Differentiation in culture of cells from an avian holocrine secretory gland: preparation of isolated cells and conditions which induce accumulation of malic enzyme.

Mammalian sebaceous glands contain cells which are constantly going through a process of cell division, differentiation, and destruction. Birds have an analogous holocrine secretory gland, the uropygial gland, which is an excellent model for mammalian sebaceous glands and for analysis of the regulation of differentiation. Isolated uropygial cells were purified in good yield, and with high viability, after enzymatic digestion of the duck uropygial gland. Almost exclusively progenitor (basal) cells are recovered after separation of isolated cells on a Percoll density gradient; mature uropygial cells are destroyed during preparation of isolated cells. In primary culture, uropygial gland cells grow to confluence and partially duplicate the in vivo differentiation pathway. Malic enzyme activity increases 30-fold during 4 wks in culture, but there is little, if any, accumulation of fatty acid synthase and only a modest deposition of fat droplets. Medium conditioned by chick embryo fibroblasts inhibits the accumulation of malic enzyme without affecting cell growth. The basement membrane components, collagen, laminin, and Matrigel, which stimulate differentiation in other cell systems, were without effect on uropygial gland cultures. Triiodothyronine, cyclic AMP, and dexamethasone together with isobutylmethylxanthine had no effect on cell growth or malic enzyme activity. Epidermal growth factor, which stimulates cell division, increased cell number with no increase in malic enzyme accumulation. Factors which would stimulate further differentiation are missing from our culture system, but may include components of the basal lamina and/or factors secreted by mesenchymal cells.