Cultured mammalian cells and small nematodes are being used as model systems to study the mechanisms of aging. During the next year, serum proteins that are still needed by human diploid fibroblasts in recently developed media that minimize serum requirements will be characterized, and detailed studies of nutrient effects on cellular aging will be undertaken. Growth requirements of cells from individuals with premature aging syndromes will also be studied. High voltage electron microscopy will be used to compare the ultrastructure of whole WI-38 and IMR-90 cells, and to characterize further their cytoplasmic organization and histochemical localization of acid phosphatase and ATPase as they age. Cellular hybrids will be used to study dominance of senescent and transformed phenotypes, and to evaluate the role of sensitivity to G1 inhibition in senescence of cells. Studies of cell lineages and cell death in nematode development and aging will be continued, and the accumulation of fluorescent pigment during aging will be analyzed in detail, including a search for mutants that do not accumulate such pigment as they age. The long-term goal of this research program is to understand aging in terms of molecular events occurring within and among the individual cells of aging organisms. BIBLIOGRAPHIC REFERENCES: Ham, Richard G., S.L. Hammond, and L.L. Miller. 1976. Critical adjustment of cysteine and glutamine concentrations for improved clonal growth of WI-38 cells. In Vitro, in press. McKeehan, W.L., W. G. Hamilton, and R.G. Ham. 1976. Selenium is an essential nutrient for growth of WI-38 human diploid fibroblasts in culture. Proc. Natl. Acad. Sci. USA 73: 2023-2027.