Postmitotic differentiation of human monocytes requires cohesin-structured chromatin

RAD21 mutations in acute myeloid leukemia

The cohesin complex is a ring-shaped protein structure involved in DNA repair and chromosomal segregation. Studies have showed that genomic alterations in the cohesin complex members are among the initial occurrences in the development of acute myeloid leukemia (AML). STAG2 is the most commonly mutated and best-studied member of the cohesin complex in AML and mutations in this gene have been associated with adverse outcomes and are diagnostically relevant. However, the exact role of mutations in other members of the cohesin complex in the development of myeloid neoplasia is controversial. In this single institution study, we retrospectively reviewed data from the molecular profiles of 1,381 AML patients and identified 14 patients with mutations in RAD21, another member of the cohesin complex. We evaluated the frequency, mutational profile, clinico-pathologic features, and prognostic impact of RAD21 in this cohort. This study showed that RAD21-mutated AML often associates with monocytic differentiation, CD7 expression, co-existing mutations in epigenetic regulators, a normal karyotype, and poor prognosis. Our findings provide additional insights into the morphologic, immunophenotypic, and genomic profile of RAD21 mutation-positive AML and suggest that RAD21 mutations should be evaluated for independent prognostic significance in AML.

SIRT1 Coordinates Transcriptional Regulation of Neural Activity and Modulates Depression-Like Behaviors in the Nucleus Accumbens

BACKGROUND

Major depression and anxiety disorders are significant causes of disability and socioeconomic burden. Despite the prevalence and considerable impact of these affective disorders, their pathophysiology remains elusive. Thus, there is an urgent need to develop novel therapeutics for these conditions. We evaluated the role of SIRT1 in regulating dysfunctional processes of reward by using chronic social defeat stress to induce depression- and anxiety-like behaviors. Chronic social defeat stress induces physiological and behavioral changes that recapitulate depression-like symptomatology and alters gene expression programs in the nucleus accumbens, but cell type-specific changes in this critical structure remain largely unknown.

METHODS

We examined transcriptional profiles of D1-expressing medium spiny neurons (MSNs) lacking deacetylase activity of SIRT1 by RNA sequencing in a cell type-specific manner using the RiboTag line of mice. We analyzed differentially expressed genes using gene ontology tools including SynGO and EnrichR and further demonstrated functional changes in D1-MSN-specific SIRT1 knockout (KO) mice using electrophysiological and behavioral measurements.

RESULTS

RNA sequencing revealed altered transcriptional profiles of D1-MSNs lacking functional SIRT1 and showed specific changes in synaptic genes including glutamatergic and GABAergic (gamma-aminobutyric acidergic) receptors in D1-MSNs. These molecular changes may be associated with decreased excitatory and increased inhibitory neural activity in Sirt1 KO D1-MSNs, accompanied by morphological changes. Moreover, the D1-MSN-specific Sirt1 KO mice exhibited proresilient changes in anxiety- and depression-like behaviors.

CONCLUSIONS

SIRT1 coordinates excitatory and inhibitory synaptic genes to regulate the GABAergic output tone of D1-MSNs. These findings reveal a novel signaling pathway that has potential for the development of innovative treatments for affective disorders.

Hi-C, a chromatin 3D structure technique advancing the functional genomics of immune cells

The functional performance of immune cells relies on a complex transcriptional regulatory network. The three-dimensional structure of chromatin can affect chromatin status and gene expression patterns, and plays an important regulatory role in gene transcription. Currently available techniques for studying chromatin spatial structure include chromatin conformation capture techniques and their derivatives, chromatin accessibility sequencing techniques, and others. Additionally, the recently emerged deep learning technology can be utilized as a tool to enhance the analysis of data. In this review, we elucidate the definition and significance of the three-dimensional chromatin structure, summarize the technologies available for studying it, and describe the research progress on the chromatin spatial structure of dendritic cells, macrophages, T cells, B cells, and neutrophils.

Chromatin Organization and Transcriptional Programming of Breast Cancer Cell Identity

The advent of sequencing technologies for assessing chromosome conformations has provided a wealth of information on the organization of the 3-dimensional genome and its role in cancer progression. It is now known that changes in chromatin folding and accessibility can promote aberrant activation or repression of transcriptional programs that can drive tumorigenesis and progression in diverse cancers. This includes breast cancer, which comprises several distinct subtypes defined by their unique transcriptomes that dictate treatment response and patient outcomes. Of these, basal-like breast cancer is an aggressive subtype controlled by a pluripotency-enforcing transcriptome. Meanwhile, the more differentiated luminal subtype of breast cancer is driven by an estrogen receptor-dominated transcriptome that underlies its responsiveness to antihormone therapies and conveys improved patient outcomes. Despite the clear differences in molecular signatures, the genesis of each subtype from normal mammary epithelial cells remains unclear. Recent technical advances have revealed key distinctions in chromatin folding and organization between subtypes that could underlie their transcriptomic and, hence, phenotypic differences. These studies also suggest that proteins controlling particular chromatin states may be useful targets for treating aggressive disease. In this review, we explore the current state of understanding of chromatin architecture in breast cancer subtypes and its potential role in defining their phenotypic characteristics.

Three-dimensional genome organization in immune cell fate and function

Immune cell development and activation demand the precise and coordinated control of transcriptional programmes. Three-dimensional (3D) organization of the genome has emerged as an important regulator of chromatin state, transcriptional activity and cell identity by facilitating or impeding long-range genomic interactions among regulatory elements and genes. Chromatin folding thus enables cell type-specific and stimulus-specific transcriptional responses to extracellular signals, which are essential for the control of immune cell fate, for inflammatory responses and for generating a diverse repertoire of antigen receptor specificities. Here, we review recent findings connecting 3D genome organization to the control of immune cell differentiation and function, and discuss how alterations in genome folding may lead to immune dysfunction and malignancy.