Gametogenesis and Fertilization Flashcards
Exam 2
What happens to the sperm organelles after sperm cell-egg fusion?
- Centriole
Mitotic spindle to complete meiosis
What is the acrosome?
Part of the sperm head (with nucleus) that contains enzymes to digest extracellular coats surrounding egg
Advantages of undergoing capacitation? (5)
- Recognizing guiding cues to egg
- hyperactivation
- chemotaxis
- perform acrosomal rxn
- fusion with egg membrane
Compare oogenesis and spermatogenesis: Transcription and recombination
Oogenesis: Equivalent transcription & recombination
Spermatogenesis: Excluded from recombination and transcription
Mammalian Egg Anatomy (5)
- Ovum
- Cumulus
- Polar body
- Zona pellucida
- Cortical granule
What are spermatids?
Haploid sperm cells following the second meiotic division
What happens to the sperm organelles after sperm cell-egg fusion?
- Flagellum
Degraded
How are sea urchin sperm able to locate eggs even though both types of gametes are released into a potentially large surrounding body of water, such as the open ocean?
A. Using sperm-activating peptides (SAP)
B. By sensing appropriate currents
C. By the ability of mature sea urchins to sense and approach others prior to gamete release
D. Using chemotactic agents released by sperm to bind to eggs
A. Using sperm-activating peptides (SAP)
Define Metaphase 1 in meiosis.
Homologous pairs line up at the equator of the cell
What happens to the sperm organelles after sperm cell-egg fusion?
- Nucleus
nucleus decondensation &
chromatin remodeling to form male pronucleus
During what stage in do mammalian sperm cells lose cytoplasm and undergo additional modifications to enable motility and penetration of an egg?
A. Proliferative mitosis
B. Spermiogenesis
C. Crossing over
D. The termination of meiosis II
B. Spermiogenesis
What is Ovastacin?
Protease released in mammalian eggs after fertilization to digest ZP2
Bindin function and process in development
Process: Acrosomal process of sea urchin sperm
Function: Mediates the species-specific recognition between the sperm and the egg vitelline envelope during fertilization
What structure contains the enzymes needed by sperm to penetrate external egg structures?
A. The axoneme
B. The acrosome
C. The end piece
D. The centrioles
B. The acrosome
What are sperm activating peptides (SAPs)?
Chemoattractant that allows sperm of the same species to find the correct egg
What are Primary spermatocytes?
Cells are derived from the mitotic division of the type B spermatogonia
- Undergo a period of growth and then enter meiosis
What is the cumulus?
Layer of cells surrounding the egg that nurture the egg until it is released from the ovary
What is the fertilization envelope formed in external fertilization?
Forms from the vitelline envelope of the sea urchin egg following cortical granule release
Why do immature sperm need to undergo capacitation?
Get held up in the cumulus matrix
Define Telophase 1 in meiosis.
Homologous chromosomes are segregated into 2 cells
What is the cortical granule reaction in preventing polyspermy in external fertilization?
Cortical granule enzymes contribute to the formation of a fertilization envelope to block further sperm entry
Fate of gonocytes XY vs XX
XY: Arrest in mitosis
XX: Arrest in meiosis
What is Spermatogonia?
Sperm stem cells
What is the axoneme?
Portion of a cilium or flagellum
What is hyperactivation?
Increased and more forceful motility displayed by capacitated sperm
What is believed to aid in the prevention of polyspermy in mammals?
A. An electrical response to the fusion of sperm and egg membranes.
B. The intake by the egg of Zinc.
C. The release of protein-digesting enzymes from cortical granules.
D. The inhibition of ovastacin.
C. The release of protein-digesting enzymes from cortical granules.
What is polyspermy?
Entrance of more than one sperm during fertilization
What are cortical granules?
Contain enzymes to prevent polyspermy
THINK: ZPs
What is spermatogenesis?
The production of sperm
Describe the sperm movement to egg in mammals (3)
- Uterus contraction (moving sperm up)
- Sperm motility (ability of sperm to move efficiently)
-** Sperm rheotaxis** (moving against current)
How does sperm cell fuse with the egg membrane in mammals?
Acrosomal rxn w proteins located on outside of sperm (AKA equatorial region)
Lateral fusion
What is the pronucleus?
Male and female haploid nuclei within a fertilized egg fuse to form the zygote nucleus
What is monospermy?
Only one sperm enters the egg
Compare oogenesis and spermatogenesis: Initiation
Oogenesis: Once per lifetime
Spermatogenesis: Continuously dividing
What is capacitation?
Mammalian immature sperm to mature sperm
Describe the steps during external fertilization (7)
- Egg releaves sperm-activating peptides and chemotaxis
- Sperm contacts jelly layer
- Acrosome reaction
- Acrosome process
- Digestion of jelly layer
- Binding to vitelline envelope via bindin
- Fusion of acrosomal process membrane & egg membrane via fertilization cone
What is crossing over?
The exchange of genetic material during meiosis…
i.e. Genes from one chromatid are exchanged with homologous genes from another
Does a zygote prophase exist?
No; after fusion it goes straight to mitosis
What occurs in the transition between PGC to Germ Cells?
XX: Retinoic acid (RA) → Stra8/Wnt4 → Meiosis
XY: RA → Fgf9 –| Stra8 –| Meiosis
Compare oogenesis and spermatogenesis: Meiosis arrested
Oogenesis: first meiotic prophase
Spermatogenesis: No cell cycle arrest
What are gonocytes?
differentiated PGCs but not fully differentiated gametes
Explain the consequence of intracellular calcium release on the egg during the external fertilization (5)
- Egg activates
- Lipid metabolism to form new PM
- Protein synthesis
- DNA replication
- Resumption of meiosis
What is oocyte?
Development of the egg (ovum)
How long does spermatogenesis take?
65 days
Explain gene imprinting in mammals
(key terms: paternal allele, maternal allele, silencing)
Silencing of parent-specific alleles to control embryonic growth via differences in DNA methylation
Parental alleles associated with growth (silencing of maternal allele equivalent)
Maternal alleles associated with suppressing growth
Sea Urchin Egg Anatomy (5)
- Female pronucleus
- Egg cell membrane
- Vitelline envelope
- Jelly coat
- Cortical granule
Which of the events listed is one of the events enabled by capacitation?
A. The acrosome reaction
B. The arrangement of cumulus cells around the egg
C. Movement of cilia in the oviduct
D. Initiation of the slow block to polyspermy
A. The acrosome reaction
Define Anaphase 1 in meiosis.
Homologous chromosomes are pulled apart and move to opposite poles
Comparison between chicken and human egg
Chicken have more yolk
What is meiosis 2?
MAT2; the separation of the Sister chromatids
Describe the different phases of oogenesis (6).
IN EMBRYO
1. Oogonia
2. Primary oocytes (step: meiotic phase)
PUBERTY
3. Secondary oocytes (@ puberty, meiosis 1)
4. Arresting in M2
5. Maturation
6. Egg/ovum
Wnt Signaling Pathway Steps (6 steps, 5 arrows)
Wnt
↓ (binds)
Frizzled
↓(Recruits)
Dishevelled (Dsh)
┴ (Recruits)
GSK3
┴ (Phosphorylates, target for degration)
B-catenin
↓ (To nucleus)
Activates transcription w/ TCF/Lef
What happens to the sperm organelles after sperm cell-egg fusion?
- Mitochondria
Degraded
What is oogonia?
XX Germ line cells that become oocytes.
What occurs during the acrosomal reaction?
Fusion of the sperm acrosome with the sperm cell membrane to result in the acrosomal process
Why do the primary oocytes arrest before fertilization? During what stage does this occur?
So they can focus on transcription/translation
Metaphase 2
Explain the steps of polyspermy (3 steps)
- Each sperm contributes centriole –> created an additional spindle pole
- Causes improper chromosome alignment during first mitosis
- Results in aneuploidy in daughter cells of zygote
What occurs from spermatids –> sperm cells?
Incuded by RA (sertoli cells), thus inducing meiosis
Which of the following refers to the silencing of parent-specific alleles during early development?
A. Germ-cell inhibition
B. Sex-specific repression
C. Genomic imprinting
D. Splicing
C. Genomic imprinting
What is the calcium wave to polyspermy during external fertilization?
Calcium ions moves in “waves”first near sperm entry and them throughout egg
What is the end product of meiosis?
4 haploid cells (23 chromosomes)
Note: 23 from mother, 23 from father to have DIPLOD cells (46 chromosomes)
How do sperm cross the cumulus and the zona pellucida?
Via hyperactivation and enzymes from acrosome
What determines which cells will become germ cells?
Pole cells in the posterior side embryo
External fertilization: What does species-specific sperm attraction mean?
Cannot fertilize cross species.
Ex: Mouse sperm cannot fertilize human
Is there DNA synthesis between M1 and M2?
No
How long does it take for slow block to polyspermy during external fertilization to occur?
Takes place about 1 minute after fast block
What is Spermiogenesis?
Sperm maturation
List how polyspermy is prevented during external fertilization
- Fast block (Na+ membrane potential)
- Cortical granules
- Calcium sparks and wave
What causes the fertilization cone?
Polymerization of actin in sperm during acrosomal process
List the organelles of the sperm cell (5)
- Acrosome
- Axoneme
- Nucleus
- Centrioles
- Mitochondria
How does fusion of the male and female pronuclei occur in external fertilization?
Male nucleus rotation and migration to female pro-nucleus. Connected at the internuclear bridge to form zygote diploid nucleus
DNA and protein synthesis occurs
Compare oogenesis and spermatogenesis: Completion of meiosis delays
Oogenesis: Months or years
Spermatogenesis: Days or weeks
Describe the different phases of spermatogenesis (6)
- Spermatogonia (step: differentiation)
- Primary spermatocytes (steps: meiosis)
- Secondary spermatocytes
- Spermatids (steps: spermiogenesis)
- Residual bodies
- Sperm cells AKA Spermatozoa
What is the first polar body?
Smaller cell produced that is mostly cytoplasm
Sperm capacitation in mammals mechanism steps (2 pathways, 4 total steps)
1. Albumin removes cholesterol (↑ membrane fluidity)
↓
2. Opens Ca2+ channels
↓ phosphorylation of sperm
Mature sperm
AT THE SAME TIME
1. Progesterone receptors
↓ degrade inhibitor
2. Opens Ca2+ channels
Compare oogenesis and spermatogenesis: Number of games produced
Oogenesis: One per meiosis
Spermatogenesis: 4 per meiosis
Do mammals have a fast-block to prevent polyspermy?
No
List the steps of meiosis (8)
- Interphase (DNA synthesis)
- Prophase 1
- Metaphase 1
- Anaphase 1
- Telophase 1
- Metaphase 2
- Anaphase 2
- Telophase 2
FGF and RTK Signaling Pathway Steps (9 steps; 7 arrows)
FGF
↓ (binds)
Tyrosine Kinase Receptor
↓(Dimerization, phosphorylation, recruit/activate)
GAP / GEF
┴ (GTP to GDP = inhibit) / ↓**(GDP to GTP = activates)*
RAS
↓ (recruits)
Raf
↓ (Phosphorylates)
MEK
↓ (Phosphorylates)
ERK
↓ (To nucleus and phosphorylates)
Ets fam transcription factors
↓
Regulate transcription
When does gametogenesis occur in humans?
12-14 dpf
Define prophase 1 and its 4 steps
- Leptotene: Chromosomes start to condense
- Zygotene: Homologous chromosomes pair up
- Pachytene: Crossing over occurs
- Dipotene: Synaptonemal complex dissolves but remain attached at crossing-over points
THINK: “Lazy Zebras Play Dodgeball”
What is fast block to polyspermy during external fertilization?
Additional sperm are prevented from fusing with egg by changing the electric potential
Negative inside (less Na+)–> Sperm enters –> Na+ channels open –> More positive inside
What is the cortical flash and wave in polyspermy prevention during external fertilization?
List the steps involved (6)
Influx of calcium ions into the egg’s cytoplasm before moving throughout egg
Bindin
↓ (binds)
TK receptor
↓ (activates)
PLC
↓ (activates)
IP3
↓ (binds)
IP3 receptor in Ca2+ channels
↓ (opens channels)
Ca2+ released from ER to cytoplasm
Vitelline envelope vs zona pellucida
Vitelline Envelope: Surrounds egg (NOT MAMMALIAN)
Zona Pellucida: Surrounds the mammalian egg
What occurs during the acrosomal process?
Fingerlike process in sperm head extended that contains surface molecules for species-specific recognition between sperm and egg
What is the fertilization cone?
Location where the egg and sperm fuse during fertilization
What are the secondary oocytes?
Oocyte after first meiotic division that generates first polar body
Describe the cause and the event happening upon egg activation in mammals.
Ca2+ pulses –> complete meiosis –> form female pronucleus
