CSB328 Midterm Study Notes

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Cell and Systems Biology
Stephanie Lepage

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 1 cleavage = meridional o 2 cleavage = meridional rd o 3thleavage = equatorial o 4 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  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 1 cleavage = incomplete radial (equal) meridional nd o 2 rdeavage = incomplete radial (equal) meridional o 3 cleavage = unequal equatorial o Cleavage continues synchronously until MBT - MBT  initiation of zygotic transcription; cleavages slow down and become asynchronous; after 12 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)  Embryo is dorsalized  dorsal (anterior) structures are induced to form at the expense of ventral (posterior) - Gastrulation  movement of vegetal cells to contact blastocoel roof
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