The role of Star in the production of an activated ligand for the EGF receptor signaling pathway

The Star gene is a member of the EGFR signaling pathway which has diverse functions throughout Drosophila development. In order to investigate the protein distribution for Star, we have generated a polyclonal antibody. Here, we show that the Star protein is expressed perinuclearly in the early female germline and later is found in the oocyte cytoplasm. Star is expressed at low levels in other tissues. The subcellular localization of the protein has been determined when Star is overexpressed in the eye disc. Star is located in the nuclear and contiguous endoplasmic reticulum membranes. A functional assay in the wing disc demonstrates that Star expression can activate a nonprocessed membrane-bound form of the EGFR ligand Spitz and overexpression of Star in the eye disc promotes the formation of smaller Spitz proteins. Based on these results, we propose that the Star protein is likely to be involved in Spitz ligand processing. (C) 1999 Academic Press.