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Updated: Dec 18, 2025
An Epithelial Abrasion Model for Studying Corneal Wound Healing
Published on: December 29, 2021
Wounding Induces Facultative Opn5-Dependent Circadian Photoreception in the Murine Cornea
Nicolás M Díaz1, Richard A Lang1,1,1,1, Russell N Van Gelder1,1
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Purpose:
Autonomous molecular circadian clocks are present in the majority of mammalian tissues. These clocks are synchronized to phases appropriate for their physiologic role by internal systemic cues, external environmental cues, or both. The circadian clocks of the in vivo mouse cornea synchronize to the phase of the brain's master clock primarily through systemic cues, but ex vivo corneal clocks entrain to environmental light cycles. We evaluated the underlying mechanisms of this difference.
Methods:
Molecular circadian clocks of mouse corneas were evaluated in vivo and ex vivo for response to environmental light. The presence of opsins and effect of genetic deletion of opsins were evaluated for influence on circadian photoresponses. Opn5-expressing cells were identified using Opn5Cre;Ai14 mice and RT-PCR, and they were characterized using immunocytochemistry.
Results:
Molecular circadian clocks of the cornea remain in phase with behavioral circadian locomotor rhythms in vivo but are photoentrainable in tissue culture. After full-thickness incision or epithelial debridement, expression of the opsin photopigment Opn5 is induced in the cornea in a subset of preexisting epithelial cells adjacent to the wound site. This induction coincides with conferral of direct, short-wavelength light sensitivity to the circadian clocks throughout the cornea.
Conclusions:
Corneal circadian rhythms become photosensitive after wounding. Opn5 gene function (but not Opn3 or Opn4 function) is necessary for induced photosensitivity. These results demonstrate that opsin-dependent direct light sensitivity can be facultatively induced in the murine cornea.
Insights
Corneal circadian clocks gain light sensitivity after injury through the induction of Opn5, an opsin photopigment. This facultative photosensitivity allows ex vivo corneal clocks to entrain to light cycles, a mechanism distinct from in vivo synchronization.
Area of Science:
- Chronobiology
- Ophthalmology
- Molecular Biology
Background:
- Mammalian tissues possess autonomous molecular circadian clocks synchronized by internal and external cues.
- In vivo corneal circadian clocks align with the brain's master clock via systemic cues.
- Ex vivo corneal clocks, however, entrain to environmental light cycles, suggesting a different synchronization mechanism.
Purpose of the Study:
- To investigate the mechanisms underlying the differential photoentrainment of in vivo versus ex vivo mouse corneal circadian clocks.
- To evaluate the role of opsins in mediating corneal circadian photoresponses.
Main Methods:
- In vivo and ex vivo assessment of mouse corneal molecular circadian clock responses to light.
- Evaluation of opsin presence and the effect of genetic opsin deletion on circadian photoresponses.
- Identification and characterization of Opn5-expressing cells using specific mouse models and techniques like RT-PCR and immunocytochemistry.
Main Results:
- Ex vivo corneal clocks are photoentrainable, while in vivo clocks remain synchronized to behavioral rhythms.
- Wounding (incision or debridement) induces Opn5 expression in corneal epithelial cells.
- Induced Opn5 expression confers direct, short-wavelength light sensitivity to corneal circadian clocks.
Conclusions:
- Corneal circadian rhythms acquire photosensitivity following injury.
- Opn5 gene function is essential for this induced photosensitivity, while Opn3 and Opn4 are not.
- The study demonstrates facultative, opsin-dependent induction of direct light sensitivity in the murine cornea.
