Genome dynamics最新文献

The genus Burkholderia consists of a number of very diverse species, both in terms of lifestyle (which varies from category B pathogens to apathogenic soil bacteria and plant colonizers) and their genetic contents. We have used 56 publicly available genomes to explore the genomic diversity within this genus, including genome sequences that are not completely finished, but are available from the NCBI database. Defining the pan- and core genomes of species results in insights in the conserved and variable fraction of genomes, and can verify (or question) historic, taxonomic groupings. We find only several hundred genes that are conserved across all Burkholderia genomes, whilst there are more than 40,000 gene families in the Burkholderia pan-genome. A BLAST matrix visualizes the fraction of conserved genes in pairwise comparisons. A BLAST atlas shows which genes are actually conserved in a number of genomes, located and visualized with reference to a chosen genome. Genomic islands are common in many Burkholderia genomes, and most of these can be readily visualized by DNA structural properties of the chromosome. Trees that are based on relatedness of gene family content yield different results depending on what genes are analyzed. Some of the differences can be explained by errors in incomplete genome sequences, but, as our data illustrate, the outcome of phylogenetic trees depends on the type of genes that are analyzed.

During the first meiotic cell division (meiosis I), homologous chromosomes pair, synapse, recombine, and segregate, using highly coordinated and tightly regulated mechanisms. The synaptonemal complex (SC), a proteinaceous tripartite structure, plays an important role both as a scaffold for the close juxtaposition of homologous chromosomes and in regulating the overall process of homologous recombination. Specifically, it mediates chromosome synapsis during the lengthy prophase of meiosis I. The SC consists of two parallel lateral elements, one central element, and numerous transverse filaments. Recent genetic studies in mice have provided novel insights into the mechanisms by which the SC regulates meiosis and into the etiology of diseases such as aneuploidy. Even though the tripartite ultrastructure and meiotic functions of the SC are similar in different species, the SC components are not well-conserved at the protein sequence level. This review will focus on the identification, characterization, and functions of the synaptonemal complex proteins in mammals.

Segregation of the homologous chromosomes is the most important feature of meiosis as it ensures the faithful haploidization of the genome. It essentially depends on an accurate prearrangement of chromosomes that culminates in a precise and unambiguous pairing of the homologs, which in turn is a prere - quisite for their correct segregation. Pairing with the right partner is accompanied by, moreover it implicitly requires characteristic chromosomal movements that, remarkably, appear to be driven by the chromosomal ends. In prophase I, telomeres firmly attach to the nuclear envelope and move to congregate in a small cluster, thus trailing homologs into close vicinity, a condition that was suggested to promote homolog recognition and alignment. The evolutionarily highly conserved phenomenon of the telomere driven meiotic chromosome rearrangement is yet known for a long time, but the molecular mechanisms responsible for telomere attachment and their directed movements have remained largely unknown. However, in the recent years significant progress has been made in this issue, which has provided some novel clues about the molecular requirements and function of the characteristic meiotic telomere dynamics.

Aneuploidy is the leading cause of mental deficiency in human newborns. Indirect studies suggest that, in most of the cases, the extra chromosome comes from an inaccurate meiotic division. But, particularly, all results seem to indicate that oogenesis is more prone to err than is spermatogenesis. Unfortunately, due to the time-frame in which meiosis takes place in the mammalian males and females, most of the studies performed so far have focused on analyzing male meiosis. Recently, some studies focusing on human meiosis have been published. Some of them revealed important sex-specific differences that may be involved in the predominant involvement of the human female in the genesis of aneuploidy. In this article, the current knowledge we have about human female meiotic synapsis and recombination is summarized and we try to relate it to the human aneuploidy origin.

Among the 130 species that constitute the genus Mycobacterium, the great majority are harmless saprophytes. However, a few species have very efficiently adapted to a pathogenic lifestyle. Among them are two of the most important human pathogens, Mycobacterium tuberculosis and Mycobacterium leprae, and one emerging pathogen, Mycobacterium ulcerans. Their slow growth, virulence for humans and particular physiology make these organisms very difficult to work with, however the need to develop new strategies in the fight against these pathogens requires a clear understanding of their genetic and physiological repertoires and the mechanisms that have contributed to their evolutionary success. The rapid development of mycobacterial genomics following the completion of the Mycobacterium tuberculosis genome sequence provides now the basis for finding the important factors distinguishing pathogens and non-pathogens. In this chapter we will therefore present some of the major insights that have been gained from recent studies, with focus on the roles played by various evolutionary processes in shaping the structure of mycobacterial genomes and pathogen populations.

In the last 30 years it has become evident that patterns of meiotic recombination can be highly variable among individuals. The evidence comes from both low and high resolution analyses of hotspots of recombination in human and other species. In addition, a comparison of the recombination profiles in closely related species such as human and chimpanzee reveals essentially no correlation in the position of hotspots. Although the variation in hotspots of meiotic recombination is clearly documented, the mechanisms responsible for such variation are far from being understood. Here we will review the available evidence of natural variation in meiotic recombination and will discuss potential implications of this variation on the functional mechanisms of crossover formation and control.

Efforts have been made in recent years to clarify molecular meiotic processes in a large variety of higher eukaryotes. In plants, such studies have enjoyed a boom in the last years with the use of Arabidopsis thaliana together with maize, rice and tomato as model systems. Owing to direct and reverse genetic screens, an increasing number of genes involved in meiosis have been characterized in plants. In parallel, the improvement of cytological and genetical tools has allowed a precise description of meiotic recombination events. Thus, it appears that meiotic studies in plants are reaching a new stage and can provide new insights into meiotic recombination mechanisms. In this review, we intend to give an overview of these recent advances in the understanding of meiotic recombination in plants.

The pathogenicity of Staphylococcus aureus is determined by its ability to express multiple virulence factors. Thus far the virulence potential of S. aureus isolates has been described by the virulence gene repertoire, which, in part, varies considerably among the different isolates. Extracellular proteins constitute a reservoir of virulence factors and have been shown to play an important role in the pathogenicity of bacteria. Analyses of the expression of these virulence factors and elucidation of regulatory networks involved in S. aureus virulence by using gel based proteomics can yield information important for our understanding of the virulence potential of this pathogen and its interaction with the host. In addition, these approaches are critical for a comprehensive understanding of secretion and modification of virulence factors.

Protein-protein interaction (PPI) studies are frequently used as a starting point for the functional annotations of unknown proteins according to the principle of 'guilty by association'. Moreover, they deliver information for the understanding of specific virulence mechanisms. We provide an overview about the approaches used for the identification of PPIs in human bacterial pathogens, commenting on advantages and pitfalls of the methods. Furthermore, this review intends to show the impact of PPI studies on future research, taking Helicobacterpylori, one of the first sequenced human pathogens, as model organism.