The BMP-related protein Radar: a maintenance factor for dorsal neuroectoderm cells?

We have previously cloned several members of the TGF-beta superfamily of gr owth factors in zebrafish, one of which, Radar, belongs to the Dpp-Vg1-rela ted (DVR) subgroup, with highest homology to GDF6. The pattern of expressio n of Radar suggested a possible involvement in several induction steps duri ng embryogenesis including in the dorsal neural tube, red blood cells, the dorsal fin and the retina. We have analyzed the pattern of expression of Ra dar in comparison with that of a marker of dorsal neural tube structures, m sxC and show that Radar and msxC are expressed in similar and/or adjacent t issues throughout embryogenesis. In order to demonstrate a functional relat ionship between these two proteins, we have generated a full-length cDNA fo r Radar and shown that Radar overexpression by DNA injection maintains expr ession of msxC in tissues where it is normally expressed then turned off, i n particular in the dorsal neurectoderm. Study of the phenotype of a mutant carrying a deletion of Radar shows a loss of identity and death of the cel ls of the dorsal neural tube. Taken together these results suggest that Rac ial could be involved in maintaining the identity of cells of the dorsal-mo st neural tube and of at least a subset of neural crest cells. (C) 1999 Els evier Science Ireland Ltd. All rights reserved.