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

We examine the light-dependent subcellular translocation of the visual G(q)alpha protein between the signaling compartment, the rhabdomere and the cell body in Drosophila photoreceptors. We characterize the translocation of G(q)alpha and provide the first evidence implicating the involvement of the photoreceptor-specific myosin III NINAC in G(q)alpha transport. Translocation of G(q)alpha from the rhabdomere to the cell body is rapid, taking less than 5 minutes. Higher light intensities increased the quantity of G(q)alpha translocated out of the rhabdomeres from 20% to 75%, consistent with a mechanism for light adaptation. We demonstrate that translocation of G(q)alpha requires rhodopsin, but none of the known downstream phototransduction components, suggesting that the signaling pathway triggering translocation occurs upstream of G(q)alpha. Finally, we show that ninaC mutants display a significantly reduced rate of G(q)alpha transport from the cell body to the rhabdomere, suggesting that NINAC might function as a light-dependent plus-end motor involved in the transport of G(q)alpha.