ESTABLISHMENT AND INITIAL CHARACTERIZATION OF THE OVINE MAMMARY EPITHELIAL-CELL LINE NISH

Analysis of the molecular mechanisms involved in the differentiation a nd formation of the characteristic three-dimensional structures of the developing mammary gland of the major milk-producing livestock (ducts , end buds, and alveoli) requires in vitro model cell cultures. The fe w cell lines that have been established from dairy animals do not full y reproduce the entire program of mammary differentiation. Here we pre sent the initial characterization of a unique mammary epithelial cell line derived spontaneously from midpregnant sheep (NISH). These cells form in vitro functional structures resembling ducts, lateral buds, an d alveoli that secrete beta-lactoglobulin (BLG) in an ECM (extracellul ar matrix)-dependent manner. Interestingly, the presence of growth hor mone dramatically increased BLG secretion from WISH cells cultured on ECM. It appears that GH is required not only to establish the structur al organization but also is continuously needed to maintain BLG expres sion. Stable transfection of NISH cells with BLG/Human Serum Albumin ( HSA) hl:brid gene constructs revealed that the relative level of expre ssion was comparable to the in vivo secretion of HSA in transgenic mic e carrying these gene sequences. No expression could be detected in ce lls transfected with hybrid genes carrying either HSA cDNA or the enti re HSA gene, and HSA expression was dependent on the presence of intro nic sequences. These results demonstrate that NISH cells may prove a u seful tool for studying the differentiation and organogenesis of mamma ry epithelial cells under defined culture conditions. Furthermore. tra nsfected WISH cells may be an alternative for the transgenic mouse mod el in evaluating the potential of gene constructs to be efficiently ex pressed in the mammary gland of transgenic farm animals.