The Bw cells, a novel B cell population conserved in the whole genus Mus

In common laboratory mouse strains, which are derived from the crossing between three subspecies, peritoneal B cells are enriched in B-1a cells characterized by the CD5(+)Mac-1(+)B220(low)IgM(high)IgD(low)CD43(+)CD9(+) phenotype. Intriguingly in other vertebrates, CD5(+)Mac-1(+) cells have never been found in a specific anatomic site. To ascertain the peculiarity of the CD5(+) peritoneal B cells in laboratory mice, we analyzed the peritoneal B cell subsets in 9 inbred and 39 outbred wild-derived mouse strains belonging to 13 different species/subspecies. We found that most of these strains do not have the CD5(+) B-1a cell population. However, all of these strains including classical laboratory mouse strains, have variable proportions of a novel B cell population: Bw, which is characterized by a unique phenotype (CD5(-)Mac-1(+)B220(high)IgM(high)IgD(high)CD43(-)CD9(-)) and is not restricted to the peritoneal cavity. Bw cells are also distinct from both B-1 and B-2 cells from a functional point of view both by proliferative responses, cytokine secretion and Ab synthesis. Moreover, transfer experiments show that bone marrow and fetal liver cells from wild mice can give rise to Bw cells in alymphoid mice. The conservation of this B cell population, but not of the CD5(+) B-1a, during evolution of the genus Mus, its readiness to respond to TLR ligands and to produce high concentration of autoantibodies suggest that Bw cells play a key role in innate immunity.     

Comparing clines on molecular and phenotypic traits in hybrid zones: a window on tension zone models

The study of zones of secondary contact provides insight into the maintenance of reproductive isolation. Tension zone theory supplies powerful tools for assessing how dispersal and selection shape hybrid zones. We present a multimodal analysis of phenotypic clines in conjunction with clines at molecular markers in a hybrid zone between Larus glaucescens and Larus occidentalis. We developed a new method to analyze simultaneously clines of quantitative traits and molecular data. Low linkage disequilibrium and the lack of coincidence between clines at six microsatellites, a mitochondrial DNA region, and two phenotypic traits indicated introgression. However, the hypothesis of neutral diffusion was rejected based on evidence that all of the clines were concordant and narrower than expected for neutral clines, indicating some indirect selection. The analysis of phenotypic variance gave evidence of restricted phenotypic introgression and together with the bimodal distribution of phenotypes suggested that disruptive selection is acting across the hybrid zone, especially on the coloration of bare parts. Multimodal analysis of phenotypic clines also highlighted a shift between the peak of intermediates and the cline center, left behind by hybrid zone motion. High-resolution analysis of phenotypes distribution thus proved useful for detecting hybrid zone movement even without temporal data.     

Identification of a new family of genes involved in beta-1,2-mannosylation of glycans in Pichia pastoris and Candida albicans

Structural studies of cell wall components of the pathogenic yeast Candida albicans have demonstrated the presence of beta-1,2-linked oligomannosides in phosphopeptidomannan and phospholipomannan. During C. albicans infection, beta-1,2-oligomannosides play an important role in host/pathogen interactions by acting as adhesins and by interfering with the host immune response. Despite the importance of beta-1,2-oligomannosides, the genes responsible for their synthesis have not been identified. The main reason is that the reference species Saccharomyces cerevisiae does not synthesize beta-linked mannoses. On the other hand, the presence of beta-1,2-oligomannosides has been reported in the cell wall of the more genetically tractable C. albicans relative, P. pastoris. Here we present the identification, cloning, and characterization of a novel family of fungal genes involved in beta-mannose transfer. Employing in silico analysis, we identified a family of four related new genes in P. pastoris and subsequently nine homologs in C. albicans. Biochemical, immunological, and structural analyses following deletion of four genes in P. pastoris and deletion of four genes acting specifically on C. albicans mannan demonstrated the involvement of these new genes in beta-1,2-oligomannoside synthesis. Phenotypic characterization of the strains deleted in beta-mannosyltransferase genes (BMTs) allowed us to describe the stepwise activity of Bmtps and acceptor specificity. For C. albicans, despite structural similarities between mannan and phospholipomannan, phospholipomannan beta-mannosylation was not affected by any of the CaBMT1-4 deletions. Surprisingly, depletion in mannan major beta-1,2-oligomannoside epitopes had little impact on cell wall surface beta-1,2-oligomannoside antigenic expression.     

The Ig light chain restricted B6.kappa(-)lambda(SEG) mouse strain suggests that the IGL locus genomic organization is subject to constant evolution

In laboratory mice, the different Ig lambda light chain subtypes (lambda 1, lambda 2, lambda x and lambda 3) are expressed on 60, 16, 16 and 8%, respectively, of the lambda-positive peripheral B cells. Eighteen years ago, our laboratory characterized a lambda 1(-) wild mouse strain: SPE ( Mus spretus). In this report, we describe the characterization of another wild-derived Mus spretus inbred strain, SEG, that presents the same characteristic, namely the absence of lambda 1 expression. An almost congenic strain, B6.lambda(SEG), was detected in a series of recombinant congenic strains carrying 2% of SEG/Pas genome in a C57BL/6J background. This B6.lambda(SEG) strain was crossed to Igh (a) C kappa (-) mice in order to derive two different additional congenic strains: B6.kappa(-)lambda(SEG) Igh (a) and B6.kappa(-)lambda(SEG) Igh (b). In this paper, we characterize the genomic organization and the expression of the SEG IGL locus. Altogether, our data show that the SEG IGL locus is constituted by a single functional IGLJ2SEG-IGLC2SEG, two pseudo IGLJ4SEG1/2-IGLC4SEG1/2 gene clusters and two V gene segments: IGLV2SEG and IGLVXSEG. In particular, we show the absence of IGLV1 and IGLVSD26 gene segments. IGLVSD26 was reported to be present in some Mus m. musculus mice and absent in BALB/c. Here, we confirm its presence not only in other Mus m. musculus mice but also in Mus spretus mice. Consequently, we propose that IGLVSD26-related gene segments define a new family that we name V lambda 4. The study of the organization of different IGL loci, in addition to the V lambda 4(+) reported here, could elucidate questions concerning the evolution of the lambda locus.     

Members 5 and 6 of the Candida albicans BMT family encode enzymes acting specifically on β-mannosylation of the phospholipomannan cell-wall glycosphingolipid

A family of nine genes encoding proteins involved in the synthesis of β-1,2 mannose adhesins of Candida albicans has been identified. Four of these genes, BMT1-4, encode enzymes acting stepwise to add β-mannoses on to cell-wall phosphopeptidomannan (PPM). None of these acts on phospholipomannan (PLM), a glycosphingolipid member of the mannose-inositol-phosphoceramide family, which contributes with PPM to β-mannose surface expression. We show that deletion of BMT5 and BMT6 led to a dramatic reduction of PLM glycosylation and accumulation of PLM with a truncated β-oligomannoside chain, respectively. Disruptions had no effect on sphingolipid biosynthesis and on PPM β-mannosylation. β-Mannose surface expression was not affected, confirming that β-mannosylation is a process based on specificity of acceptor molecules, but liable to global regulation.     

Climate-driven diversification in two widespread Galerida larks

Background

The major impact of Plio-Pleistocene climatic oscillations on the current genetic structure of many species is widely recognised but their importance in driving speciation remains a matter of controversies. In addition, since most studies focused on Europe and North America, the influence of many other biogeographic barriers such as the Sahara remains poorly understood. In this paper, climate-driven diversification was investigated by using a comparative phylogeographic approach in combination with phenotypic data in two avian species groups distributed on both sides of the deserts belt of Africa and Asia. In particular, we tested whether: 1) vicariance diversification events are concomitant with past climatic events; and 2) current ecological factors (using climate and competition as proxies) contribute to phenotypic divergence between allopatric populations.

Results

Mitochondrial and nuclear sequence data indicated that the crested and Thekla lark species groups diverged in the early Pliocene and that subsequent speciation events were congruent with major late Pliocene and Pleistocene climatic events. In particular, steep increase in aridity in Africa near 2.8 and 1.7 million years ago were coincident with two north-south vicariance speciation events mediated by the Sahara. Subsequent glacial cycles of the last million years seem to have shaped patterns of genetic variation within the two widespread species (G. cristata and G. theklae). The Sahara appears to have allowed dispersal from the tropical areas during climatic optima but to have isolated populations north and south of it during more arid phases. Phenotypic variation did not correlate with the history of populations, but was strongly influenced by current ecological conditions. In particular, our results suggested that (i) desert-adapted plumage evolved at least three times and (ii) variation in body size was mainly driven by interspecific competition, but the response to competition was stronger in more arid areas.

Conclusion

Climatic fluctuations of the Plio-Pleistocene strongly impacted diversification patterns in the Galerida larks. Firstly, we found that cladogenesis coincides with major climatic changes, and the Sahara appears to have played a key role in driving speciation events. Secondly, we found that morphology and plumage were strongly determined by ecological factors (interspecific competition, climate) following vicariance.     

Complexity,polymorphism, and recombination of mouse T-cell receptor α gene families

Genomic DNA from a large panel of inbred strains of mice were hybridized sequentially with 15 V_α, 2 V_δ, 1 C_α, and 1 C_δ probes. Most of the V_α probes detected a high degree of plymorphism and have allowed the definition of five mouse T-cell receptor α (Tcr _α) haplotypes. One of these haplotypes (Tcr _α ^e ) appears to arise from a recombination between theTcr _α ^b andTcr _α ^a haplotypes, the latter being the most frequently found in the conventional inbred strains. This recombination event clearly indicates that the members of at least 11 V_α subfamilies are not closely linked but highly interspersed with one another on chromosome 14.