Practice question

Gastrulation movements begin with formation of ventral furrow along ventral midline where presumptive mesoderm resides. Cells destined for mesoderm express concertina and folded gastrulation downstream of Dorsal targets twist, snail, triggering RhoGEF2 localization and Myosin II activation causing apical constriction. This coordinated shape change bends epithelium inward creating invagination tube that internalizes mesoderm beneath ectoderm. Dorsal side remains external ectoderm at this stage. After furrow closure mesodermal tube collapses and cells undergo epithelial-mesenchymal transition spreading dorsally to form muscle and cardiovascular precursors establishing germ layers.