TORSO-LIKE ENCODES THE LOCALIZED DETERMINANT OF DROSOPHILA TERMINAL PATTERN-FORMATION

Differentiation of the anterior and posterior poles of the Drosophila embryo requires seven maternally expressed genes including torso-like (tsl and torso (tor). The tor gene encodes a receptor tyrosine kinase that is expressed throughout the embryo but is activated specifically at the poles. Genetic mosaic analysis has shown that tsl is required d uring oogenesis in follicle cells at each end of the oocyte. We cloned the tsl locus and showed that it was expressed specifically in follic le cells at the anterior and posterior ends of the oocyte. tsl encodes a novel protein with a putative amino-terminal signal sequence. Ectop ic expression of tsl produced embryos with a phenotype similar to that resulting from constitutively active Tor alleles. These results sugge st that localized TSL controls the localized activation of TOR.