Expression patterns of retinoblastoma and E2F family proteins during corneal development

To determine the expression patterns of the retinoblastoma protein and the E2F transcription factor families in limbal and corneal epithelia and in corneal keratocytes in situ during corneal development and differentiation.

Retinoblastoma protein (pRb) and its family members p107 and p130; E2F-1, -2, and -4, members of the E2F family of transcription factors; and Ki67, a marker of actively cycling cells, were localized by indirect immunofluorescence microscopy, in corneas of neonatal, juvenile, and adult rats. Presence of mRNA for pRb, p107, p130, and E2F types 1 to 5 in adult corneal epithelium was determined by reverse transcription-polymerase chain reaction.

mRNA for all members of pRb and E2F families was present in adult corneal epithelium. The greatest number of Ki67-positive corneal and limbal epithelial cells were present at days 13 to 19, and Ki67-positive stromal keratocytes at day 2. pRb and E2F-2 were localized to all cells in neonatal, juvenile, and adult corneas. With age, p130 localization became more intense and nuclear in stromal keratocytes and suprabasal cells of corneal and limbal epithelia; p107, initially nuclear in limbal and corneal epithelia, became increasingly cytoplasmic in corneal epithelium. E2F-1 was initially nuclear in keratocytes and diminished after day 10. E2F-1 was localized in the basal cell layer of limbal and corneal epithelia after day 10. E2F4 was always nuclear in limbal epithelium and cytoplasmic in corneal epithelium.

Expression patterns of pRb and E2F family proteins vary with corneal cell differentiation, but are most apparent with p130 and p107. Nuclear localization of p130 appears to correlate with terminal differentiation in epithelium and entrance into a quiescent state by keratocytes. In contrast, p107 is nuclear in the undifferentiated limbal basal cells and is cytoplasmic in the remainder of the corneal epithelial cells.