Isolation, expression and regulation of a zebrafish paraxis homologue.

The formation of somites involves the subdivision of segmented presomitic mesoderm into segmentally arranged somite blocks. In mice and chicks, the basic-helix-loop-helix (bHLH) gene, paraxis, is involved in this process. Here, we report the isolation of a zebrafish homologue of paraxis, par1. par1 is expressed in presomitic paraxial mesoderm from late gastrula stages, and expression is maintained in ventrolateral cells after somite formation. In spt- embryos, par1 expression is both delayed and severely reduced whereas in flh- embryos, ectopic transcripts are detected in axial mesoderm. Spatial regulation of par1 expression within the somites is affected in several mutants with defects in axial midline tissues. Copyright 1998 Elsevier Science Ireland Ltd. All Rights Reserved