Gene encoding cytoskeletal proteins in Drosophila rhabdomeres.

Abstract

The ninaC gene is one of eight nina (neither inactivation nor afterpotential) genes identified from mutations that drastically reduce the amount of rhodopsin in the compound eye of Drosophila melanogaster. The gene has been cytogenetically localized to the 27E-28B region of the second chromosome. NaDodSO4/PAGE analysis of eye proteins of flies carrying one, two, or three copies of the ninaC region shows that two eye-specific proteins of molecular weight 170,000 and 130,000 display a strong dependence on the dosage of the ninaC gene, although the dependence is evident only when the dosage is decreased and not when it is increased. All mutations in the ninaC gene studied to date have pronounced effects on these two polypeptides. These results suggest that the ninaC locus encodes these two polypeptides. Ultrastructural studies show that the polypeptides encoded by ninaC are very likely to be important components of the cytoskeletal structure of rhabdomeral microvilli.Among the many Drosophila melanogaster mutants that have been isolated in this laboratory on the basis of their defects in light-evoked electrical responses of the eye (1, 2) are those with greatly reduced amounts ofthe visual pigment, rhodopsin (2-4). These mutants were isolated on the basis of their defect in the prolonged depolarizing afterpotential (PDA) produced by a bright blue stimulus that photoconverts a substantial net amount of rhodopsin to metarhodopsin (Fig.

Subcellular translocation of the eGFP-tagged TRPL channel inDrosophilaphotoreceptors requires activation of the phototransduction cascade

“…Because myosin III is a plus ended myosin and the plus ends of actin filaments are oriented towards the tips of the microvilli (Lee and Montell, 2004), it is not feasible that this myosin mediates the transport of proteins out of the rhabdomere. However, the ninaC 5 mutant exhibits secondary defects such as disruption of the actin cytoskeleton and retinal degeneration (Matsumoto et al, 1987;Hicks and Williams, 1992). We suggest that the observed partial inhibition of TRPL-eGFP transport from the rhabdomere to the cell body is due to these secondary defects.…”

“…8C,D). Thus, this protein, which affects organization of the cytoskeleton (Matsumoto et al, 1987) is not required for the incorporation of TRPL-eGFP into the rhabdomere, but its mutation affects translocation of TRPL-eGFP to the cell body.…”

Phototransduction and retinal degeneration in Drosophila

“…2f). A single myosin III appears to span the small distance between the actin filament and the rhabdomeral membrane [22,23]. The extremely small size of a microvillus has important implications concerning the mechanism of signal amplification.…”

Light-dependent subcellular translocation of Gqα in Drosophila photoreceptors is facilitated by the photoreceptor-specific myosin III NINAC

“…We cannot, however, rule out the possibility that NINAC, which contains a protein-kinase domain and has been implicated as a signaling protein in phototransduction (Hofstee et al, 1996;Porter et al, 1995;Wes et al, 1999b), is involved in signaling Gqα translocation. ninaC null mutants have also been shown to exhibit a loss of the axial cytoskeleton from rhabdomeres and undergo retinal degeneration Matsumoto et al, 1987), making it possible that slowed Gqα transport is due in part to rhabdomeric cytoskeletal degeneration. However, if slowed G qα transport is indeed a secondary effect of retinal degeneration, we would expect the effect to be rather nonspecific.…”