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A. H. Conrad, M. A. Albrecht, M. L. Pettit-Scott, G. W. Conrad; Embryonic Corneal Schwann Cells Express Some Schwann Cell Marker mRNAs, but No Schwann Cell Marker Proteins, an Example of Translational Regulation. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2585.
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© ARVO (1962-2015); The Authors (2016-present)
Embryonic chick trigeminal nerve fibers encircle the cornea in pericorneal tissue until Embryonic Day 9 [E9], then penetrate anterior corneal stroma, invade from stroma into epithelium by E12, and branch over the corneal surface by E20. Schwann cells (SCs) associate with nerve fibers and augment nerve repair following injury. Adult mammalian corneal SCs are reported to be non-myelinating. This study evaluates SC differentiation in embryonic chick corneas.
Chick eggs were incubated from E0 at 38oC, 45% relative humidity. Eyes were removed on E9-E20. From E9, E12, E14, and E20 corneas, dissected free of pericorneal tissue, whole cell RNA was isolated with RNeasy, cDNA synthesized with iScript, and mRNA expression assessed by Real-Time PCR. E14 corneas were paraffin-embedded, sectioned, and processed by in situ hybridization for corneal, nerve-related, and SC-specific gene expressions. E14, E17, and E19 corneas plus pericorneal tissue were immunostained for SC-marker proteins.
Real-Time PCR reveals unchanging low/moderate expressions for neuroguidance SLIT2/ROBO and NTN/UNC5 families, SC-supporting neuregulin processor BACE1, and myelination-required CADM3/CADM4 from E9-E20. Myelination-inducing EGR2 and POU3F1 expressions never surpass myelination-suppressing PAX3 expression. NTN receptor NEO1 expression is constantly high, but in epithelial tissues NEO can function as a survival factor for non-neuronal cells. NTN epithelial receptor ITGNA6/ITGNB4 expression increases 20-fold. ITGNB1 expression is high from E9-E20, characteristic of non-myelinating SCs. SC-specific S100 and MBP expressions increase from E9-E20, but MAG, GFAP, and SCMP are very, very lowly expressed. In situ hybridization shows SLIT2 expression in anterior stroma and epithelium, more SOX10-expressing cells in epithelium than in stroma, and MPZL1 expression in epithelium. Antibodies against MPZ, MAG, S100, and SCMP, but not GFAP, immunostain sites along pericorneal nerves, but none of them stains sites along central cornea nerves.
Chick embryonic corneal SCs transcribe more PAX3 than myelin-inducer EGR2, and some SC-marker mRNAs, but do not synthesize detectable SC-marker proteins, suggesting an immature stage of differentiation and strong translational regulation of gene expression.
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