A NEW TINMAN-RELATED GENE, NKX2.7, ANTICIPATES THE EXPRESSION OF NKX2.5 AND NKX2.3 IN ZEBRAFISH HEART AND PHARYNGEAL ENDODERM

The Drosophila homeobox gene tinman and its vertebrate homologs Nkx-2. 5 and Nkx-2.3 are critical determinants of cardiac development, We rep ort here the identification of a new tinman-related gene, nkx2.7, as w ell as orthologs of Nkx-2.5 and Nkx-2,3 in the zebrafish. Analysis of their expression in the developing zebrafish embryo reveals that nkx2. 7 transcripts are the first to appear in cardiac mesodermal and pharyn geal endodermal precursors of the anterior hypoblast, anticipating bot h temporally and spatially the later expression of nkx2.5 and nkx2.3 i n these lineages, The preeminence of nkx2.7 in these embryonic lineage s is consistent with a key role in cell fate determination, perhaps in part through the induction of nkx2.5 and nkx2,3. The findings provide the first molecular clues as to the spatial organization of endoderma l and cardiac mesodermal precursors in the zebrafish hypoblast immedia tely following gastrulation. They suggest a coordinate role for these three tinman-related genes in the development of the heart and pharyng eal arches, and reinforce the paradigm of gene duplication and subspec ialization between Drosophila and vertebrate species. The results prov ide a framework in which to analyze potential changes in tinman-relate d gene expression during abnormal zebrafish development. (C) 1996 Acad emic Press, Inc.