Evolution of Ftz protein function in insects

The Drosophila, gene fushi tarazu (ftz) encodes a homeodomain-containing tr anscriptional regulator (Ftz) required at several stages during development . Drosophila melanogaster ftz (Dm-ftz) is first expressed in seven stripes defining alternate parasegments of the embryo-a "pair-rule" segmentation fu nction [1, 2]. It is then expressed in specific neural precursor cells in t he central nervous system and finally in the developing hindgut [3]. An Ort hopteran ortholog of ftz (Sg-ftz, formally Dax) has been isolated from the grasshopper Schistocerca gregaria [4]. The pattern of Sg-ftz expression in Schistocerca, embryos suggests that some developmental roles of the ftz gen e are likely to be conserved between these two species (e.g., CNS functions ) while others may have diverged (e.g., segmentation functions). To test wh ether the function of the Ftz protein itself differs between these two spec ies, here we compare the functions of Sg-Ftz and Dm-Ftz proteins by express ing both in Drosophila embryos. Sg-ftz mimics only poorly several segmentat ion roles of Dm-ftz (engrailed activation, wingless repression, and embryon ic cuticle transformation). However, the two proteins are similarly active in the rescue of a CNS-specific ftz mutant. These findings argue that this ftz CNS function is mediated by conserved parts of the protein, while effic ient pair-rule function requires sequences present specifically in the Dros ophila protein.