BCL-2 EXPRESSION IN ADULT AND EMBRYONIC NONHEMATOPOIETIC TISSUES

The B-cell leukaemia/lymphoma-2 (bcl-2) proto-oncogene is unusual as its product appears to provide survival advantage to B cells by blocking apoptosis. In this study, the expression of bcl-2 has been examined in normal non-haematopoietic tissues, embryos. and psoriatic skin by immunohistochemical staining. Bcl-2 protein expression is mainly observed in cell populations with a long life and/or proliferating ability such as duct cells in exocrine glands, basal keratinocytes, cells at the bottom of colon crypts, and neurons. In the skin of both adult and embryo and also embryonic kidney and cartilage, bcl-2 expression was observed in cells which were undergoing morphological transition from undifferentiated 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 stimulation such as in the endometrium and myometrium suggests that the gene expression may be related to hormone responsiveness. As no bcl-2 localization was seen in the benign hyperproliferative skin condition psoriasis. this does not suggest a straight-forward link to proliferation. These observations support the view that the bcl-2 gene may have an important role in cell development, maturation, and the path to terminal differentiation.