REGULATION, FUNCTION AND POTENTIAL ORIGIN OF THE DROSOPHILA GENE SPALT ADJACENT, WHICH ENCODES A SECRETED PROTEIN EXPRESSED IN THE EARLY EMBRYO

During early embryogenesis of Drosophila the spatial and temporal expr ession patterns of the region-specific homeotic gene spalt (sal) and t he neighbouring gene spalt adjacent (sala) extensively overlap. We sho w that the initial expression patterns of the two genes in the blastod erm also have identical genetic contols. However, while sal encodes a transcription factor, sala encodes a precursor protein from which a fu nctional signal peptide is cleaved off to generate the secreted sala p rotein. Ectopic expression or absence of sala protein does not affect embryonic development, adult viability or fertility. In addition to sa l and sala, we identified a third gene nearby, termed spalt related (s alr), which shares coding sequence similarity and a late embryonic exp ression pattern with sal, but lacks the early expression domains that are shared by sal and sala. These results suggest that the three genes and their present cis-regulatory regions arose through a chromosomal rearrangement involving local duplication and transposition events in the 32F/33A region on the left arm of the second chromosome.