The Chromatin Regulator Mll1 Supports T Follicular Helper Cell Differentiation by Controlling Expression of Bcl6, LEF-1, and TCF-1.

T follicular helper (TFH) cells are essential for developing protective Ab responses following vaccination. Greater understanding of the genetic program leading to TFH differentiation is needed. Chromatin modifications are central in the control of gene expression. However, detailed knowledge of how chromatin regulators (CRs) regulate differentiation of TFH cells is limited. We screened a large short hairpin RNA library targeting all known CRs in mice and identified the histone methyltransferase mixed lineage leukemia 1 (Mll1) as a positive regulator of TFH differentiation. Loss of Mll1 expression reduced formation of TFH cells following acute viral infection or protein immunization. In addition, expression of the TFH lineage-defining transcription factor Bcl6 was reduced in the absence of Mll1. Transcriptomics analysis identified Lef1 and Tcf7 as genes dependent on Mll1 for their expression, which provides one mechanism for the regulation of TFH differentiation by Mll1. Taken together, CRs such as Mll1 substantially influence TFH differentiation.

Cutting Edge: NFAT Transcription Factors Promote the Generation of Follicular Helper T Cells in Response to Acute Viral Infection.

Follicular CD4(+) Th (Tfh) cells provide B cell help in germinal center reactions that support class switching, somatic hypermutation, and the generation of high-affinity Abs. In this article, we show that deficiency in NFAT1 and NFAT2 in CD4(+) T cells leads to impaired germinal center reactions upon viral infection because of reduced Tfh cell differentiation and defective expression of proteins involved in T/B interactions and B cell help, including ICOS, PD-1, and SLAM family receptors. Genome-wide chromatin immunoprecipitation data suggest that NFAT proteins likely directly participate in regulation of genes important for Tfh cell differentiation and function. NFAT proteins are important TCR and Ca(2+)-dependent regulators of T cell biology, and in this article we demonstrate a major positive role of NFAT family members in Tfh differentiation.

A cis-regulatory map of the Drosophila genome.

Systematic annotation of gene regulatory elements is a major challenge in genome science. Direct mapping of chromatin modification marks and transcriptional factor binding sites genome-wide has successfully identified specific subtypes of regulatory elements. In Drosophila several pioneering studies have provided genome-wide identification of Polycomb response elements, chromatin states, transcription factor binding sites, RNA polymerase II regulation and insulator elements; however, comprehensive annotation of the regulatory genome remains a significant challenge. Here we describe results from the modENCODE cis-regulatory annotation project. We produced a map of the Drosophila melanogaster regulatory genome on the basis of more than 300 chromatin immunoprecipitation data sets for eight chromatin features, five histone deacetylases and thirty-eight site-specific transcription factors at different stages of development. Using these data we inferred more than 20,000 candidate regulatory elements and validated a subset of predictions for promoters, enhancers and insulators in vivo. We identified also nearly 2,000 genomic regions of dense transcription factor binding associated with chromatin activity and accessibility. We discovered hundreds of new transcription factor co-binding relationships and defined a transcription factor network with over 800 potential regulatory relationships.