Fig. 7. The mechanism of G_q translocation from the cell body to the rhabdomere involves the photoreceptor-specific myosin NINAC. (A) Cross-sections from wild-type (WT) and the null mutant ninaC⁵ were immunostained for G_q. Flies were light-exposed for 2.5 hours (Lex) and then dark-incubated (LD) for 0 minutes, 60 minutes or 240 minutes. Light-exposed WT and ninaC⁵ flies displayed normal translocation of G_q to the cell bodies. After 60 minutes of dark incubation, near-complete recovery of G_q to the rhabdomeres was observed in the WT, whereas ninaC⁵ mutants required up to 240 minutes of dark incubation for complete recovery of G_q to the rhabdomeres. Total G_q protein remained constant in light-exposed and dark-incubated samples as tested by immunoblot analysis (data not shown). (B) Quantitation of G_q in the rhabdomeres from cross-sections of dark-raised wild-type (filled circles) and ninaC⁵ (open squares) flies, exposed to light for 5 minutes or 60 minutes. Images used for quantitation were taken at the same exposure time as dark-raised samples. Values are expressed as a percentage of G_q signal measured in the rhabdomeres of dark-raised flies. In both dark-raised WT and ninaC⁵ flies, G_q protein is exclusively localized to the rhabdomeres, whereas, after 5 minutes of illumination at 50.7x10³ lumens meter^-2, the maximum amount (50%) of G_q translocates out of the rhabdomere. (C) Quantitation of G_q in the rhabdomeres from cross-sections of WT and ninaC⁵ flies that were light exposed for 2.5 hours and then incubated in the dark for 60 minutes, 150 minutes or 240 minutes. Values are expressed as a percentage of G_q signal in the rhabdomeres of the corresponding dark-raised flies. The recovery of G_q to the rhabdomeres was significantly slower in ninaC⁵ mutants. In the WT flies, 90% of G_q is localized in the rhabdomeres within 60 minutes, whereas, in ninaC⁵ mutants, only 50% is localized in the rhabdomeres. After 60 minutes and 150 minutes of dark incubation, differences between WT and ninaC⁵ were statistically significant (Student's t-test, P<0.05). Full recovery of G_q to the rhabdomeres in ninaC⁵ mutants was complete by 240 minutes.