A Narrow Quantitative Trait Locus in C. elegans Coordinately Affects Longevity, Thermotolerance, and Resistance to Paraquat

Anthony Vertino,John J Thaden,Robert J Shmookler Reis,Srinivas Ayyadevara

doi:10.3389/fgene.2011.00063

Abstract

By linkage mapping of quantitative trait loci, we previously identified at least 11 natural genetic variants that significantly modulate Caenorhabditis elegans life-span (LS), many of which would have eluded discovery by knock-down or mutation screens. A region on chromosome IV between markers stP13 and stP35 had striking effects on longevity in three inter-strain crosses (each P < 10−9). In order to define the limits of that interval, we have now constructed two independent lines by marker-based selection during 20 backcross generations, isolating the stP13–stP35 interval from strain Bergerac-BO in a CL2a background. These congenic lines differed significantly from CL2a in LS, assayed in two environments (each P < 0.001). We then screened for exchange of flanking markers to isolate recombinants that partition this region, because fine-mapping the boundaries for overlapping heteroallelic spans can greatly narrow the implicated interval. Recombinants carrying the CL2a allele at stP35 were consistently long-lived compared to those retaining the Bergerac-BO allele (P < 0.001), and more resistant to temperature elevation and paraquat (each ∼1.7-fold, P < 0.0001), but gained little protection from ultraviolet or peroxide stresses. Two rounds of recombinant screening, followed by fine-mapping of break-points and survival testing, narrowed the interval to 0.18 Mb (13.35–13.53 Mb) containing 26 putative genes and six small-nuclear RNAs – a manageable number of targets for functional assessment.

Highlights

Longevity is largely under genetic control in all animal species studied, with genetic factors contributing roughly half of lifespan (LS) variance in Caenorhabditis elegans (Johnson and Wood, 1982; Ebert et al, 1993, 1996; Ayyadevara et al, 2001, 2003)
Specific genes controlling LS were first discovered through screens for long-lived mutants of C. elegans (Klass, 1983; Yang and Wilson, 1999) or from study of mutants originally noted for other phenotypes in this nematode (Apfeld and Kenyon, 1999; McElwee et al, 2004; Morley and Morimoto, 2004; Hansen et al, 2005; Ayyadevara et al, 2008)
SURVIVAL ANALYSIS OF BACKCROSSED LINES Since quantitative trait locus (QTL)-mapping in several C. elegans inter-strain crosses had indicated the existence of a natural polymorphism, termed lsq4, near the center of chromosome IV with strong effects on longevity and stress-resistance (Ebert et al, 1996, 1993; Ayyadevara et al, 2003, 2001; Shmookler Reis et al, 2007), we attempted to define that region by isolating genetic recombinants from a cross between strains C. elegans var. Cl2a (CL2a) (DR1345) and Bergerac-C. elegans var. Bergerac-BO (BO) (RW7000), after 20 generations of marker-directed backcrossing into CL2a to remove most of the Bergerac-BO-derived DNA not tightly linked to lsq4

Summary

INTRODUCTION

Longevity is largely under genetic control in all animal species studied, with genetic factors contributing roughly half of lifespan (LS) variance in Caenorhabditis elegans (Johnson and Wood, 1982; Ebert et al, 1993, 1996; Ayyadevara et al, 2001, 2003). Pleiotropy between stress-survival traits and longevity has been found repeatedly, evidenced both by coincident mapping of QTLs (Shmookler Reis et al, 2007) and by the observation of extended LS in mutants or drugs initially screened for a specific stress-resistance (Sampayo et al, 2000; Benedetti et al, 2008), or vice versa (Ayyadevara et al, 2008; Onken and Driscoll, 2010; Shmookler Reis et al, 2011) Such pleiotropy is predominantly concordant, it can be antagonistic (Magwire et al, 2010); that is, the longer-lived allele is usually but not always the more stress-resistant allele. A second round of recombinant screening further narrowed this span to less than 0.2 Mb, providing a manageable set of positional candidate genes to examine for expression and coding-sequence differences, and to test for functional consequences of altered expression – results that will be presented elsewhere (Ayyadevara et al, submitted)

RESULTS

DISCUSSION

MATERIALS AND METHODS