Expression of five novel T-box genes and brachyury during embryogenesis, and in developing and regenerating limbs and tails of newts.

Several T-box genes are considered to play important roles in developing limbs, tails and neural retinae. Five novel T-box genes in the Japanese newt were isolated and their expression was analyzed, together with another T-box gene of brachyury, during embryogenesis and in the developing and regenerating limbs and tail. Four are designated CpTbx2, CpTbx3, CpTbx6R and CpEomesodermin based on molecular phylogenetic analyses, and the other is named CpUbiqT from its ubiquitous expression. While all were expressed during embryogenesis, only four of them (CpTbx2, CpTbx3, CpUbiqT and brachyury) were detected in developing limbs and/or tails. Except for brachyury, they were continuously expressed in normal adult appendages and showed elevated expression levels in regenerating limbs, whereas only CpTbx2 showed significant up-regulation in regenerating tails. Compared with orthologous genes in other species, CpTbx2, CpTbx3 and CpEomesodermin showed several notable differences such as an abundance of maternal transcripts of CpEomesodermin, a unique insertion sequence within the T-box domain of CpTbx2, and a lack of visible expression of CpTbx2and CpTbx3 in the apical ectodermal region of developing limbs. In view of the uniqueness of the newt, these results are discussed with respect to the possibility of their involvement in regeneration.