bioRxiv : the preprint server for biologyDec 22, 2025

Melanopsin's role in daily light responses in mice varies between males and females

Circadian Biology Weekly Brief ↗PubMed ↗DOI ↗

Updated Jun 27, 2026

Abstract

Essence

Melanopsin appears to shape circadian light responses more strongly in female mice than in male mice.

Evidence

This mouse circadian biology study compared melanopsin expression and circadian photic responses between female and male mice in the ipRGC-SCN pathway.

Caveat

The abstract reports sex-dependent mouse findings and does not establish whether the same retinal mechanism explains circadian light responses in humans.

Simplified

Proper entrainment of the body's circadian rhythms to the environment is critical to human health. Light is one of the strongest cues driving circadian photoentrainment of the central circadian pacemaker, the suprachiasmatic nucleus (SCN), via projections from the melanopsin-expressing intrinsically photosensitive retinal ganglion cells (ipRGCs). Circadian research has historically centered males, and recent work has revealed multiple sex-differences in circadian circuitry and function, indicating that our understanding of this system in females is severely limited. Moreover, while recent studies have investigated the role of hormonal modulation of light responses, the additional possibility that ipRGC inputs may also be sex-dependent has not been directly tested. Here, we report that not only do ipRGCs in female mice show higher levels of melanopsin expression, but that melanopsin also plays a larger role in shaping circadian photic responses in females compared to males. Collectively, these results define a new retinal source for sex-dependent differences in circadian behavior.