BIOMG 1350 Lecture Notes - Lecture 22: African Clawed Frog, Polarity In Embryogenesis, Conjoined Twins
28 Nov 2016
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Biomg1350 lecture 22 induction: from classical embryology to molecular biology. Xenopus laevis as developmental model: large eggs: 1 mm, rapid development to tadpole: 4. 5 days, experimental manipulations are possible: Cannot isolate mutants (long generation time & large size) But gene knockdowns are possible (antisense oligos, etc. ) Creates a morphogen gradient that patterns the embryo along the dorsal ventral axis. The xenopus egg and its asymmetries: vegetal pole contains the yolk. In amphibians, light and clear: animal pole contains the maternal nucleus. In amphibians, darker color: after fertilization, grey crescent appears. Cleavage almost always cuts this crescent in half. Spemann"s litigation experiment: fist cleavage grey crescent separation of blastomeres and development, development of two normal tadpoles, however sometimes, But other is just a belly piece : this happens because the separation didn"t separate the grey crescent equally, this experiment revealed the existence of cytoplasmic determinants that specify the dorsal side of the embryo.
