Baf60c is a component of the neural progenitor-specific BAF complex in developing retina

Remodeling of the chromatin network plays an important role regulating embryonic development as well as differentiation. The SWI/SNF complex is an ATP-dependent chromatin-remodeling complex. It consists of several proteins, including an ATPase subunit, either Brg1 or Brm. Two subunits of this complex, Baf53a and Baf45, have been previously identified as being neural progenitor-specific. In this study, we show that Baf60c, another important part of this large complex, acts in a similar neural progenitor-specific manner. We show that during development Baf60c is expressed in neural progenitors in human retinas as well as mouse retina, cortex and spinal cord. Baf60c expression is lost during neural differentiation and its overexpression keeps the progenitors in a proliferative state through its interaction with the Notch pathway. Finally, we show that Baf60c is re-expressed in the Müller glial cells that re-enter the cell cycle after neurotoxic damage.     

BAF250B-associated SWI/SNF chromatin-remodeling complex is required to maintain undifferentiated mouse embryonic stem cells

Whether SWI/SNF chromatin remodeling complexes play roles in embryonic stem (ES) cells remains unknown. Here we show that SWI/SNF complexes are present in mouse ES cells, and their composition is dynamically regulated upon induction of ES cell differentiation. For example, the SWI/SNF purified from undifferentiated ES cells contains a high level of BAF155 and a low level of BAF170 (both of which are homologs of yeast SWI3 protein), whereas that from differentiated cells contains nearly equal amounts of both. Moreover, the levels of BAF250A and BAF250B decrease during the differentiation of ES cells, whereas that of BRM increases. The altered expression of SWI/SNF components hinted that these complexes could play roles in ES cell maintenance or differentiation. We therefore generated ES cells with biallelic inactivation of BAF250B and found that these cells display a reduced proliferation rate and an abnormal cell cycle. Importantly, these cells are deficient in the self-renewal capacity of undifferentiated ES cells and exhibit certain phenotypes of differentiated cells, including reduced expression of several pluripotency-related genes and increased expression of some differentiation-related genes. These data suggest that the BAF250B-associated SWI/SNF is essential for mouse ES cells to maintain their normal proliferation and pluripotency. The work presented here underscores the importance of SWI/SNF chromatin remodeling complexes in pluripotent stem cells.     

The expression of the SWI/SNF ATPase subunits BRG1 and BRM in normal human tissues.

SWI/SNF is a chromatin-remodeling complex important in gene regulation, cytokine responses, tumorigenesis, differentiation, and development. As a multitude of signaling pathways require SWI/SNF, loss of SWI/SNF function is expected to have an impact on cellular phenotypes. The SWI/SNF ATPase subunits, BRG1 and BRM, have been shown to be lost in a subset of human cancer cell lines and human primary cancers and may represent tumor suppressor proteins. To better understand the biology of these proteins, the authors examined the expression pattern of BRG1 and BRM in a variety of normal tissues. BRG1 expression was predominantly seen in cell types that constantly undergo proliferation or self-renewal; in contrast, BRM was preferentially expressed in brain, liver, fibromuscular stroma, and endothelial cell types, cell types not constantly engaged in proliferation or self-renewal. This differential expression suggests that these proteins serve distinct functions in human tissues.     

Regulation of Mec1 kinase activity by the SWI/SNF chromatin remodeling complex

ATP-dependent chromatin remodeling complexes alter chromatin structure through interactions with chromatin substrates such as DNA, histones, and nucleosomes. However, whether chromatin remodeling complexes have the ability to regulate nonchromatin substrates remains unclear. Saccharomyces cerevisiae checkpoint kinase Mec1 (ATR in mammals) is an essential master regulator of genomic integrity. Here we found that the SWI/SNF chromatin remodeling complex is capable of regulating Mec1 kinase activity. In vivo, Mec1 activity is reduced by the deletion of Snf2, the core ATPase subunit of the SWI/SNF complex. SWI/SNF interacts with Mec1, and cross-linking studies revealed that the Snf2 ATPase is the main interaction partner for Mec1. In vitro, SWI/SNF can activate Mec1 kinase activity in the absence of chromatin or known activators such as Dpb11. The subunit requirement of SWI/SNF-mediated Mec1 regulation differs from that of SWI/SNF-mediated chromatin remodeling. Functionally, SWI/SNF-mediated Mec1 regulation specifically occurs in S phase of the cell cycle. Together, these findings identify a novel regulator of Mec1 kinase activity and suggest that ATP-dependent chromatin remodeling complexes can regulate nonchromatin substrates such as a checkpoint kinase.     

Brg1调控重组人骨形态发生蛋白2诱导成骨细胞分化

背景：Brg1是依赖ATP的染色质改变复合物的核心催化亚基,该亚基在基因的转录调控、复制、重组,骨骼肌的分化、抑制肿瘤的发生等活动中起着重要的作用。 目的：探索Brg1基因在骨形态发生蛋白2诱导成骨细胞分化过程中的调控机制。 方法：采用胶原酶消化法进行小鼠颅骨成骨细胞的原代培养;分别用0,50,200 μg/L的重组人骨形态发生蛋白2诱导原代培养的成骨细胞的分化,摸索骨形态发生蛋白2的最佳作用剂量;实时荧光定量PCR和Western blot进行骨形态发生蛋白2对Brg1的作用时间的动力学分析;实时荧光定量PCR和钙钴染色法检测敲除Brg1对骨形态发生蛋白2诱导的成骨分化的影响;构建Dlx5腺病毒重组表达载体,实时荧光定量PCR和钙钴染色法检测Brg1在骨形态发生蛋白2诱导的成骨分化过程中对Dlx5的调控作用。 结果与结论：用自行合成的重组人骨形态发生蛋白2可诱导原代培养小鼠成骨细胞分化,200 μg/L剂量有着较好的诱导分化效果;重组人骨形态发生蛋白2可诱导Brg1基因转录水平和翻译水平表达水平上调;敲除Brg1可抑制重组人骨形态发生蛋白2诱导的成骨分化;Brg1能够调控Dlx5的表达水平。说明Brg1通过调控Dlx5的表达水平调控重组人骨形态发生蛋白2诱导的小鼠成骨细胞的分化。     

SWI/SNF-deficient head and neck neoplasms: An overview

With wide-spread use of next generation sequencing tools in surgical pathology, a variety of neoplasms have been increasingly recognized to be associated with specific recurrent defining genetic abnormalities. This has led to recognition of new genetically defined entities and refinements of preexisting heterogeneous neoplastic categories. Among these, neoplasms associated with inactivating mutations involving different subunits of the SWI/SNF chromatin remodeling complex have received special attention. In the head and neck area, SMARCB1 (INI1) and SMARCA4 (BRG1) are the main two SWI/SNF components responsible for several recently described highly aggressive undifferentiated malignancies with predilection for the soft tissue of the neck (SMARCB1-deficient malignant rhabdoid tumors in children and rare epithelioid sarcoma cases in adults) and the sinonasal tract (SMARCB1-deficient sinonasal carcinoma including a small subset of adenocarcinomas, SMARCA4-deficient sinonasal undifferentiated carcinoma and SMARCA4-deficient sinonasal teratocarcinosarcoma). Molecular studies confirmed paucity of additional genetic abnormalities in these diseases underlining the central role of SWI/SNF deficiency as the primary and frequently sole genetic driver of these lethal diseases. Initiation of clinical trials using drugs that target the SWI/SNF collapse encourages recognition and correct classification of these morphologically frequently overlapping malignancies and underpins the role of SWI/SNF immunohistochemistry as emerging powerful adjunct tool in surgical pathology of the head and neck.