Fig. 4. Milk protein gene expression at secretory activation in PKN1 transgenic mice. (A) Expression of the milk proteins WAP, β-casein, -lactalbumin and WDNM on lactation day 1 in animals of the indicated genotype. Data were derived from microarray analyses of triplicate samples for each group. There were no significant differences by Student's t-test. Error bars represent the s.e.m. (B) Immunohistochemical detection of β-casein in mammary glands of mice of the indicated genotype on the first day of lactation using a secondary antibody coupled to Cy3. Nuclei were stained with DAPI and Oregon-Green-488-coupled WGA was used to label the alveolar lumina. In contrast to wild-type animals, β-casein staining is not restricted to the apical part of the cells in PKN1 transgenic mice (lower right panel). (C) Transmission electron micrographs of wild-type and transgenic mammary epithelial cells at the second day of lactation. Cytoplasm is reduced in transgenic animals and highly vacuolarized with a big lipid droplet and casein (arrow) being detained in the cytoplasm.