Defining spatial nonuniformities of all ipRGC types using an improved Opn4cre recombinase mouse line

Intrinsically photosensitive retinal ganglion cells (ipRGCs) play a crucial role in several physiological light responses. In this study, we generate an improved Opn4cre knockin allele (Opn4cre(DSO)), which faithfully reproduces endogenous Opn4 expression and improves compatibility with widely used reporters. We evaluated the efficacy and sensitivity of Opn4cre(DSO) for labeling in retina and brain and provide an in-depth comparison with the extensively utilized Opn4cre(Saha) line. Through this characterization, Opn4cre(DSO) demonstrated higher specificity in labeling ipRGCs with minimal recombination escape. Leveraging a combination of electrophysiological, molecular, and morphological analyses, we confirmed its sensitivity in detecting all ipRGC types (M1–M6) and defined their unique topographical distribution across the retina. In the brain, the Opn4cre(DSO) line labels ipRGC projections with minimal labeling of cell bodies. Overall, the Opn4cre(DSO) mouse line represents an improved tool for studying ipRGC function and distribution, offering a means to selectively target these cells to study light-regulated behaviors and physiology. [Display omitted] •An improved Opn4cre knockin mouse line better captures endogenous expression patterns•Opn4cre(DSO) is compatible with sensitive Cre-dependent reporter lines (Ai9 and Ai14)•IpRGC distributions are easily defined within the retina using the Opn4cre(DSO) line•Opn4cre(DSO) has limited off-target recombination within the central nervous system There is a critical need for more specific genetic tools to label intrinsically photosensitive retinal ganglion cells (ipRGCs) that express melanopsin. Our aim was to design a Cre recombinase mouse line that was compatible with sensitive Cre-dependent reporters and to use this genetic tool to assess the local distribution of ipRGCs within the retina. Photosensitive retinal ganglion cells play important roles in light-regulated physiology. Dyer et al. develop an Opn4cre(DSO) mouse line that displays minimal off-target recombination with sensitive reporter lines and use it to uncover the distribution of melanopsin-expressing cells in the retina and brain.