BIOL 443 Lecture Notes - Lecture 9: Polarity In Embryogenesis, Fate Mapping, Endoderm
Document Summary
Snail development: spirally cleaving embryos produce a very small or no blastocoel, fewer cleavages occur before gastrulation, spiral cleavage results in stereoblastulae, the snail fate map shows that. Head ectoderm arises from 1st quartet micromeres. Nervous system arises from 1st and 2nd quartet micromeres. Muscle mesoderm (ectomesoderm) arises from 2nd and 3rd quartet micromeres. Most mesoderm (kidney, heart, primordial germ cells, ect. ) arises from the 4d micromere: many mollusks use a polar lobe to sequester morphogenic determinants (mras for transcription factors and paracrine factors). Suppressing b-catenin leads to no heart muscles, or hindgut. This role of b-catenin in autonomously specifying endoderm and ectoderm is found across the animal kingdom. Nanos also plays a role in the 4d micromere function, including specifying. Still going with snail development germ cells: gastrulation proceeds relatively early in snails. It proceeds by invagination of the endoderm to form the primitive gut by epiboly: animal cap micromeres multiply and overgrow the vegetal macromeres.
