Dosage-dependent phenotypes in models of 16p11.2 lesions found in autism

Recurrent Copy Number Variations (CNVs) of human 16p11.2 have been associated with a variety of developmental/neurocognitive syndromes. In particular, deletion of 16p11.2 is found in patients with autism, developmental delay, and obesity. Patients with deletions or duplications have a wide range of clinical features, and siblings carrying the same deletion often have diverse symptoms. To study the consequence of 16p11.2 CNVs in a systematic manner, we used chromosome engineering to generate mice harboring deletion of the chromosomal region corresponding to 16p11.2, as well as mice harboring the reciprocal duplication. These 16p11.2 CNV models have dosage-dependent changes in gene expression, viability, brain architecture, and behavior. For each phenotype, the consequence of the deletion is more severe than that of the duplication. Of particular note is that half of the 16p11.2 deletion mice die postnatally; those that survive to adulthood are healthy and fertile, but have alterations in the hypothalamus and exhibit a ‘behavior trap’ phenotype—a specific behavior characteristic of rodents with lateral hypothalamic and nigrostriatal lesions. Our findings indicate that 16p11.2 CNVs cause both brain and behavioral anomalies, providing new insight into human neurodevelopmental disorders. We analyzed gene expression profiles in the brain and determined whether expression corresponded with gene dosage. We measured mRNA intensities in 37 microarray hybridizations representing four brain regions (olfactory bulbs, cortex, cerebellum and brain stem; 5 samples were hybridized twice for estimation of technical errors) in two df/+ mice heterozyous for the deletion of the chromosomal region syntenic to human 16p11.2, three +/+ (wild type) mice and three dp/+ mice heterozyous for the duplication of the chromosomal region syntenic to human 16p11.2. All mice were F1 C57BL/6N: 129Sv hybrid males; therefore, other than the engineered CNV, their genomes were identical.

人类16p11.2区域的复发性拷贝数变异（Recurrent Copy Number Variations, CNVs）已被证实与多种发育/神经认知综合征密切相关。其中，16p11.2区域缺失常见于自闭症、发育迟缓及肥胖症患者。携带该区域缺失或重复的患者临床表现具有显著异质性，即便为携带同一缺失的同胞兄妹，其临床症状也往往存在明显差异。为系统探究16p11.2 CNVs的致病效应，本研究通过染色体工程技术构建了携带对应人类16p11.2区域缺失的小鼠模型，以及携带该区域反向重复的小鼠模型。上述16p11.2 CNV小鼠模型在基因表达水平、生存能力、脑组织结构及行为学特征上均呈现剂量依赖性改变，且缺失型模型的表型严重程度显著高于重复型模型。尤为值得关注的是，半数16p11.2缺失型小鼠于出生后死亡；存活至成年的个体虽健康且可育，但下丘脑结构存在异常，并表现出“行为陷阱（behavior trap）”表型——该行为特征与下丘脑外侧及黑质纹状体损伤的啮齿类动物高度一致。本研究结果表明，16p11.2 CNVs可同时引发脑结构与行为学异常，为人类神经发育障碍的发病机制研究提供了全新视角。我们对小鼠脑组织的基因表达谱进行了系统分析，以验证基因表达水平是否与基因剂量呈对应关系。本次研究共完成37次微阵列杂交实验，检测了与人类16p11.2区域同线（syntenic）的16p11.2缺失杂合（df/+）小鼠（2只，其中5个样本进行了两次杂交以评估技术误差）、野生型（wild type, +/+）小鼠（3只）以及16p11.2重复杂合（dp/+）小鼠（3只）的四个脑区——嗅球、皮层、小脑及脑干的mRNA表达强度。所有受试小鼠均为F1代C57BL/6N:129Sv杂交雄性个体，除经工程改造的CNV区域外，其基因组背景完全一致。