Expression of dominant-negative ErbB2 in the mammary gland of transgenic mice reveals a role in lobuloalveolar development and lactation

Overexpression of the receptor tyrosine kinase ErbB2/HER2/Neu (ErbB2) occurs in 15-40% of human breast cancers. To determine the function of ErbB2 signaling during normal mouse mammary gland development, me expressed a carboxyl-terminal truncated dominant negative allele of ErbB2 (ErbB2 Delta IC) in the developing mouse mammary gland. Despite ErbB2 Delta IC expression within mammary glands of pubescent virgin and pregnant mice, a phenotype was not observed until late in pregnancy. At 1 day post-partum, lactationally active, distended lobuloalveoli failed to form. This phenotype was exaggerated in multiparous females expressing ErbB2 Delta IC. Immunohistochemical staining for ErbB2 Delta IC revealed a concordance between high levels of ErbB2 Delta IC protein expression and the absence of lactational products within the lumens of ErbB2 Delta IC stained lobuloalveoli. These results demonstrate that ErbB2 signaling is required for proper mammary development and lactation at parturition.