Basement membrane disruption in mammary glands of PR-A transgenic mice: regulation by ovarian hormones. (a) Laminin-5 (LN-5), collagen IV (CoIV) and collagen III (CoIII) immunoreactivity (green) circumscribed the mammary epithelium of wild-type (WT) mice, but were decreased in the glands of PR-A transgenic mice. Nuclei were counterstained with 4',6-diamino-2-phenylindole (blue). (b) Ovariectomy (Ovx) of PR-A mice led to a recovery of the basement membrane integrity as shown by the continuous laminin staining. Upon treatment with estrogen 1 μg and progesterone 1 mg for 4 days (OvxE+P), however, the staining was lost.