Fig. 3. Mammary gland morphology in PKN1 transgenic mice of line 933. Whole mount preparations (A,C,G) and tissue sections stained with hematoxylin and eosin (B,D,E) of wild-type and transgenic mammary glands are shown. The respective developmental stage is indicated (P18, Pregnancy day 18; L1, Lactation day one; L2, Lactation day two; L10, Lactation day ten). (A) Regular side branching and alveolar budding in late pregnancy in PKN1 transgenic mice. (B) Accumulation of intracellular lipid droplets (arrow) in the wild type as well as in PKN1 transgenic mammary epithelial cells indicative of proper differentiation at the end of pregnancy. (C) Sparse alveoli with significant intervening adipose tissue in PKN1 transgenic mice at the onset of lactation. (D) Failure of transgenic alveoli to expand at secretory activation. (E) Condensed alveoli in PKN1 transgenic mice on the second day of lactation. Note that alveolar lumina are filled with thickened secretion product frequently containing apoptotic bodies (arrow). (F) In situ hybridization to detect transgene expression at the second day of lactation. Tissue sections from transgenic animals of line 933 were hybridized to a probe comprising the transcribed portion of the SV40 polyadenylation sequence in either the sense or antisense direction. Note the abundance of transgene-expressing cells in condensed alveoli (arrow). (G) Mammary gland regression in PKN1 transgenic mice after ten days of lactation. Note the segmental distribution of the epithelial decline.