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Background: Alpha-thalassemia/mental retardation, X-linked, or ATRX, is an autism susceptibility gene that encodes a chromatin remodeler. Mutations of ATRX result in the ATR-X intellectual disability syndrome and have been identified in autism spectrum disorder (ASD) patients. The mechanisms by which ATRX mutations lead to autism and autistic-like behaviours are not yet known. To address this question, we generated mice with postnatal Atrx inactivation in excitatory neurons of the forebrain and performed a battery of behavioural assays that assess autistic-like behaviours., Methods: Male and female mice with a postnatal conditional ablation of ATRX were generated using the Cre/lox system under the control of the αCaMKII gene promoter. These mice were tested in a battery of behavioural tests that assess autistic-like features. We utilized paradigms that measure social behaviour, repetitive, and stereotyped behaviours, as well as sensory gating. Statistics were calculated by two-way repeated measures ANOVA with Sidak's multiple comparison test or unpaired Student's t tests as indicated., Results: The behaviour tests revealed no significant differences between Atrx-cKO and control mice. We identified sexually dimorphic changes in odor habituation and discrimination; however, these changes did not correlate with social deficits., Conclusion: The postnatal knockout of Atrx in forebrain excitatory neurons does not lead to autism-related behaviours in male or female mice.

Background: Alpha thalassemia/mental retardation X-linked syndrome (ATR-X) is caused by a mutation at the chromatin regulator gene ATRX . The mechanisms involved in the ATR-X pathology are not completely understood, but may involve epigenetic modifications. ATRX has been linked to the regulation of histone H3 and DNA methylation, while mutations in the ATRX gene may lead to the downstream epigenetic and transcriptional effects. Elucidating the underlying epigenetic mechanisms altered in ATR-X will provide a better understanding about the pathobiology of this disease, as well as provide novel diagnostic biomarkers., Results: We performed genome-wide DNA methylation assessment of the peripheral blood samples from 18 patients with ATR-X and compared it to 210 controls. We demonstrated the evidence of a unique and highly specific DNA methylation "epi-signature" in the peripheral blood of ATRX patients, which was corroborated by targeted bisulfite sequencing experiments. Although genomically represented, differentially methylated regions showed evidence of preferential clustering in pericentromeric and telometric chromosomal regions, areas where ATRX has multiple functions related to maintenance of heterochromatin and genomic integrity., Conclusion: Most significant methylation changes in the 14 genomic loci provide a unique epigenetic signature for this syndrome that may be used as a highly sensitive and specific diagnostic biomarker to support the diagnosis of ATR-X, particularly in patients with phenotypic complexity and in patients with ATRX gene sequence variants of unknown significance.

ATRX is a chromatin remodeling protein involved in deposition of the histone variant H3.3 at telomeres and pericentromeric heterochromatin. It also influences the expression level of specific genes; however, deposition of H3.3 at transcribed genes is currently thought to occur independently of ATRX. We focused on a set of genes, including the autism susceptibility gene Neuroligin 4 (Nlgn4), that exhibit decreased expression in ATRX-null cells to investigate the mechanisms used by ATRX to promote gene transcription. Overall TERRA levels, as well as DNA methylation and histone modifications at ATRX target genes are not altered and thus cannot explain transcriptional dysregulation. We found that ATRX does not associate with the promoter of these genes, but rather binds within regions of the gene body corresponding to high H3.3 occupancy. These intragenic regions consist of guanine-rich DNA sequences predicted to form non-B DNA structures called G-quadruplexes during transcriptional elongation. We demonstrate that ATRX deficiency corresponds to reduced H3.3 incorporation and stalling of RNA polymerase II at these G-rich intragenic sites. These findings suggest that ATRX promotes the incorporation of histone H3.3 at particular transcribed genes and facilitates transcriptional elongation through G-rich sequences. The inability to transcribe genes such as Nlgn4 could cause deficits in neuronal connectivity and cognition associated with ATRX mutations in humans., (© The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

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.