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

K.O. Hartley, Z. Hardcastle, R.V. Friday, E. Amaya and N. Papalopulu

Developmental Biology 238:168-184 (2001) Full Article (1012K)

Abstract

In vertebrates, BMP signalling before gastrulation suppresses neural development. Later in development, BMP

signalling specifies a dorsal and ventral fate in the forebrain and dorsal fate in the spinal cord. It is therefore possible

that a change in the competence of the ectoderm to respond to BMP signalling occurs at some point in development. We

report that exposure of 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 embryos and implanted beads soaked in BMP4 in the anterior neural plate. Suppression of most

anterior neural markers was observed. We conclude that most neural genes continue to require suppression of BMP

signalling into the neurula stages. Additionally, we report that BMP4 and BMP7 are abundantly expressed in the

prechordal mesoderm of the neurula stage embryo. This poses the paradox of how is the expression of most neural

genes maintained if they can be inhibited by BMP signalling. We show that at least one gene in the anterior neural plate

suppresses the response of the ectoderm to BMP signalling. We propose that the suppressive effect of BMP signalling

on the expression of neural genes coupled with localised suppressors of BMP signalling result in the fine-tuning of

gene expression in the anterior neural plate.

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