Stem cells of stratified epithelia : a generic stem cell?

Squamous stratified epithelia tissues are self-renewing, which quality implies the existence of stem cells. In skin the presence of bona fide multipotent stem cells has been demonstrated by long-term, serial grafting assays. We isolated, cultivated and expanded clonogenic keratinocytes from stratified epithelia of rodents (mouse and/or rat cornea, hairy and glabrous skin, oesophagus, buccal cavity and vagina). Just like mutipotent stem cells present in skin, clonogenic epithelial cells present in the stratified epithelia of rodents are able to respond to skin and hair morphogenetic signals, thereby forming de novo cycling hair follicles, sebaceous glands and contributing to skin formation in transplantation assays. Our results show that, irrespective of their germ layer origin, the ability of clonogenic cells from stratified epithelia to respond to skin and hair morphogenetic signals is part of their intrinsic competence. Our RT-PCR results indicate that cell culture acts as a revealer of this competence and that cell culture does not alter this intrinsic competence. These observations strongly suggest that stem cells of stratified epithelia, irrespective of their germ layer origin, share common characteristics and are closely related, if not functionally identical. Therefore they may be interchangeable, thus opening the door for therapeutic use of one stratified epithelium to heal another.