Radial intercalation – a common morphogenetic process in which cells from germ layers deep in developing embryos interdigitate into more superficial layers – is essential for the tissue rearrangements that occur during gastrulation. Here (), Erich Damm and Rudolf Winklbauer use scanning electron microscopy and time-lapse recordings to analyse radial intercalation in the prechordal mesoderm (PCM) during Xenopus gastrulation. They show that this process involves cell reorientation in response to a long-range platelet-derived growth factor A (PDGF-A) signal and directional intercellular migration towards the ectoderm, the source of this signal. The PCM, they report, fails to spread during gastrulation when endogenous PDGF-A signalling is inhibited. However, expression of a short-splicing isoform of PDGF-A, but not of a long-splicing form that binds to the extracellular matrix, rescues PCM radial intercalation. These results provide the first insights into the molecular basis of radial intercalation movements in the vertebrate gastrula and identify distinct roles for PDGF-A isoforms during gastrulation.
