Growth and morphogenesis of epithelial cell organoids from peripheral and medial mammary parenchyma of prepubertal heifers

Collagen gel cell cultures were used to test the hypothesis that cells from peripheral parenchymal zones of the developing bovine mammary gland have g reater proliferative and morphogenic potential than cells from the medial p arenchymal mass. Tritiated thymidine was incorporated to assess cell prolif eration. Dose responses for insulin-like growth factor one (IGF-I, 0 to 50 ng/ml) and transforming growth factor beta one (0 to 5 ng/ml) were determin ed for each cell population. Cells from the peripheral regions were two to three times more sensitive to the mitogenic action of IGF-I or serum. Trans forming growth factor beta one concentrations of 12.5 to 500 pg/ml stimulat ed cell proliferation, but concentrations above 1 ng/ml were inhibitory. Pe ripheral cells showed a distinct biphasic response to addition of transform ing growth factor beta one. Morphology of organoids was evaluated daily dur ing culture and by histologic examination at the end of culture. Peripheral zone cells formed multi-layered cell structures that resembled native mamm ary parenchyma with serum or mammary gland extract. Our results indicate th at epithelial cells of the peripheral and medial parenchymal zones in the r uminant mammary gland can differ in their proliferative and morphogenetic r esponse to growth factor treatment in vitro. These differences likely refle ct local tissue regulation necessary for sequential ductular and lobuloalve olar development in vivo.