Several molecular theories of aging postulate that there are age-dependent changes in gene expression and that these changes contribute to the reduction in the viability of senescent cells. High-resolution, semiautomated, quantitative two-dimensional gel electrophoresis of many soluble proteins was used to test this hypothesis in Drosophila. Two-dimensional protein gel patterns were analyzed for each of three age groups of [35S]methionine-labeled adult male Drosophila melanogaster, which, except for their spermatocytes, consist entirely of fixed postmitotic cells. Seven relatively abundant polypeptides expressed in middle-aged (28-day-old) flies were absent in both young(10-day-old) and old (44-day-old) flies. Quantitative analyses of an additional 100 polypeptides were carried out by computer-assisted microdensitometry of fluorograms of the gel preparations. These analyses revealed a significant age-related heterogeneity in the quantitative distribution of radiolabel in these proteins. The data indicate that the qualitative pattern of gene expression is identical in young and old flies, but that profound quantitative changes occur in the expression of proteins during the Drosophila life-span.

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