TY - JOUR
T1 - Molecular determinants of response kinetics of mouse M1 intrinsically-photosensitive retinal ganglion cells
AU - Sheng, Yanghui
AU - Chen, Lujing
AU - Ren, Xiaozhi
AU - Jiang, Zheng
AU - Yau, King Wai
N1 - Funding Information:
We thank Dr. Randall Reed for advice on generating CRISPR point mutation knock-in mouse models, and the Johns Hopkins University Transgenic Core Laboratory for expert support in generating CRISPR mouse lines. We thank Dr. Robert Lefkowitz (Duke University) for β-arrestin (arrestin 2 and 3)-single knockouts and the Grk3−/− mice, Dr. Gerald Dorn (Washington University in St. Louis) for the Grk2fl/fl mice, Dr. Gang Pei (Tongji University) for the β-arrestin1,2fl/fl mice, Dr. Cheryl Craft (University of Southern California) for the retina arrestins (arrestin 1 and 4) knockouts, Dr. Ching-Kang Jason Chen (Baylor College of Medicine) for the Gnb5−/− mice, Dr. Josef Penninger (University of British Columbia) for the Rgs2−/− mice, and Dr. Tian Xue (University of Science and Technology of China) for sharing mutant Opn4 cDNA plasmid. We also thank Drs. Tian Xue, Yuqian Ma, Huan Zhao, Jeremy Nathans, Dwight Bergles, and members of the K.-W.Y. laboratory for discussions. This work was supported by NIH Grant EY14596 and the Beckman-Argyros Vision Award.
Publisher Copyright:
© 2021, The Author(s).
PY - 2021/12
Y1 - 2021/12
N2 - Intrinsically-photosensitive retinal ganglion cells (ipRGCs) are non-rod/non-cone retinal photoreceptors expressing the visual pigment, melanopsin, to detect ambient irradiance for various non-image-forming visual functions. The M1-subtype, amongst the best studied, mediates primarily circadian photoentrainment and pupillary light reflex. Their intrinsic light responses are more prolonged than those of rods and cones even at the single-photon level, in accordance with the typically slower time course of non-image-forming vision. The short (OPN4S) and long (OPN4L) alternatively-spliced forms of melanopsin proteins are both present in M1-ipRGCs, but their functional difference is unclear. We have examined this point by genetically removing the Opn4 gene (Opn4−/−) in mouse and re-expressing either OPN4S or OPN4L singly in Opn4−/− mice by using adeno-associated virus, but found no obvious difference in their intrinsic dim-flash responses. Previous studies have indicated that two dominant slow steps in M1-ipRGC phototransduction dictate these cells’ intrinsic dim-flash-response kinetics, with time constants (τ1 and τ2) at room temperature of ~ 2 s and ~ 20 s, respectively. Here we found that melanopsin inactivation by phosphorylation or by β-arrestins may not be one of these two steps, because their genetic disruptions did not prolong the two time constants or affect the response waveform. Disruption of GAP (GTPase-Activating-Protein) activity on the effector enzyme, PLCβ4, in M1-ipRGC phototransduction to slow down G-protein deactivation also did not prolong the response decay, but caused its rising phase to become slightly sigmoidal by giving rise to a third time constant, τ3, of ~ 2 s (room temperature). This last observation suggests that GAP-mediated G-protein deactivation does partake in the flash-response termination, although normally with a time constant too short to be visible in the response waveform.
AB - Intrinsically-photosensitive retinal ganglion cells (ipRGCs) are non-rod/non-cone retinal photoreceptors expressing the visual pigment, melanopsin, to detect ambient irradiance for various non-image-forming visual functions. The M1-subtype, amongst the best studied, mediates primarily circadian photoentrainment and pupillary light reflex. Their intrinsic light responses are more prolonged than those of rods and cones even at the single-photon level, in accordance with the typically slower time course of non-image-forming vision. The short (OPN4S) and long (OPN4L) alternatively-spliced forms of melanopsin proteins are both present in M1-ipRGCs, but their functional difference is unclear. We have examined this point by genetically removing the Opn4 gene (Opn4−/−) in mouse and re-expressing either OPN4S or OPN4L singly in Opn4−/− mice by using adeno-associated virus, but found no obvious difference in their intrinsic dim-flash responses. Previous studies have indicated that two dominant slow steps in M1-ipRGC phototransduction dictate these cells’ intrinsic dim-flash-response kinetics, with time constants (τ1 and τ2) at room temperature of ~ 2 s and ~ 20 s, respectively. Here we found that melanopsin inactivation by phosphorylation or by β-arrestins may not be one of these two steps, because their genetic disruptions did not prolong the two time constants or affect the response waveform. Disruption of GAP (GTPase-Activating-Protein) activity on the effector enzyme, PLCβ4, in M1-ipRGC phototransduction to slow down G-protein deactivation also did not prolong the response decay, but caused its rising phase to become slightly sigmoidal by giving rise to a third time constant, τ3, of ~ 2 s (room temperature). This last observation suggests that GAP-mediated G-protein deactivation does partake in the flash-response termination, although normally with a time constant too short to be visible in the response waveform.
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U2 - 10.1038/s41598-021-02832-9
DO - 10.1038/s41598-021-02832-9
M3 - Article
C2 - 34873237
AN - SCOPUS:85120870869
SN - 2045-2322
VL - 11
JO - Scientific reports
JF - Scientific reports
IS - 1
M1 - 23424
ER -