Lifespan regulation by evolutionarily conserved genes essential for viability

Abstract

Evolutionarily conserved mechanisms that control aging are predicted to have prereproductive functions in order to be subject to natural selection. Genes that are essential for growth and development are highly conserved in evolution, but their role in longevity has not previously been assessed. We screened 2,700 genes essential for Caenorhabditis elegans development and identified 64 genes that extend lifespan when inactivated postdevelopmentally. These candidate lifespan regulators are highly conserved from yeast to humans. Classification of the candidate lifespan regulators into functional groups identified the expected insulin and metabolic pathways but also revealed enrichment for translation, RNA, and chromatin factors. Many of these essential gene inactivations extend lifespan as much as the strongest known regulators of aging. Early gene inactivations of these essential genes caused growth arrest at larval stages, and some of these arrested animals live much longer than wild-type adults. daf-16 is required for the enhanced survival of arrested larvae, suggesting that the increased longevity is a physiological response to the essential gene inactivation. These results suggest that insulin-signaling pathways play a role in regulation of aging at any stage in life.

Figure 1. Representation of the Postdevelopmental RNAi Screen for Longevity

Embryos from gravid C. elegans hermaphrodites were isolated by hypochlorite treatment and allowed to hatch overnight in the absence of food. The synchronized L1 larvae were then placed on OP50 agar plates at 20 °C and allowed to develop to L4/young adult stage. The L4/young adult animals were then washed from the plates, cleaned from bacteria by sucrose flotation, and placed on six-well RNAi plates (∼30 worms/well). From three replicates of the first pass, 470 RNAi clones were identified as positive and were retested in the second pass under similar conditions while increasing the stringency for scoring positive. A total of 134 RNAi clones passed the second pass criteria and were scored longitudinally in the third pass against blind positive (daf-2 RNAi) and negative (empty vector, eri-1 RNAi, and daf-16 RNAi) controls. A total of 64 RNAi clones increased mean lifespan by >10% compared to the negative controls.

Figure 2. Identification of RNAi Clones that Act through DAF-16

(A) Shading indicates that daf-16(mgDf47); eri-1(mg366) is epistatic to the lifespan extension observed in eri-1(mg366) (Table S2). (B) DAF-16 nuclear localization after feeding RNAi clone is shown. Light shading indicates some nuclear localization, and medium shading indicates more nuclear localization (Figure S4). (C) sod-3p::gfp expression after RNAi feeding is shown. Light shading indicates weak expression, medium shading indicated modest expression, and dark shading indicates strong expression.