07 Development - De lopm nt ve e Xenopus Egg Xenopus Adult Main S s of De lopm nt tage ve e rtilization Fe s Produce thezygote le C avage ll ce

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Development Xenopus Egg Xenopus Adult
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Main Stages of Development Fertilization Produces the zygote Cleavage cell division to produce blastula Gastrulation formation of germ cell layers, primitive gut Organogenesis formation of organs and tissues
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Step 1. Fertilization and Establishing the Three Axes Animal and Vegetal Poles In many species (not including humans), the Anterior-Posterior axis is determined prior to fertilization by the uneven distribution of substances in the cytoplasm including specific mRNAs, proteins, and yolk (stored nutrients). In the egg of the frog, a concentration of dark pigment granules at one pole (the animal pole) , and a concentration of yolk at the other (the vegetal pole ) make this uneven distribution of substances clearly visible.
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The Dorsal-Ventral Axis is Established by Rearrangement of the Cytoplasm and Formation of the Gray Crescent Fig. 20.2 Purves Cortical Rotation Gray Crescent After fertilization the plasma membrane and cortex rotate toward the point of sperm entry forming the Grey Crescent . The grey crescent defines the site of the dorsal side of the embryo
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The “Definition” of Dorsal is Under the Control of Cytoplasmic Determinants Fig. 20.3 Purves Blue = GSK-3: a protein kinase, phosphorylates b-catenin to target it for degradation (Maternal effect gene) Red = GSK-3 Inhibitor: is concentrated at the vegetal pole Peach = b-catenin: a component of cell-cell signaling cascade that specifies “dorsal” as development proceeds
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The Three Axes Once the anterior-posterior and dorsal- ventral are established, left and right are fixed by the first cleavage (ce ll division) which bisects the grey crescent.
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Step 2. Cleavage Cell division (without growth) Formation of Blastula and Blastocoel
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This note was uploaded on 11/12/2010 for the course BSCI BSCI 110B taught by Professor Johnson during the Spring '09 term at Vanderbilt.

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07 Development - De lopm nt ve e Xenopus Egg Xenopus Adult Main S s of De lopm nt tage ve e rtilization Fe s Produce thezygote le C avage ll ce

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