A NOVEL FAMILY OF T-BOX GENES IN URODELE AMPHIBIAN LIMB DEVELOPMENT AND REGENERATION - CANDIDATE GENES INVOLVED IN VERTEBRATE FORELIMB HINDLIMB PATTERNING/

In certain urodeles, a lost appendage, including hand and foot, can be completely replaced through epimorphic regeneration. The regeneration process involves cellular activities similar to those described for e mbryogenesis. Working on the assumption that the morphological pattern specific for a forelimb or a hindlimb is controlled by different gene activities in the two limbs, we employed a mRNA differential display screen for the detection of candidate limb identity genes, Using this approach, we have isolated a newt gene which in regenerating and devel oping limbs reveals properties expected of a gene having a role in con trolling limb morphology: (1) it is exclusively expressed in the forel imbs, but not hindlimbs, (2) during embryonic development its expressi on is co-incident with forelimb bud formation, (3) it has an elevated message level throughout the undifferentiated limb bud and the blastem a, respectively, and (4) it is expressed only in mesenchymal, but not in epidermal tissues, This novel newt gene shares a conserved DNA-bind ing domain, the T-box, with putative transcription factors including t he Brachyury (T) gene product, In a following PCR-based screen, we use d the evolutionarily conserved T-box motif and amplified a family of r elated genes in the newt; their different expression patterns in norma l and regenerating forelimbs, hindlimbs and tail suggest, in general, an important role of T-domain proteins in vertebrate pattern formation .