Zinc-finger Paralogues tsh and tio Are Functionally Equivalent During Imaginal Development in Drosophila and Maintain Their Expression Levels Through Auto- and Cross-Negative Feedback Loops

teashirt (tsh) and tiptop (tio) are two Drosophila gene paralogues encoding zinc-finger transcription factors. While tsh is an important developmental regulator, do null individuals are viable and fertile. Here, we show that do and tsh have coincident expression domains in the imaginal discs, the precursors of the adult body, and that both genes show similar functional properties when expressed ectopically. Furthermore, do is able to rescue the development of tsh mutants, indicating that both genes are functionally equivalent during imaginal development. Of interest, the transcriptional regulation of do and tsh is linked by a negative feedback loop. This mechanism might be required to maintain a tight control on the total levels of tio/tsh and could help explaining why Drosophila keeps an apparently dispensable gene. Developmental Dynamics 238:19-28, 2009. (C) 2008 Wiley-Liss, Inc.