GRM6 and retinal degeneration: The 4xGrm6-SV40 cell‐specific promoter has previously been shown to be active in ON‐bipolar cells in this mouse model [11, 12, 21, 22, 26], although one study using intravitreally delivered chimeric optogenetic protein struggled to confirm this in advanced and very late stage of retinal degeneration [24] suggesting potential degeneration‐dependent downregulation of Grm6 promoter driven gene expression.