Figure 4.

Localization of type I serine/threonine kinases in the mammary gland. Antisense riboprobes of ALK-5 (A–D) and ALK-3 (E–H) were hybridized to sections from mammary glands from wild-type mice that were virgin (A and E), 12.5 d pregnant (B and F), lactating 1 d (C and G), or involuting 3 d (D and H). Toluidine blue–stained phase contrast (A–H) and dark-field (A′–H′) images are shown. Black arrows indicate epithelium; black arrowheads indicate stroma; and white arrowheads indicate blood vessels. ALK-5 localized to the epithelium (A–D) in all stages of development and to the surrounding stroma in the virgin and pregnant mammary gland (A and B). ALK-3 localized to ductal epithelium during involution (H), to the stroma in the virgin (E), pregnant (F), and involuting gland (H), and to blood vessels in all stages of development (E–H). No hybridization was detected when the sections were hybridized to sense riboprobes. Magnification, 200×.