Lumen formation and redistribution of inframembranous proteins during differentiation of ducts in the rat mammary gland.

Abstract

During the development of the rat mammary gland, ducts are formed from end-buds, which contain the stem cells. In this process a lumen is formed in the semisolid mass of the end-bud, and the cells acquire polarity. We have studied this process by following the localization of three inframembranous proteins present in the cells'of both end-buds and ducts; microvillin, the microvillar protein p80, and the desmosomal plaque protein p205. We find that the development of ducts is accompanied by a redistribution of these proteins, which in immature parts of the end-buds are found together in the cell. Microvillin and p80 go together to the apical pole of the cells, in contact with the lumen, whereas p205 goes to the basal surface, in contact with cells of the myoepithelial lineage. The acquisition of polarity occurs at the same time as a lumen begins to form by local'gaps between clls. It seems likely that the redistribution of the inframembraneous proteins is the consequence of the localization of surface glycoproteins that affect in opposite ways the adhesion between the cells. characterized. In these cells microvillin is an inframembranous protein present, in association with other proteins, in microvilli. We show here that the distribution of microvillin in cells of end-buds and ducts of the rat mammary gland undergoes changes correlated with the formation of the lumen. The changes concern not only the cell types in which the protein is expressed but also the part of the cell in which it is localized. 13y using the monoclonal antibody it is possiThe publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact. 5763 ble to follow the redistribution of components of the outer layer of the cytoplasm that accompanies the development of cell polarity and lumen formation.In this study we have also used antibodies to two other proteins with inframembranous localization: a protein of the brush border, which is also present in the microvilli of mammary cells (p80) (4), and a component of demosomal plaques (p205) (5). We show that they also change localization within cells as they differentiate. The pattern of redistribution of p80 is exactly the same as that of microvillin, whereas that of p205 differs, taking a complementary path.MATERIALS AND METHODS Animals. Sprague-Dawley rats, either 3 or 7 weeks old, were used. Cryostat sections were cut at 5 ,tm thickness from whole fourth and fifth glands frozen at -30'C.Reagents. Rabbit antisera to the microvillar 80-kDa protein was generously provided by A. Bretscher (4), to the demosomal plaque 205-kDa protein by D. R. Garrod (6), and to collagen IV by L. A. Liotta. Monoclonal antibody 9B16-12 specific for microvillin has been described (3). Immunofluorescence. Immunofluorescence was carried out by the sandwich technique as described (1). RESULTSIn normal mammary glands of 3-or 7-week-old rats microvillin is restricted to the epi...

Slit2 and netrin 1 act synergistically as adhesive cues to generate tubular bi-layers during ductal morphogenesis

“…Although desmosomal components mediate these contacts in mature ducts (Runswick et al, 2001), they are not assembled during branching morphogenesis (Dulbecco et al, 1984;Nanba et al, 2001). Consequently, we entertained the possibility that contact between layers was mediated, either directly or indirectly, by SLIT2 and NTN1.…”

“…Candidates that mediate interactions between LEC and MECs, such as desmoglein or desmocollin, function in the mature gland (Runswick et al, 2001), and although they are present in the developing gland, they have not yet formed adhesive junctional complexes (Dulbecco et al, 1984;Nanba et al, 2001). Consequently, we favor the first model in which SLIT2 and ROBO1 act directly as cell-adhesion proteins, but currently our data do not rule out the second model.…”

“…Consequently, the identity of the adhesion system, if any, that mediates interactions between the MEC and LEC bi-layers during ductal morphogenesis is uncertain. Desmosomal constituents are present during postnatal mammary gland development, but they appear diffuse within cells and are not organized into mature junctional structures (Dulbecco et al, 1984;Nanba et al, 2001). This suggests that desmosomal components of cell adhesion are held in store and their assembly is delayed during development, perhaps allowing flexible movement of cells during tissue extension and tube formation.…”

Functional Disruption of the Netrin-1 Guidance Gue Leads to Disruption in Mammary Gland Development and Increased Tumor Incidence

“…It has been shown that desmosomes mediate contacts between these cell layers in mature ducts (Runswick et al, 2001), so we performed immunohistochemical staining with antibodies directed against desmosomal components. Punctate staining characteristic of desmosomes was not observed, suggesting that even in wildtype tissue, desmosomes are not fully assembled during branching morphogenesis (data not shown) (Dulbecco et al, 1984). Consequently, to investigate the interaction between luminal and myoepithelial cells, we used in vitro aggregation assays to examine whether primary cells, harvested from Slit2-/-;Ntnl-/-outgrowths, were impaired in their ability to generate bi-layered epithelial structures.…”

“…Consequently, the identity of the adhesion system, if any, that mediates interactions between the myoepithelial and luminal epithelial bi-layers during ductal morphogenesis is uncertain. Desmosomal constituents are present during postnatal mammary gland development, but they appear diffuse within cells and may not be organized into mature plaques (Dulbecco et al, 1984). This suggests that desmosomal components of cell adhesion are held in store, and their assembly is delayed during development, perhaps allowing flexible movement of cells during tissue extension and tube formation.…”