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The Mobile Genetic Elements and Genome Evolution conference was hosted by Keystone Symposia in Santa Fe, NM USA, 9 March through 14 March 2014. The goal of this conference was to bring together scientists from around the world who study transposable elements in diverse organisms and researchers who study the impact these elements have on genome evolution. The meeting included over 200 scientists who participated through poster presentations, short talks selected from abstracts, and invited speakers. The talks were organized into eight sessions and two workshops. The topics varied from diverse mechanisms of mobilization to the evolution of genomes and their defense strategies against transposable elements [ABSTRACT FROM AUTHOR]

Transposable elements and their remnants constitute a substantial fraction of eukaryotic genomes. Host genomes have evolved defence mechanisms, including chromatin modifications and RNA interference, to regulate transposable elements. Here we describe a genome surveillance mechanism for retrotransposons by transposase-derived centromeric protein CENP-B homologues of the fission yeast Schizosaccharomyces pombe. CENP-B homologues of S. pombe localize at and recruit histone deacetylases to silence Tf2 retrotransposons. CENP-Bs also repress solo long terminal repeats (LTRs) and LTR-associated genes. Tf2 elements are clustered into ‘Tf’ bodies, the organization of which depends on CENP-Bs that display discrete nuclear structures. Furthermore, CENP-Bs prevent an ‘extinct’ Tf1 retrotransposon from re-entering the host genome by blocking its recombination with extant Tf2, and silence and immobilize a Tf1 integrant that becomes sequestered into Tf bodies. Our results reveal a probable ancient retrotransposon surveillance pathway important for host genome integrity, and highlight potential conflicts between DNA transposons and retrotransposons, major transposable elements believed to have greatly moulded the evolution of genomes. [ABSTRACT FROM AUTHOR]

In this issue of Molecular Cell, describe their exciting discovery that, in Saccharomyces cerevisiae, the integrase of retrotransposon Ty5 is phosphorylated, and this modification stabilizes the interaction between integrase and Sir4p that directs integration to heterochromatin. [Copyright &y& Elsevier]

Understanding how complex networks of genes integrate to produce dividing cells is an important goal that is limited by the difficulty in defining the function of individual genes. Current resources for the systematic identification of gene function such as siRNA libraries and collections of deletion strains are costly and organism specific. We describe here integration profiling, a novel approach to identify the function of eukaryotic genes based upon dense maps of transposon integration. As a proof of concept, we used the transposon Hermes to generate a library of 360,513 insertions in the genome of Schizosaccharomyces pombe. On average, we obtained one insertion for every 29 bp of the genome. Hermes integrated more often into nucleosome free sites and 33% of the insertions occurred in ORFs. We found that ORFs with low integration densities successfully identified the genes that are essential for cell division. Importantly, the nonessential ORFs with intermediate levels of insertion correlated with the nonessential genes that have functions required for colonies to reach full size. This finding indicates that integration profiles can measure the contribution of nonessential genes to cell division. While integration profiling succeeded in identifying genes necessary for propagation, it also has the potential to identify genes important for many other functions such as DNA repair, stress response, and meiosis. [ABSTRACT FROM AUTHOR]

Summary: The LTR-retrotransposon Tf1 preserves the coding capacity of its host Schizosaccharomyces pombe by integrating upstream of open reading frames (ORFs). To determine which features of the target sites were recognized by the transposon, we introduced plasmids containing candidate insertion sites into S. pombe and mapped the positions of integration. We found that Tf1 was targeted specifically to the promoters of Pol II-transcribed genes. A detailed analysis of integration in plasmids that contained either ade6 or fbp1 revealed insertions occurred in the promoters at positions where transcription factors bound. Further experiments revealed that the activator Atf1p and its binding site were required for directing integration to the promoter of fbp1. An interaction between Tf1 integrase and Atf1p was observed, indicating that integration at fbp1 was mediated by the activator bound to its promoter. Surprisingly, we found Tf1 contained sequences that activated transcription, and these substituted for elements of the ade6 promoter disrupted by integration. [Copyright &y& Elsevier]

Currently, no transposon-based method for the mutagenesis of Schizosaccharomyces pombe exists. We have developed such a system based on the introduction of the hermes transposon from the housefly into S. pombe. This system efficiently disrupts open reading frames and allows the insertion sites to be readily identified. [ABSTRACT FROM AUTHOR]