Three structurally and functionally conserved Hlx genes in zebrafish

For the Hlx class, which includes homeodomains (HD) that are similar to Dro sophila H2.0, few members have been identified in vertebrates. In this repo rt, we describe three zebrafish genes, hlx1, hlx2 and hlx3, related to the murine Dbx genes. The proteins encoded by hlx1 and hlx2 have about the same sequence identity to Dbx1 (similar to 60%), suggesting that they derive fr om a duplication in the fish lineage. This is supported by similarities in the embryonic expression patterns and promoter sequence conservation. The z ebrafish Hlx3 protein is related to murine Dbx2, but it is apparently too d iverged to be orthologous. Our phylogenetic analysis of all the known HD se quences of the Hlx class also shows that it can be divided into at least tw o distinct families. All the Dbx-like genes have similar expression in the embryonic nervous system. However, the initial expression patterns of the z ebrafish hlx genes are quite unique, suggesting that some functional diverg ence has occurred between fish and mammals. (C) 1999 Elsevier Science B.V. All rights reserved.