Abstract
Purpose: :
To investigate the possible role of sub–epithelial corneal nerves in epithelial homeostasis of the mouse eye.
Methods: :
Ubiquitous GFP mice and corn1 mice, whose cornea develops epithelial hyperplasia and vascularization, were used. Flat whole–mounts of ocular surface were prepared from these mice of various ages, and distribution of sub–epithelial nerves was determined by immnohistochemistry with antibodies to ß–tubulin III, neurofilament 200kDa, or thy1.2. In some mice, limbal epithelium was mechanically scraped to trigger conjunctivalization of the corneal surface. Radial stripes of epithelial GFP were used as a marker of centripetal movement of epithelial cells.
Results: :
In newborn mice, epithelial GFP exhibited a mosaic pattern throughout the cornea. Similarly, sub–basal nerves were present in the entire cornea, originating from six to eight major trunks that entered from deep stroma of the limbus. At 3 weeks after birth, epithelial GFP stripes emerged at the limbus and entered into the peripheral cornea while a mosaic pattern persisted in the central cornea. On the other hand, sub–basal nerve fibers exhibited a radial pattern that extended to the central cornea, generating a vortex near the center. GFP stripes from all circumferences eventually reached the central cornea at 8–10 weeks, and as a result a whorl–like pattern developed, similar to the nerve fiber profile at 3 weeks. Thus, a radial pattern of sub–epithelial nerves was laid out ahead, developmentally, of migrating epithelial cells that originated at the limbus. In adult GFP mice, distribution patterns of epithelial GFP stripes paralleled those of underlying sub–basal nerve fibers. In a conjunctivalized cornea, in which epithelial cells remain stationary, sub–basal nerve fibers exhibited crisscross patterns without orderly, radial stripes. Similarly, in adult corn1 mice, in which corneal epithelium exhibits hyperplasia and concomitant disruption of centripetal cell movement, sub–basal nerves were also found to be highly disorganized.
Conclusions: :
Correlation between the orderly distribution of sub–basal nerve fibers and the centripetal movement of corneal epithelial cells raises a possibility that sub–basal nerves play a regulatory role in ocular surface homeostasis by guiding epithelial cell movement.
Keywords: cornea: basic science • microscopy: light/fluorescence/immunohistochemistry • anatomy