Stem cells in mammary gland differentiation and XXXX .

@entity1 @entity0 @entity5 @entity535 @entity377 @entity133 @entity513 @entity460 @entity73216 @entity35 @entity18715
Evidence based on ultrastructure and immunocytochemical staining suggests that morphological gradations between epithelial and myoepithelial cells, and possibly between epithelial and alveolar-like cells, can occur in terminal ductal structures of @entity35 and @entity1 mammary glands. In @entity5 the benign, carcinogen-induced @entity35 and benign, @entity1 mammary @entity5 can contain epithelial, @entity133 , whereas their malignant counterparts mainly contain only epithelial-like cells. Clonal epithelial cell lines from normal @entity35 mammary glands, from @entity5 and from SV40-transformed @entity1 mammary cultures can differentiate to either @entity133 . In those of the @entity35 , the differentiation processes occur in steps, intermediate cells along the myoepithelial-like pathway resemble the morphological intermediates in the terminal ductal structures in vivo. Changes in specific polypeptides characterize each of the intermediate cells in vitro. One of the earliest increases observed in the myoepithelial-like pathway in vitro is that due to a novel protein @entity73216 , whereas the major increases in @entity18715 and the basement membrane proteins laminin and type IV collagen occur at later steps. The @entity377 sequence of the gene for @entity73216 is related to that of the small, regulatory @entity460 -binding proteins, and antibodies raised to synthetic fragments of its predicted @entity535 sequence react with only myoepithelial cells within the @entity35 mammary parenchyma. Increases in the production of @entity73216 and @entity18715 are largely due to increases in their messenger RNAs, possibly arising at the level of transcription of the DNA, whereas the increases in production of laminin and type IV collagen occur at a post-transcriptional level. The normal transcriptional promoter sequences of TATA or CAAT are not found adjacent to the genes for @entity73216 or @entity18715 . Cells and cell lines from malignant @entity35 mammary @entity5 of increasing metastatic potential and from malignant areas of @entity1 @entity513 largely fail to yield fully differentiated @entity133 in culture; however, weakly metastasizing @entity35 cells yield variants which may retain a vestige of the myoepithelial phenotype. It is suggested that novel regulatory transcriptional element(s) may control the production of some of the proteins along the normal myoepithelial-like pathway, and that these elements may be relatively unique in their capacity to become inoperative in the @entity0 cell.
