In a screen to identify neuralizing factors from a Xenopusanterior neuroectoderm (ANE) cDNA library, Osada and colleagues discovered XMAN1 (see ), a nuclear envelope protein that is a novel antagonist of BMP signalling — the first finding that a nuclear membrane protein functions in this way.XMAN1 is expressed in the ANE at the neural stage of development, and induces anterior neural markers in ectoderm explants and a partial secondary axis when expressed ventrally. Importantly, XMAN1 inhibits BMP signalling downstream of the Alk3 BMP receptor in various assays, an inhibitory activity that resides in the C terminus of the protein, which can bind to Smads 1, 5 and 8 — intracellular mediators of BMP signalling. Exactly how this nuclear envelope protein regulates BMP signalling requires further study, but these findings highlight a new role for such proteins in this pathway.
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