3d and 3e Flashcards
PIP2 messenger system
-slow block to block polyspermy
how it works
1) Activation of bindin receptors activated phospholipase C (PLC)
2) PLC cleaves PIP2 in egg plasma, releasing IP3
3) IP3 released into egg cytoplasm
4) ip3 diffuses into ER. where it opens calcium channels
Specifically how is phospholipase C (which is activated by bindin) activated
two ways, not sure which one
either
Soluble factors released from sperm membrane fusion
or
thorugh signal transduction by activation of receptor tyrosine kinase on egg membrane
chromosome things fgor sea urchins
-female completed meiosis before fertilization
-sperm must decondense chromosomes by remvoing hisotones and adding female histones
-pronuclei of male and female migrate and fuse
-dna rep occurs after fusion of pronuclei
-SPERM centriole used to make mitotic spindle,
-sperm mitochondria and flagellum disintegrate
Mammalian Fertilization
-begins in oviduct with binding of free swimming sperm to the ovulated egg extracellular coat (zona pellucida)
-forms zygote (activated cell)
everal recognizable events include:
the sperm acrosome reaction (a form of cellular exocytosis)
penetration of the egg ZP by sperm
fusion of egg and sperm membranes
the egg cortical reaction
zona reaction (results in alteration of the ZP such that free-swimming sperm are unable to bind to fertilized eggs)
What are the three stages of human oogenesis
OOgenisis is theprocess of which eggs cells ar emade in the ovary
1) Meiotic prophase events of senapses and recombination which occurs in fetal ovary
2)Follicle formation: second tri of fetal develop
3)Oocyte growth: occurs in adult ovary
Oogina vs primary oocytes vs secondary oocyte
Oogina: undifferentiated ovarian germ cells that give rise to the oocytes
Primary oocytes: oogonia that have initiated meiosis
Secondary: completion of 1st meiotic division produces small cell called polar body and large secondart ooycte
Ova: egg
dictyotene stage
resting phase of the oocyte in mammals
-in humans can last from birth up to12-50 years depending on the time of follicle maturation and ovulation
-chromosomes condensed here
-primary oocytes are arrested in first meiotic prophase and remain here
Meiosis prophase 1 arrest vs metaphose 2 arrest
dictotene phase
metaphase 2 arrest is second arrest point
what is the order of mammalian oogensis
Primordial germ cell
oogina(entry into meiosis)
primary oocyte (m phase 1)
seocondary oocyte (meiosis 2 and growth)
ova
fertilization triggers completion of m phase 2 (2nd meiotic fividion)
Sperm motility
-UTERINE MUSCLE CONTRACTION (needed to get sperm into oviduct (ampulla region)
-sperm becomes hyperactive in oviduct
-direction cues given from temperature gradient in oviduct
-chemical cues from cumulus or oocyte
-sperm become mature during voyage to oviduct
What is the ampulla region
oviduct, distal to uterus and near ovary where fertilization takes place
provides great environment for fertilization and helps transport gametes
What region may slow down sperm and release them slowly into ampulla
isthmus:narrow segment of the oviduct, next to uterus
found before ampulla
What is capacitation
-set of changes that allow sperm to become able to fertilize egg (become primed to undergo acrosomal rxn and primed to fuse to cell membrane)
when sperm become mature during voyage ti oviduct, if not wont be able to fertilize egg
-sperm released during ejaculation ar able to move but they vannot yet fertilize egg, need to be matured in reproductive tract
-this is because sperm is quiescent transcriptionally and translationally (means dormant) sothey rely on post translational modifications such as phosphorylation of proteins to control maturation process
-this occurs as sperm comes in contatt with natural conception lubrication
-this needed to be understood to have successful ivf treatments and stuff
how is oocytes moved
cumulus needed to :cumulus attaches to fimbria, which transports the ooycte to ampulla also through MUSCLE CONTRACTIONS AND CILIA BEATING (CILIARY LINING) those two points more important
What happens during capacitation
- Albumin proteins (present in reproductive tract of females) remove cholestrol from sperm membrane
-changes position of lipids that house receptors now allowing for it to be in right place - Proteins and carbs are lost
- Membrane potential becomes negative (facilittes sperm fusion)
- Protein phosphorylation: two are phophorylated at sperm head, essential part of zona pellucida receptor
- Acrosomal membrane comes ont. contact with sperm cell membrane
Does increasing cholesterol increase membrane fluidity
NO increasing cholesterol decreases fluidity
What are three differences between capacitated sperm and uncapacitated
- Cap are hyperactive: swim faster
- Cap show thermotaxis (will move from cooler regions of isthmus to warmer amopulla)
- Cap show chemotaxis: will move towards molecules released by cumulus
- Cap can undergo acrosomal rxn: sucessful sperm undergo this rxn before they reach cumulus
-higher progesterone levels near site may trigger acrosomal rxn - Acrosomal rxn is final stage of cap, proteins that were once on inner membrane of acrsome are now on tip of sperm, these are needed to bind to zona pellucida
What are the three major glycoproteins of the zona pellucida
ZP1, ZP2 , ZP3
bind with other proteins to form glycoprotein matrix (which binds sperm)
zona pellucida is like vitiline envelope but thicker and denser and binding to it is relatively species specific not absolutely
Sperm membrane proteins bind to what proteins of oocute
ZP proteins
Acromosal rxn in mammals old thoughts vs new thoughts
OLD:
1) sperm proteins bind to zp3 protein on zona pellucida
2)zp3 causes acromosal rxn to occur
3)enzymes released right where needed to digest thorugh zona pellucida
so zp3 protein was thought to be needed for acrosomal reaction to occur
HOWEVEAR NEW TOUGHT:
after imaging techniques, saw that sperm that binds to zona have already undergone acrosome reaction and can do this without zp3 gene
-so zp3 is not needed into acrosomal reaction but it is able to be
zp2 is sufficient for binding of sperm to human egg abd allows for movement
Sperm is in what position to egg when sperm egg fusion occurs
lateral to egg membrane
fusion initiated at equitoral region
In mammals is there a fast block to block for polyspermy
NO
three versions of slow block exist
1)fusion of cortical granules with egg membrane
-zona pellucida modified so that it can no longer bind sperm (zona rxn)
2) Zinc Shield
-after calcium splash when sperm enters, zin ions are released via exocytosis from oocyte (stored in cortex) and bind to zona pellucida, giving it a shield
3) OOcyte membrane protein JUNO
-can bind to any sperm in the previtilline space and prevent it from binding to any juno still on membrane
-also removed docking sites
Wha does membrane fusion of eggand sperm intail
-IgG like protein found on INNER ACROSOMAL MEMBRANE called IZUMO
-also oocyte memrbane protein called JUNO
mutants of juno or izumo prevent fertilization
Zona reaction
enzymes released when cortical granules bind to zona modify zp proteins and the sperm receptors on the zona pellucida so it cant bind
zp2 is cleaved by ovastacin
Nacetylglusoamine of ZP3 removed by nacetylglusoaminase
What is ZP2 cleaved by
OVastacin, released when cortical granules bind to zona pellucida
necessary to block polyspermy in mammals
Wat is necessary for the block to polyspermy in mammals
Cleaved Zp2
Decondensing of sperm dna
must be decondensed, tightly packed with protamines, disulfide bonds must be reduced
egg cytoplasm contains glutathione, and maternal histones replace rprotamines
Whattriggers the completeion of meiosis two in the oocyte
waves of calcium when sperm enters activates kinase that triggers the completion of meiosis 2 via degredatio of cuclin and securin (leads to degredation of chromatin cohesion)
-nuclear enveloped break down and the chromosomes of both assemble on shared mitotic spindle
What is the first division called
gonomeric division
pronucleis dont fuse at this point but nuclear envelopes breakdown and first mitotic division occurs
What is glutathione and why is it found in abundance in eggs
-reducing agent
-importnat antioxidant
-protects against damage due to reactive oxygen species
- so as disulfide bonds are reduced it is oxidized which is whythe cell has it in abundance because disulfide bonds are reduced when chromatin of sperm is condensed
Does the sperm head disconnect from its flagellum
NO, the entire sperm cell in mammals (incliding mitochondria and flagellum) enter the egg at fertilization
sperms mitochondria gets degraded inside and sperm centriole used for the mitotic spindle
Increase in Ca…
necessary for egg activation
-resumes meiosis, cortical granule exocytosis, release of stored mRNA inhibition
-released due to phospholipase C released IP3 which binds and releases ca from endo
Where is there a single wave ca increase and where is there a series
Single wave: sea urchin
mammals: series of waves
causes released of metaphase 2 block
- release of the metaphase II block
- cortical granule exocytosis (= cortical granule reaction)
- release of mRNA inhibition (maternal stores)
what is dependent on ca increase
- release of the metaphase II block
- cortical granule exocytosis (= cortical granule reaction)
- release of mRNA inhibition (maternal stores)
ip3 is the product of what
phosphlipase c cleaving PIP2
What is the CA wave inducer
PLC zeta
expression induces ca oscillations
cleavage divisions
-Mitotic divisions: divide egg into smaller nucleated cells known as blastomeres
-no cellular growth: overall cytoplasmic volume remains the same
-initiation of mitosis
early cleavage divison are INDEPENDENT OF EMBRYO GENOME and controlled by maternal stockpiles
CDK
-mitosis promoting factor
-depends on association with cyclin B (regulated by accumulation or destruction of cyclin B)
Mid blastula transition
Mid-blastula transition: The transition from the early rapid biphasic (only M and S phases) mitoses of the embryo to a stage characterized by
(1) mitoses that include the “gap” stages (G1 and G2) of the cell cycle
(2) loss of syncronicity of cell division
(3) transcription of new (zygotic) mRNAs needed for gastrulation and cell specification.
Cleavage divisions
Karyokinesis: division of nucleus during mitosis
-rewuires mitotic spindle
Cytokenesis:
the division of cell during mitosis
-contractile ring of microfilaments needed
Yolk cleavage divisions
eggs having little yolk that is equally distrubuted are isolecithal and generally undergo holoblastic cleavage –depending on orientation of mitotic spindles, holoblastic cleavage can be radial, spiral, bilateral, or rotational
eggs that have more yolk at one end than the other are mesolecithal and also undergo holoblastic cleavage – but cleavage rates are slower in the yolkier side (in frog embryos like Xenopus, the more active side is known as the animal hemisphere/pole and the less active yolky side is known as the vegetal hemisphere/pole)
eggs where only one small area is free of yolk are telolecithal and undergo meroblastic cleavage – in mammals and birds this type of meroblastic cleavage is called discoidal cleavage
eggs have much yolk in interior and are centrolecithal and display superficial cleavage – common in insects where a syncytial stage precedes the cellular blastoderm stage
