Postsynaptic FMRP Regulates Synaptogenesis In Vivo in the Developing Cochlear Nucleus
Postsynaptic FMRP Regulates Synaptogenesis In Vivo in the Developing Cochlear Nucleus
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DOI：
10.1523/jneurosci.0665-18.2018
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发表时间：
2018-07-18
影响因子：
5.3
通讯作者：
Wang, Yuan
中科院分区：
文献类型：
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作者：
Wang, Xiaoyu;Zorio, Diego A. R.;Wang, Yuan
脆性 X 智力低下蛋白（FMRP；由 Fmr1 基因编码）的整体缺失会导致感觉功能障碍和智力障碍。这些表型的一种潜在机制是突触的结构和功能缺陷。在这里，我们确定了突触后 FMRP 在电路形成、突触发生和突触成熟中的自主功能。在正常耳蜗核中，突触前听觉轴突在突触后丛状神经元的细胞体上形成大的轴体端球突触。药物诱导的 Fmr1-shRNA 构建体的卵内电穿孔在鸡（无论性别）浓密神经元中产生 FMRP 表达嵌合，导致转染神经元中 FMRP 水平降低，但邻近未转染神经元中的 FMRP 水平不降低。结构分析表明，突触后 FMRP 减少导致个体突触前终球在早期和晚期发育阶段尺寸更小且形态异常。我们进一步研究了 FMRP 减少是否会影响树突发育，作为缺陷终球形成的潜在机制。通常，鸡的浓密神经元在早期阶段会生长出广泛的树突，并在终球开始形成时缩回这些树突。转染 Fmr1 shRNA 的神经元在分支收缩方面表现出显着的延迟，无法为大终球的及时形成和生长提供必要的体细胞表面。膜片钳记录验证了树突和突触缺陷对神经传递的功能影响，显示自发和诱发 EPSC 的振幅更小，动力学更慢。总之，这些数据表明，体细胞树突形态的及时成熟需要适当水平的突触后 FMRP，其延迟可能会影响突触发生，从而导致兴奋性突触的长期缺陷。
A global loss of the fragile X mental retardation protein (FMRP; encoded by the Fmr1 gene) leads to sensory dysfunction and intellectual disabilities. One underlying mechanism of these phenotypes is structural and functional deficits in synapses. Here, we determined the autonomous function of postsynaptic FMRP in circuit formation, synaptogenesis, and synaptic maturation. In normal cochlea nucleus, presynaptic auditory axons form large axosomatic endbulb synapses on cell bodies of postsynaptic bushy neurons. In ovo electroporation of drug-inducible Fmr1-shRNA constructs produced a mosaicism of FMRP expression in chicken (either sex) bushy neurons, leading to reduced FMRP levels in transfected, but not neighboring nontransfected, neurons. Structural analyses revealed that postsynaptic FMRP reduction led to smaller size and abnormal morphology of individual presynaptic endbulbs at both early and later developmental stages. We further examined whether FMRP reduction affects dendritic development, as a potential mechanism underlying defective endbulb formation. Normally, chicken bushy neurons grow extensive dendrites at early stages and retract these dendrites when endbulbs begin to form. Neurons transfected with Fmr1 shRNA exhibited a remarkable delay in branch retraction, failing to provide necessary somatic surface for timely formation and growth of large endbulbs. Patch-clamp recording verified functional consequences of dendritic and synaptic deficits on neurotransmission, showing smaller amplitudes and slower kinetics of spontaneous and evoked EPSCs. Together, these data demonstrate that proper levels of postsynaptic FMRP are required for timely maturation of somatodendritic morphology, a delay of which may affect synaptogenesis and thus contribute to long-lasting deficits of excitatory synapses.