Exam 2 Flashcards
General steps of fertilization
Contact and recognition between gametes, regulation of entry, fusion of pronuclei/membranes, and activation of the egg to start development of the new organism
What is the sperm’s main goal
Get it’s pronuclei to the egg’s
Sperm characteristics
Small, very little cytoplasm, haploid, contains acrosomal vesicle, 1 centromere (2 centrosomes) and dynein
Acrosomal vesicle
Formed during spermatogenesis from golgi, membrane bound pocket of enzymes that help sperm access the egg and digest the outer layer of the egg
Dynein
Motor proteins that move the tail of the sperm
Egg characteristics
Larger, haploid, contains everything zygote will need except the other half of the DNA, outer jelly layer
Purpose of outer jelly layer of egg
Regulates sperm binding, only sperm of the same species have enzymes that will digest the outer layer to get to the egg membrane
Vitelline membrane
Outer jelly layer of non-mammal eggs that regulates sperm binding
Zona pellucida
Outer jelly layer surrounding mammalian eggs
Cumulus layer
Cells surrounding the egg that help it develop and stay with the egg for some time
What is included in the egg cytoplasm
Maternal mRNA, ribosomes and tRNA, morphogenetic, nutrient proteins, and protective chemicals
Acrosomal process
Fingerlike structure that helps the sperm penetrate the egg jelly coat, surrounded by bindin, molecules that help sperm bind to egg membrane
Cortical granule
Membrane bound Golgi derived structures that prevents multiple sperm from fertilizing the egg
Steps of sperm recognition
Chemoattraction, binding of the sperm to egg ECM, exocytosis of acrosome, and fusion of the egg and sperm membranes
Chemoattraction of sperm
Occurs through chemical gradient, chemicals being released by egg cells, species specific
Acrosome reaction
Once the sperm reaches the egg outer layer, digestive enzymes are released to help the sperm get through the vitilline membrane, acrosomal process pushes membrane out to help the sperm bind to the egg
Fusion of gamete membranes
Fertilization cone is formed out of actin, sperm nucleus and centriole pass through
Monospermy
Only one sperm enters egg, how it is supposed to happen
Polyspermy
Multiple sperm enter the egg, usually not viable, prevented by fast and slow block mechanisms
Fast block mechanism
As a sperm binds to the membrane, Na+ is released and the membrane potential changes from -70mV to about +20mV (sperm cannot bind to membranes with a positive membrane potential), only lasts about a minute
Slow block mechanism
Cortical granule reaction, cortical granules fuse with the egg membrane and release contents into the extracellular membrane forming fertilization envelope and cleaving bindin connections from other sperm
Fertilization envelope
Jelly system after fertilization, space that prevents any sperm from getting into egg
Ca2+ role in fertilization
Release of calcium ions when sperm binds to egg membrane activates cortical granules, also activates egg’s metabolism and initiates development of the new organism, and attracts sperm to egg
Nuclear fusion
Egg kinases decondense sperm chromatin and recondense with egg histones, and then DNA polymerase begins replication
Difference between sea urchin and mammalian fertilization
Conditions are different (translocation), mammalian sperm go through capacitation before they can fertilize, and there’s a different mechanism to prevent polyspermy
Capacitation
Maturation of sperm while in the reproductive tract, induced by oviduct cells, likely triggered by cholesterol efflux, allow sperm to bind to zona pellucida
Translocation
Movement of sperm through the reproductive tract through sperm motility, uterine muscle contractions, and Soren rheotaxis
Rheotaxis
How sperm migrate against the flow using calcium channels to monitor the direction of calcium flow
Capacities induced by the oviduct
Sperm gains capacity to recognize signaling cues that guide them to the egg, undergoing acrosome reaction, and fusing with the egg cell membrane
Egg glycoproteins that make up the zona pellucida
ZP1, ZP2, and ZP3, sperm binds to these and continues through the egg membrane
Izumo
Protein exposed by the acrosomal reaction, interacts with egg’s Juno to create fusion complex for binding and membrane fusion
Juno
Egg protein that interacts with Izumo to create fusion complex for membrane fusion
Mammalian blocks to polyspermy
Egg release of ovastacin, zinc spark/shield, and release of Juno from egg membrane
Egg releasing ovastacin
Induced by cortical granules fusing with egg cell membrane, cleaves ZP2 protein, blocking any sperm from binding
Zinc shield/spark
After entry of the first sperm, zinc ions are released and bind to the zona pellucida. Zinc ions inhibit acrosomal proteins from binding/ getting to egg membrane
Release of Juno
As egg and sperm membranes fuse, protein Juno is released from the egg, leaving nowhere for other sperm Izumos to bind and inhibiting Izumo on free sperm
Anamniotic vertebrates
Do not form the amnion that allows for development on dry land, fish and amphibians
What is significant about the point of sperm entry?
It influences dorsal ventral polarity, marking the ventral side
where does pattering start?
fertilization
cortical rotation
movement of the outer cytoplasm relative to the inner cytoplasm, induced by sperm binding to egg membrane, moves dorsal determinants (mRNA and proteins) to dorsal side
Mid-Blastula transition
during blastula stage, embryo begins to transcribe it’s own genes
movements of amphbian gastrulaiton
epiboly, vegetal rotation, invagination and bottle cells, involution, and convergent extension
epiboly
thinning and spreading of the animal cap cells over vegetal, done by increasing the number of cells and radial intercalation
radial intercalation
movement of cells between layers, thinning and spreading so the ectoderm can surround the endoderm
vegetal rotation
meso and endoderm cells asymmetrically press up against the inner blastocoel roof on the dorsal side, positions the pharyngel endoderms most anterior
blastopore
formed by the invagination of cells opposite of sperm entry, most dorsal
dorsal blastopre lip
formed by the bottle cells and involution of cells in the marginal zone
bottle cells
cells along the blastopore lip that pinch the tissues to give a spot of involution, do this through apical constriction
cleft of brachet
space separating the ectoderm from the endomesoderm (endo and mesoderm)
involution process
pharyngeal endoderm cells are first to involute into the embryo, then cells of the prechordal plate, and finally chordamesoderm
prechordal plate
precursor of head mesoderm, transcribe goosecoid gene, which represses Wnt 8 (which represses head development).
chordamesoderm
cells that will form the notochord, which induces and patterns the nervous system.
Involuting marginal zone
Cells at the blastopore lip that include the bottle cells, pharyngeal endoderm, prechordal plate (head meso), and chordamesoderm (notochord)
Mechanism of involution
Leading edge cells are connected directly to fibronectin, a protein of the ectoderm extra cellular matrix. The leading cells pull the following cells and are connected to them through a cadherin keratin complex
Significance of keratin/intermediate filaments
Prevent following cells from separating from leading cells
Collective cell migration
Mechanism that involves leading cells and following cells moving together in a fountain like manner, allows endo and mesoderm components to move into the embryo and spread
General description of movements of germ layers during morphogenesis
Endo and mesoderm involute through the embryo while the ectoderm thins and spreads to surround the internal tissues
Convergent extension
extension of the anterior-posterior axis while shrinking the left-right axis, involves mediolateral intercalation and other mechanisms
mediolateral intercalation
cells within a layer compressing and squeezing together
mechanisms of convergent extension
differential adhesion, planar cell polarity pathway (PCP), and Ca2+ signaling
what occurs during convergent extension
as chordamesoderm tissues enter, they separate into notochord and somites, other mesoderm tissues enter through the ventral and lateral blastopore, endoderm IMZ cells coat archenteron roof, and vegetal ventral cells become archenteron floor
mesoderm mantle
structure formed by the mesoderm tissues entering through the ventral and lateral blastopore
Signaling pathways of gastrulation
VegT, Wnt, TGF-b, and FGF
Start of signaling for gastrulation
Vegetal cells at the bottom, after fertilization VegT mRNAs are transcribed and activate Sox17 transcription factor which is critical for endoderm
VegT functions
Activates Sox17 for endoderm, activates Nodal in upper vegetal region for mesoderm
Nodal
TGF-beta factor that triggers Smad2 phosphorylation, which induces eomesodermin and brachyury (mesoderm inducers)
Mesoderm formation is dependent on
positive feedback loop between Nodal, Eomes, VegT, Vg1, and Wnt inhibition. in absence of this induction, cells become ectoderm
Dorsal ventral axis formation
Involves Nieuwkoop center, b-catenin, nodal-related gradient, and the organizer
Nieuwkoop center
area of cells in the dorsal region of the endoderm that generates signals to induce the dorsal organizer
cortical rotation’s role in d/v axis
positions GSK binding proteins (GBP) and Dishevelled to dorsal side. GSK degrades beta-catenin, but when GBP binds to it it cannot. These two combine, along with Wnt11, to stabilize beta-catenin to induce dorsal
what happens to ventral beta-catenin
it gets degraded by unbound GSK, creates a beta-catenin gradient
beta-catenin
dorsalizing, binds to Tcf3 and creates the organizer tissue by inducing organizer proteins chordin, noggin, and goosecoid
ventral mesoderm signals
VegT and Vg1, low nodal-related
high nodal-related
Beta-catenin and VegT, establish nodal-related gradient
default state of ectodermal tissues
neural, because of siamois and twin translation
BMP inhibitors
chordin, noggin, and follistatin
Wnt inhibitors
Cerberus, Frzb, Dickkopf, and IGF
BMP
bone morphogenetic proteins, induce ectoderm to become epidermal
organizer’s role, d/v axis formation
secrete BMP inhibitors Chordin, Noggin, and Follistatin, which block BMPs from inducing the ectoderm to be epidermal, so the ectodermal cells develop as neural`
functions of the organizer
self differentiating into dorsal mesoderm, dorsalizing neighbor meso into paraxial mesoderm, dorsalizing neighbor ectoderm (inducing neural tube), and initiating gastrulation movements
anterior-posterior axis formation
Wnt gradient
Left-right axis formation
Signaling gradients from A/P and D/V and also the expression of Nodal in lateral plate mesoderm on the left side
Xnr
Xenopus nodal related, expressed on the left side of the embryo and results in the heart being on the left side of the organism
Why is Nodal expressed on the left side?
specialized cillia rotate and push molecular determinents, including Nodal, to the left from the right. Nodal then induces Pitx2 and other left side genes
Zebrafish cleavage pattern
meroblastic, does not divide the yolk, occurs on the blastodisc at the top of the egg
blastoderm of zebrafish
cells atop the yolk that will become the embryo
