Adnani Lata, Langevin Lisa Marie, Gautier Elodie, Dixit Rajiv, Parsons Kari, Li Saiqun, Kaushik Gaurav, Wilkinson Grey, Wilson Richard, Childs Sarah, Nguyen Minh Dang, Journot Laurent, Dehay Colette, Schuurmans Carol
Departments of Biochemistry and Molecular Biology, Alberta Children's Hospital Research Institute, Hotchkiss Brain Institute, University of Calgary, Calgary, Alberta, Canada, T2N 4N1.
Institute of Functional Genomics, F-34094 Montpellier, France, and.
J Neurosci. 2015 Sep 30;35(39):13430-47. doi: 10.1523/JNEUROSCI.0777-15.2015.
Imprinted genes are dosage sensitive, and their dysregulated expression is linked to disorders of growth and proliferation, including fetal and postnatal growth restriction. Common sequelae of growth disorders include neurodevelopmental defects, some of which are indirectly related to placental insufficiency. However, several growth-associated imprinted genes are also expressed in the embryonic CNS, in which their aberrant expression may more directly affect neurodevelopment. To test whether growth-associated genes influence neural lineage progression, we focused on the maternally imprinted gene Zac1. In humans, either loss or gain of ZAC1 expression is associated with reduced growth rates and intellectual disability. To test whether increased Zac1 expression directly perturbs neurodevelopment, we misexpressed Zac1 in murine neocortical progenitors. The effects were striking: Zac1 delayed the transition of apical radial glial cells to basal intermediate neuronal progenitors and postponed their subsequent differentiation into neurons. Zac1 misexpression also blocked neuronal migration, with Zac1-overexpressing neurons pausing more frequently and forming fewer neurite branches during the period when locomoting neurons undergo dynamic morphological transitions. Similar, albeit less striking, neuronal migration and morphological defects were observed on Zac1 knockdown, indicating that Zac1 levels must be regulated precisely. Finally, Zac1 controlled neuronal migration by regulating Pac1 transcription, a receptor for the neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP). Pac1 and Zac1 loss- and gain-of-function presented as phenocopies, and overexpression of Pac1 rescued the Zac1 knockdown neuronal migration phenotype. Thus, dysregulated Zac1 expression has striking consequences on neocortical development, suggesting that misexpression of this transcription factor in the brain in certain growth disorders may contribute to neurocognitive deficits. Significance statement: Altered expression of imprinted genes is linked to cognitive dysfunction and neuropsychological disorders, such as Angelman and Prader-Willi syndromes, and autism spectrum disorder. Mouse models have also revealed the importance of imprinting for brain development, with chimeras generated with parthenogenetic (two maternal chromosomes) or androgenetic (two paternal chromosomes) cells displaying altered brain sizes and cellular defects. Despite these striking phenotypes, only a handful of imprinted genes are known or suspected to regulate brain development (e.g., Dlk1, Peg3, Ube3a, necdin, and Grb10). Herein we show that the maternally imprinted gene Zac1 is a critical regulator of neocortical development. Our studies are relevant because loss of 6q24 maternal imprinting in humans results in elevated ZAC1 expression, which has been associated with neurocognitive defects.
印记基因对剂量敏感，其表达失调与生长和增殖紊乱有关，包括胎儿期和出生后的生长受限。生长紊乱的常见后遗症包括神经发育缺陷，其中一些与胎盘功能不全间接相关。然而，一些与生长相关的印记基因也在胚胎中枢神经系统中表达，其异常表达可能更直接地影响神经发育。为了测试与生长相关的基因是否影响神经谱系的进展，我们重点研究了母系印记基因Zac1。在人类中，ZAC1表达的缺失或增加均与生长速率降低和智力残疾有关。为了测试Zac1表达增加是否直接扰乱神经发育，我们在小鼠新皮质祖细胞中错误表达了Zac1。结果令人震惊：Zac1延迟了顶端放射状胶质细胞向基底中间神经元祖细胞的转变，并推迟了它们随后向神经元的分化。Zac1的错误表达还阻碍了神经元迁移，在运动神经元经历动态形态转变的时期，过表达Zac1的神经元更频繁地停顿，形成的神经突分支更少。在敲低Zac1时也观察到了类似但不太明显的神经元迁移和形态缺陷，这表明必须精确调节Zac1的水平。最后，Zac1通过调节Pac1转录来控制神经元迁移，Pac1是神经肽垂体腺苷酸环化酶激活多肽（PACAP）的受体。Pac1和Zac1功能的缺失和获得呈现为表型模拟，Pac1的过表达挽救了敲低Zac1后的神经元迁移表型。因此，Zac1表达失调对新皮质发育有显著影响，这表明在某些生长紊乱中该转录因子在大脑中的错误表达可能导致神经认知缺陷。重要性声明：印记基因表达的改变与认知功能障碍和神经心理疾病有关，如天使综合征和普拉德-威利综合征，以及自闭症谱系障碍。小鼠模型也揭示了印记对大脑发育的重要性，用孤雌生殖（两条母源染色体）或雄核发育（两条父源染色体）细胞产生的嵌合体显示出大脑大小改变和细胞缺陷。尽管有这些显著的表型，但已知或怀疑只有少数印记基因调节大脑发育（例如，Dlk1、Peg3、Ube3a、necdin和Grb10）。在此我们表明，母系印记基因Zac1是新皮质发育的关键调节因子。我们的研究具有相关性，因为人类6q24母系印记的缺失会导致ZAC1表达升高，这与神经认知缺陷有关。
