Taranis regulates posterior identity during imaginal disc regeneration. Keaton J Schuster, Andrea Skinner, Rachel K Smith-Bolton. Cell & Developmental Biology, University of Illinois at Urbana-Champaign, Urbana, IL.

   During regeneration, proper patterning must be re-established in order to generate a functional organ or appendage. How a regenerating structure repatterns is still an open question. We address this problem using a genetic ablation system in wing imaginal discs of Drosophila melanogaster. Our initial characterization of patterning during regeneration showed dramatic changes in gene expression, signaling and patterning. Furthermore, we observed pattering intermediates not seen during normal development. Therefore, we hypothesized that regeneration-specific mechanisms help pattern the regrown tissue after damage. To discover novel factors that regulate cell fate and patterning during regeneration, we are performing a dominant modifier screen using isogenic deficiencies. We identified a deficiency that, when heterozygous, resulted in regenerated wings with posterior to anterior fate transformations, but did not affect normal development. In these mutant regenerating wing discs, expression of the posterior selector gene engrailed was initially elevated before decreasing, allowing cells to adopt anterior fates. Alleles of taranis (tara), which encodes a putative Trithorax Group protein and a member of the TRIP-Br family, recapitulated this regeneration-specific transformation phenotype. We will present evidence that Tara regulates the expression of engrailed during regeneration to ensure maintenance of posterior cell fate. Thus we have both demonstrated that regeneration-specific mechanisms are key for regulating cell fate during regrowth, and identified and characterized one such mechanism.