Figure 1.

Brca1 and Brca2 expression are a function of proliferative state. (A) mRNA expression of Brca1, Brca2, histone H2B, and actin in actively growing (Act) or confluent (Con) murine cell lines. Cell line RNAs analyzed were prepared from NIH 3T3 fibroblasts (3T3), nontransformed mammary epithelial cells (HC11), or transformed mammary epithelial cells derived from breast tumors arising in transgenic mice overexpressing either activated c-neu, c-myc, or int-2, as indicated. (B) mRNA expression of Brca1, Brca2, histone H2B, and actin in actively growing (Act) or serum starved (G₀) nontransformed mammary epithelial cell lines, as indicated. mRNA expression was quantitated by RNase protection (Brca1, Brca2, and actin) or Northern blot hybridization (histone H2B). The 28S RNA band from an ethidium bromide-stained nitrocellulose blot used as a loading control is shown.