BIOL303 Lecture Notes - Western Clawed Frog, Regional Differentiation, Polarity In Embryogenesis
27 Nov 2013
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Visually, animal pole is dark and vegetal pole is light. Animal pole = upper part of egg, no yolk. Vegetal pole = lower part of egg, yolk. Fertilization can occur anywhere on the animal hemisphere. Sperm centrioles organize the microtubules in the egg. Microtubules in vegetal pole are arranged parallel to one another. The microtubule tracks allow for the cortical cytoplasm to rotate (30 degrees) within the inner cytoplasm. The cortical rotation can reveal a gray band of inner cytoplasm called the gray crescent. A rotation of the cortical cytoplasm 30 degrees with respect to the internal cytoplasm in the marginal region of the 1-cell amphibian embryo. The cortical rotation breaks the radial symmetry of the amphibian egg, specifying the orientation of the embryonic body axes. The entire outer cortex of the fertilised egg rotates relative to the mass of inner cytoplasm by an angle of about. 30 about an axis perpendicular to the primary animal-vegetal axis.
