in first differentiative event
* Differentiation of:
o ICM=embryo proper
o Trophectoderm=extra-embryonic lineages
28
What follows blastocyst expansion?
* Hatching
o ICM differentiates into hypoblast and epiblast (bilaminar disk)
29
What does hatching require?
* Release of enzymes (ex. strypsin) to break down matrices comprising zona pellucida
30
Hatching is governed by 3 forces
1. Growth and fluid accumulation within blastocyst
2. Production of enzymes by trophectoderm cells to break down the matrices comprising the ZP
3. Contraction of the blastocyst (=now free-floating embryo within lumen of uterus)
31
Equine zona pellucida and capsule
* Embryo does NOT hatch from ZP b/c ZP disintegrates around d7-d8 post-ovulation
* D6.5: trophectoderm begins to secrete glycoprotein containing CAPSULE beneath ZP and capsule remains until d22 of pregnancy
