Localization of DNIIR mRNA in the mammary gland. An antisense DNIIR riboprobe was hybridized to sections of zinc-treated wild type (A), MT-DNIIR-4 (B), and MT-DNIIR-28 (C) mammary glands. Toluidine blue–stained bright-field (A–D) and dark-field (A′–D′) images are shown. Arrows indicate stroma (St) and ductal epithelium (Du). DNIIR hybridization was detected in the stroma surrounding the ductal epithelium in zinc-treated MT-DNIIR-4 and -28 mammary glands. No hybridization was detected in untreated MT-DNIIR-28 (D) or zinc-treated wild-type (A) mammary glands. St, stroma; Du, duct; BV, blood vessel. Sections were also hybridized to a sense DNIIR riboprobe, and no hybridization was detected. Magnification, 200×.