Identification of cell types in the developing goat mammary gland

The goat was chosen as the model system for investigating mammary gland dev elopment in the ruminant. Histological and immunocytochemical staining of g oat mammary tissue at key stages of development was performed to characteri ze the histogenesis of the ruminant mammary gland. The mammary gland of the virgin adult goat consisted of a ductal system terminating in lobules of d uctules. Lobuloalveolar development of ductules occurred during pregnancy a nd lactation which was followed by the regression of secretory alveoli at i nvolution. The ductal system was separated from the surrounding stroma by a basement membrane which was defined by antisera raised against laminin and Type IV collagen. Vimentin, smooth-muscle actin and myosin monoclonal anti sera as well as antisera to cytokeratin 18 and multiple cytokeratins staine d a layer of myoepithelial cells which surround the ductal epithelium. Stai ning of luminal epithelial cells by monoclonal antibodies to cytokeratins w as dependent on their location along the ductal system, from intense staini ng in ducts to variable staining in ductules. The staining of epithelial ce lls by monoclonals to cytokeratins also varied according to the development al status of the goat, being maximal in virgin and involuting glands, lowes t at lactation and intermediate during gestation. In addition, cuboidal cel ls, situated perpendicular to myoepithelial cells and adjacent to alveolar cells in secretory alveoli, were also stained by cytokeratin monoclonal ant ibodies and antisera to the receptor protein, erbB-2, in similar fashion to luminal epithelial cells. These results demonstrate that caprine mammary e pithelial cell differentiation along the alveolar pathway is associated wit h the loss of certain types of cytokeratins and that undifferentiated and s ecretory alveolar epithelial cells are present within lactating goat mammar y alveoli.