Regulation of Zebrafish Gastrulation Movements by slb/wnt11 (original) (raw)

Epiboly movements Shortly after midblastula transition, the embryo consists of a mass of cells, the blastoderm, positioned on top of a big yolk cell; this stage is the so-called blastula stage. The blastoderm can be subdivided into an outer epithelium of enveloping layer (EVL) cells that cover the non-epithelial deep layer (DEL) cells, from which the embryo proper will form. Epiboly starts when EVL and DEL cells begin to spread over the yolk cell. In the DEL, epiboly is triggered by radial intercalations of cells deep within the blastula that move upwards into more superficial layers, thereby thinning the DEL along its 'innerouter' extent and expanding its coverage over the yolk cell (figure 1 A,B). The EVL layer, by contrast, does not undergo radial cell intercalations. Instead, it connects at its leading edge to the yolk cell membrane and moves towards the vegetal pole of the et al., 2004; Solnica-Krezel, 2005). Alternatively, since hypoblast cells simultaneously internalize around the circumference of the germ-ring, prechordal plate progenitor cells could be pushed away from the germring towards the animal pole by newly ingressing cells at the blastoderm margin rather than actively migrate into the anterior direction. This assumption is supported by studies showing that single wild-type cells transplanted into the germ-ring of mzoep mutantswhich lack nearly all mesendodermal induction and internalization-are able to internalize, but hardly move towards the animal pole, pointing at the possibility that this movement requires the simultaneous ingression of other mesendodermal cells (Carmany-Rampey and Schier, 2001; Montero et al., 2003). zebrafish schmalspur/sur mutants) and regulate the transcription of specific target genes. Among these genes are determinants of mesendodermal fates, like goosecoid (gsc) or no