Terminal differentiation in the avian uropygial gland. Accumulation of fatty acid synthase and malic enzyme in non-dividing cells

Abstract

The secretory tissue of the uropygial gland is of the holocrine type, containing both dividing progenitor cells and lipid-filled differentiated cells. In this study, we examined the relationship between cell division and differentiation. The location of dividing cells was determined by autoradiography of tissue sections from ducklings injected intra-abdominally with 3H-thymidine. Only cells on the basal lamina of the tubules contained labeled nuclei. Dividing cells were distributed uniformly over the length of the tubules. Over the next five days, most of the labeled cells migrated to the lumen of the tubules and disappeared. Cells containing the "lipogenic" enzymes, fatty acid synthase and malic enzyme, were localized either immunocytochemically using affinity-purified antibodies or cytochemically using a specific assay for malic enzyme activity. Fatty acid synthase and malic enzyme were undetectable in dividing basal cells but present at high levels in differentiating and differentiated cells. Thus, basal cells lying along the basal lamina of the tubules were replacing lipid-laden cells that were continually sloughed into the lumens of the tubules. The signals for differentiation and enzyme accumulation appear to be linked to one another and to cessation of cell division.

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

“…In the domestic Pekin duck, as in other waterfowl, this gland is particularly large and active, and so represents a n attractive model for study of the regulation of differentiation in sebaceous glands. (Buckner and Kolattukudy, 1976;Kolattukudy, 1981;Jenik et al, 1987).…”

“…Only the basal cells undergo cell division; over a period of five days, daughter cells move towards the central lumen, accumulate lipid, and are lost (Jenik et al, 1987). Furthermore, immunocytochemical studies indicate that the lipogenic enzymes, malic enzyme and fatty acid synthase, begin to accumulate only after the daughter cells have moved away from the basal lamina.…”

“…The progenitor cells and mature cells are easily identified by virtue of their morphology and their enzyme and lipid content. Two enzymes in particular, malic enzyme and fatty acid synthase (FAS), can be used as markers for the differentiated state since they are expressed at high activity in mature uropygial cells (Sawaya and Kolattukudy, 1972;Tang and Hansen, 1972;Goodridge et al, 1984;Jenik et al, 1987) and are readily assayed.…”