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Updated: Dec 10, 2025
Author Spotlight: Advancing Corneal Innervation Research Through Innovative Models
Published on: December 8, 2023
Diurnal Control of Sensory Axon Growth and Shedding in the Mouse Cornea
Sonali Pal-Ghosh1, Gauri Tadvalkar1, Beverly A Karpinski1
1Department of Anatomy and Cell Biology, The George Washington University School of Medicine and Health Sciences, Washington, District of Columbia, United States.
Purpose:
The circadian clock plays an important role in the expression and regulation of various genes and cellular processes in the body. Here, we study diurnal regulation of the growth and shedding of the sensory axons in the mouse cornea.
Methods:
Male and female BALB/cN mice were euthanized 90 minutes before and after the lights are turned on and off; at 5:30 AM, 8:30 AM, 5:30 PM, and 8:30 PM. Nerve terminal growth, shedding and overall axon density were assessed at these four time points using confocal imaging after staining axons in en face whole mount corneas with antibodies against βIII tubulin, GAP43, and L1CAM. In addition, corneal epithelial cell proliferation, thickness, and desquamation were assessed using ki67, LAMP1, Involucrin, and ZO1.
Results:
Nerve terminal shedding took place between 5:30 AM and 8:30 AM and correlated positively with the timing of apical cell desquamation. After shedding the tips of the nerve terminals, axonal growth increased as indicated by increased axonal GAP43 expression. At 5:30 PM and 8:30 PM before and after the lights are turned off, cell proliferation was reduced, and epithelial thickness was maximal.
Conclusions:
Intraepithelial corneal nerve growth and shedding are under diurnal control regulated by the time of day and whether lights are on or off. Axons extend during the day and are shed within 90 minutes after lights are turned on. The data presented in this article shed light on the potential role that circadian clock plays in corneal pain and discomfort.
Insights
Corneal sensory axons exhibit diurnal shedding and growth patterns, with shedding occurring after lights turn on and growth during the day. This circadian regulation may influence corneal pain.
Area of Science:
- Ophthalmology
- Neuroscience
- Chronobiology
Background:
- The circadian clock regulates numerous physiological processes.
- Understanding diurnal rhythms in the cornea is crucial for ocular health.
Purpose of the Study:
- To investigate the diurnal regulation of sensory axon growth and shedding in the mouse cornea.
- To correlate corneal nerve dynamics with circadian light-dark cycles.
Main Methods:
- BALB/cN mice were analyzed at four time points across a 24-hour cycle.
- Confocal imaging assessed nerve terminal growth, shedding, and density using specific antibodies.
- Corneal epithelial cell proliferation, thickness, and desquamation were evaluated using markers like ki67 and ZO1.
Main Results:
- Nerve terminal shedding occurred between 5:30 AM and 8:30 AM, coinciding with epithelial cell desquamation.
- Axonal growth, indicated by GAP43 expression, increased after nerve terminal shedding.
- Epithelial thickness was maximal, and cell proliferation was reduced in the evening (5:30 PM and 8:30 PM).
Conclusions:
- Intraepithelial corneal nerve growth and shedding are under diurnal control, influenced by light-dark cycles.
- Axons extend during the day and are shed shortly after lights turn on.
- These findings suggest a role for the circadian clock in corneal pain and discomfort.
