Altered visual function and interneuron survival in Atrx knockout mice: inference for the human syndrome
ABSTRACT ATRX is an SWI/SNF-like chromatin remodeling protein that is mutated in several X-linked mental retardation syndromes, including the ATR-X syndrome. In mice, Atrx expression is widespread and attempts to understand its function in brain development are hampered by the lethality associated with ubiquitous or forebrain-restricted ablation of this gene. One way to circumvent this problem is to study its function in a region of the brain that is dispensable for long-term survival of the organism. The retina is a well-characterized tractable model of CNS development and in our review of 202 ATR-X syndrome patients, we found ocular defects present in approximately 25% of the cases, suggesting that studying Atrx in this tissue will provide insight into function. We report that Atrx is expressed in the neuroprogenitor pool in embryonic retina and in all cell types of the mature retina with the exception of rod photoreceptors. Conditional inactivation of Atrx in the retina during embryogenesis ultimately results in a loss of only two types of neurons, amacrine and horizontal cells. We show that this defect does not arise from a failure to specify these cells but rather a defect in interneuron differentiation and survival post-natally. The timing of cell loss is concomitant with light-dependent changes in synaptic organization in the retina and with a change in Atrx subnuclear localization within these interneurons. Moreover, these interneuron defects are associated with functional deficits as demonstrated by reduced b-wave amplitudes upon electroretinogram analysis. These results implicate a role for Atrx in interneuron survival and differentiation.
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ABSTRACT: Background: The transcription factor Rx1, also known as Rax, controls key properties of retinal precursors including migration behavior, proliferation and maintenance of multipotency. However, Rx1 effector genes are largely unknown. Results: To identify genes controlled by Rx1 in early retinal precursors, we compared the transcriptome of Xenopus embryos overexpressing Rx1 to that of embryos in which Rx1 was knocked-down. In particular, we selected 52 genes coherently regulated, i.e., actived in Rx1 gain of function and repressed in Rx1 loss of function experiments, or vice versa. RT-qPCR and in situ hybridization confirmed the trend of regulation predicted by microarray data for the selected genes. Most of the genes upregulated by Rx1 are coexpressed with this transcription factor, while downregulated genes are either not expressed or expressed at very low levels in the early developing retina. Putative direct Rx1 target genes, activated by GR-Rx1 in the absence of protein synthesis, include Ephrin B1 and Sh2d3c, an interactor of ephrinB1 receptor, which represent candidate novel effectors for the migration promoting activity of Rx1. Conclusions: This study identifies previously undescribed Rx1 regulated genes mainly involved in transcription regulation, cell migration/adhesion and cell proliferation that contribute to delineate the molecular mechanisms underlying Rx1 activities. Developmental Dynamics, 2014. © 2014 Wiley Periodicals, Inc.Developmental Dynamics 10/2014; 243(10). DOI:10.1002/dvdy.24145 · 2.67 Impact Factor
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ABSTRACT: The regulation of genome architecture is essential for a variety of fundamental cellular phenomena that underlie the complex orchestration of mammalian development. The ATP-dependent chromatin remodeling protein ATRX is emerging as a key regulatory component of nucleosomal dynamics and higher order chromatin conformation. Here we provide an overview of the role of ATRX at chromatin and during development, and discuss recent studies exposing a repertoire of ATRX functions at heterochromatin, in gene regulation, and during mitosis and meiosis. Exciting new progress on several fronts suggest that ATRX operates in histone variant deposition and in the modulation of higher order chromatin structure. Not surprisingly, dysfunction or absence of ATRX protein has devastating consequences on embryonic development and leads to human disease.Biochemistry and Cell Biology 08/2011; 89(5):435-44. DOI:10.1139/o11-038 · 2.35 Impact Factor
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ABSTRACT: The rapidly emerging science of epigenetics and epigenomic medicine promises to reveal novel insights into the susceptibility to and the onset and progression of epileptic disorders. Epigenetic regulatory mechanisms are now implicated in orchestrating aspects of neural development (e.g., cell fate specification and maturation), homeostasis and stress responses (e.g., immediate early gene transcription), and neural network function (e.g., excitation-inhibition coupling and activity-dependent plasticity). These same neurobiological processes are responsible for determining the heterogeneous features of complex epileptic disease states. Thus, we highlight recent evidence that is beginning to elucidate the specific roles played by epigenetic mechanisms, including DNA methylation, histone code modifications and chromatin remodeling, noncoding RNAs and RNA editing, in human epilepsy syndromes and in the process of epileptogenesis. The highly integrated layers of the epigenome are responsible for the cell type specific and exquisitely environmentally responsive deployment of genes and functional gene networks that underlie the molecular pathophysiology of epilepsy and its associated comorbidities, including but not limited to neurotransmitter receptors (e.g., GluR2, GLRA2, and GLRA3), growth factors (e.g., BDNF), extracellular matrix proteins (e.g., RELN), and diverse transcriptional regulators (e.g., CREB, c-fos, and c-jun). These important observations suggest that future epigenetic studies are necessary to better understand, classify, prevent, and treat epileptic disorders.Neurobiology of Disease 02/2010; 39(1):53-60. DOI:10.1016/j.nbd.2010.02.005 · 5.20 Impact Factor