Transgenic Xenopus embryos reveal that anterior neural development requires continued suppression of BMP signaling after gastrulation

In vertebrates, BMP signaling before gastrulation suppresses neural develop ment. Later in development, BMP signaling specifies a dorsal and ventral fa te in the forebrain and dorsal fate in the spinal cord. It is therefore pos sible that a change in the competence of the ectoderm to respond to BMP sig naling occurs at some point in development. We report that exposure of the anterior neural plate to BMP4 before gastrulation causes suppression of all neural markers tested. To determine the effects of BMP4 after gastrulation , we misexpressed BMP4 using a Pax-6 promoter fragment in transgenic frog e mbryos and implanted beads soaked in BMP4 in the anterior neural plate. Sup pression of most anterior neural markers was observed. We conclude that mos t neural genes continue to require suppression of BMP signaling into the ne urula stages. Additionally, we report that BMP4 and BMP7 are abundantly exp ressed in the prechordal mesoderm of the neurula stage embryo. This poses t he paradox of how the expression of most neural genes is maintained if they can be inhibited by BMP signaling. We show that at least one gene in the a nterior neural plate suppresses the response of the ectoderm to BMP signali ng. We propose that the suppressive effect of BMP signaling on the expressi on of neural genes coupled with localized suppressors of BMP signaling resu lt in the fine-tuning of gene expression in the anterior neural plate. (C) 2001 Academic Press.