The differential expression of desmocollin isoforms in mammary epithelia.

In the mammary gland, cell-cell contacts influence epithelial morphogenesis during the formation of ducts and alveoli. Desmosomes are adhesive intercellular junctions that are widespread in epithelia and other tissues. Although the components of desmosomes have been characterised at the molecular level, their precise function in epithelial organisation and morphogenesis has not been determined. Desmosomal adhesion is partly mediated by one of its components, desmocollin, a family of transmembrane proteins which belongs to the cadherin superfamily of calcium-dependent adhesion molecules. To date, three desmocollin isoforms have been characterised and are called Dsc I , Dsc2 and Dsc3. In addition, each isoform can be alternatively spliced cytoplasmically to give either the “a” or “b” forms. The desmocollins have been demonstrated to have tissue-specific localisation [ I ] . We propose that desmosomes containing different desmocollin isoforms reflect differences in cell-cell adhesion An ideal system for the study of simple epithelia morphogenesis and one that can be manipulated in culture is the mammary gland. Luminal epithelial cells form monolayers when plated on tissue culture plastic, but in the presence of EHS matrix undergo striking morphogenetic events to form spherical alveolar structures. This cellular remodelling mimics developmental events occurring in vivo during alveoli formation in pregnancy [2]. In this work we demonstrate the differential distribution of desmocollin isoforms present in mammary epithelia in vivo by indirect-immunofluorescence. This has been done by using monoclonal and polyclonal antibodies specific to desmocollin isoforms. Furthermore, it has been possible to establish the localisation of the desmocollins in the different mammary epithelia. Both luminal epithelial cells and myoepithelial cells can be identified by cytoskeletal markers. Luminal epithelial cells can be detected by cytokeratins 7, 8, 18 and 19, while myoepithelial cells contain cytokeratins 5 and 14. Cryosections of bovine mammary gland were doublestained with antibodies for either Dscl, Dsc2 or Dsc3 and myoepithelial-specific cytokeratin (K14) or luminal epithelialspecific cytokeratin (K7 & K8). We show that Dsc2 is present in the luminal epithelial layer, whereas Dsc3 is restricted to the myoepithelial layer and Dsc 1 is completely absent from mammary epithelia (figure 1). In addition, the expression of Dsc2 and Dsc3, but not Dscl in mammary epithelia at the mRNA level has been confirmed by RT-PCR using desmocollin isoform specific primers. The parenchyma of both mammary ducts of alveoli consists of a layer of myoepithelial cells which surround the luminal epithelial component. We propose that differential adhesiveness between desmosomes containing Dsc2 or Dsc3 may contribute to the cellular organization of mammary epithelia, thereby contributing to the formation of luminal epithelial tubes situated within a myoepithelial sheath. A B