Aging research: current and future.

The key events that lead to organismic senescence appear to occur in cells that have been genetically programmed to arrest their own proliferation. After arrest, a variety of subcellular events occur, among the more important of which are the accumulation of waste product pigments, an increase in the fraction of inactive enzymes, and (probably of central importance) the loss of key genes, specifically those that code for rRNA. An understanding of the senescence of the epidermis and dermis would almost certainly provide answers to related problems in those organ systems whose sudden or slow failure leads to individual death.