Expression of BRCA1 and BRCA2 in Normal and Neoplastic Cells

Current evidence strongly supports a role forthe breast cancer susceptibility genes, BRCA1 and BRCA2, in both normal development and carcinogenesis.Valuable clues regarding the function of these genes have been garnered through studies of theirpatterns of expression. A central feature of the in vivopattern of BRCA1 and BRCA2 expression is that each ofthese putative tumor suppressor genes is expressed at maximal levels in rapidly proliferatingcells. This feature is consistent with in vitroobservations that BRCA1 and BRCA2 are expressed in acell cycle-dependent manner. This feature is also wellillustrated during mammary gland development wherein theexpression of BRCA1 and BRCA2 is induced in rapidlyproliferating cellular compartments undergoingdifferentiation, such as terminal end buds duringpuberty and developing alveoli during pregnancy.Strikingly, the spatial and temporal patterns of BRCA1and BRCA2 expression are virtually indistinguishableduring embryonic development and in multiple adulttissues despite the fact that these genes areunrelated. These observations have contributed to theemerging hypothesis that these genes function in similarregulatory pathways.