Characterization of luminal and basal cells flow-sorted from the adult rat mammary parenchyma.

Differentially expressed membrane antigens have been used to flow-sort viable luminal epithelial and myoepithelial cells from freshly disaggregated adult virgin rat mammary parenchyma. Resulting cultures and clones have been characterized morphologically and by a panel of antibodies that recognise cell-type-specific cytoskeletal antigens in the intact mammary gland. Five clonal phenotypes were recognisable by morphological criteria, three (types 1-3) exclusively associated with sorted luminal epithelial (25.5-positive) cells, and two (types 4 and 5) generated from the sorted myoepithelial (CALLA/neutral endopeptidase 24.11-positive) cells. All clones derived from myoepithelial cells continued to express a basal parenchymal marker in the form of the rat equivalent of human cytokeratin 14, while smooth muscle alpha-actin was expressed by the small slowly growing type 4 clones but was found in fewer cells in rapidly proliferating type 5 myoepithelially derived clones. Two of the luminal clone types, characterized by an attenuated appearance and slow growth (types 1/2), expressed only luminal-specific markers, including the equivalent of human cytokeratins 7/18/19. Type 3 clones, by contrast, consisted of rapidly proliferating cells, many of which either co-expressed CK14 and CK18 antigens (type 3a) or were composed of a mosaic of CK14+/CK18-, CK14+/CK18+ and CK14-/CK18+ cells (type 3b). The sorted myoepithelially derived clones grew faster than clones from sorted luminal cells as evidenced by the larger fraction of cells synthesizing DNA. All types of clone could be obtained from both isolated ducts and alveoli, when these were cloned separately, although there were some differences in their relative frequency.(ABSTRACT TRUNCATED AT 250 WORDS)