The transposable element environment of human genes is associated with histone and expression changes in cancer.

BACKGROUND: Only 2 % of the human genome code for proteins. Among the remaining 98 %, transposable elements (TEs) represent millions of sequences. TEs have an impact on genome evolution by promoting mutations. Especially, TEs possess their own regulatory sequences and can alter the expression pattern of neighboring genes. Since they can potentially be harmful, TE activity is regulated by epigenetic mechanisms. These mechanisms participate in the modulation of gene expression and can be associated with some human diseases resulting from gene expression deregulation. The fact that the TE silencing can be removed in cancer could explain a part of the changes in gene expression. Indeed, epigenetic modifications associated locally with TE sequences could impact neighboring genes since these modifications can spread to adjacent sequences. RESULTS: We compared the histone enrichment, TE neighborhood, and expression divergence of human genes between a normal and a cancer conditions. We show that the presence of TEs near genes is associated with greater changes in histone enrichment and that differentially expressed genes harbor larger histone enrichment variation related to the presence of particular TEs. CONCLUSIONS: Taken together, these results suggest that the presence of TEs near genes could favor important variation in gene expression when the cell environment is modified.

The evening complex coordinates environmental and endogenous signals in Arabidopsis.

Plants maximize their fitness by adjusting their growth and development in response to signals such as light and temperature. The circadian clock provides a mechanism for plants to anticipate events such as sunrise and adjust their transcriptional programmes. However, the underlying mechanisms by which plants coordinate environmental signals with endogenous pathways are not fully understood. Using RNA-sequencing and chromatin immunoprecipitation sequencing experiments, we show that the evening complex (EC) of the circadian clock plays a major role in directly coordinating the expression of hundreds of key regulators of photosynthesis, the circadian clock, phytohormone signalling, growth and response to the environment. We find that the ability of the EC to bind targets genome-wide depends on temperature. In addition, co-occurrence of phytochrome B (phyB) at multiple sites where the EC is bound provides a mechanism for integrating environmental information. Hence, our results show that the EC plays a central role in coordinating endogenous and environmental signals in Arabidopsis.

A SAM oligomerization domain shapes the genomic binding landscape of the LEAFY transcription factor.

Deciphering the mechanisms directing transcription factors (TFs) to specific genome regions is essential to understand and predict transcriptional regulation. TFs recognize short DNA motifs primarily through their DNA-binding domain. Some TFs also possess an oligomerization domain suspected to potentiate DNA binding but for which the genome-wide influence remains poorly understood. Here we focus on the LEAFY transcription factor, a master regulator of flower development in angiosperms. We have determined the crystal structure of its conserved amino-terminal domain, revealing an unanticipated Sterile Alpha Motif oligomerization domain. We show that this domain is essential to LEAFY floral function. Moreover, combined biochemical and genome-wide assays suggest that oligomerization is required for LEAFY to access regions with low-affinity binding sites or closed chromatin. This finding shows that domains that do not directly contact DNA can nevertheless have a profound impact on the DNA binding landscape of a TF.