The Saccharomyces cerevisiae Histone Chaperone Rtt106 Mediates the Cell Cycle Recruitment of SWI/SNF and RSC to the HIR-Dependent Histone Genes

In Saccharomyces cerevisiae, three out of the four histone gene pairs (HTA1-HTB1, HHT1-HHF1, and HHT2-HHF2) are regulated by the HIR co-repressor complex. The histone chaperone Rtt106 has recently been shown to be present at these histone gene loci throughout the cell cycle in a HIR- and Asf1-dependent manner and involved in their transcriptional repression. The SWI/SNF and RSC chromatin remodeling complexes are both recruited to the HIR-dependent histone genes; SWI/SNF is required for their activation in S phase, whereas RSC is implicated in their repression outside of S phase. Even though their presence at the histone genes is dependent on the HIR complex, their specific recruitment has not been well characterized. In this study we focused on characterizing the role played by the histone chaperone Rtt106 in the cell cycle-dependent recruitment of SWI/SNF and RSC complexes to the histone genes.Using GST pull-down and co-immunoprecipitation assays, we showed that Rtt106 physically interacts with both the SWI/SNF and RSC complexes in vitro and in vivo. We then investigated the function of this interaction with respect to the recruitment of these complexes to HIR-dependent histone genes. Using chromatin immunoprecipitation assays (ChIP), we found that Rtt106 is important for the recruitment of both SWI/SNF and RSC complexes to the HIR-dependent histone genes. Furthermore, using synchronized cell cultures, we showed by ChIP assays that the Rtt106-dependent SWI/SNF recruitment to these histone gene loci is cell cycle regulated and restricted to late G1 phase just before the peak of histone gene expression in S phase.Overall, these data strongly suggest that the interaction between the histone chaperone Rtt106 and both the SWI/SNF and RSC chromatin remodeling complexes is important for the cell cycle regulated recruitment of these two complexes to the HIR-dependent histone genes

LINE-1 Evasion of Epigenetic Repression in Humans

Epigenetic silencing defends against LINE-1 (L1) retrotransposition in mammalian cells. However, the mechanisms that repress young L1 families and how L1 escapes to cause somatic genome mosaicism in the brain remain unclear. Here we report that a conserved Yin Yang 1 (YY1) transcription factor binding site mediates L1 promoter DNA methylation in pluripotent and differentiated cells. By analyzing 24 hippocampal neurons with three distinct single-cell genomic approaches, we characterized and validated a somatic L1 insertion bearing a 3' transduction. The source (donor) L1 for this insertion was slightly 5' truncated, lacked the YY1 binding site, and was highly mobile when tested in\ua0vitro. Locus-specific bisulfite sequencing revealed that the donor L1 and other young L1s with mutated YY1 binding sites were hypomethylated in embryonic stem cells, during neurodifferentiation, and in liver and brain tissue. These results explain how L1 can evade repression and retrotranspose in the human body

L1 Mosaicism in Mammals:Extent, Effects, and Evolution

The retrotransposon LINE-1 (long interspersed element 1, L1) is a transposable element that has extensively colonized the mammalian germline. L1 retrotransposition can also occur in somatic cells, causing genomic mosaicism, as well as in cancer. However, the extent of L1-driven mosaicism arising during ontogenesis is unclear. We discuss here recent experimental data which, at a minimum, fully substantiate L1 mosaicism in early embryonic development and neural cells, including post-mitotic neurons. We also consider the possible biological impact of somatic L1 insertions in neurons, the existence of donor L1s that are highly active (‘hot’) in specific spatiotemporal niches, and the evolutionary selection of donor L1s driving neuronal mosaicism

Communication between hospitals, Family Medicine Groups and community pharmacists during transitions of care interventions

International audienceBackground: Pharmacist-led transitions of care (TOC) interventions have been associated with improved health outcomes. Community pharmacists' (CP) TOC communications have been described whereas limited evidence is available for hospital pharmacists (HP) and none for non-dispensing pharmacists, integrated into Family Medicine Groups (FMG).Objective: To assess information needs and perceptions about TOC communications of HP, FMG pharmacists (FMG-P) and CP and to identify optimal TOC practices and their barriers.Methods: In a cross-sectional design, a survey was distributed via email to the 70 pharmacists who participated in a multicenter, single group, longitudinal TOC intervention study for older adults at risk of medication-related harm. All pharmacists were surveyed on their TOC practices before the TOC study, as part of usual care. Pharmacists who followed TOC study patients were also surveyed on their TOC practices during the TOC study.Results: Survey responses were received from 35 pharmacists (50%), including 8 HP, 6 FMG-P and 21 CP. The frequency of communication between pharmacists of different settings increased significantly during the TOC study, with more than 80% of pharmacists reporting satisfaction with the quality of the information provided. At hospital discharge, in optimal TOC, the FMG-P and CP reported that the most important information to transfer was the reasons of hospitalization, patient weight and height, and the therapeutic intent of the medications. The main barriers to TOC implementation were the lack of clinical information about patients for FMG-P and CP and understaffing for HP. FMG-P and CP reported a similar high degree of interest in assuming responsibility for the new extended scope of practice activities of medication adjustments according to therapeutic targets or laboratory results and the implementation of a plan for gradual dose increases or drug tapering.Conclusions: The surveyed pharmacists reported an increased frequency of communication and satisfaction with the information exchanged between the pharmacists of different settings during the TOC study compared to usual care, before the study. The pharmacists extended scope of practice offers new opportunities to optimize TOC interventions