APROCTOUS, A LOCUS THAT IS NECESSARY FOR THE DEVELOPMENT OF THE PROCTODEUM IN DROSOPHILA EMBRYOS, ENCODES A HOMOLOG OF THE VERTEBRATE BRACHYURY GENE

The proctodeum of the Drosophila embryo originates from the posterior end of the blastoderm and forms the hindgut. By enhancer-trap mutagene sis, using a P-element-lacZ vector, we identified a mutation that caus ed degeneration of the proctodeum during shortening of the germ band a nd named it aproctous (apro). Expression of the lacZ reporter gene, wh ich was assumed to represent expression of the apro gene, began at the cellular blastoderm stage in a ring that encompassed about 10-15% of the egg's length (EL) and included the future proctodeum, anal pads, a nd posterior-most part of the visceral mesoderm. In later stages, stro ng expression of lacZ was detected in the developing hindgut and anal pads. Expression continued in the anal pads and epithelium of the hind gut of larvae; the epithelium of the hindgut of the adult fly also exp ressed lacZ. The spatial patterns of the expression of lacZ in various mutants sug gested that the embryonic expression of apro was regulate d predominantly by two gap genes, tailless (tll) and huckebein (hkb): tll is necessary for the activation of apro, while hkb suppressed the expression of apro in the region posterior to 10% EL. Cloning and sequ encing of the apro cDNA revealed that apro was identical to the T-rela ted gene (Trg) that is a Drosophila homolog of the vertebrate Brachyur y gene. apro appears to play a key role in the development of tissues derived from the proctodeum.