New genes tied to endocrine, metabolic, and dietary regulation of lifespan from a Caenorhabditis elegans genomic RNAi screen

Abstract

Most of our knowledge about the regulation of aging comes from mutants originally isolated for other phenotypes. To ask whether our current view of aging has been affected by selection bias, and to deepen our understanding of known longevity pathways, we screened a genomic Caenorhabditis elegans RNAi library for clones that extend lifespan. We identified 23 new longevity genes affecting signal transduction, the stress response, gene expression, and metabolism and assigned these genes to specific longevity pathways. Our most important findings are (i) that dietary restriction extends C. elegans' lifespan by down-regulating expression of key genes, including a gene required for methylation of many macromolecules, (ii) that integrin signaling is likely to play a general, evolutionarily conserved role in lifespan regulation, and (iii) that specific lipophilic hormones may influence lifespan in a DAF-16/FOXO-dependent fashion. Surprisingly, of the new genes that have conserved sequence domains, only one could not be associated with a known longevity pathway. Thus, our current view of the genetics of aging has probably not been distorted substantially by selection bias.

Figure 1. The Dauer-Constitutive Phenotype of daf-2(e1370) Is Enhanced by Many RNAi Clones That Extend Lifespan in a daf-16-Dependent Fashion

Relative dauer formation of daf-2(e1370) animals grown at 22.5 °C on RNAi clones versus vector control is shown, average of two to three experiments. 30–50% of the animals on vector control become dauers at 22.5 °C. Total number of dauers/total number of animals observed is noted on top of bars. Error bars: ± SEM. ‘*', previously characterized RNAi clones [9] served as negative (daf-16, RNAi insert consists of first 1.2 kb cDNA) and positive (daf-2, RNAi insert consists of first 2.2 kb cDNA; see also Figure S2) controls for the dauer experiment. daf-2(e1370) worms grown on ddl-3 RNAi gave rise to almost no progeny; therefore, this daf-16-dependent RNAi clone was not assayed.

Figure 2. sams-1, rab-10, and drr-1 RNAi Affect Reproduction

Progeny profile of N2 animals grown on RNAi clones for (A) sams-1, (B) rab-10, (C) drr-1, and (D) drr-2 (note that drr-2 RNAi did not affect reproduction). Number of progeny per worm at each time interval is shown. Error bars: ± SEM. (E) Total brood size of N2 worms grown on RNAi clones for either sams-1, rab-10, drr-1, or drr-2. The number of progeny produced by each worm was calculated from the progeny profile data in (A)–(D) and averaged. The p-values were calculated relative to control of the experiment as Student's t-test.

Figure 3. mRNA Levels of sams-1, rab-10, drr-1, and drr-2 Are Reduced in eat-2(ad1116) Mutants

Relative mRNA levels of sams-1, rab-10, drr-1, and drr-2 in eat-2(ad1116) compared to N2 were measured by quantitative PCR, and average of four different sample sets are shown. The relative mRNA levels were normalized against the act-1 (beta-actin) level in each sample. The RNAi clone for gei-9 is shown as a control; this clone does not cause significant lifespan extension when fed to N2 or eat-2 worms (Table S1, and data not shown). Error bars: ± SEM.