Abstract
Purpose: :
The cornea is one of the most highly innervated tissues in the body. Neural-crest derived corneal nerve fibers encircle the cornea in the pericorneal space from Embryonic Day 6 [E6] to E9, then penetrate the anterior corneal stroma on E9, invade from the stroma into the epithelium on E12, innervate the entire corneal surface by E14, and continue to defasiculate and grow into the anterior cornea through E18. However, in adult human patients, if corneal nerves are cut for corneal transplant surgery or LASIK during adult life, regeneration of corneal nerves is very slow and incomplete. Schwann cells protect nerve fibers and can augment nerve repair following injury. In mammals, only non-myelinating Schwann cells are reported in the cornea. This study examines evidence for Schwann cell differentiation in the embryonic chick cornea.
Methods: :
Chick eggs were incubated from E0 at 37oC, 45% humidity. Eyes were removed on E7, E9, E12, E14, E15, E16, E19, E20; corneas plus pericorneal tissue were dissected, fixed, and stained immunohistochemically for Schwann cell proteins. In addition, corneas were dissected free of pericorneal tissue, whole-cell RNA was isolated from them with RNeasy, cDNA synthesized with iScript, and mRNA expression assessed by Real-time-PCR using iQSupermix.
Results: :
Antibodies for Schwann cell markers MPZ [P0], MAG [myelin-associated glycoprotein], and S100 show positive immunocytochemical staining along pericorneal nerves from E14 to E19, but no staining along nerves in the central cornea. In contrast, antibodies for Schwann cell markers Glial Fibrillary Acidic Protein [GFAP] and Schwann-cell myelin protein [SCMP] do not react with pericorneal or central corneal cells. Real-time PCR confirms increasing expressions of MPZ-like [MPZL] isoforms 1 and 3 and S100 from E9 until E20 in the cornea, but detects no expression of MAG, GFAP, or SCMP at any age. In situ hybridization experiments are in progress to determine whether cells in the central cornea are transcribing but not translating mRNAs for MPZL and S100 genes.
Conclusions: :
Chick central corneal Schwann cells do not synthesize Schwann-cell marker proteins, but appear to transcribe some Schwann-cell marker mRNAs.
Keywords: cornea: basic science • differentiation • nerve fiber layer