Intrinsically photosensitive retinal ganglion cells (ipRGCs) are rare mammalian photoreceptors essential for non-image-forming vision functions, such as circadian photoentrainment and the pupillary light reflex. They comprise multiple subtypes distinguishable by morphology, physiology, projections, and levels of expression of melanopsin (Opn4), their photopigment. The molecular programs that distinguish ipRGCs from other ganglion cells and ipRGC subtypes from one another remain elusive. Here, we present comprehensive gene expression profiles of early postnatal and adult mouse ipRGCs purified from two lines of reporter mice that mark different sets of ipRGC subtypes. We find dozens of novel genes highly enriched in ipRGCs. We reveal that Rasgrp1 and Tbx20 are selectively expressed in subsets of ipRGCs, though these molecularly defined groups imperfectly match established ipRGC subtypes. We demonstrate that the ipRGCs regulating circadian photoentrainment are diverse at the molecular level. Our findings reveal unexpected complexity in gene expression patterns across mammalian ipRGC subtypes.

14Intrinsically photosensitive retinal ganglion cells (ipRGCs) are rare mammalian photoreceptors 15 essential for non-image-forming vision functions, such as circadian photoentrainment and the 16 pupillary light reflex. They comprise multiple subtypes distinguishable by morphology, physiology, 17 projections, and levels of expression of melanopsin (Opn4), their photopigment. The molecular 18 programs that differentiate ipRGCs from other ganglion cells and ipRGC subtypes from one 19 another remain elusive. Here, we present comprehensive gene expression profiles of early 20 postnatal and adult mouse ipRGCs purified from two lines of reporter mice marking different sets 21 of ipRGC subtypes. We find dozens of novel genes highly enriched in ipRGCs. We reveal that 22 Rasgrp1 and Tbx20 are selectively expressed in subsets of ipRGCs, though these molecularly 23 defined groups imperfectly match established ipRGC subtypes. We demonstrate that the ipRGCs 24 regulating circadian photoentrainment are unexpectedly diverse at the molecular level. Our 25 findings reveal unexpected complexity in gene expression patterns across mammalian ipRGC 26 subtypes.