Anne Roig

Cholinesterases from the common oyster (Crassostrea gigas): Evidence for the presence of a soluble acetylcholinesterase insensitive to organophosphate and carbamate inhibitors

Marine bivalves such as oysters and mussels are widely used as bioindicators of contamination in the monitoring of pollutant effects. As filter feeders, these species are known to be good general indicators of chemical contamination. However, the efficient use of decreased acetylcholinesterase activity in the oyster as a biomarker of exposure to neurotoxic compounds requires a definition of the different types of cholinesterases coexisting in this mollusk. This study reports the partial purification, separation and characterization of two cholinesterases extracted from the oyster Crassostrea gigas. Differences in apparent molecular weight, type of glycosylation and hydrophobicity, and sensitivity to inhibitors suggest that they are encoded by two different genes. ‘A’ cholinesterase (apparent molecular weight 200 kDa) is anchored to the membrane via a glycolipid, is not glycosylated but sensitive to organophosphate and carbamate inhibitors. ‘B’ cholinesterase (molecular weight 330 kDa) is hydrophilic, glycosylated and highly resistant to organophosphate and carbamate inhibitors. The kinetic properties of these two cholinesterases were compared with those of other invertebrate cholinesterases. The presence of a cholinesterase insensitive to insecticides suggests that a significant improvement in the use of oyster cholinesterases as biomarkers of pollutant effects could be achieved by simple separation of the two forms.

High-resolution comparative mapping among man, cattle and mouse suggests a role for repeat sequences in mammalian genome evolution

BackgroundComparative mapping provides new insights into the evolutionary history of genomes. In particular, recent studies in mammals have suggested a role for segmental duplication in genome evolution. In some species such as Drosophila or maize, transposable elements (TEs) have been shown to be involved in chromosomal rearrangements. In this work, we have explored the presence of interspersed repeats in regions of chromosomal rearrangements, using an updated high-resolution integrated comparative map among cattle, man and mouse.ResultsThe bovine, human and mouse comparative autosomal map has been constructed using data from bovine genetic and physical maps and from FISH-mapping studies. We confirm most previous results but also reveal some discrepancies. A total of 211 conserved segments have been identified between cattle and man, of which 33 are new segments and 72 correspond to extended, previously known segments. The resulting map covers 91% and 90% of the human and bovine genomes, respectively. Analysis of breakpoint regions revealed a high density of species-specific interspersed repeats in the human and mouse genomes.ConclusionAnalysis of the breakpoint regions has revealed specific repeat density patterns, suggesting that TEs may have played a significant role in chromosome evolution and genome plasticity. However, we cannot rule out that repeats and breakpoints accumulate independently in the few same regions where modifications are better tolerated. Likewise, we cannot ascertain whether increased TE density is the cause or the consequence of chromosome rearrangements. Nevertheless, the identification of high density repeat clusters combined with a well-documented repeat phylogeny should highlight probable breakpoints, and permit their precise dating. Combining new statistical models taking the present information into account should help reconstruct ancestral karyotypes.

A first generation bovine BAC-based physical map

A first generation clone-based physical map for the bovine genome was constructed combining, fluorescent double digestion fingerprinting and sequence tagged site (STS) marker screening. The BAC clones were selected from an Inra BAC library (105 984 clones) and a part of the CHORI-240 BAC library (26 500 clones). The contigs were anchored using the screening information for a total of 1303 markers (451 microsatellites, 471 genes, 127 EST, and 254 BAC ends). The final map, which consists of 6615 contigs assembled from 100 923 clones, will be a valuable tool for genomic research in ruminants, including targeted marker production, positional cloning or targeted sequencing of regions of specific interest.

Analysis of molecular forms and pharmacological properties of acetylcholinesterase in several mosquito species.

Two acetylcholinesterases (AChE1 and AChE2) have recently been characterized in the common mosquito Culex pipiens. This situation appeared to be an exception among insects, where only one acetylcholinesterase gene had previously been repeatedly reported. In the present study, acetylcholinesterase was studied in five mosquito species: Aedes aegypti, Anopheles gambiae, Anopheles stephensi, Culiseta longeareolata and Culex hortensis, in order to test whether or not two different acetylcholinesterase enzymes could be detected as occurs in C. pipiens. Molecular forms and catalytic properties of the enzyme show that only one enzyme species was detected in the five species. This suggests that a duplication of a single locus Ace probably occurred recently in the phylogeny tree leading to C. pipiens, and produced two distinct acetylcholinesterases: AchE1 and AChE2.

Transcriptome versus Genomic Microsatellite Markers: Highly Informative Multiplexes for Genotyping Abies alba Mill. and Congeneric Species

The availability of high-resolution, cost-effective polymorphic genetic markers displaying Mendelian inheritance is a prerequisite for fine-scale population genetic analyses as well as informed conservation and sustainable management. Silver fir (Abies alba Mill.) is a widespread European species of economic and ecological importance for which genetic markers are needed but difficult to develop, as in most conifer species. In this work, we introduce two sets of new multiplexed transcriptome-derived expressed sequence tag microsatellites (EST-simple sequence repeats (SSRs)) which we compare to a set of multiplexed genomic microsatellites (gSSRs). For both marker types, transferability was tested in 17 congeneric taxa. A total of 16 new EST-SSRs and two new gSSRs were developed. The EST-SSR multiplexes produced easily scorable amplification patterns that allow rapid and cost-effective genotyping at low-error rates, and include loci that display very low null allele frequencies. Generally, EST-SSRs displayed lower polymorphism and frequency of null alleles, but higher genetic differentiation among populations than gSSRs. Preliminary tests revealed that the EST-SSR markers are highly transferable and polymorphic across Abies species. This study also confirmed that SSRs can be successfully developed using next-generation sequencing technology also in large genome species such as conifers.

Surviving in mountain climate refugia: new insights from the genetic diversity and structure of the relict shrub Myrtus nivellei (Myrtaceae) in the Sahara Desert.

The identification of past glacial refugia has become a key topic for conservation under environmental change, since they contribute importantly to shaping current patterns of biodiversity. However, little attention has been paid so far to interglacial refugia despite their key role for the survival of relict species currently occurring in climate refugia. Here, we focus on the genetic consequences of range contraction on the relict populations of the evergreen shrub Myrtus nivellei, endemic in the Saharan mountains since at least the end of the last Green Sahara period, around 5.5 ka B.P. Multilocus genotypes (nuclear microsatellites and AFLP) were obtained from 215 individuals collected from 23 wadis (temporary rivers) in the three main mountain ranges in southern Algeria (the Hoggar, Tassili n’Ajjer and Tassili n’Immidir ranges). Identical genotypes were found in several plants growing far apart within the same wadis, a pattern taken as evidence of clonality. Multivariate analyses and Bayesian clustering revealed that genetic diversity was mainly structured among the mountain ranges, while low isolation by distance was observed within each mountain range. The range contraction induced by the last episode of aridification has likely increased the genetic isolation of the populations of M. nivellei, without greatly affecting the genetic diversity of the species as a whole. The pattern of genetic diversity observed here suggests that high connectivity may have prevailed during humid periods, which is consistent with recent paleoenvironmental reconstructions.

Quantitative trait loci linked to PRNP gene controlling health and production traits in INRA 401 sheep

In this study, the potential association of PrP genotypes with health and productive traits was investigated. Data were recorded on animals of the INRA 401 breed from the Bourges-La Sapinière INRA experimental farm. The population consisted of 30 rams and 852 ewes, which produced 1310 lambs. The animals were categorized into three PrP genotype classes: ARR homozygous, ARR heterozygous, and animals without any ARR allele. Two analyses differing in the approach considered were carried out. Firstly, the potential association of the PrP genotype with disease (Salmonella resistance) and production (wool and carcass) traits was studied. The data used included 1042, 1043 and 1013 genotyped animals for the Salmonella resistance, wool and carcass traits, respectively. The different traits were analyzed using an animal model, where the PrP genotype effect was included as a fixed effect. Association analyses do not indicate any evidence of an effect of PrP genotypes on traits studied in this breed. Secondly, a quantitative trait loci (QTL) detection approach using the PRNP gene as a marker was applied on ovine chromosome 13. Interval mapping was used. Evidence for one QTL affecting mean fiber diameter was found at 25 cM from the PRNP gene. However, a linkage between PRNP and this QTL does not imply unfavorable linkage disequilibrium for PRNP selection purposes.

Genetic structure and diversity of the endangered fir tree of Lebanon (Abies cilicica Carr.): implications for conservation

The threatened conifer Abies cilicica currently persists in Lebanon in geographically isolated forest patches. The impact of demographic and evolutionary processes on population genetic diversity and structure were assessed using 10 nuclear microsatellite loci. All remnant 15 local populations revealed a low genetic variation but a high recent effective population size. FST-based measures of population genetic differentiation revealed a low spatial genetic structure, but Bayesian analysis of population structure identified a significant Northeast-Southwest population structure. Populations showed significant but weak isolation-by-distance, indicating non-equilibrium conditions between dispersal and genetic drift. Bayesian assignment tests detected an asymmetric Northeast-Southwest migration involving some long-distance dispersal events. We suggest that the persistence and Northeast-Southwest geographic structure of Abies cilicica in Lebanon is the result of at least two demographic processes during its recent evolutionary history: (1) recent migration to currently marginal populations and (2) local persistence through altitudinal shifts along a mountainous topography. These results might help us better understand the mechanisms involved in the species response to expected climate change.

New insights into the polyploid complex Cenchrus ciliaris L. (Poaceae) show its capacity for gene flow and recombination processes despite its apomictic nature

Cenchrus ciliaris L. is a C4 perennial grass of arid lands which is under the focus of different ecological issues such as response to desertification, quality of forage grass and impacts of invasions. Here, molecular and morphological analyses of the genetic diversity of several Tunisian provenances of C. ciliaris were performed to better understand the phenotypic polymorphism of this agamospermous and polyploid grass. Ten phenotypic traits associated with productivity were measured in a common garden environment. Amplified Fragment Length Polymorphism (AFLP) markers were developed to investigate the structure of genetic diversity among and within provenances and between the three ploidy levels. Heritable phenotypic traits showed considerable differences within provenances. Surprisingly, AFLP markers revealed the existence of genotypic variations between individuals of the same sibship and a high G/N value (0.55). A neighbour-joining tree based on AFLP markers revealed three major groups; tetraploid, pentaploid and a mix of pentaploid and hexaploids. These groups do not correspond completely to the geographical origin of samples. The results underline the possibility of sexual reproduction, recombination and gene flow within and between populations of C. ciliaris. In respect with the well known dynamic nature of polyploid genomes, these results should have strong consequences for the future management of this grass for both conservation and invasion issues.

Reconstruction of a windborne insect invasion using a particle dispersal model, historical wind data, and Bayesian analysis of genetic data

Understanding how invasive species establish and spread is vital for developing effective management strategies for invaded areas and identifying new areas where the risk of invasion is highest. We investigated the explanatory power of dispersal histories reconstructed based on local-scale wind data and a regional-scale wind-dispersed particle trajectory model for the invasive seed chalcid wasp Megastigmus schimitscheki (Hymenoptera: Torymidae) in France. The explanatory power was tested by: (1) survival analysis of empirical data on M. schimitscheki presence, absence and year of arrival at 52 stands of the wasps obligate hosts, Cedrus (true cedar trees); and (2) Approximate Bayesian analysis of M. schimitscheki genetic data using a coalescence model. The Bayesian demographic modeling and traditional population genetic analysis suggested that initial invasion across the range was the result of long-distance dispersal from the longest established sites. The survival analyses of the windborne expansion patterns derived from a particle dispersal model indicated that there was an informative correlation between the M. schimitscheki presence/absence data from the annual surveys and the scenarios based on regional-scale wind data. These three very different analyses produced highly congruent results supporting our proposal that wind is the most probable vector for passive long-distance dispersal of this invasive seed wasp. This result confirms that long-distance dispersal from introduction areas is a likely driver of secondary expansion of alien invasive species. Based on our results, management programs for this and other windborne invasive species may consider (1) focusing effort at the longest established sites and (2) monitoring outlying populations remains critically important due to their influence on rates of spread. We also suggest that there is a distinct need for new analysis methods that have the capacity to combine empirical spatiotemporal field data, genetic data, and environmental data to investigate dispersal and invasion.