Homeobox genes in the Australian lungfish, Neoceratodus forsteri

The aim of the present study was to determine whether the postulated gnatho stome duplication from four to eight; Hox clusters occurred before or after the split between the actinopterygian and sarcopterygian fish by character izing Hox genes from the sarcopterygian lungfish, Neoceratodus forsteri. Si nce lungfish have extremely large genomes, we took the approach of extracti ng pure high molecular weight (MW) genomic DNA to act as template for polym erase chain reaction (PCR) of the conserved homeobox domain of the highly c onserved HOX. genes. The 21 clones thus obtained were sequenced and transla ted in a BLASTX protein database search to designate Hox gene identity. Fou rteen of the clones were from Hox genes, two were Hox pseudogenes, four wer e Gbx genes, and one most closely resembled the homeobox gene, insulin upst ream factor 1. The Hox genes identified were from all four tetrapod cluster s A, B, C, and D, confirming their presence in lungfish, and there is no ev idence to suggest more than these four functional Hox clusters, as is the c ase in teleosts. A comparison of Hox group 13 amino acid sequences of lungf ish, zebrafish, and mouse provides firm evidence that the expansion of Hox clusters, as seen in zebrafish, occurred after separation of the actinopter ygian and sarcopterygian lineages. (C) 1999 Wiley-Liss, Inc.