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Aging, Metabolism, Stress, Pathogenesis, and Small RNAs, Madison, WI,
2010]
In Caenorhabditis elegans, development is spatially and temporally determined; adult cell number and anatomy are nearly invariant. Cohorts of isogenic animals synchronously express genes that cause individuals to molt to successive larval stages within a few hours of one other. Yet, even isogenic cohorts cultured in homogenous, liquid environments show 20-fold variation in individual lifespan. Five years ago, we (Johnson lab) found (REA et al. 2005) in isogenic populations that level of expression of a heat-shock promoter-GFP fusion construct (Phsp-16.2::gfp) after mild heat stress predicts subsequent lifespan. Thus, Phsp-16.2 reporter expression on the first day of adult life is a physiological variable (or 'biomarker') predictive of subsequent lifespan. In metazoans, the components and mechanism(s) underlying expression variation of the Phsp-16.2::gfp biomarker (or any other gene) remain mostly unknown. For that reason we have initiated work on Phsp-16.2::gfp expression modeled on previous work in S.cerevisiae. In these yeast studies, we (Brent lab) and others have dissected and quantified different contributions to 'stochastic' variation in gene expression and on cell fate decisions (COLMAN-LERNER et al. 2005). As in these studies, we are quantifying gene expression and variation, dissecting the different contributions to those quantities, and using genetics to understand control of the individual sources of variation. To do so, we measure expression of different-colored fluorescent reporter proteins, under the control of identical or of different promoters, quantify components of the variation based on simple mathematical models, and use the results to guide subsequent hypothesis-directed experiments. At this point, we have some genetic data identifying physiological subsystems that control the amount of worm-to-worm variation in gene expression. We have used defined site, single copy reporter integration technology (MosSCI technology) to determine how variance in gene expression manifests when using single copy reporter genes vs tandem arrays and to minimize variation in gene expression due to chromosomal position and silencing. We are using these reporters to quantify the amount of worm-to-worm variation due to intrinsic noise and that due to the different physiological subsystems. Colman-Lerner,A., A. Gordon,E. Serra, T. Chin, O.Resnekov et al., 2005 Regulated cell-to-cellvariation in a cell-fate decision system. Nature 437: 699-706. Rea, S.L., D. Wu,J. R. Cypser, J. W.Vaupel and T. E.Johnson, 2005 Astress-sensitive reporter predicts longevity in isogenic populations of Caenorhabditis elegans. Nat Genet 37: 894-898.