Caenorhabditis elegans PI3K mutants reveal novel genes underlying exceptional stress resistance and lifespan.

Authors: Ayyadevara S; Tazearslan C; Bharill P; Alla R; Siegel E; Shmookler Reis RJ

Abstract: Two age-1 nonsense mutants, truncating the class-I phosphatidylinositol 3-kinase catalytic subunit (PI3K(CS)) before its kinase domain, confer extraordinary longevity and stress-resistance to Caenorhabditis elegans. These traits, unique to second-generation homozygotes, are blunted at the first generation and are largely reversed by additional mutations to DAF-16/FOXO, a transcription factor downstream of AGE-1 in insulin-like signaling. The strong age-1 alleles (mg44, m333) were compared with the weaker hx546 allele on expression microarrays, testing four independent cohorts of each allele. Among 276 genes with significantly differential expression, 92% showed fewer transcripts in adults carrying strong age-1 alleles rather than hx546. This proportion is significantly greater than the slight bias observed when contrasting age-1 alleles to wild-type worms. Thus, transcriptional changes peculiar to nonsense alleles primarily involve either gene silencing or failure of transcriptional activation. A subset of genes responding preferentially to age-1-nonsense alleles was reassessed by real-time polymerase chain reaction, in worms bearing strong or weak age-1 alleles; nearly all of these were significantly more responsive to the age-1(mg44) allele than to age-1(hx546). Additional mutation of daf-16 reverted the majority of altered mg44-F2 expression levels to approximately wild-type values, although a substantial number of genes remained significantly distinct from wild-type, implying that age-1(mg44) modulates transcription through both DAF-16/FOXO-dependent and -independent channels. When age-1-inhibited genes were targeted by RNA interference (RNAi) in wild-type or age-1(hx546) adults, most conferred significant oxidative-stress protection. RNAi constructs targeting two of those genes were shown previously to extend life, and RNAi's targeting five novel genes were found here to increase lifespan. PI3K-null mutants may thus implicate novel mechanisms of life extension.

Keywords: Alleles; Animals; Binding Sites; Caenorhabditis elegans/*enzymology/genetics; Caenorhabditis elegans Proteins/genetics/*metabolism; *Gene Expression Regulation; Longevity; *Mutation; Oligonucleotide Array Sequence Analysis; Phosphatidylinositol 3-Kinases/genetics/*metabolism; RNA Interference; Stress, Physiological; Transcription, Genetic
Journal: Aging cell
Volume: 8
Issue: 6
Pages: 706-25
Date: Sept. 22, 2009
PMID: 19764929
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Ayyadevara S, Tazearslan C, Bharill P, Alla R, Siegel E, Shmookler Reis RJ (2009) Caenorhabditis elegans PI3K mutants reveal novel genes underlying exceptional stress resistance and lifespan. Aging cell 8: 706-25.

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