University:
Amherst College
Course:
BIOL 220 | Developmental Biology
Academic year:

2022
Views:

22

Pages:

13
Author:

Kyler Larsen

What is Regulation? • Regulation is the ability to make up for missing parts • Sea urchin embryos are highly regulative – separate first 2 cells or first 4 cells small but normal larvae – but if you separate top and bottom halves (animal and vegetal) you get exaggerated cilia from animal and gut with a little skeleton (spicules) from vegetal – isolated micromeres only form skeleton Quads from One Embryo Is There a Pre-Partitioned Gradient of Animalizing and Vegetalizing Stuff? Micromeres Will Induce Gut from Pre-Ectoderm (Communication) SU Gastrulation: 3 Steps • How does sea urchin accomplish gastrulation? • Where do the forces come from? • Step 1 – cells form vegetal plate, elongating – vegetal plate invaginates forming archenteron – 1o mesenchyme cells break free and ingress • later form skeleton SU Early Gastrula SU Gastrulation: Step I What Happens to the Vegetal Plate? – Changes in plate • ~ 1/3 ultimate invagination • use microfilaments to bend by change cell shapes – Local forces • isolated vegetal plate buckles – Adhesion changes • two hyaline layers • chondroitin sulfate secreted into the inner layer takes up water • buckles like a thermopile Mechanism of SU Gastrulation I What Happens to the Vegetal Plate? SU Gastrulation: Step I What Happens to the Primary Mesencyhme? • Fate of 1o mesenchyme – changes in cell affinities • to hyaline and other cells declines • to basement lamina increase • opposite to cells of vegetal plate – express new surface molecules and migrate on ECM fibronectin (expt: antibodies block) – go to targets at equator and stop in bilateral pattern – fuse to make spicules (skeleton) Mechanism of SU Gastrulation I What Happens to the Primary Mesencyhme? SU Gastrulation: Step II How Is Most of the Extension Accomplished? • further elongation of gut wall • cells migrate over one another • convergent extension – flattening of individual cells – intercalation • thins and elongates wall Mechanism of SU Gastrulation II SU Gastrulation: Step III How is the Final Extension Accomplished? • Completion of gastrulation – requires 2o mesenchyme • escape from roof of advancing archenteron • form pseudopods • attach to wall of blastula at site of future mouth – expt: distort wall, still finds target • attaches to roof of archenteron and pulls it up – expt: swell to break contacts, springs apart – expt: laser ablate some of cells, slows in proportion to loss • creates a tube (gut)

Developmental Patterns What is Regulation

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