Video 2. Drosophila R1-R8s in dissociated ommatidia contract photomechanically.
Wild-type and trp/trpl-mutant R1-R8 photoreceptors contract photomechanically to light flashes. The panels show: top, a sideview of ex vivo wild-type R1-R8 photoreceptors of a single dissociated ommatidium contracting to 1 ms bright light flash; bottom left, R1-R8 of a trp/trpl null-mutant, which express normal phototransduction reactants but lack completely their light-gated ion channels, contracting to a similar flash. Notably, trp/trpl photoreceptors cannot generate electrical responses to light, with their eyes showing no ERG signal (Appendix 7). Nonetheless, trp/trpl-mutant photoreceptors contract photomechanically (but require ~5 min dark-adaptation between flashes to restore their contractility). These observations are consistent with the hypothesis of the light-induced phosphatidylinositol 4,5-bisphosphate (PIP2) cleaving from the microvillar photoreceptor plasma membrane causing the rhabdomere contractions (Hardie and Franze, 2012). Video playback slowed down and down-sampled to reveal the contractions, which otherwise would be too fast to see with a naked eye. Each video clip is repeated three times with a running timer giving the time course of the contractions. Notice that the longitudinal contractions reduce the photoreceptor length. Thus, in an intact compound eye, the rhabdomeres would move inwards, away from the lens, likely narrowing their receptive fields (see Appendix 7, Appendix 7—figure 10 and Appendix 8, Appendix 8—figure 3).