Distribution of myoepithelial cells and basement membrane proteins in the resting, pregnant, lactating, and involuting rat mammary gland.

Abstract

Using antisera to specific proteins, the localization of the rat mammary parenchymal cells (both epithelial and myoepithelial), the basement membrane, and connective tissue components has been studied during the four physiological stages of the adult rat mammary gland, viz. resting, pregnant, lactating, and involuting glands. Antisera to myosin and prekeratin were used to localize myoepithelial cells, antisera to rat milk fat globule membrane for epithelial cells, antisera to laminin and type IV collagen to delineate the basement membrane and antisera to type I collagen and fibronectin as markers for connective tissue. In the resting, virgin mammary gland, myoepithelial cells appear to form a continuous layer around the epithelial cells and are in turn surrounded by a continuous basement membrane. Antiserum to fibronectin does not delineate the basement membrane in the resting gland. The ductal system is surrounded by connective tissue. Only the basal or myoepithelial cells in the terminal end buds of neonatal animals demonstrate cytoplasmic staining for basement membrane proteins, indicating active synthesis of these proteins during this period. In the secretory alveoli of the lactating rat, the myoepithelial cells no longer appear to form a continuous layer beneath the epithelial cells and in many areas the epithelial cells appear to be in contact with the basement membrane. The basement membrane in the lactating gland is still continuous around the ducts and alveoli. In the lactating gland, fibronectin appears to be located in the basement membrane region in addition to being a component of the stroma. During involution, the alveoli collapse, and appear to be in a state of dissolution. The basement membrane is thicker and is occasionally incomplete, as also are the basket-like myoepithelial structures. Basement membrane components can also be demonstrated throughout the collapsed alveoli.

Human S100A4 (p9Ka) induces the metastatic phenotype upon benign tumour cells

“…The Methacarn-®xed and para n-embedded sections were dewaxed and processed as previously described (Warburton et al, 1982). They were incubated with 1/600 rabbit antimouse laminin, 1/250 rabbit anti-human callus keratin, 1/ 6000 rabbit anti-rat milk fat globule membrane after prior treatment with pronase (Warburton et al, 1982), with 1/50 horseradish peroxidase-conjugated peanut lectin after prior treatment with neuraminidase (Newman et al, 1979) or with 1/250 mouse monoclonal antibody (MAb) to smooth muscle actin (Cambridge BioScience, Cambridge: C34931), 1/50 MAb to vimentin (Dako Ltd, Bucks: M0725), 1/750 rabbit anti-rat recombinant S100A4 (p9Ka) (Gibbs et al, 1995).…”

“…They were incubated with 1/600 rabbit antimouse laminin, 1/250 rabbit anti-human callus keratin, 1/ 6000 rabbit anti-rat milk fat globule membrane after prior treatment with pronase (Warburton et al, 1982), with 1/50 horseradish peroxidase-conjugated peanut lectin after prior treatment with neuraminidase (Newman et al, 1979) or with 1/250 mouse monoclonal antibody (MAb) to smooth muscle actin (Cambridge BioScience, Cambridge: C34931), 1/50 MAb to vimentin (Dako Ltd, Bucks: M0725), 1/750 rabbit anti-rat recombinant S100A4 (p9Ka) (Gibbs et al, 1995). The primary antibodies were detected using commercially-available antibody complexes containing horseradish peroxidase (Hsu et al, 1981) (Dako Ltd, Bucks), with the appropriate anti-rabbit or anti-mouse biotinylated secondary antibodies (Amersham Int, Bucks), as described previously (Gibbs et al, 1995).…”

“…The stained sections were examined as for histology and all photographs were recorded with a Kodak Wratten #44 ®lter. Control sections incubated with antibody absorbed with the requisite antigen in place of the primary antibody (Gibbs et al, 1995;Warburton et al, 1982) and with the speci®c competing sugar for peanut lectin (Newman et al, 1979), all failed to stain.…”

Involvement of extracellular matrix constituents in breast cancer

“…29 Interestingly, type I-trimer collagen otherwise only found in preadult breast tissues, is reexpressed in ductal infiltrating carcinomas. 30 Type V collagen appears to be mainly associated with basement membranes from glands of lactating animals, 18 although it can be detected in the human mammary glands before pregnancy where its expression is subject to regulation during menstrual cycles. 22 In cases of ductal infiltrating carcinomas, this molecule is overexpressed.…”

“…17 Thus, in the mammary gland, these molecules are synthesized and deposited when active growth, characterized by elongation and dichotomous branching of mammary ducts, takes place during development. 18 The most conspicuous alterations in basement membrane structure occur during involution when ECM degrading proteases break down the basement membrane with accompanying apoptosis and loss of milk secretory function. [19][20][21] However, even in the resting mammary gland, laminin, type IV collagen and heparan sulfate proteoglycan display estrous cycle-dependent regulation.…”