Localization of casein-rich, fat-rich and DNA-synthesizing cells in monolayer cultures of mid-pregnant mouse mammary epithelium

Identification of mouse mammary epithelial cells by immunofluorescence with rabbit and guinea pig antikeratin antisera

Few markers are available to identify the three types of mammary epithelial cells--ductal, alveolar, and myoepithelial--especially in pathological conditions and in cell cultures. We have used antisera to human keratins in immunofluorescence to facilitate the identification of the three mouse mammary epithelial cell types. In frozen tissue sections and primary cell cultures, a rabbit antikeratin antiserum specifically stained cytoplasmic filaments in all three types of epithelial cells. A guinea pig antiserum against the same keratin preparation, however, reacted preferentially with filaments in myoepithelial cells and readily detected this cell type in normal, dysplastic, and malignant mammary tissues and cell cultures. Neither antisera reacted with fibroblasts or any other mesenchymal cells. The combined use of the two antikeratin antisera thereby permits rapid surveys of tissue sections and cultures for the localization of not only all epithelial cells but also the subpopulation of myoepithelial cells. Moreover, when mammary cultures established from late-pregnant or lactating mice were stained simultaneously with guinea pig antikeratin and rabbit anticasein antisera, three populations of epithelial cells were mutually exclusive: those stained by anticasein antiserum, those stained by guinea pig antikeratin antiserum, and those stained by neither, consistent with properties of alveolar, myoepithelial, and ductal cells, respectively. These antisera thus offer a tool for studying different epithelial cell types during mammary development, tumorigenesis, and malignant progression.

Difficulties involved in diaminobenzidine histochemistry of endogenous peroxidase

Basically peroxidase (PO) histochemistry is used in different areas: haematologic physiopathology, estrogen-dependent genito-mammary physiopathology and immunoperoxidase histochemistry, both in electron microscopic cytochemistry and at the light microscopic level. In immunochemistry, endogenous peroxidatic activity is inhibited by means of various procedures. On the contrary, in haematology and in reproduction biology stainability of endogenous PO is mandatory; controls are achieved using different inhibitors. Literature data on the most appropriated technical conditions concerning fixation, processing and incubation, for PO staining are reviewed.

A possible mammary stem cell line

The cell line Rama 25 is derived from a mammary tumor induced in a rat by dimethylbenzanthracene. During rapid proliferation, Rama 25 cells appear as a single undifferentiated epithelial type; at high cell densities, however, small numbers of two other cell types are formed, which respectively resemble secretory and myoepithelial cells of the mammary gland, as judged by light and electron microscopy and immunofluorescent staining for casein (milk proteins). These additional cell types cannot be explained as contaminating cell populations since the cell line has been cloned several times; furthermore, the proportion of either can be increased by dimethylsulphoxide under different conditions. Specific epithelial features are seen by histological and ultrastructural examination of tumors formed by Rama 25 cells in immunodeficient mice. A line of the myoepithelial-like cells, Rama 29, isolated from a Rama 25 culture by cloning, is also described. We propose that the undifferentiated cell type is a form of mammary stem cell which can differentiate in culture.