Department of Physiology, Development and Neuroscience

Phototransduction, TRP channels, lipid and Calcium signalling in Drosophila

Above: Molecular model of the TRP channel pore based on crystal structure of KcsA. By site-directed mutagenesis we identified aspartate 621 (D621) as the critical acidic residue conferring the high Ca²⁺ selectivity of the channel (P_Ca:P_Na ≈ 50:1). In transgenic flies where the aspartate was neutralised (TRP^D621G) the channels became impermeable to Ca²⁺, allowing only currents mediated by monovalent cations. In these photoreceptors all Ca²⁺ dependent amplification, kinetics and adaptation were eliminated ((Liu et al 2007)

Above: Drosophila phototransduction cascade. Inset Cross section of a Drosophila rhabdomere composed of tightly packed microvilli. (1) Photoisomerization of rhodopsin to metarhodopsin (Rh M, encoded by ninaE gene) activates Gq (2) Gq activates phospholipase C (PLC), generating InsP3 and DAG from PIP2. DAG may release polyunsaturated fatty acids (PUFAs) via action of DAG lipase; (3) Two classes of light-sensitive channels (trp and trpl genes) are activated by an unknown mechanism. Several components of the cascade are coordinated into a signalling complex by the scaffolding protein, INAD. (4) At the base of the microvilli there is a system of submicrovillar cisternae (SMC). Although these may represent Ca2+ stores endowed with InsP3 receptors, they may play a more important role in phosphoinositide turnover (5).

Above: Dissociated Drosophila ommatidia. The light absorbing rhabdomere has been labelled by a genetically targeted GFP-tagged ion channel protein (Kir2.1). As well as visualizing the rhabdomere, this ion channel is specifically activated by PIP2 and can be used as an electrophysiological biosensor to monitor PIP2 levels in real time in vivo

© Department of Anatomy, University of Cambridge