Identification of a new cis-regulatory element of the terminal deoxynucleotidyl transferase gene in the 5' region of the murine locus

H3K4 tri-methylation provides an epigenetic signature of active enhancers

Combinations of post-translational histone modifications shape the chromatin landscape during cell development in eukaryotes. However, little is known about the modifications exactly delineating functionally engaged regulatory elements. For example, although histone H3 lysine 4 mono-methylation (H3K4me1) indicates the presence of transcriptional gene enhancers, it does not provide clearcut information about their actual position and stage-specific activity. Histone marks were, therefore, studied here at genomic loci differentially expressed in early stages of T-lymphocyte development. The concomitant presence of the three H3K4 methylation states (H3K4me1/2/3) was found to clearly reflect the activity of bona fide T-cell gene enhancers. Globally, gain or loss of H3K4me2/3 at distal genomic regions correlated with, respectively, the induction or the repression of associated genes during T-cell development. In the Tcrb gene enhancer, the H3K4me3-to-H3K4me1 ratio decreases with the enhancer's strength. Lastly, enhancer association of RNA-polymerase II (Pol II) correlated with the presence of H3K4me3 and Pol II accumulation resulted in local increase of H3K4me3. Our results suggest the existence of functional links between Pol II occupancy, H3K4me3 enrichment and enhancer activity.

Transcription initiation platforms and GTF recruitment at tissue-specific enhancers and promoters

Recent work has shown that RNA polymerase (Pol) II can be recruited to and transcribe distal regulatory regions. Here we analyzed transcription initiation and elongation through genome-wide localization of Pol II, general transcription factors (GTFs) and active chromatin in developing T cells. We show that Pol II and GTFs are recruited to known T cell-specific enhancers. We extend this observation to many new putative enhancers, a majority of which can be transcribed with or without polyadenylation. Importantly, we also identify genomic features called transcriptional initiation platforms (TIPs) that are characterized by large areas of Pol II and GTF recruitment at promoters, intergenic and intragenic regions. TIPs show variable widths (0.4-10 kb) and correlate with high CpG content and increased tissue specificity at promoters. Finally, we also report differential recruitment of TFIID and other GTFs at promoters and enhancers. Overall, we propose that TIPs represent important new regulatory hallmarks of the genome.

Characterization of sINR, a strict version of the Initiator core promoter element

The proximal promoter consists of binding sites for transcription regulators and a core promoter. We identified an overrepresented motif in the proximal promoter of human genes with an Initiator (INR) positional bias. The core of the motif fits the INR consensus but its sequence is more strict and flanked by additional conserved sequences. This strict INR (sINR) is enriched in TATA-less genes that belong to specific functional categories. Analysis of the sINR-containing DHX9 and ATP5F1 genes showed that the entire sINR sequence, including the strict core and the conserved flanking sequences, is important for transcription. A conventional INR sequence could not substitute for DHX9 sINR whereas, sINR could replace a conventional INR. The minimal region required to create the major TSS of the DHX9 promoter includes the sINR and an upstream Sp1 site. In a heterologous context, sINR substituted for the TATA box when positioned downstream to several Sp1 sites. Consistent with that the majority of sINR promoters contain at least one Sp1 site. Thus, sINR is a TATA-less-specific INR that functions in cooperation with Sp1. These findings support the idea that the INR is a family of related core promoter motifs.