A novel follicle-cell-dependent dominant female sterile allele, Star(Kojak), alters receptor tyorsine kinase signaling in Drosophila

We describe a new dominant allele, Star(Kojak), that alters receptor tyrosi ne kinase signaling in the follicle cells and in the eyes in Drosophila. We isolated Star(Kojak) in a screen for follicle-cell-dependent dominant fema le sterile mutations. We show that Star(Kojak) and revertants of Star(Kojak ) do not complement Star loss-of-function mutations. We propose that Star(K ojak) is a novel type of allele of Star that has both dominant gain-of-func tion phenotypes early in development and dominant loss-of-function phenotyp es later in development. Star encodes a putative transmembrane protein that has previously been shown to be a critical component of the epidermal grow th factor receptor tyrosine kinase signaling pathway. Early in oogenesis, S tar mRNA expression is higher in Star(Kojak) egg chambers than in wild-type egg chambers, consistent with its gain-of-function phenotype. Later in oog enesis, Star mRNA expression is lower in Star(Kojak) follicle cells than in wild-type follicle cells, consistent with its loss-of-function phenotype. By genetically analyzing Star(Kojak) and its revertants, we present evidenc e that Star is involved in anterior-posterior axis formation both in the fe male germline cells and in the somatic follicle cells. We also demonstrate that at least part of the dominant female sterile phenotype of Star(Kojak) is restricted to the :posterior-pole follicle cells. We propose that Star f unctions by processing pro-Gurken to mature Gurken, which is thereby releas ed in the region between the oocyte and the follicle cells and binds to the epidermal growth factor receptor in the follicle cells. (C) 1999 Academic Press.