Dependence on a Retinophilin/Myosin Complex for Stability of PKC and INAD and Termination of Phototransduction

Abstract

Normal termination of signaling is essential to reset signaling cascades, especially those such as phototransduction that are turned on and off with great rapidity. Genetic approaches in Drosophila led to the identification of several proteins required for termination, including protein kinase C (PKC), NINAC (neither inactivation nor afterpotential C) p174, which consists of fused protein kinase and myosin domains, and a PDZ (postsynaptic density-95/Discs Large/zona occludens-1) scaffold protein, INAD (inactivation no afterpotential D). Here, we describe a mutation affecting a poorly characterized but evolutionarily conserved protein, Retinophilin (Retin), which is expressed primarily in the phototransducing compartment of photoreceptor cells, the rhabdomeres. Retin and NINAC formed a complex and were mutually dependent on each other for expression. Loss of retin resulted in an age-dependent impairment in termination of phototransduction. Mutations that affect termination of the photoresponse typically lead to a reduction in levels of the major rhodopsin (Rh1) to attenuate signaling. Consistent with the slower termination in retin 1 , the mutant photoreceptor cells exhibited increased endocytosis of Rh1 and a decline in Rh1 protein. The slower termination in retin 1 was a consequence of a cascade of defects, which began with the reduction in NINAC p174 levels. The diminished p174 concentration caused a decrease in INAD. Because PKC requires interaction with INAD for protein stability, this leads to reduction in PKC levels. The decline in PKC was age dependent and paralleled the onset of the termination phenotype in retin 1 mutant flies. We conclude that the slower termination of the photoresponse in retin 1 resulted from a requirement for the Retin/NINAC complex for stability of INAD and PKC.

A Model of Toxic Neuropathy inDrosophilaReveals a Role for MORN4 in Promoting Axonal Degeneration

“…From this collection we identified the MORN family member retinophilin ( rtp , also called undertaker ( uta )). Retinophilin participates in termination of phototransduction in the fly retina (Mecklenburg et al, 2010; Venkatachalam et al, 2010) and in store-operated calcium release and phagocytosis in fly embryonic macrophages (Cuttell et al, 2008). It contains four MORN repeats, regions that can bind to phospholipid membranes (Ma et al, 2006).…”

“…The RNAi protection is quantitatively modest, but consistent (Figure 5B). To test whether loss of Retinophilin is responsible for this phenotype, we generated a transheterozygote between two previously characterized loss-of-function mutant alleles of rtp (Mecklenburg et al, 2010; Venkatachalam et al, 2010). Axons in this rtp mutant are preserved following taxol treatment (Figure 5C and D), confirming that removal of retinophilin is indeed axoprotective.…”

“…The following strains were used in this study: Canton S (wild type), elav-GAL4 (Yao and White, 1994), pickpocket 5 -EGFP (referred to as ppkEGFP , Grueber et al, 2003), pickpocket-CD8:3xGFP (referred to as ppkCD8GFP , Shimono et al, 2009), ppk-GAL4 (Grueber et al, 2007), wnd 2 and wnd 3 mutant alleles (Collins et al, 2006), UAS-dmNMNAT (MacDonald et al, 2006), retin 1 (Venkatachalam et al, 2010), and rtp 1 (Mecklenburg et al, 2010). All other strains are from the Bloomington Stock Center.…”

Genome-wide profiling of diel and circadian gene expression in the malaria vector Anopheles gambiae

“…We found that ninaC peaks later in the night than inaD, stops, and norpA, but similar to the time of peaking of another gene encoding a retinophilin (RTP) (AGAP003547). In Drosophila, NINAC and RTP are binding partners, and their protein levels are codependent (87). We find in An.…”

“…aegypti noted apparent dramatic diel changes in rhabdom volume (88). These changes might be driven by the circadian system through both NINAC and RTP, which are both required for normal rhabdomere volume in Drosophila (87,89). Many of these visual system genes continue to be rhythmic in DD conditions, suggesting that components of visual transduction are under circadian clock control (Fig.…”