Reorientation of the primary body axis by ectopic embryonic cWnt signaling.

Gastrulation is a crucial time during embryogenesis when cells make important decisions on what larval or adult tissues (i.e. ectodermal, mesodermal, or endodermal) are going to generate. The evolution of gastrulation was a pivotal event during metazoan evolution, as it paved the way for diversification of the metazoan clade from a hollow, ciliated, radially symmetrical ancestor (1, 2). The position of the site of gastrulation (that segregates internal endomesodermal precursors from outer ectodermal tissue) has played a role in our understanding patterns of body plan evolution (e.g. deuterostomes vs protostomes) and is tightly regulated during development. In bilaterians (a large clade of bilaterally symmetrical animals that represent over 99% of all extant species), the site of gastrulation is determined by a localized molecular asymmetry resulting from a differential distribution of maternal determinants (3) along the so-called an ...