Drosophila JAB1/CSN5 acts in photoreceptor cells to induce glial cells.

Different classes of photoreceptor neurons (R cells) in the Drosophila compound eye form connections in different optic ganglia. The R1-R6 subclass connects to the first optic ganglion, the lamina, and relies upon glial cells as intermediate targets. Conversely, R cells promote glial cell development including migration of glial cells into the target region. Here, we show that the JAB1/CSN5 subunit of the COP9 signalosome complex is expressed in R cells, accumulates in the developing optic lobe neuropil, and through the analysis of a unique set of missense mutations, is required in R cells to induce lamina glial cell migration. In these CSN5 alleles, R1-R6 targeting is disrupted. Genetic analysis of protein null alleles further revealed that the COP9 signalosome is required at an earlier stage of development for R cell differentiation.