Biology 3338A Lecture Notes - Lecture 16: Invagination, Regional Differentiation, Beta-Catenin
9 Jul 2016
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Gastrulation in mammals is complicated, the idea is the same; you start off with circular egg and make 3 layers (ectoderm, endoderm and mesoder; ie lots of induciton), and you need to make the 3 axis. With sea urchin its simple cus you only make 1 axis (anterior/posterior), sea urchin isn"t bilateral, it"s a circle (we are bilateral ie 3 axis). In sea erchins you have defined cleavages, and you always end up with micromeres at the bottom. That bottom is where the vegital plate is, its where blastopore forms, its posterior (anus). this is related to gravity. We are not 100% sure if gravity is the reason for posterior position at the bottom. Sea urchins only need anterior posterior so gravity is posterior and the other end is anterior (its simple). When you deal with vertebrates, gravity can"t be used to define all the 3 axis, we need something else.
