Expression of Hox A11 in the limb and the regeneration blastema of adult newt.

Homeoproteins are functionally involved in pattern formation of developing systems and are potentially good candidates to regulate positional information during limb regeneration in the newt. Here we report the molecular structure of Hox A11 and its pattern of expression during the regeneration of adult newt appendages. The transcriptional unit of the gene is composed of two exons separated by an intron. Northern blots revealed two major transcripts; a size difference would result from using two different polyadenylation signals. Therefore, the gene would encode a single protein that is very homologous to other vertebrate counterparts. The pattern of expression of Hox A11 in the adult newt shows interesting findings in relation to limb regeneration. First, expression is found in both intact limb and tail, showing maintenance of expression of an important regulator of development in the appendages of the adult newt. Second, Hox A11 is expressed mainly in the muscle and the bone of intact limbs, two tissue fractions known to participate in blastemal fate determination. Third, the level of Hox A11 expression increases drastically in both limb and tail regeneration blastemas, suggesting that the population of expressing cells is preferentially recruited during blastemal formation. Finally, proximal blastemas (mid-humerus) significantly express higher levels of transcript compared with distal ones (mid-radius and ulna). These features of expression suggest that Hox A11 may participate in limb pattern formation by specifying positional information to the progenitor cells of the regenerate.