ARGOS IS REQUIRED FOR PROJECTION OF PHOTORECEPTOR AXONS DURING OPTIC LOBE DEVELOPMENT IN DROSOPHILA

The Drosophila argos gene encodes a secreted protein with an epidermal growth factor (EGF) motif, which acts as an inhibitor of cell recruit ment in the developing eye and wing. Here, we have analyzed the role o f argos during optic lobe development. argos expression was observed i n the optic lobes throughout the developmental stages. In argos mutant s, neuropiles failed to develop normally during embryonic and larval s tages, and photoreceptor axons did not project properly into the lamin a. Ubiquitous expression of argos, under control of the hsp70 promoter , rescued the defects in optic lobes. We have found that glial cells f ailed to differentiate in the larval optic lobes of argos mutants. Cor respondingly, in loss-of-function repo mutants, whose glial cells also fail to differentiate, photoreceptor axons showed the impaired projec tion pattern similar to the argos phenotype, These results suggest tha t glial cells play a role for guidance of photoreceptor axons. The los s-of-function Star mutation (Star(X155)) dominantly suppressed the def ects in the argos optic lobes, suggesting that these two genes act in an antagonistic fashion during optic lobe development. (C) 1996 Wiley- Liss, Inc.