Adult corneal epithelium basal cells possess the capacity to activate epidermal, pilosebaceous and sweat gland genetic programs in response to embryonic dermal stimuli

Recent work has shown remarkable plasticity between neural and hematopoeiti c, as well as between hematopoeitic and muscle stem cells, depending on env ironmental stimuli (Fuchs, E. and Segre, J. A. (2000) Cell 100, 143-155), S tem cells give rise to a proliferative transient amplifying population (TA) , which is generally considered to be irreversibly committed, Corneal epith elium provides a particularly useful system for studying the ability of TA cells to activate different genetic programs in response to a change in the ir fibroblast environment, Indeed, corneal stem and TA cells occupy differe nt localities - stem cells at the periphery, and TA cells more central (Leh rer, M. S., Sun, T. T. and Lavker, R. M. (1998) J. Cell Sci. 111, 2867-2875 ) - and thus can be discretely dissected from each other, It is well known that pluristratified epithelia of cornea and skin display distinct programs of differentiation: corneal keratinocytes express keratin pair K3/K12 and epidermal keratinocytes keratin pair K12/K10; moreover, the epidermis forms cutaneous appendages, which express their own set of keratins, In our expe riments, central adult rabbit corneal epithelium was thus associated either with a mouse embryonic dorsal, upper-lip or plantar dermis before grafting onto nude mice, Complementary experiments were performed using adult mouse corneal epithelium from the Rosa 26 strain, The origin of the differentiat ed structures were identified in the first case by Hoechst staining and in the second by the detection of beta -galactosidase activity, The results sh ow that adult central corneal cells are able to respond to specific informa tion originating from embryonic dermis, They give rise first to a new basal stratum, which does not express anymore corneal-type keratins, then to pil osebaceous units,. or sweat glands, depending of the dermis, and finally to upper layers expressing epidermal-type keratins, Our results provide the f irst evidence that a distinct TA cell population can be reprogrammed.