The Drosophila melanogaster retinophilin gene encodes the peripheral membrane protein in photoreceptor cells

The Drosophila melanogaster retinophilin (rtp) gene encoding the protein containing MORN (Membrane Occupation and Recognition Nexus) motifs that are known to interact with the plasma membrane has been identified to be expressed predominantly in adult eyes by several independent studies. Isolation and characterization of rtp mutant flies showed that the gene is involved in the phototransduction process by interacting with NINAC (neither inactivation nor afterpotential C) protein in adult photoreceptor cells. The gene was also reported to be involved in phagocytosis in embryos. We examined rtp gene expression during D. melanogaster development and in adult head tissues. The results showed that the gene is expressed at detectable levels only in adult photoreceptor cells but not in other developmental stages and other adult tissues, confirming its phototransduction functions. The RTP protein contains only 4 MORN motifs, whereas 8 MORN motifs are reported to be required for interactions with the plasma membrane. We found that RTP protein is present free in the cytosol and also is bound peripherally to the plasma membrane; this binding ability was found to be modulated by light. Our results suggest that the D. melanogaster RTP protein is a light-regulated peripheral membrane protein of photoreceptor cells.