A new role for PGRP-S (Tag7) in immune defense: lymphocyte migration is induced by a chemoattractant complex of Tag7 with Mts1

PGRP-S (Tag7) is an innate immunity protein involved in the antimicrobial defense systems, both in insects and in mammals. We have previously shown that Tag7 specifically interacts with several proteins, including Hsp70 and the calcium binding protein S100A4 (Mts1), providing a number of novel cellular functions. Here we show that Tag7–Mts1 complex causes chemotactic migration of lymphocytes, with NK cells being a preferred target. Cells of either innate immunity (neutrophils and monocytes) or acquired immunity (CD4⁺ and CD8⁺ lymphocytes) can produce this complex, which confirms the close connection between components of the 2 branches of immune response.     

Epigenetic Changes and Repositioning Determine the Evolutionary Fate of Duplicated Genes

Consideration of epigenetic silencing, perhaps by DNA methylation, led to an epigenetic complementation (EC) model for evolution by gene duplication (Rodin and Riggs (2003) J. Mol. Evol., 56, 718-729). This and subsequent work on genome-wide analyses of gene duplicates in several eukaryotic species pointed to a fundamental link between localization in the genome, epigenetic regulation of expression, and the evolutionary fate of new redundant gene copies, which can be either non- or neo-functionalization. Our main message in this report is that repositioning of a new duplicate to an ectopic site epigenetically alters its expression pattern, and concomitantly the rate and direction of mutations. Furthermore, comparison of syntenic vs. non-syntenic pairs of gene duplicates of different age unambiguously indicates that repositioning saves redundant gene duplicates from pseudogenization and hastens their evolution towards a new development-time and tissue-specific pattern of function.     

Filtering for Compound Heterozygous Sequence Variants in Non-Consanguineous Pedigrees

The identification of disease-causing mutations in next-generation sequencing (NGS) data requires efficient filtering techniques. In patients with rare recessive diseases, compound heterozygosity of pathogenic mutations is the most likely inheritance model if the parents are non-consanguineous. We developed a web-based compound heterozygous filter that is suited for data from NGS projects and that is easy to use for non-bioinformaticians. We analyzed the power of compound heterozygous mutation filtering by deriving background distributions for healthy individuals from different ethnicities and studied the effectiveness in trios as well as more complex pedigree structures. While usually more then 30 genes harbor potential compound heterozygotes in single exomes, this number can be markedly reduced with every additional member of the pedigree that is included in the analysis. In a real data set with exomes of four family members, two sisters affected by Mabry syndrome and their healthy parents, the disease-causing gene PIGO, which harbors the pathogenic compound heterozygous variants, could be readily identified. Compound heterozygous filtering is an efficient means to reduce the number of candidate mutations in studies aiming at identifying recessive disease genes in non-consanguineous families. A web-server is provided to make this filtering strategy available at www.gene-talk.de.     

Genome-Wide Massively Parallel Sequencing of Formaldehyde Fixed-Paraffin Embedded (FFPE) Tumor Tissues for Copy-Number- and Mutation-Analysis

Background

Cancer re-sequencing programs rely on DNA isolated from fresh snap frozen tissues, the preparation of which is combined with additional preservation efforts. Tissue samples at pathology departments are routinely stored as formalin-fixed and paraffin-embedded (FFPE) samples and their use would open up access to a variety of clinical trials. However, FFPE preparation is incompatible with many down-stream molecular biology techniques such as PCR based amplification methods and gene expression studies.

Methodology/Principal Findings

Here we investigated the sample quality requirements of FFPE tissues for massively parallel short-read sequencing approaches. We evaluated key variables of pre-fixation, fixation related and post-fixation processes that occur in routine medical service (e.g. degree of autolysis, duration of fixation and of storage). We also investigated the influence of tissue storage time on sequencing quality by using material that was up to 18 years old. Finally, we analyzed normal and tumor breast tissues using the Sequencing by Synthesis technique (Illumina Genome Analyzer, Solexa) to simultaneously localize genome-wide copy number alterations and to detect genomic variations such as substitutions and point-deletions and/or insertions in FFPE tissue samples.

Conclusions/Significance

The application of second generation sequencing techniques on small amounts of FFPE material opens up the possibility to analyze tissue samples which have been collected during routine clinical work as well as in the context of clinical trials. This is in particular important since FFPE samples are amply available from surgical tumor resections and histopathological diagnosis, and comprise tissue from precursor lesions, primary tumors, lymphogenic and/or hematogenic metastases. Large-scale studies using this tissue material will result in a better prediction of the prognosis of cancer patients and the early identification of patients which will respond to therapy.     

Structure of the O-polysaccharide from the lipopolysaccharide of Providencia alcalifaciens O12

The O-polysaccharide was obtained by mild acid degradation of the lipopolysaccharide of Providencia alcalifaciens O12. Its structure was studied by sugar analysis using GLC of the alditol acetates and (S)-2-octyl glycosides, methylation analysis, Smith degradation, and ¹H and ¹³C NMR spectroscopy, including 2D ¹H-¹H COSY, TOCSY, ROESY, ¹H-¹³C HSQC, and HMBC experiments. It was found that the polymer is a neutral heteropolysaccharide and has a branched heptasaccharide repeating unit with the following structure:     

Identification of signature and primers specific to genus <Emphasis Type="Italic">Pseudomonas</Emphasis> using mismatched patterns of 16S rDNA sequences

Background

Pseudomonas, a soil bacterium, has been observed as a dominant genus that survives in different habitats with wide hostile conditions. We had a basic assumption that the species level variation in 16S rDNA sequences of a bacterial genus is mainly due to substitutions rather than insertion or deletion of bases. Keeping this in view, the aim was to identify a region of 16S rDNA sequence and within that focus on substitution prone stretches indicating species level variation and to derive patterns from these stretches that are specific to the genus.

Results

Repeating elements that are highly conserved across different species of Pseudomonas were considered as guiding markers to locate a region within the 16S gene. Four repeating patterns showing more than 80% consistency across fifty different species of Pseudomonas were identified. The sub-sequences between the repeating patterns yielded a continuous region of 495 bases. The sub-sequences after alignment and using Shanon's entropy measure yielded a consensus pattern. A stretch of 24 base positions in this region, showing maximum variations across the sampled sequences was focused for possible genus specific patterns. Nine patterns in this stretch showed nearly 70% specificity to the target genus. These patterns were further used to obtain a signature that is highly specific to Pseudomonas. The signature region was used to design PCR primers, which yielded a PCR product of 150 bp whose specificity was validated through a sample experiment.

Conclusions

The developed approach was successfully applied to genus Pseudomonas. It could be tried in other bacterial genera to obtain respective signature patterns and thereby PCR primers, for their rapid tracking in the environmental samples.

     

Repositioning-dependent fate of duplicate genes

Gene duplication is the main source of evolutionary novelties. However, the problem with duplicates is that the purifying selection overlooks deleterious mutations in the redundant sequence, which therefore, instead of gaining a new function, often degrades into a functionless pseudogene. This risk of functional loss instead of gain is much higher for small populations of higher organisms with a slow and complex development. We propose that it is the epigenetic tissue/stage-complementary silencing of duplicates that makes them exposable to the purifying selection, thus saving them from pseudogenization and opening the way towards new function(s). Our genome-wide analyses of gene duplicates in several eukaryotic species combined with the phylogenetic comparison of vertebrate alpha- and beta-globin gene clusters strongly support this epigenetic complementation (EC) model. The distinctive condition for a new duplicate to survive by the EC mechanism seems to be its repositioning to an ectopic site, which is accompanied by changes in the rate and direction of mutagenesis. The most distinguished in this respect is the human genome. In this review, we extend and discuss the data on the EC- and repositioning-dependent fate of gene duplicates with the special emphasis on the problem of detecting brief postduplication period of adaptive evolution driven by positive selection. Accordingly, we propose a new CpG-focused measure of selection that is insensitive to translocation-caused biases in mutagenesis.     

Position-Associated GC Asymmetry of Gene Duplicates

It is well known that repositioning of a gene often exerts a strong impact on its own expression and whole development. Here we report the results of genome-wide analyses suggesting that repositioning may also radically change the evolutionary fate of gene duplicates. As an indicator of these changes, we used the GC content of gene pairs which originated by duplication. This indicator turned out to be duplicate-asymmetric, which means that genes in a pair differ significantly in GC content despite their apparent origin from a common ancestor. Such an asymmetry necessarily implies that after duplication two originally identical genes mutated in opposite directions—toward GC-rich and GC-poor content, respectively. In mammalian genomes, this trend is definitely associated with presumably methylated hypermutable CpG sites, and in a typical GC-asymmetric gene pair, its two member genes are embedded in GC-contrasting isochores. However, we unexpectedly found similar significant GC asymmetry in fish, fly, worm, and yeast. This means that neither methylation alone nor methylation in combination with isochores can be counted as a primary cause of the GC asymmetry; rather they represent specific realizations of some universal principle of genome evolution. Remarkably, genes from pairs with the greatest GC asymmetry tend to be on different chromosomes, suggesting that the mutational difference between gene duplicates is associated with translocation of a new gene to a different place in the genome, whereas GC symmetric pairs demonstrate the opposite tendency. A recently emerged extra gene copy is usually on the same chromosome as is its parent but quickly, by 0.05 substitution per synonymous site, either has perished or occupies a different chromosome. During this earliest posttranslocation period, the ratio of nonsynonymous/synonymous base substitutions is unusually high, suggesting a rapid adaptive evolution of novel functions. In a general context of evolution by gene duplication, our interpretation of this position-dependent GC asymmetry between duplicated genes is that evolution of redundant genes toward a new function has often been associated with their very early, postduplication repositioning in the genome, with a concomitant abrupt change in epigenetic control of tissue/stage-specific expression and an increase in the mutation rate. Of eight eukaryotic genomes studied, the most distinguished in this respect is the human genome.Reviewing Editor: Dr. Manyuan Long     

Meiotic analysis of four cross-pollinated generations in a synthetic autotetraploid population of husk tomato (<i>Physalis ixocarpa</i>)

The cultivated husk tomato (Physalis ixocarpa) (2n = 2x = 24) is native from Mexico and Central America and shows a wide genetic variation. Presently, it is the fourth horticultural crop in cultivation surface in Mexico. The working team of this research previously developed an autotetraploid population by using colchicine. The objectives of the present work were to analyze the ploidy level and meiotic behavior of the subsequent generations (C3, C4, C5, C6) from the original (C2) composed only by plants with the duplicated genome from the Rendidora cultivar, and to determine pollen viability. As a diploid control the cultivar Rendidora of P. ixocarpa was used. Ploidy level was determined by flow citometry and meiotic analysis. For the meiotic study, the microsporocytes were prepared by the squash method, stained with carmin and analyzed in diakinesis. Pollen viability was evaluated through 0.01% Buffalo Black staining. The tetraploid condition prevailed through four cross-pollinating generations, maintaining a constant chromosome number 2n = 4x = 48. In diakinesis, the chromosomes of the diploid cultivar were associated into bivalents, whereas in tetraploid plants the chromosomes associated into univalents, bivalents and trivalents. Highly significant differences in bivalent pairing were detected between autotetraploid plants and between generations. Pollen viability did not show significant differences between generations and allowed reproduction. These results indicate that it is possible to develop an autotetraploid cultivar, because the polyploid state is naturally maintained and the plants are fertile. Furthermore, given the differences in bivalent pairing between plants and generations, a response to selection toward meiotic stability is expected.