Conservation of sequence and expression of Xenopus and zebrafish dHAND during cardiac, branchial arch and lateral mesoderm development

dHAND and eHAND are related basic helix-loop-helix transcription factors th at are expressed in the cardiac mesoderm and in numerous neural crest-deriv ed cell types in chick and mouse. To better understand the evolutionary dev elopment of overlapping expression and function of the HAND genes during em bryogenesis, we cloned the zebrafish and Xenopus orthologues. Comparison of dHAND sequences in zebrafish, Xenopus, chick, mouse and human demonstrated conservation throughout the protein. Expression of dHAND in zebrafish was seen in the earliest precursors of all lateral mesoderm at early gastrulati on stages. At neurula and later stages, dHAND expression was observed in la teral precardiac mesoderm, branchial arch neural crest derivatives and post erior lateral mesoderm. At looping heart stages, cardiac dHAND expression r emained generalized with no apparent regionalization. Interestingly, no eHA ND orthologue was found in zebrafish. In Xenopus, dHAND and eHAND were co-e xpressed in the cardiac mesoderm without the segmental restriction seen in mice. Xenopus dHAND and eHAND were also expressed bilaterally in the latera l mesoderm without any left-right asymmetry. Within the branchial arches, X dHAND was expressed in a broader domain than XeHAND, similar to their mouse counterparts. Together, these data demonstrate conservation of HAND struct ure and expression across species. (C) 2000 Elsevier Science Ireland Ltd. A ll rights reserved.