FIG. 4.

A block in ductal-side branching and alveologenesis in the mammary gland of the hormone-treated PR^d/d mouse. (a) Whole-mount of a mammary gland obtained from a WT mouse previously treated with E2P4 for three weeks; (b) higher magnification image of a region of this tissue. Note the widespread presence of extensive ductal side-branching and alveologenesis. (c), (d) and (e), (f), show low and high magnification images of mammary tissue derived from the similarly treated PRKO and PR^d/d mouse respectively. Note the absence of ductal side branches and alveolar bodies in the PRKO and PR^d/d mammary glands. (g) and (h) show numerous luminal epithelial cells scoring positive (arrowhead) in the alveolar and ductal compartment of the E2P4 treated WT mammary gland respectively. (i) and (j) show a single cell registering positive for BrdU incorporation (arrowhead) in the ductal compartment of the similarly treated PRKO and PR^d/d mammary gland respectively. (k) A histogram displaying the percentage of BrdU positive luminal epithelial cells in the mammary gland of the hormone treated WT, PRKO, and PR^d/d mouse. Scale bar in (a) and (b) applies to (c), (e), and (d), (f), respectively; LN denotes lymph node (a structural reference point).