Developmental changes in the expression of S-acyl fatty acid synthase thioesterase gene and lipid composition in the uropygial gland of mallard ducks (Anas platyrhynchos).

Developmental changes in the composition of the uropygial gland secretory lipids of the postembryonic mallard ducks (Anas platyrhynchos) were determined. During the first 3 weeks after hatching, the composition of the secretory lipids remained constant; the lipids consisted of long-chain wax esters composed of a complex mixture of n-, monomethyl, and dimethyl fatty acids esterified to n-C16 and n-C18 fatty alcohols. Afterward, as the ducks began to acquire adult feathers, short-chain wax esters composed of 2- and 4-monomethyl fatty acids began to appear with 2-methylhexanoyl and 4-methylhexanoyl as the major acyl components; esters of short-chain monomethyl fatty acids (less than or equal to C12) constituted 90% of the lipids when the ducks were 2 months old and had acquired adult plumage. The appearance of the short-chain acids in the acyl portion of the wax esters was accompanied by the appearance of S-acyl fatty acid synthase thioesterase, which can hydrolytically release short-chain acids from fatty acid synthase in the gland. Northern blot analysis showed that the gland-specific thioesterase gene transcripts began to appear in the gland only 3 weeks after hatching. The appearance of the transcripts and immunologically detectable thioesterase protein reached maximum levels 2 months after hatching, with the acquisition of the adult plumage. Thus, the developmental changes in lipid composition correlated with the changes in the level of expression of the thioesterase gene. Expression of other gland-specific genes has been previously found to begin just prior to hatching. The gland-specific thioesterase is the first case of delayed expression of a gland-specific gene.