Transducin translocation contributes to rod survival and enhances synaptic transmission from rods to rod bipolar cells

Abstract

In rod photoreceptors, several phototransduction components display light-dependent translocation between cellular compartments. Notably, the G protein transducin translocates from rod outer segments to inner segments/spherules in bright light, but the functional consequences of translocation remain unclear. We generated transgenic mice where light-induced transducin translocation is impaired. These mice exhibited slow photoreceptor degeneration, which was prevented if they were dark-reared. Physiological recordings showed that control and transgenic rods and rod bipolar cells displayed similar sensitivity in darkness. After bright light exposure, control rods were more strongly desensitized than transgenic rods. However, in rod bipolar cells, this effect was reversed; transgenic rod bipolar cells were more strongly desensitized than control. This sensitivity reversal indicates that transducin translocation in rods enhances signaling to rod bipolar cells. The enhancement could not be explained by modulation of inner segment conductances or the voltage sensitivity of the synaptic Ca 2+ current, suggesting interactions of transducin with the synaptic machinery.retina | adaptation | presynaptic modulation | SNARE complex | palmitoylation

The Auxiliary Calcium Channel Subunit α2δ4 Is Required for Axonal Elaboration, Synaptic Transmission, and Wiring of Rod Photoreceptors

“…5F). We estimated the Ca 2+ current density in WT and α2δ4 KO rods during whole cell recordings using an internal solution that allowed the isolation of the synaptic Ca 2+ current (Majumder et al, 2013). Voltage clamp recordings held the rod’s membrane potential near its normal resting value (V m = −40 mV), and we ramped the membrane potential between −80 mV and +40 mV over a period of 1s.…”

Differential Light-induced Responses in Sectorial Inherited Retinal Degeneration

“…Despite these studies, no definitive answer has been provided about the link between light and sector RP, and it is not clear whether the direct action of light on Rh, or other unknown light-sensitive factors located in the retina, may cause this particular phenotype. The detailed molecular basis of light-dependent translocation of proteins from the inner segment to the outer segment in photoreceptor cells, such as arrestin (61), or from the outer segment to the inner segment, like Gt (62), is still largely undeciphered, but appears to be a finely regulated machine, and a small change in one of the partners could significantly affect the function of the others. Here, we show that N55K presents a different behavior upon illumination by forming a photointermediate unable to completely finish the retinal release process from its binding pocket.…”

Palmitoylation of Progressive Rod-Cone Degeneration (PRCD) Regulates Protein Stability and Localization

“…Acyl-RAC Purification of Palmitoylated Proteins-Palmitoyl modification of PRCD was assessed using previously published methods (23,24). Retina or transiently transfected hRPE1 cells were homogenized in ice-cold lysis buffer (25 mM HEPES, pH 7.5, 150 mM NaCl, 1 mM EDTA, 0.5% Triton X-100 plus protease and phosphatase inhibitors).…”

“…proteins in mouse retina as described earlier (23,24). Briefly, this method uses hydroxylamine to remove the labile palmitoyl group, leading to the generation of free cysteine residues in palmitoylated proteins.…”