Neuroanatomy and Behaviour in Mice with a Haploinsufficiency of AT-Rich Interactive Domain 1B (ARID1B) Throughout Development

Background - One of the causal mechanisms underlying neurodevelopmental disorders (NDDs) is chromatin modification, and the genes that regulate chromatin. AT-Rich Interactive Domain 1B (ARID1B), a chromatin modifier, has been shown to be reduced in autism spectrum disorder (ASD) and to affect rare and inherited genetic variation in a broad set of NDDs. Methods - A novel preclinical mouse model of Arid1b deficiency was created and validated to characterize and define neuroanatomical, behavioural and tran¬scriptional phenotypes. Neuroanatomy was assessed ex vivo in adult animals and in vivo longitudinally from birth to adulthood. Behavioural testing was also performed throughout development and tested all aspects of motor, learning, sociability, repetitive behaviours, seizure susceptibility and general milestones delays. Results – We validated decreased Arid1b mRNA and protein in Arid1b+/- mice, with signatures of increased axonal and synaptic gene expression and decreased transcriptional regulator and RNA processing expression in adult Arid1b+/- cerebellum. During neonatal development, Arid1b+/- mice exhibited robust impairments in ultrasonic vocalizations (USVs) and metrics of developmental growth. In addition, a striking sex dependence was observed throughout development; males had an early emergence of this neuroanatomical phenotype at postnatal day 7, whereas females had a delayed emergence around postnatal day 40. Behaviourally, as adults, Arid1b+/- mice showed low motor skills in open field exploration and normal three chambered approach. Arid1b+/- mice had learning and memory deficits in novel object recognition but not in visual discrimination and reversal touchscreen tasks. Social interactions in the male-female social dyad with USVs revealed social deficits on some but not all parameters. No repetitive behaviours were observed. Brains of adult Arid1b+/- mice had a smaller cerebellum and a larger hippocampus and corpus callosum. These results stand in contrast to previously reported data highlighting losses in corpus callosum volume in mice. Limitations – The behaviour and neuroimaging analyses were done on separate cohorts of mice, which did not allow a direct correlation between the imaging and behavioural findings, and the transcriptomic analyses was exploratory, with no validation of altered expression beyond Arid1b. Conclusions – This study represents a full validation and investigation of a novel model of Arid1b+/- haploinsufficiency throughout development and highlights the importance of examining both sexes throughout development in NDDs. Characterization of differential gene expression changes with heterozygous Arid1b knockout.

背景——神经发育障碍（Neurodevelopmental Disorders, NDDs）的潜在致病机制之一为染色质修饰及其调控基因。富含AT相互作用结构域1B（AT-Rich Interactive Domain 1B, ARID1B）作为一种染色质修饰因子，已被证实于自闭症谱系障碍（Autism Spectrum Disorder, ASD）中表达下调，并可影响广泛神经发育障碍的罕见及遗传性遗传变异。
方法——本研究构建并验证了一种新型Arid1b缺陷临床前小鼠模型，以表征并明确其神经解剖学、行为学与转录组学表型。对成年小鼠的神经解剖结构进行离体评估，并对其从出生到成年的纵向在体神经解剖变化进行检测。同时在整个发育阶段开展行为学测试，涵盖运动能力、学习能力、社交能力、重复行为、癫痫易感性及整体发育里程碑延迟等所有维度。
结果——本研究证实Arid1b+/-小鼠的Arid1b mRNA与蛋白表达水平降低，成年Arid1b+/-小鼠小脑中可见轴突与突触相关基因表达上调，而转录调控因子及RNA加工相关基因表达下调的特征。在新生发育阶段，Arid1b+/-小鼠的超声发声（Ultrasonic Vocalizations, USVs）与发育生长指标均出现显著损伤。此外，整个发育过程中观察到显著的性别依赖性：雄性小鼠在出生后第7天即出现神经解剖学表型，而雌性小鼠则在出生后第40天左右才出现延迟的表型出现。行为学方面，成年Arid1b+/-小鼠在旷场探索中表现出运动能力低下，但在三箱社交实验中表现正常。Arid1b+/-小鼠在新物体识别任务中存在学习与记忆缺陷，但在视觉辨别与反转学习触屏任务中无此类缺陷。在雌雄配对社交互动实验中，结合超声发声检测结果显示，部分参数存在社交缺陷，但并非所有参数均受影响。未观察到重复行为。成年Arid1b+/-小鼠的大脑表现为小脑体积减小，而海马体与胼胝体体积增大，这一结果与此前报道的小鼠胼胝体体积丢失的研究数据相悖。
局限性——本研究的行为学与神经影像学分析分别在不同的小鼠队列中开展，无法直接关联影像学与行为学研究结果；且转录组学分析仅为探索性研究，除Arid1b外，未对其他差异表达基因的表达变化进行验证。
结论——本研究全面验证并探究了一种新型Arid1b+/-单倍剂量不足小鼠模型在整个发育阶段的表型，同时强调了在神经发育障碍研究中对雌雄两性进行全发育阶段分析的重要性。本研究还表征了Arid1b杂合敲除后的差异基因表达变化。