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 li mbs, tails and neural retinae. Five novel T-box genes in the Japanese newt were isolated and their expression was analyzed, together with another T-bo x gene of brachyury, during embryogenesis and in the developing and regener ating limbs and tail. Four are designated CpTbx2, CpTbx3, CpTbx6R and CpEom esodermin based on molecular phylogenetic analyses, and the other is named CpUbiqT from its ubiquitous expression. While all were expressed during emb ryogenesis, 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 expre ssion levels in regenerating limbs, whereas only CpTbx2 showed significant up-regulation in regenerating tails. Compared with orthologous genes in oth er species, CpTbx2, CpTbx3 and CpEomesodermin showed several notable differ ences such as an abundance of maternal transcripts of CpEomesodermin, a uni que insertion sequence within the T-box domain of CpTbx2; and a lack of vis ible expression of CpTbx2 and CpTbx3 in the apical ectodermal region of dev eloping limbs. In view of the uniqueness of the newt, these results are dis cussed with respect to the possibility of their involvement in regeneration .