Ebert RHA et al. (1993) Genetics "Longevity-determining genes in Caenorhabditis elegans: chromosomal mapping of multiple noninteractive loci."

Perrin TE, Shmookler Reis RJ, Dennis RA, Cherkasova VA, Ruggles S, Wu JH, Ebert RHA

[Genetics, 1993]

We have used chromosome mapping with polymorphic markers to define genetic components governing life span in the nematode Caenorhabditis elegans. A complex recombinant-inbred population was derived from an interstrain cross, yielding gt 1000 genotypes, each a composite of homozygous segments from the two parental strains. Genotypes were analyzed for the last-surviving 1-5% of worms in aging cohorts, and for young controls, by multiplex polymerase chain reaction using polymorphic markers to distinguish the parental alleles. We identified five regions of the genome at which one parental allele was significantly enriched in long-lived subpopulations. At four of five loci, the same alleles were selected in aging cohorts maintained under two different conditions, implying that these genes determine life span in differing environments.

Ebert RHA et al. (1996) Dev Genet "Defining genes that govern longevity in Caenorhabditis elegans."

Sohal BH, Egilmez NK, Ebert RHA, Shmookler Reis RJ, Shammas MA, Ruggles S, Sohal RS

[Dev Genet, 1996]

We previously identified five regions on the chromosomal map of Caenorhabditis elegans, containing genes that help specify life span in this species, by comparing the genotypes of young and long-lived progeny from a cross between strains Bristol-N2 and Bergerac-BO [Ebert et al. (1993): Genetics 135:1003-1010]. Analyses of additional crosses, and of putative polymorphisms for the implicated genes, are necessary to clarify the roles of naturally occurring polymorphic alleles in determining longevity. We therefore carried out a second multigenerational cross, between strains Bristol-N2 and DH424 (both nonmutators at 20 degrees C), to create a different heterogeneous recombinant-inbred population. We again found strong evidence implicating multiple genes, which differ between the parental strains, in the determination of life span. Increased variance of survival, for F2 and homozygous F25 worms relative to F1 hybrids, is consistent with such alleles assorting randomly in the cross progeny. Moreover, chromosome mapping data corroborate the polygenic nature of this quantitative trait. Genotypes of young and very long-lived adult worms from a synchronous F15 population were determined by polymerase chain reaction, to identify the parental strain of origin for each of 10 polymorphic loci. Two regions, on chromosomes II and IV, each contain at least one gene with allelic differences in associated longevity. A recombinant-inbred Bergerac-BO x Bristol-N2 population, derived from the earlier cross between those strains, was exposed to an acute toxic level of hydrogen peroxide. Genotyping of H2O2-resistant worms implicated at least one of the five chromosomal regions previously identified in the same cross progeny as harboring a longevity-determining gene. Superoxide dismutase and catalase levels, determined for the three parental strains as they aged, confirm the existence of polymorphisms in the corresponding genes (or their regulatory mechanisms) inferred from the chromosome-II mapping data, and are consistent with the hypothesis that increased longevity is conferred by high levels of these enzymes late in life.

Walstrom KM et al. (2005) Mech Dev "RNA helicase A is important for germline transcriptional control, proliferation, and meiosis in C. elegans."

Bean CJ, Walstrom KM, Kelly WG, Schmidt D

[Mech Dev, 2005]

RNA helicase A (RHA) is a multifunctional protein with established roles in chromatin regulation. The protein is conserved in worms, Drosophila, and mammals, but its role in worms has not been previously studied. We found that a deletion mutant lacking rha-1 has a temperature-sensitive defect in germline transcriptional silencing, consistent with RHA-1 having a function in transcription regulation. Transcriptional desilencing in these rha-1(tm329) mutants was associated with a loss of lysine 9 methylation on histone H3 that is normally associated with silenced chromatin. Other histone modifications are also mis-localized in the germ cells in the mutants. These defects in histone modifications suggest that there is a general transcription regulation defect in the mutant worms that results in a temperature-sensitive sterile phenotype. At the restrictive temperature, the extent of germ cell mitoses is reduced, and the mutants are sterile due to defects in meiosis and gametogenesis. Our results suggest that RHA-1 is a conserved transcription regulation protein that controls germline proliferation and development in C. elegans.

Egilmez NK et al. (1995) J Mol Evol "Strain evolution in Caenorhabditis elegans: transposable elements as markers of interstrain evolutionary history."

Ebert RHA, Shmookler Reis RJ, Egilmez NK

[J Mol Evol, 1995]

Evolutionary relationships across taxa can be deduced from sequence divergence of proteins, RNA, or DNA; sequences which diverge rapidly, such as those of mitochondrial genes, have been especially useful for comparisons of closely related species, and-within limits-of strains within a species. We have utilized the transposable element Tc1 as a polymorphic marker to evaluate the evolutionary relationships among nine Caenorhabditis elegans strains. For five low-Tc1-copy strains, we compared patterns of restriction fragments hybridizing to a cloned Tc1 probe. Twenty of the 40 Tc1 insertion sites thus characterized were common to all five strains, and so presumably preceded strain divergence; the 20 differential bands were used to construct a maximum-parsimony tree relating these strains. In four high-copy-number stocks (three wild-type strains and a subline), we determined occupancy of 35 individual Tc1 insertion sites by a polymerase chain reaction assay. Surprisingly, the high-copy strains share a common subset of these Tc1 insertions, and the chromosomal distribution of conserved Tc1 sites is ''clustered'' with respect to the other elements tested. These data imply a close evolutionary relationship among the high-copy strains, such that two of these strains appear to have been derived from the highest-copy-number lineage (represented by two stocks) through crossing with a low-Tc1 strain. Abundances of Tc1 elements were also estimated for the four high-copy-number stocks, at similar to 200-500 copies per haploid genome, by quantitative dot-blot hybridization relative to two low-copy strains. annealing with P-32-labeled probes corresponding to full-length Tc1, an oligonucleotide within the Tc1 terminal inverted repeats, and an internal Tc1 oligonucleotide, gave essentially identical results-indicating that Tc1 termini exist in the genome primarily as components of full-length Tc1 elements. A composite evolutionary tree is proposed, based on the locations and numbers of Tc1 elements in these strains, which is consistent with a four-branch intraspecific tree deduced previously by maximum-parsimony analyses of mitochondrial sequence changes; it also serves to elucidate the evolutionary history of transposon mobility.

van Swinderen B et al. (1997) Proc Natl Acad Sci U S A "Quantitative trait loci controlling halothane sensitivity in Caenorhabditis elegans."

Ebert RHA, Johnson TE, Cherkasova VA, van Swinderen B, Shmookler Reis RJ, Shook DR, Crowder CM

[Proc Natl Acad Sci U S A, 1997]

Genetic analysis is an essential tool for defining the molecular mechanisms whereby volatile anesthetics (VA) disrupt nervous system function. However, the degree of natural variation of the genetic determinants of VA sensitivity has not been determined nor have mutagenesis approaches been very successful at isolating significantly resistant mutant strains. Thus, a quantitative genetic approach was taken toward these goals. Recombinant-inbred strains derived from two evolutionarily distinct lineages of the nematode Caenorhabditis elegans were tested for sensitivity to clinically relevant concentrations (0.3-0.5 mM) of the VA halothane. The halothane sensitivities of coordinated movement and male mating behavior were highly variant among the recombinant-inbred strains with a range of EC50 values of 13- and 4-fold, respectively. Both traits were highly heritable (H2 = 0.82, 0.87, respectively). Several strains were found to be significantly resistant to halothane when compared with the wild-type strain N2. A major locus or loci mapping to the middle of chromosome V accounted for more than 40% of the phenotypic variance for both traits. Five weaker loci, four of which interact, explained most of the remaining variance. None of the halothane-sensitivity quantitative trait loci significantly affected behavior in the absence of halothane or halothane's potency for C. elegans immobilization, which requires 5-fold higher drug concentrations. Thus, the quantitative trait loci are unlikely to result from differences in halothane-independent (native) behavior or differences in halothane metabolism or permeability. Rather, these loci may code for targets and/or downstream effectors of halothane in the C. elegans nervous system or for modifiers of such gene products.