BRCA1 expression during prenatal development of the human mammary gland.

Germ-line alterations of BRCA1 are associated with elevated risk of breast cancer. Evidence for the involvement of Brca1 in cellular differentiation and morphogenesis has been obtained in mouse models during embryogenesis. Although the presence of well-conserved functional domains might suggest a similar function for both human and mouse genes, very few data on BRCA1 expression in human fetal tissues are available. We have, therefore, investigated the expression of BRCA1 in the mammary gland from human female fetuses aged between 15 and 33 weeks. Quantification of BRCA1 transcripts, using a competitive reverse transcriptase PCR method, indicates a progressive decrease in BRCA1 expression with increasing fetal age between the 15th and 30th week of gestation. Subsequently, the amount of BRCA1 transcripts becomes similar to that found in adult mammary gland. Analysis of BRCA1 protein revealed, in fetal samples, a 220 kDa band corresponding to the 220 kDa BRCA1 protein described in human cell lines. These later experiments confirm that the relative level of the 220 kDa BRCA1 protein is highest in the early stages of mammary gland development. The temporal patterns of BRCA1 expression in human fetuses suggest a role for BRCA1 in the morphogenesis and differentiation of the human mammary gland.