CSB328H1 Study Guide - Midterm Guide: Dishevelled, Cyclin-Dependent Kinase 1, Pronucleus

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Published on 7 Sep 2012
School
UTSG
Department
Cell and Systems Biology
Course
CSB328H1
CSB328 MIDTERM REVIEW
SEA URCHIN LIFE CYCLE
- Fertilization
o Sperm binds to jelly layer
Egg releases ligand from vitelline envelope or jelly layer
Sperm receives ligand by receptors on head
Acrosome binds to sperm cell membrane
Acrosome releases enzymes into jelly layer by exocytosis
o Sperm cell membrane binds to egg cell membrane
Sperm sends acrosomal process (actin) towards vitelline envelope
Egg sends process (actin) towards sperm
Bindin on acrosomal process binds to bindin receptors on vitelline envelope and breaks down
vitelline envelope
Egg membrane and sperm membrane fuse
o Sperm haploid nucleus and centriole enter egg
Centriole rotates 180 degrees
o Female pronucleus and male pronucleus fuse
Centriole sends out microtubules toward the egg nucleus
Female pronucleus and male pronucleus become diploid nucleus
Centriole duplicate and position at opposite poles of the egg cell
Cell division by mitosis
o Fast block (transient; 1 minute)
Sperm touches vitelline envelope
Influx of Na+ ions into egg
o Slow block (permanent, physical)
Wave of Ca2+ release into cytoplasm around the egg
Cortical granules fuse with cell membrane
Release glycoproteins into space between vitelline envelope and cell membrane
Glycoproteins attract water
Separate vitelline envelope from cell membrane
Cleave bindin receptors on vitelline envelope
- Holoblastic cleavage (isolecithal) evenly distributed yolk
o 1st cleavage = meridional
o 2nd cleavage = meridional
o 3rd cleavage = equatorial
o 4th cleavage:
Animal pole = meridional
Vegetal pole = equatorial
- Gastrulation
o Ingression of skeletogenic mesenchyme (derived from autonomously specified micromeres) into
blastocoel
Skeletogenic mesenchyme cells lose affinity for hyaline layer on apical side
Skeletogenic mesenchyme cells gain affinity for basal lamina/ECM on basal side
Loss of adhesion molecules like cadherin
Cells undergo EMT and ingress into blastocoel
Skeletogenic mesenchyme cells migrate on ECM fibrils using integrins
Skeletogenic mesenchyme cells extend filopodia towards target
Form stable contact with ectodermal cells in that region by β-catenin-cadherin complex
o Localized between ectoderm and endoderm on vegetal pole (localized around
forming archenteron)
FGF and VEGF are signaling molecules secreted between endoderm and
ectoderm
o Localized to ventral side (localized around future mouth)
o Invagination of non-skeletogenic mesenchyme and endoderm into blastocoel
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Archenteron formation
Non-skeletogenic mesenchyme initiate invagination by apical constriction or bottle cell
formation
Endodermal cells undergo convergent extension to extend archenteron
Non-skeletogenic mesenchyme extend and contract filopodia towards basal side of
ventral ectoderm (mouth)
Ectoderm cell death when in contact with tip of archenteron
Mesenchymal cells ingress into blastocoel to become connective tissue leaving endoderm
epithelium
o Formation of gut tube from anus (dorsal or aboral) to mouth (ventral or oral)
Mouth (foregut) from endoderm that moves in first (secondary opening on ectoderm)
Anus (hindgut) from endoderm that moves in last (blastopore)
o Generation of dorsal-ventral axis
FROG LIFE CYCLE
- Holoblastic cleavage (mesolectithal) modedrate vegetal yolk deposition
o 1st cleavage = incomplete radial (equal) meridional
o 2nd cleavage = incomplete radial (equal) meridional
o 3rd cleavage = unequal equatorial
o Cleavage continues synchronously until MBT
- MBT initiation of zygotic transcription; cleavages slow down and become asynchronous; after 12th cleavage
o MPF is maternally deposited in the cytoplasmic egg and is progressively depleted as cleavage occur
Heterodimer (Cyclin B and cdc2)
Cyclin B regulates cdc2
Cyclin B is synthesized and degraded by other maternal factors
Active MPF heterodimer (Cyclin B and cdc2) M phase
Inactive MPF heterodimer (cdc2) S phase
o Volume of the cytoplasm is decreases as cleavage occurs which will deplete cytoplasmic pool of MPF
o Increasing DNA to cytoplasm ratio is sufficient to induce premature MBT
Inject extra male pro-nucleus into egg cell
Inject DNA
- Generation of dorsal-ventral axis specified upon fertilization
o Point of sperm entry on animal pole
o Cortical rotation 30° toward vegetal pole
o Reveal gray crescent from inner cytoplasm
o Cortical rotation is necessary for dorsal tissue development
Dsh (and β-catenin) localized to vegetal pole prior to cortical rotation
Dsh (and β-catenin) translocated to dorsal side after cortical rotation upon fertilization
Experiment 1
UV frog embryo or Dsh mutant or Dsh inhibitor
Depolymerize microtubules required for cortical rotation
Cortical rotation fails and Dsh remains at vegetal pole and prevents dorsal-ventral axis
formation
Embryo is ventralized ventral (posterior) structures are induced to form at the expense
of dorsal (anterior)
Microtubules are necessary for cortical rotation
Microtubules are necessary for dorsal development
Cortical rotation is necessary for dorsal development indirectly
Experiment 2
LiCl treatment on frog embryo
LiCl inhibits GSK3
Nuclear accumulation of β-catenin is sufficient to induce dorsal tissue on ventral side
(ectopic)
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Document Summary

Fertilization: sperm binds to jelly layer. Egg releases ligand from vitelline envelope or jelly layer. Sperm receives ligand by receptors on head. Acrosome releases enzymes into jelly layer by exocytosis: sperm cell membrane binds to egg cell membrane. Sperm sends acrosomal process (actin) towards vitelline envelope. Bindin on acrosomal process binds to bindin receptors on vitelline envelope and breaks down vitelline envelope. Egg membrane and sperm membrane fuse: sperm haploid nucleus and centriole enter egg. Centriole rotates 180 degrees: female pronucleus and male pronucleus fuse. Centriole sends out microtubules toward the egg nucleus. Female pronucleus and male pronucleus become diploid nucleus. Centriole duplicate and position at opposite poles of the egg cell. Cell division by mitosis: fast block (transient; 1 minute) Influx of na+ ions into egg: slow block (permanent, physical) Wave of ca2+ release into cytoplasm around the egg. Release glycoproteins into space between vitelline envelope and cell membrane.

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