Temporal Dynamics and Linkage Disequilibrium in Natural C. elegans Populations.

International audienceCaenorhabditis elegans is a major laboratory model system yet a newcomer to the field of population genetics, and relatively little is known of its biology in the wild. Recent studies of natural populations at a single timepoint revealed strong spatial population structure and suggested that these populations may be very dynamic. We have therefore studied several natural C. elegans populations over time and genotyped them at polymorphic microsatellite loci. While some populations appear to be genetically stable over the course of observation, others seem to go extinct, with full replacement of multilocus genotypes upon population regrowth. The frequency of heterozygotes indicates that outcrossing occurs at a mean frequency of 1.7% and is variable between populations. However, in genetically stable populations, linkage disequilibrium between different chromosomes can be maintained over several years, at a level much higher than expected from the heterozygote frequency. C. elegans seems to follow metapopulation dynamics, and the maintenance of linkage disequilibrium despite a low yet significant level of outcrossing suggests that selection may act against the progeny of outcrossings

High local genetic diversity and low outcrossing rate in Caenorhabditis elegans natural populations

Background: Caenorhabditis elegans is a major model system in biology, yet very little is known about its biology outside the laboratory. Especially, its unusual mode of reproduction with self-fertile hermaphrodites and facultative males raises the question of its frequency of outcrossing in natural populations. Results: We describe the first analysis of C. elegans individuals sampled directly from natural populations. C. elegans is found predominantly in the dauer stage and with a very low frequency of males compared with hermaphrodites. While C. elegans was previously shown to display a low worldwide genetic diversity, we find by comparison a surprisingly high local genetic diversity of C. elegans populations; this local diversity is contributed in great part by immigration of new alleles rather than by mutation. Our results on heterozygote frequency, male frequency and linkage disequilibrium furthermore show that selfing is the predominant mode of reproduction in C. elegans natural populations, yet that infrequent outcrossing events occur, at a rate of approximately 1%. Conclusions: Our results give a first insight in the biology of C. elegans in the natural populations. They demonstrate that local populations of C. elegans are genetically diverse and that a low frequency of outcrossing allows for the recombination of these locally diverse genotypes

Leadership assessment: A tool for developing future hospitality leaders

The purpose of this paper is to identify and confirm important key leadership behaviors and characteristics of successful hotel and hospitality leaders with the intentions of validating key leadership theories and making suggestions for future hotel and hospitality leaders. Two very relevant theories of leadership are explored- Transactional and Transformational. The traits and behaviors contained within the theories are identified and subsequently mapped against past and present hospitality industry leaders. As a result, the paper identifies the critical few traits and behaviors necessary for future leaders to be successful. Finally, a tool has been developed to be used to identify leadership development opportunities in these future leaders. The tool can be part of an integrated performance management plan

Cis and trans-bis(tetrathiafulvalene-acetylide) platinum(II) complexes: syntheses, crystal structures, and influence of the ancillary ligands on their electronic properties.

International audienceA series of four platinum(II) complexes bearing two tetrathiafulvalene acetylide ligands coordinated either cis or trans to the metal center are reported: cis-Pt(bipy)(C≡CMe(3)TTF)(2), cis-Pt(tBu(2)bipy)(C≡CMe(3)TTF)(2), cis-Pt(dppe)(C≡CMe(3)TTF)(2) and trans-Pt(PPh(3))(2)(C≡CMe(3)TTF)(2). The X-ray diffraction studies of the four complexes are reported and discussed. The electrochemical investigations carried out by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) evidenced different redox behavior as a function of the ancillary ligand. Only for the cis-Pt(dppe)(C≡CMe(3)TTF)(2) complex is the first oxidation wave resolved (ΔE = 70 mV) into two one-electron processes. Spectroelectrochemical investigations performed on the four complexes did not evidence any electronic interactions between the two organic electrophores. The splitting of the first oxidation wave observed in cis-Pt(dppe)(C≡CMe(3)TTF)(2) is mainly explained by the non-equivalence of the two TTF moieties induced by the geometrical constraint imposed by the ancillary dppe ligand as found by density functional theory calculations

Microsporidia Are Natural Intracellular Parasites of the Nematode Caenorhabditis elegans

For decades the soil nematode Caenorhabditis elegans has been an important model system for biology, but little is known about its natural ecology. Recently, C. elegans has become the focus of studies of innate immunity and several pathogens have been shown to cause lethal intestinal infections in C. elegans. However none of these pathogens has been shown to invade nematode intestinal cells, and no pathogen has been isolated from wild-caught C. elegans. Here we describe an intracellular pathogen isolated from wild-caught C. elegans that we show is a new species of microsporidia. Microsporidia comprise a large class of eukaryotic intracellular parasites that are medically and agriculturally important, but poorly understood. We show that microsporidian infection of the C. elegans intestine proceeds through distinct stages and is transmitted horizontally. Disruption of a conserved cytoskeletal structure in the intestine called the terminal web correlates with the release of microsporidian spores from infected cells, and appears to be part of a novel mechanism by which intracellular pathogens exit from infected cells. Unlike in bacterial intestinal infections, the p38 MAPK and insulin/insulin-like growth factor (IGF) signaling pathways do not appear to play substantial roles in resistance to microsporidian infection in C. elegans. We found microsporidia in multiple wild-caught isolates of Caenorhabditis nematodes from diverse geographic locations. These results indicate that microsporidia are common parasites of C. elegans in the wild. In addition, the interaction between C. elegans and its natural microsporidian parasites provides a system in which to dissect intracellular intestinal infection in vivo and insight into the diversity of pathogenic mechanisms used by intracellular microbes

Detecting heterozygosity in shotgun genome assemblies: Lessons from obligately outcrossing nematodes

The majority of nematodes are gonochoristic (dioecious) with distinct male and female sexes, but the best-studied species, Caenorhabditis elegans, is a self-fertile hermaphrodite. The sequencing of the genomes of C. elegans and a second hermaphrodite, C. briggsae, was facilitated in part by the low amount of natural heterozygosity, which typifies selfing species. Ongoing genome projects for gonochoristic Caenorhabditis species seek to approximate this condition by intense inbreeding prior to sequencing. Here we show that despite this inbreeding, the heterozygous fraction of the whole genome shotgun assemblies of three gonochoristic Caenorhabditis species, C. brenneri, C. remanei, and C. japonica, is considerable. We first demonstrate experimentally that independently assembled sequence variants in C. remanei and C. brenneri are allelic. We then present gene-based approaches for recognizing heterozygous regions of WGS assemblies. We also develop a simple method for quantifying heterozygosity that can be applied to assemblies lacking gene annotations. Consistently we find that ∼10% and 30% of the C. remanei and C. brenneri genomes, respectively, are represented by two alleles in the assemblies. Heterozygosity is restricted to autosomes and its retention is accompanied by substantial inbreeding depression, suggesting that it is caused by multiple recessive deleterious alleles and not merely by chance. Both the overall amount and chromosomal distribution of heterozygous DNA is highly variable between assemblies of close relatives produced by identical methodologies, and allele frequencies have continued to change after strains were sequenced. Our results highlight the impact of mating systems on genome sequencing projects

Distinct Functional Constraints Partition Sequence Conservation in a cis-Regulatory Element

Different functional constraints contribute to different evolutionary rates across genomes. To understand why some sequences evolve faster than others in a single cis-regulatory locus, we investigated function and evolutionary dynamics of the promoter of the Caenorhabditis elegans unc-47 gene. We found that this promoter consists of two distinct domains. The proximal promoter is conserved and is largely sufficient to direct appropriate spatial expression. The distal promoter displays little if any conservation between several closely related nematodes. Despite this divergence, sequences from all species confer robustness of expression, arguing that this function does not require substantial sequence conservation. We showed that even unrelated sequences have the ability to promote robust expression. A prominent feature shared by all of these robustness-promoting sequences is an AT-enriched nucleotide composition consistent with nucleosome depletion. Because general sequence composition can be maintained despite sequence turnover, our results explain how different functional constraints can lead to vastly disparate rates of sequence divergence within a promoter

Neuronal specification in C. elegans: combining lineage inheritance with intercellular signaling

International audienceThe nervous system is composed of a high diversity of neuronal types. How this diversity is generated during development is a key question in neurobiology. Addressing this question is one of the reasons that led Sydney Brenner to develop the nematode C. elegans as a model organism. While there was initially a debate on whether the neuronal specification follows a ‘European’ model (determined by ancestry) or an ‘American’ model (determined by intercellular communication), several decades of research have established that the truth lies somewhere in between. Neurons are specified by the combination of transcription factors inherited from the ancestor cells and signaling between neighboring cells (especially Wnt and Notch signaling). This converges to the activation in newly generated postmitotic neurons of a specific set of terminal selector transcription factors that initiate and maintain the differentiation of the neuron. In this review, we also discuss the evolution of these specification mechanisms in other nematodes and beyond

Labelling of Active Transcription Sites with Argonaute NRDE-3 — Image Active Transcription Sites in vivo in Caenorhabditis elegans

International audienceLive labelling of active transcription sites is critical to our understanding of transcriptional dynamics. In the most widely used method, RNA sequence MS2 repeats are added to the transcript of interest, on which fluorescently tagged Major Coat Protein binds, and labels transcription sites and transcripts. Here we describe another strategy, using the Argonaute protein NRDE-3, repurposed as an RNA-programmable RNA binding protein. We label active transcription sites in C. elegans embryos and larvae, without editing the gene of interest. NRDE-3 is programmed by feeding nematodes with double-stranded RNA matching the target gene. This method does not require genome editing and is inexpensive and fast to apply to many different genes