01:119:116 Lecture Notes - Lecture 17: Cleavage Furrow, Polarity In Embryogenesis, Maternal Effect
21 Mar 2017
School
Department
Course
Professor
Document Summary
In sea urchin: eggs have already completed meiosis. Increases protein synthesis-uses maternal mrna already in cell. Sperm nucleus guided to egg nucleus by microtubules. Karyogamy-several hours in humans; 20 min in sea urchins. Zygote: diploid and totipotent (totally to do anything) after 3 hours it cannot. Characterized by rapid mitosis, very short/no g1 or g2 (gap) phases, no growth or protein synthesis. Presence of yolk effects pattern of division: stages. Mammals: 12-26 hours after sperm binds to egg. And the division pattern is uniform across the embryo. Holoblastic cleavage-yolk slows down cytokinesis but furrow passes through egg. In birders, other reptiles, many fishes, and insects: gastrulation. 3 embryonic germ layers (diploblastic vs. triploblastic: gastrulation in sea urchins. Sequence of events: mesenchyme at vegetal pole-migrate to blastocoel, cells at vegetal pole flatten-causing invagination, endoderm cells form archenteron, filopodia contract & drag archenteron, archenteron fuses with blastocoel wall (remember archenteron = primitive gut, gastrulation in frogs.
