GENETIC SCREENS TO IDENTIFY ELEMENTS OF THE DECAPENTAPLEGIC SIGNALINGPATHWAY IN DROSOPHILA

Pathways for regulation of signaling by transforming growth factor-bet a family members are poorly understood at present. The best geneticall y characterized member of this family is encoded by the Drosophila gen e decapentaplegic (dpp), which is required for multiple events during fly development. We describe here the results of screens for genes req uired to maximize dpp signaling during embryonic dorsal-ventral patter ning. Screens for genetic interactions in the zygote have identified a n allele of tolloid, as well as two novel alleles of screw a gene rece ntly shown to encode another bone morphogenetic protein-like polypepti de. Both genes are required for patterning the dorsalmost tissues of t he embryo. Screens for dpp interactions with maternally expressed gene s have identified loss of function mutations in Mothers against dpp an d Medea. These mutations are homozygous pupal lethal, engendering gut defects and severely reduced imaginal disks, reminiscent of dpp mutant phenotypes arising during other dpp dependent developmental events. G enetic interaction phenotypes are consistent with reduction of dpp act ivity in the early embryo and in the imaginal disks. We propose that t he novel screw mutations identified here titrate out some component(s) of the dpp signaling pathway. We propose that Mad and Medea encode ra te-limiting components integral to dpp pathways throughout development .