Genetic evidence for posterior specification by convergent extension in the Xenopus embryo.

Genetic studies substantiate that mesodermal convergent extension expressed behind the anteroposterior borderline, in the form of a gradient with the posterior apex after gastrulation, regulates morphogenesis of the posterior zone at the dorsal and dorso-lateral levels which is in full agreement with the model of dorsalization-caudalization. In contrast, how anteroposterior specification of mesodermal tissues occurs at the ventral and latero-ventral levels is not yet understood.