THE HEART OF METAMORPHOSING MEXICAN AXOLOTL BUT NOT THAT OF THE CARDIAC MUTANT IS ASSOCIATED WITH THE UP-REGULATION OF HOX A5

The Mexican axolotl (Ambystoma mexicanum) is a facultative neotene whi ch rarely undergoes metamorphosis in the wild. We now report for the f irst time a dramatic increase in the expression of HoxA5 in axolotl he arts as determined by RT-PCR and in situ hybridization analyses during spontaneous metamorphosis. The Mexican axolotl has a naturally occurr ing mutation called gene c which allows hearts in homozygous (c/c) emb ryos to form but never to beat. RT-PCR analysis has not shown any sign ificant differences of HoxA5 expression in normal and mutant hearts. T he predicted open reading frame of our already published partial cDNA clone of HoxA6 was confirmed by expressing it as a fusion protein with Glutathione transferase (GST fusion protein). Phylogenetic analysis w ith the deduced amino acid sequence of the isolated cDNA of the axolot l homolog of the murine HoxA5 shows that the axolotl sequence clusters more closely with the human and mouse HoxA5 homologs than with axolot l sequence. Western blot analysis revealed that anti-mouse HoxA5 antib ody recognizes the axolotl HoxA5 protein. (C) 1998 Academic Press.