Possible roles for Wnt genes in growth and axial patterning during regeneration of the tail in urodele amphibians.

Urodele amphibians are nearly the only adult vertebrates able to regenerate their missing or amputated tail. An interesting aspect of this biological model lies in the ability of regenerates to differentiate the spinal cord (SC), the vertebral cartilage, and muscles. The main questions addressed in this study concern the possible roles of Wnt genes in these regenerative processes. We have previously reported the expression pattern of a Pleurodeles Waltl wnt-10a gene (Pwnt-10a) in tail blastema (Caubit et al. [1997] Dev. Dyn. 208:139-148). We report here the cloning and tissue distribution of three additional Wnt genes (Pwnt-5a, Pwnt-5b, and Pwnt-7a) in adult and regenerating tail tissues and in the central nervous system (CNS) of adult newt. In adult and regenerating tails, Pwnt-5a and Pwnt-5b transcripts exhibit a graded distribution along the antero-posterior (A-P) axis, the maximal accumulation of these transcripts being detected in the mesenchyme within the subectodermal apical region of the normal tail and blastema. In contrast to Pwnt-5a and Pwnt-5b, Pwnt-7a is expressed in adult normal tail skin and in the epidermis of the regenerating tail. In the adult CNS, Pwnt-5a, Pwnt-5b, Pwnt-7a, and Pwnt-10a genes are expressed in sharp overlapping but not identical domains along the A-P axis. The sustained expression of Wnt genes in the adult newt and the spatial distribution of transcripts in adult and regenerating tail tissues suggest roles of these genes in continuous growth capacities in the urodeles and may explain the ability for CNS and tail regeneration.