Brg1 coordinates multiple processes during retinogenesis and is a tumor suppressor in retinoblastoma

Epigenetic Switches in Retinal Homeostasis and Target for Drug Development

Retinal homeostasis, a tightly regulated process maintaining the functional integrity of the retina, is vital for visual function. Emerging research has unveiled the critical role of epigenetic regulation in controlling gene expression patterns during retinal development, maintenance, and response to mutational loads and injuries. Epigenetic switches, including DNA methylation, histone modifications, and non-coding RNAs, play pivotal roles in orchestrating retinal gene expression and cellular responses through various intracellular, extracellular, and environmental modulators. This review compiles the current knowledge on epigenetic switches in retinal homeostasis, providing a deeper understanding of their impact on retinal structural integrity and function and using them as potential targets for therapeutic interventions.

Unlocking cellular plasticity: Enhancing human iPSC reprogramming through bromodomain inhibition and extracellular matrix gene expression regulation

The transformation of fibroblasts into epithelial cells is critical for iPSC reprogramming. In this report, we describe studies with PFI-3, a small molecule inhibitor that specifically targets the bromodomains of SMARCA2/4 and PBRM1 subunit of SWI/SNF complex, as an enhancer of iPSC reprogramming efficiency. Our findings revealed that PFI-3 induces cellular plasticity in multiple human dermal fibroblasts, leading to a mesenchymal-epithelial transition (MET) during iPSC formation. This transition was characterized by the upregulation of E-cadherin expression, a key protein involved in epithelial cell adhesion. Additionally, we identified COL11A1 as a reprogramming barrier and demonstrated COL11A1 knockdown increased reprogramming efficiency. Notably, we found that PFI-3 significantly reduced the expression of numerous extracellular matrix (ECM) genes, particularly those involved in collagen assembly. Our research provides key insights into the early stages of iPSC reprogramming, highlighting the crucial role of ECM changes and cellular plasticity in this process.

SWI/SNF complexes are required for retinal pigmented epithelium differentiation and for the inhibition of cell proliferation and neural differentiation programs

During embryonic development, tissue-specific transcription factors and chromatin remodelers function together to ensure gradual, coordinated differentiation of multiple lineages. Here, we define this regulatory interplay in the developing retinal pigmented epithelium (RPE), a neuroectodermal lineage essential for the development, function and maintenance of the adjacent retina. We present a high-resolution spatial transcriptomic atlas of the developing mouse RPE and the adjacent ocular mesenchyme obtained by geographical position sequencing (Geo-seq) of a single developmental stage of the eye that encompasses young and more mature ocular progenitors. These transcriptomic data, available online, reveal the key transcription factors and their gene regulatory networks during RPE and ocular mesenchyme differentiation. Moreover, conditional inactivation followed by Geo-seq revealed that this differentiation program is dependent on the activity of SWI/SNF complexes, shown here to control the expression and activity of RPE transcription factors and, at the same time, inhibit neural progenitor and cell proliferation genes. The findings reveal the roles of the SWI/SNF complexes in controlling the intersection between RPE and neural cell fates and the coupling of cell-cycle exit and differentiation.

Epigenetic regulation in the commitment of progenitor cells during retinal development and regeneration

Retinal development is initiated by multipotent retinal progenitor cells, which undergo several rounds of cell divisions and subsequently terminal differentiation. Retinal regeneration is usually considered as the recapitulation of retinal development, which share common mechanisms underlying the cell cycle re-entry of adult retinal stem cells and the differentiation of retinal neurons. However, how proliferative retinal progenitor cells perform a precise transition to postmitotic retinal cell types during the process of development and regeneration remains elusive. It is proposed that both the intrinsic and extrinsic programming are involved in the transcriptional regulation of the spatio-temporal fate commitment. Epigenetic modifications and the regulatory mechanisms at both DNA and chromatin levels are also postulated to play an important role in the timing of differentiation of specific retinal cells. In the present review, we have summarized recent knowledge of epigenetic regulation that underlies the commitment of retinal progenitor cells in the settings of retinal development and regeneration.

Cell fate decisions, transcription factors and signaling during early retinal development

The development of the vertebrate eyes is a complex process starting from anterior-posterior and dorso-ventral patterning of the anterior neural tube, resulting in the formation of the eye field. Symmetrical separation of the eye field at the anterior neural plate is followed by two symmetrical evaginations to generate a pair of optic vesicles. Next, reciprocal invagination of the optic vesicles with surface ectoderm-derived lens placodes generates double-layered optic cups. The inner and outer layers of the optic cups develop into the neural retina and retinal pigment epithelium (RPE), respectively. In vitro produced retinal tissues, called retinal organoids, are formed from human pluripotent stem cells, mimicking major steps of retinal differentiation in vivo. This review article summarizes recent progress in our understanding of early eye development, focusing on the formation the eye field, optic vesicles, and early optic cups. Recent single-cell transcriptomic studies are integrated with classical in vivo genetic and functional studies to uncover a range of cellular mechanisms underlying early eye development. The functions of signal transduction pathways and lineage-specific DNA-binding transcription factors are dissected to explain cell-specific regulatory mechanisms underlying cell fate determination during early eye development. The functions of homeodomain (HD) transcription factors Otx2, Pax6, Lhx2, Six3 and Six6, which are required for early eye development, are discussed in detail. Comprehensive understanding of the mechanisms of early eye development provides insight into the molecular and cellular basis of developmental ocular anomalies, such as optic cup coloboma. Lastly, modeling human development and inherited retinal diseases using stem cell-derived retinal organoids generates opportunities to discover novel therapies for retinal diseases.

Loss of BAF (mSWI/SNF) chromatin-remodeling ATPase Brg1 causes multiple malformations of cortical development in mice

Mutations in genes encoding subunits of the BAF (BRG1/BRM-associated factor) complex cause various neurodevelopmental diseases. However, the underlying pathophysiology remains largely unknown. Here, we analyzed the function of Brg1, a core ATPase of BAF complexes, in the developing cerebral cortex. Loss of Brg1 causes several morphological defects resembling human malformations of cortical development (MCDs), including microcephaly, cortical dysplasia, cobblestone lissencephaly, and periventricular heterotopia. We demonstrated that neural progenitor cell (NPC) renewal, neuronal differentiation, neuronal migration, apoptotic cell death, pial basement membrane, and apical junctional complexes, which are associated with MCD formation, were impaired after Brg1 deletion. Furthermore, transcriptome profiling indicated that a large number of genes were deregulated. The deregulated genes were closely related to MCD formation, and most of these genes were bound by Brg1. Cumulatively, our study indicates an essential role of Brg1 in cortical development and provides a new possible pathogenesis underlying Brg1-based BAF complex-related neurodevelopmental disorders.

Deciphering the Retinal Epigenome during Development, Disease and Reprogramming: Advancements, Challenges and Perspectives

Retinal neurogenesis is driven by concerted actions of transcription factors, some of which are expressed in a continuum and across several cell subtypes throughout development. While seemingly redundant, many factors diversify their regulatory outcome on gene expression, by coordinating variations in chromatin landscapes to drive divergent retinal specification programs. Recent studies have furthered the understanding of the epigenetic contribution to the progression of age-related macular degeneration, a leading cause of blindness in the elderly. The knowledge of the epigenomic mechanisms that control the acquisition and stabilization of retinal cell fates and are evoked upon damage, holds the potential for the treatment of retinal degeneration. Herein, this review presents the state-of-the-art approaches to investigate the retinal epigenome during development, disease, and reprogramming. A pipeline is then reviewed to functionally interrogate the epigenetic and transcriptional networks underlying cell fate specification, relying on a truly unbiased screening of open chromatin states. The related work proposes an inferential model to identify gene regulatory networks, features the first footprinting analysis and the first tentative, systematic query of candidate pioneer factors in the retina ever conducted in any model organism, leading to the identification of previously uncharacterized master regulators of retinal cell identity, such as the nuclear factor I, NFI. This pipeline is virtually applicable to the study of genetic programs and candidate pioneer factors in any developmental context. Finally, challenges and limitations intrinsic to the current next-generation sequencing techniques are discussed, as well as recent advances in super-resolution imaging, enabling spatio-temporal resolution of the genome.

Building a Mammalian Retina: An Eye on Chromatin Structure

Regulation of gene expression by chromatin structure has been under intensive investigation, establishing nuclear organization and genome architecture as a potent and effective means of regulating developmental processes. The substantial growth in our knowledge of the molecular mechanisms underlying retinogenesis has been powered by several genome-wide based tools that mapped chromatin organization at multiple cellular and biochemical levels. Studies profiling the retinal epigenome and transcriptome have allowed the systematic annotation of putative cis-regulatory elements associated with transcriptional programs that drive retinal neural differentiation, laying the groundwork to understand spatiotemporal retinal gene regulation at a mechanistic level. In this review, we outline recent advances in our understanding of the chromatin architecture in the mammalian retina during development and disease. We focus on the emerging roles of non-coding regulatory elements in controlling retinal cell-type specific transcriptional programs, and discuss potential implications in untangling the etiology of eye-related disorders.

Brahma-related gene 1 has time-specific roles during brain and eye development

During development, gene expression is tightly controlled to facilitate the generation of the diverse cell types that form the central nervous system. Brahma-related gene 1 (Brg1, also known as Smarca4) is the catalytic subunit of the SWItch/sucrose nonfermentable (SWI/SNF) chromatin remodeling complex that regulates transcription. We investigated the role of Brg1 between embryonic day 6.5 (E6.5) and E14.5 in Sox2-positive neural stem cells (NSCs). Being without major consequences at E6.5 and E14.5, loss of Brg1 between E7.5 and E12.5 resulted in the formation of rosette-like structures in the subventricular zone, as well as morphological alterations and enlargement of neural retina (NR). Additionally, Brg1-deficient cells showed decreased survival in vitro and in vivo. Furthermore, we uncovered distinct changes in gene expression upon Brg1 loss, pointing towards impaired neuron functions, especially those involving synaptic communication and altered composition of the extracellular matrix. Comparison with mice deficient for integrase interactor 1 (Ini1, also known as Smarcb1) revealed that the enlarged NR was Brg1 specific and was not caused by a general dysfunction of the SWI/SNF complex. These results suggest a crucial role for Brg1 in NSCs during brain and eye development.

Epigenetic regulation of retinal development

In the developing vertebrate retina, retinal progenitor cells (RPCs) proliferate and give rise to terminally differentiated neurons with exquisite spatio-temporal precision. Lineage commitment, fate determination and terminal differentiation are controlled by intricate crosstalk between the genome and epigenome. Indeed, epigenetic regulation plays pivotal roles in numerous cell fate specification and differentiation events in the retina. Moreover, aberrant chromatin structure can contribute to developmental disorders and retinal pathologies. In this review, we highlight recent advances in our understanding of epigenetic regulation in the retina. We also provide insight into several aspects of epigenetic-related regulation that should be investigated in future studies of retinal development and disease. Importantly, focusing on these mechanisms could contribute to the development of novel treatment strategies targeting a variety of retinal disorders.

Retinoblastoma Tumor Suppressor Protein Roles in Epigenetic Regulation

Simple Summary

Loss of function of the retinoblastoma gene (RB1) is the rate-limiting step in the initiation of both the hereditary and sporadic forms of retinoblastoma tumor. Furthermore, loss of function of the retinoblastoma tumor suppressor protein (pRB) is frequently found in most human cancers. In retinoblastoma, tumor progression is driven by epigenetic changes following pRB loss. This review focuses on the diverse functions of pRB in epigenetic regulation.

Abstract

Mutations that result in the loss of function of pRB were first identified in retinoblastoma and since then have been associated with the propagation of various forms of cancer. pRB is best known for its key role as a transcriptional regulator during cell cycle exit. Beyond the ability of pRB to regulate transcription of cell cycle progression genes, pRB can remodel chromatin to exert several of its other biological roles. In this review, we discuss the diverse functions of pRB in epigenetic regulation including nucleosome mobilization, histone modifications, DNA methylation and non-coding RNAs.

Upregulation of heme oxygenase-1 by Brahma-related gene 1 through Nrf2 signaling confers protective effect against high glucose-induced oxidative damage of retinal ganglion cells

High glucose (HG)-induced oxidative damage of retinal ganglion cells (RGCs) contributes to the pathogenesis of diabetic retinopathy, a severe complication of diabetes mellitus. Brahma-related gene 1 (Brg1) has currently emerged as a cytoprotective protein that alleviates oxidative damage induced by various stress. However, whether Brg1 is involved in the regulation of HG-induced oxidative damage of RGCs remains unknown. In this study, we aimed to investigate the potential role and underlying mechanism of Brg1 in regulating HG-induced damage of RGCs. We found that Brg1 expression was significantly downregulated in RGCs in response to HG treatment. Functional experiments showed that Brg1 knockdown enhanced HG-induced apoptosis and production of reactive oxygen species, while Brg1 overexpression suppressed HG-induced apoptosis and reactive oxygen species production, showing a protective effect. Moreover, Brg1 overexpression resulted in an increase in nuclear expression of nuclear factor-erythroid-2-related factor-2 (Nrf2) and the expression of heme oxygenase-1 (HO-1) in RGCs. Notably, inhibition of Nrf2 or HO-1 significantly blocked Brg1-mediated protection against HG-induced damage. Overall, these findings demonstrate that Brg1 protects RGCs from HG-induced oxidative damage through promotion of Nrf2/HO-1 signaling, indicating a potential role of Brg1 in the pathogenesis of diabetic retinopathy.

Deletion of Brg1 causes stereocilia bundle fusion and cuticular plate loss in vestibular hair cells

Brg1 is an ATPase subunit of the SWI/SNF chromatin-remodeling complex, and it is indispensable for the development and homeostasis of various organs. Conditional deletion of Brg1 in cochlea hair cells (HCs) leads to multiple structural defects and profound deafness. However, the premature death of Brg1-deficient cochlea HCs hindered further study of the role of Brg1. In contrast to cochlea HCs, Brg1-deficient vestibular HCs survived for a long time. Therefore, HC apical structure and vestibular function were examined in inner HC-specific conditional Brg1 knockout mice. Vestibular HCs exhibited fused and elongated stereocilia bundles after deletion of Brg1, and the cuticular plate was absent in most HCs with fused stereocilia bundles. HC loss was observed in conditional Brg1 knockout mice at the age of 12 months. Morphological defects and HC loss were primarily restricted in the striolar region of the utricle and saccule and in the central region of ampulla. The behavioral tests revealed that Brg1 deletion in HCs caused vestibular dysfunction in older adult mice. These results suggest that Brg1 may play specific roles in the maintenance of the HC stereocilia bundle and the cuticular plate.

Inhibition of EZH2 induces NK cell-mediated differentiation and death in muscle-invasive bladder cancer

Lysine-specific demethylase 6A (KDM6A) and members of the Switch/Sucrose Non-Fermentable (SWI/SNF) family are known to counteract the activity of Enhancer of Zeste Homolog 2 (EZH2), which is often overexpressed and is associated with poor prognosis in muscle-invasive bladder cancer. Here we provide evidence that alterations in chromatin modifying enzymes, including KDM6A and members of the SWI/SNF complex, are frequent in muscle-invasive bladder cancer. We exploit the loss of function mutations in KDM6A and SWI/SNF complex to make bladder cancer cells susceptible to EZH2-based epigenetic therapy that activates an immune response to drive tumor cell differentiation and death. We reveal a novel mechanism of action of EZH2 inhibition, alone and in combination with cisplatin, which induces immune signaling with the largest changes observed in interferon gamma (IFN-γ). This upregulation is a result of activated natural killer (NK) signaling as demonstrated by the increase in NK cell-associated genes MIP-1α, ICAM1, ICAM2, and CD86 in xenografts treated with EZH2 inhibitors. Conversely, EZH2 inhibition results in decreased expression of pluripotency markers, ALDH2 and CK5, and increased cell death. Our results reveal a novel sensitivity of muscle-invasive bladder cancer cells with KMD6A and SWI/SNF mutations to EZH2 inhibition alone and in combination with cisplatin. This sensitivity is mediated through increased NK cell-related signaling resulting in tumor cell differentiation and cell death.

Epigenetic control of gene regulation during development and disease: A view from the retina

Complex biological processes, such as organogenesis and homeostasis, are stringently regulated by genetic programs that are fine-tuned by epigenetic factors to establish cell fates and/or to respond to the microenvironment. Gene regulatory networks that guide cell differentiation and function are modulated and stabilized by modifications to DNA, RNA and proteins. In this review, we focus on two key epigenetic changes - DNA methylation and histone modifications - and discuss their contribution to retinal development, aging and disease, especially in the context of age-related macular degeneration (AMD) and diabetic retinopathy. We highlight less-studied roles of DNA methylation and provide the RNA expression profiles of epigenetic enzymes in human and mouse retina in comparison to other tissues. We also review computational tools and emergent technologies to profile, analyze and integrate epigenetic information. We suggest implementation of editing tools and single-cell technologies to trace and perturb the epigenome for delineating its role in transcriptional regulation. Finally, we present our thoughts on exciting avenues for exploring epigenome in retinal metabolism, disease modeling, and regeneration.

Structural changes of the macula and optic nerve head in the remaining eyes after enucleation for retinoblastoma: an optical coherence tomography study

BACKGROUND

To describe objectively the possible structural changes of the macula and optic nerve head in the free eyes of unilateral cured retinoblastoma patients and, also after enucleation using spectral domain optical coherence tomography.

METHODS

A cross sectional study involving 60 patients subdivided into three groups; 15 unilateral RB patients in whom enucleation was indicated as a sole treatment performed earlier in life [(study group (I)], 15 unilateral RB patients who had completely regressed disease with a preserved eye [(study group (II)] and 30 age and sex matched healthy controls. The remaining and free eyes in study groups and right eyes of control group had full ophthalmological examination, static automated perimetry and optical coherence tomography of the macula and optic nerve head.

RESULTS

In study group (II); a significant thinning of total macula, central fovea, ganglion cell layer (GCL), ganglion cell complex (GCC), and some sectors of outer nuclear layer (P- values ≤0.05) was found with no significant difference in peripapillary nerve fiber layer (pRNFL) thickness and optic nerve head parameters compared to the control group and the study group (I). A significantly thickened total macula, GCL, GCC, and pRNFL in study group (I) compared to study group (II). Thickened pRNFL was significantly correlated to standard automated perimetry pattern deviations. No significant difference was found between study group (I) and control group.

CONCLUSION

Retinoblastoma eyes characterized by thinning of central fovea, GCL, GCC compared to the control group. After unilateral enucleation, increased GCC and pRNFL thicknesses were detected compared to retinoblastoma group.

Polycomb repression complex 2 is required for the maintenance of retinal progenitor cells and balanced retinal differentiation

Polycomb repressive complexes maintain transcriptional repression of genes encoding crucial developmental regulators through chromatin modification. Here we investigated the role of Polycomb repressive complex 2 (PRC2) in retinal development by inactivating its key components Eed and Ezh2. Conditional deletion of Ezh2 resulted in a partial loss of PRC2 function and accelerated differentiation of Müller glial cells. In contrast, inactivation of Eed led to the ablation of PRC2 function at early postnatal stage. Cell proliferation was reduced and retinal progenitor cells were significantly decreased in this mutant, which subsequently caused depletion of Müller glia, bipolar, and rod photoreceptor cells, primarily generated from postnatal retinal progenitor cells. Interestingly, the proportion of amacrine cells was dramatically increased at postnatal stages in the Eed-deficient retina. In accordance, multiple transcription factors controlling amacrine cell differentiation were upregulated. Furthermore, ChIP-seq analysis showed that these deregulated genes contained bivalent chromatin (H3K27me3⁺ H3K4me3⁺). Our results suggest that PRC2 is required for proliferation in order to maintain the retinal progenitor cells at postnatal stages and for retinal differentiation by controlling amacrine cell generation.

Differential Expression of Sox11 and Bdnf mRNA Isoforms in the Injured and Regenerating Nervous Systems

In both the central nervous system (CNS) and the peripheral nervous system (PNS), axonal injury induces changes in neuronal gene expression. In the PNS, a relatively well-characterized alteration in transcriptional activation is known to promote axonal regeneration. This transcriptional cascade includes the neurotrophin Bdnf and the transcription factor Sox11. Although both molecules act to facilitate successful axon regeneration in the PNS, this process does not occur in the CNS. The present study examines the differential expression of Sox11 and Bdnf mRNA isoforms in the PNS and CNS using three experimental paradigms at different time points: (i) the acutely injured CNS (retina after optic nerve crush) and PNS (dorsal root ganglion after sciatic nerve crush), (ii) a CNS regeneration model (retina after optic nerve crush and induced regeneration); and (iii) the retina during a chronic form of central neurodegeneration (the DBA/2J glaucoma model). We find an initial increase of Sox11 in both PNS and CNS after injury; however, the expression of Bdnf isoforms is higher in the PNS relative to the CNS. Sustained upregulation of Sox11 is seen in the injured retina following regeneration treatment, while the expression of two Bdnf mRNA isoforms is suppressed. Furthermore, two isoforms of Sox11 with different 3′UTR lengths are present in the retina, and the long isoform is specifically upregulated in later stages of glaucoma. These results provide insight into the molecular cascades active during axonal injury and regeneration in mammalian neurons.

Samd7 is a cell type-specific PRC1 component essential for establishing retinal rod photoreceptor identity

Precise transcriptional regulation controlled by a transcription factor network is known to be crucial for establishing correct neuronal cell identities and functions in the CNS. In the retina, the expression of various cone and rod photoreceptor cell genes is regulated by multiple transcription factors; however, the role of epigenetic regulation in photoreceptor cell gene expression has been poorly understood. Here, we found that Samd7, a rod-enriched sterile alpha domain (SAM) domain protein, is essential for silencing nonrod gene expression through H3K27me3 regulation in rod photoreceptor cells. Samd7-null mutant mice showed ectopic expression of nonrod genes including S-opsin in rod photoreceptor cells and rod photoreceptor cell dysfunction. Samd7 physically interacts with Polyhomeotic homologs (Phc proteins), components of the Polycomb repressive complex 1 (PRC1), and colocalizes with Phc2 and Ring1B in Polycomb bodies. ChIP assays showed a significant decrease of H3K27me3 in the genes up-regulated in the Samd7-deficient retina, showing that Samd7 deficiency causes the derepression of nonrod gene expression in rod photoreceptor cells. The current study suggests that Samd7 is a cell type-specific PRC1 component epigenetically defining rod photoreceptor cell identity.

BANCR: a cancer-related long non-coding RNA

Long non-coding RNAs (lncRNAs) are a group of non-protein-coding RNAs with more than 200 nucleotides in length. lncRNAs are involved in diverse biological processes, including development, cell proliferation and differentiation. Emerging evidences also suggest that lncRNAs may participate in cancer development by functioning as tumor suppressors and oncogenes. BRAF-activated non-coding RNA (BANCR) was first identified as an oncogene in melanoma. Later studies demonstrated that BANCR was frequently deregulated in human cancers, including lung cancer, gastric cancer, colorectal cancer, thyroid cancer and osteosarcoma. Nevertheless, the direction of deregulation was tissue-specific in which BANCR could as an oncogene or tumor-suppressor gene. In this review, we compile current evidences concerning the functional roles and molecular mechanisms of BANCR in tumor development.

Brg1 chromatin remodeling ATPase balances germ layer patterning by amplifying the transcriptional burst at midblastula transition

Zygotic gene expression programs control cell differentiation in vertebrate development. In Xenopus, these programs are initiated by local induction of regulatory genes through maternal signaling activities in the wake of zygotic genome activation (ZGA) at the midblastula transition (MBT). These programs lay down the vertebrate body plan through gastrulation and neurulation, and are accompanied by massive changes in chromatin structure, which increasingly constrain cellular plasticity. Here we report on developmental functions for Brahma related gene 1 (Brg1), a key component of embyronic SWI/SNF chromatin remodeling complexes. Carefully controlled, global Brg1 protein depletion in X. tropicalis and X. laevis causes embryonic lethality or developmental arrest from gastrulation on. Transcriptome analysis at late blastula, before development becomes arrested, indicates predominantly a role for Brg1 in transcriptional activation of a limited set of genes involved in pattern specification processes and nervous system development. Mosaic analysis by targeted microinjection defines Brg1 as an essential amplifier of gene expression in dorsal (BCNE/Nieuwkoop Center) and ventral (BMP/Vent) signaling centers. Moreover, Brg1 is required and sufficient for initiating axial patterning in cooperation with maternal Wnt signaling. In search for a common denominator of Brg1 impact on development, we have quantitatively filtered global mRNA fluctuations at MBT. The results indicate that Brg1 is predominantly required for genes with the highest burst of transcriptional activity. Since this group contains many key developmental regulators, we propose Brg1 to be responsible for raising their expression above threshold levels in preparation for embryonic patterning.

Brahma-related-gene-1 (Brg1) is a catalytic subunit of mammalian SWI/SNF chromatin remodeling complexes. Loss of maternal Brg1 protein arrests development in mice at the 2-cell stage, while null homozygotes die at the blastocyst stage. These early requirements have precluded any analysis of Brg1’s embryonic functions. Here we present data from X. laevis and X. tropicalis, which for the first time describe a role for Brg1 during germ layer patterning and axis formation. Brg1-depleted embryos fail to develop past gastrulation. Genome-wide transcriptome analysis at late blastula stage, before the developmental arrest, shows that Brg1 is required predominantly for transcriptional activation of a limited set of genes involved in pattern specification processes and nervous system development shortly after midblastula transition. Mosaic analysis by targeted microinjection defines Brg1 as an essential amplifier of gene expression in dorsal (BCNE and Nieuwkoop center) and ventral (BMP/Vent) signaling centers, being required and sufficient to initiate axial patterning by cooperating with canonical Wnt signaling. Since Brg1-dependent genes share a high burst of transcriptional activation before gastrulation, we propose a systemic role for Brg1 as transcriptional amplifier, which balances the embryonic patterning process.

Loss of BRG1 induces CRC cell senescence by regulating p53/p21 pathway

Brahma-related gene-1 (BRG1) is the specific ATPase of switch/sucrose nonfermentable chromatin-remodeling complex that is aberrantly expressed or mutated in various cancers. However, the exact role of BRG1 in oncogenesis remains unknown. In this study, we demonstrate that the knockdown (KD) of BRG1 promotes cellular senescence by influencing the SIRT1/p53/p21 signal axis in colorectal cancer (CRC). In particular, we reveal that the expression level of BRG1 is inversely correlated with p21, one of the classic senescence regulators, and is decreased in senescent CRC cells. KD of BRG1 promoting senescence is indicated by the increase of senescence-associated β-galactosidase (SA-β-gal) activity, inhibition of cell proliferation, induction of cell cycle arrest, and formation of senescence-associated heterochromatin foci. BRG1 binds to SIRT1 and interferes with SIRT1-mediated deacetylation of p53 at K382. Rescue experiments by co-silencing p53 or treatment with EX527, a SIRT1-specific inhibitor, abrogated the cellular senescence induced by KD of BRG1. BRG1 KD cells resulted in smaller tumor formation than that in control cells in vivo. Collectively, our study shows that BRG1 has an important role in cellular senescence and tumor growth. The BRG1/SIRT1/p53 signal axis is a novel mechanism of cell senescence in CRC and is a new potential target for cancer therapy.

Epigenetic regulation of human retinoblastoma

Retinoblastoma is a rare type of eye cancer of the retina that commonly occurs in early childhood and mostly affects the children before the age of 5. It occurs due to the mutations in the retinoblastoma gene (RB1) which inactivates both alleles of the RB1. RB1 was first identified as a tumor suppressor gene, which regulates cell cycle components and associated with retinoblastoma. Previously, genetic alteration was known as the major cause of its occurrence, but later, it is revealed that besides genetic changes, epigenetic changes also play a significant role in the disease. Initiation and progression of retinoblastoma could be due to independent or combined genetic and epigenetic events. Remarkable work has been done in understanding retinoblastoma pathogenesis in terms of genetic alterations, but not much in the context of epigenetic modification. Epigenetic modifications that silence tumor suppressor genes and activate oncogenes include DNA methylation, chromatin remodeling, histone modification and noncoding RNA-mediated gene silencing. Epigenetic changes can lead to altered gene function and transform normal cell into tumor cells. This review focuses on important epigenetic alteration which occurs in retinoblastoma and its current state of knowledge. The critical role of epigenetic regulation in retinoblastoma is now an emerging area, and better understanding of epigenetic changes in retinoblastoma will open the door for future therapy and diagnosis.

Deletion of Brg1 causes abnormal hair cell planer polarity, hair cell anchorage, and scar formation in mouse cochlea

Hair cells (HCs) are mechanosensors that play crucial roles in perceiving sound, acceleration, and fluid motion. The precise architecture of the auditory epithelium and its repair after HC loss is indispensable to the function of organ of Corti (OC). In this study, we showed that Brg1 was highly expressed in auditory HCs. Specific deletion of Brg1 in postnatal HCs resulted in rapid HC degeneration and profound deafness in mice. Further experiments showed that cell-intrinsic polarity of HCs was abolished, docking of outer hair cells (OHCs) by Deiter’s cells (DCs) failed, and scar formation in the reticular lamina was deficient. We demonstrated that Brg1 ablation disrupted the Gαi/Insc/LGN and aPKC asymmetric distributions, without overt effects on the core planer cell polarity (PCP) pathway. We also demonstrated that Brg1-deficient HCs underwent apoptosis, and that leakage in the reticular lamina caused by deficient scar formation shifted the mode of OHC death from apoptosis to necrosis. Together, these data demonstrated a requirement for Brg1 activity in HC development and suggested a role for Brg1 in the proper cellular structure formation of HCs.