Serum-free medium (OptiMEM-1), Medium 199 (M199), Hanks’ balanced salt solution (HBSS), gentamicin, and trypsin-EDTA were purchased from Invitrogen-Life Technologies (Carlsbad, CA). Nerve growth factor (NGF; from mouse submaxillary glands), and bovine pituitary extract were from Biomedical Technologies (Stoughton, MA). Epidermal growth factor (EGF; from mouse submaxillary glands) was obtained from Upstate Biotechnologies (Lake Placid, NY); fetal bovine serum (FBS) from Hyclone (Logan, UT); ascorbic acid, chondroitin sulfate, calcium chloride, 0.02% EDTA solution (EDTA disodium salt), and antibiotic-antimycotic solution from Sigma-Aldrich (St. Louis, MO); cell attachment reagent (FNC Coating Mix) from Biological Research Faculty and Facility, Inc. (BRFF; Ijamsville, MD); Barron donor cornea punches (6.75 and 9.5 mm) from Katena Products, Inc. (Denville, NJ); mouse anti-MCM2 IgG from BD-Pharmingen (San Diego, CA); fluorescein (FITC)-conjugated donkey anti-mouse IgG from Jackson ImmunoResearch Laboratories, Inc. (West Grove, PA); and mounting medium with propidium iodide (Vectashield) from Vector Laboratories, Inc.; Burlingame, CA).