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Chuan-Chin Chiao, Chi-Yun Sun, Ching-Kang Jason Chen; Spatial distribution of excitatory synapses in mouse retinal ganglion cells lacking Gβ5. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):3246.
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Gβ5 is the obligate partner of R7 RGS proteins (Regulators of G-protein Signaling) and is important for timely deactivation of G-proteins in photoreceptors and ON-bipolar cells. It has been found that deactivation of Gβ5 alters dendritic morphology and number of synaptic triads in retinal outer plexiform layer (OPL). Because Gβ5 is expressed by many inner retinal neurons including retinal ganglion cells (RGCs), we hereby examine whether cell-autonomous removal of Gβ5 changes excitatory synapse distribution in certain RGC subsets.
A subset of RGCs in the Grik4Cre mice expresses Cre recombinase. We mated a floxed Gβ5 mouse line with the Grik4Cre line to conditionally inactivate Gβ5 in Cre+ RGCs. An established particle-mediated gene transfer technique was used to deliver PSD95-GFP constructs to retinal neurons. Cre-mediated tdTomato expression in the Ai9 background marks Cre expression. RGC dendritic morphology and distribution of excitatory synapses were visualized and compared between Grik4Cre/Gβ5floxed/floxed and Grik4Cre/Gβ5floxed/+ animals.
Five RGC types (G2, G6, G12, G17, and G18) were found to have slight changes in dendritic morphological patterns but no changes in dendritic stratification levels in the inner plexiform layer (IPL). The PSD95 puncta, which mark excitatory synapses appeared to be spaced regularly in 1-2 μm interval. The density of such synapses along dendrites appears to be slightly different in G2, G6, and G12 RGCs with and without Gβ5 expression.
These results showed that morphological features of RGCs are only slightly changed when Gβ5 is autonomously deleted. This suggests that, unlike the established roles of Gβ5 in photoreceptors and ON-bipolar cells, Gβ5 may not be needed for development or maintenance of dendritic morphology in examined RGC subtypes. The functional significance of Gβ5 expression in IPL and GCL may thus now be examined without worries of a conspicuous secondary morphological defect.
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