Basonuclin in murine corneal and lens epithelia correlates with cellular maturation and proliferative ability

Basonuclin is a zinc finger protein with highly restricted tissue distribut ion. It has been found in abundance only in keratinocytes of stratified epi thelia and the germ cells of the testis and ovary. We studied the expressio n pattern of basonuclin in relation to cellular proliferation and different iation in murine corneal and lens epithelia, two self-renewing tissues in t he eye which contain cells that proliferate throughout life. Mouse corneal and lens epithelial cells at various stages of development were labeled wit h BrdU for 90 min to detect cells in S phase and to establish proliferative rates. Whole eyes of mouse or rat were processed for frozen sections and c ellular basonuclin was detected by either a rabbit anti-mouse- or a rabbit anti-human-basonuclin antibody. Basonuclin was expressed in virtually all c ells in the basal layer of corneal epithelium and in the pre-equatorial len s epithelium, the respective proliferative compartments of adult corneal an d lens epithelia. Basonuclin expression in corneal epithelium began at post -natal life day 4, first in a few cells and then spread to virtually all ba sal cells at day 20. Basonuclin was consistently absent in limbal epitheliu m. Lens basonuclin, which was detected earlier than that of the cornea, was confined to the pre-equatorial epithelium and was absent in equatorial cel ls that expressed p57(KIP2), an early differentiation marker for these cell s. An important distinction between corneal and lens basonuclin is that the farmer is predominantly nuclear whereas the latter cytoplasmic.