Methods for the Study of Apical Constriction During Ascidian Gastrulation.

Gastrulation is the first major morphogenetic event during ascidian embryogenesis. Ascidian gastrulation begins with the invagination of the endodermal progenitors, a two-step process driven by individual cell shape changes of endoderm cells. During the first step, endoderm cells constrict apically, thereby flattening the vegetal side of the embryo. During the second step, endoderm cells shorten along their apicobasal axis and tissue invagination ensues. Individual cell shape changes are mediated by localized actomyosin contractile activity. Here, we describe methods used during ascidian endoderm apical constriction to study myosin activity and cellular morphodynamics with confocal and light sheet microscopy and followed by quantitative image analysis.