Two distal-less related homeobox-containing genes expressed in regeneration blastemas of the newt.

Urodeles, like the newt, are able to replace their limbs and tail following amputation by the formation of a blastema, a mass of proliferating mesenchymal cells originating from the tissue adjacent to the cut surface. As this capacity may involve genetic control, we investigated in adult tissues the expression of genes controlling embryonic development. We screened a newt cDNA library with a redundant oligonucleotide specific to the highly conserved third helix of the DNA-binding domain of homeobox genes. Five classes of cDNA have been isolated. We report the nucleotide sequence and the tissue distribution of two of them, NvHBox-4 and NvHBox-5. The amino acid sequences of both homeodomains are highly homologous (83 and 87% identity) to distal-less, a Drosophila homeobox gene expressed during the development of appendages. NvHBox-4 and NvHBox-5 express respectively 2.8 and 2 kb transcripts. The pattern of expression of both genes is identical in adult tissues of the newt. Polyadenylated transcripts are detectable in the forelimbs, hindlimbs, the tail, flank, and brain as well as in limb and tail blastemas. Analysis of dissected tissue from the hindlimbs indicated that the expression of both genes is restricted to the skin. This work is a first step toward understanding the possible relation between sustained expression of homeobox-containing genes in adult newt tissues and regeneration potential.