BCL-2 EXPRESSION IN ADULT AND EMBRYONIC NONHEMATOPOIETIC TISSUES

The B-cell leukaemia/lymphoma-2 (bcl-2) proto-oncogene is unusual as i ts product appears to provide survival advantage to B cells by blockin g apoptosis. In this study, the expression of bcl-2 has been examined in normal non-haematopoietic tissues, embryos. and psoriatic skin by i mmunohistochemical staining. Bcl-2 protein expression is mainly observ ed in cell populations with a long life and/or proliferating ability s uch as duct cells in exocrine glands, basal keratinocytes, cells at th e bottom of colon crypts, and neurons. In the skin of both adult and e mbryo and also embryonic kidney and cartilage, bcl-2 expression was ob served in cells which were undergoing morphological transition from un differentiated stem cells to committed precursor cells. The finding of bcl-2 expression in the terminal differentiated syncytial trophoblast , but not cytotrophoblast, and in some cells responsive to hormone sti mulation such as in the endometrium and myometrium suggests that the g ene expression may be related to hormone responsiveness. As no bcl-2 l ocalization was seen in the benign hyperproliferative skin condition p soriasis. this does not suggest a straight-forward link to proliferati on. These observations support the view that the bcl-2 gene may have a n important role in cell development, maturation, and the path to term inal differentiation.