A mouse model of ATRX deficiency with cognitive deficits and autistic traits

BACKGROUND

ATRX is an ATP-dependent chromatin remodeling protein with essential roles in safeguarding genome integrity and modulating gene expression. Deficiencies in this protein cause ATR-X syndrome, a condition characterized by intellectual disability and an array of developmental abnormalities, including features of autism. Previous studies demonstrated that deleting ATRX in mouse forebrain excitatory neurons postnatally resulted in male-specific memory deficits, but no apparent autistic-like behaviours.

METHODS

We generated mice with an earlier embryonic deletion of ATRX in forebrain excitatory neurons and characterized their behaviour using a series of memory and autistic-related paradigms.

RESULTS

We found that mutant mice displayed a broader spectrum of impairments, including fear memory, decreased anxiety-like behaviour, hyperactivity, as well as self-injurious and repetitive grooming. Sex-specific alterations were also observed, including male-specific aggression, sensory gating impairments, and decreased social memory.

CONCLUSIONS

Collectively, the findings indicate that early developmental abnormalities arising from ATRX deficiency in forebrain excitatory neurons contribute to the presentation of fear memory deficits as well as autistic-like behaviours.

Effects of a postnatal Atrx conditional knockout in neurons on autism-like behaviours in male and female mice

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.

Inactivation of ATRX in forebrain excitatory neurons affects hippocampal synaptic plasticity

α-Thalassemia X-linked intellectual disability (ATR-X) syndrome is a neurodevelopmental disorder caused by mutations in the ATRX gene that encodes a SNF2-type chromatin-remodeling protein. The ATRX protein regulates chromatin structure and gene expression in the developing mouse brain and early inactivation leads to DNA replication stress, extensive cell death, and microcephaly. However, the outcome of Atrx loss of function postnatally in neurons is less well understood. We recently reported that conditional inactivation of Atrx in postnatal forebrain excitatory neurons (ATRX-cKO) causes deficits in long-term hippocampus-dependent spatial memory. Thus, we hypothesized that ATRX-cKO mice will display impaired hippocampal synaptic transmission and plasticity. In the present study, evoked field potentials and current source density analysis were recorded from a multichannel electrode in male, urethane-anesthetized mice. Three major excitatory synapses, the Schaffer collaterals to basal dendrites and proximal apical dendrites, and the temporoammonic path to distal apical dendrites on hippocampal CA1 pyramidal cells were assessed by their baseline synaptic transmission, including paired-pulse facilitation (PPF) at 50-ms interpulse interval, and by their long-term potentiation (LTP) induced by theta-frequency burst stimulation. Baseline single-pulse excitatory response at each synapse did not differ between ATRX-cKO and control mice, but baseline PPF was reduced at the CA1 basal dendritic synapse in ATRX-cKO mice. While basal dendritic LTP of the first-pulse excitatory response was not affected in ATRX-cKO mice, proximal and distal apical dendritic LTP were marginally and significantly reduced, respectively. These results suggest that ATRX is required in excitatory neurons of the forebrain to achieve normal hippocampal LTP and PPF at the CA1 apical and basal dendritic synapses, respectively. Such alterations in hippocampal synaptic transmission and plasticity could explain the long-term spatial memory deficits in ATRX-cKO mice and provide insight into the physiological mechanisms underlying intellectual disability in ATR-X syndrome patients.