Department of Microbiology and Physiological Systems and Program in Neuroscience, University of Massachusetts Medical School, Worcester, Massachusetts 01655, USA.
J Neurosci. 2013 Feb 13;33(7):2860-72. doi: 10.1523/JNEUROSCI.3533-12.2013.
Dendrite and synapse development are critical for establishing appropriate neuronal circuits, and disrupted timing of these events can alter neural connectivity. Using microarrays, we have identified a nuclear factor I (NFI)-regulated temporal switch program linked to dendrite formation in developing mouse cerebellar granule neurons (CGNs). NFI function was required for upregulation of many synapse-related genes as well as downregulation of genes expressed in immature CGNs. Chromatin immunoprecipitation analysis revealed that a central feature of this program was temporally regulated NFI occupancy of late-expressed gene promoters. Developing CGNs undergo a hyperpolarizing shift in membrane potential, and depolarization inhibits their dendritic and synaptic maturation via activation of calcineurin (CaN) (Okazawa et al., 2009). Maintaining immature CGNs in a depolarized state blocked NFI temporal occupancy of late-expressed genes and the NFI switch program via activation of the CaN/nuclear factor of activated T-cells, cytoplasmic (NFATc) pathway and promotion of late-gene occupancy by NFATc4, and these mechanisms inhibited dendritogenesis. Conversely, inhibition of the CaN/NFATc pathway in CGNs maturing under physiological nondepolarizing conditions upregulated the NFI switch program, NFI temporal occupancy, and dendrite formation. NFATc4 occupied the promoters of late-expressed NFI program genes in immature mouse cerebellum, and its binding was temporally downregulated with development. Further, NFI temporal binding and switch gene expression were upregulated in the developing cerebellum of Nfatc4 (-/-) mice. These findings define a novel NFI switch and temporal occupancy program that forms a critical link between membrane potential/CaN and dendritic maturation in CGNs. CaN inhibits the program and NFI occupancy in immature CGNs by promoting NFATc4 binding to late-expressed genes. As maturing CGNs become more hyperpolarized, NFATc4 binding declines leading to onset of NFI temporal binding and the NFI switch program.
树突和突触的发育对于建立适当的神经元回路至关重要，而这些事件的时间安排不当会改变神经连接。我们使用微阵列技术，确定了一个与发育中的小鼠小脑颗粒神经元（CGN）的树突形成相关的核因子 I（NFI）调控的时间开关程序。NFI 的功能对于上调许多与突触相关的基因以及下调不成熟 CGN 中表达的基因是必需的。染色质免疫沉淀分析显示，该程序的一个核心特征是晚期表达基因启动子的 NFI 占据的时间调节。发育中的 CGN 经历膜电位的超极化偏移，去极化通过激活钙调神经磷酸酶（CaN）抑制其树突和突触成熟（Okazawa 等人，2009 年）。通过激活 CaN/活化 T 细胞核因子，细胞质（NFATc）途径并促进 NFATc4 对晚期基因的占据，将不成熟的 CGN 维持在去极化状态会阻止 NFI 对晚期表达基因的时间占据和 NFI 开关程序，这些机制抑制了树突发生。相反，在生理非去极化条件下成熟的 CGN 中抑制 CaN/NFATc 途径会上调 NFI 开关程序、NFI 时间占据和树突形成。NFATc4 占据不成熟小鼠小脑晚期表达 NFI 程序基因的启动子，其结合随发育而时间下调。此外，在 Nfatc4（-/-）小鼠发育的小脑中有更多的 NFI 时间结合和开关基因表达上调。这些发现定义了一个新的 NFI 开关和时间占据程序，它在 CGN 中的膜电位/CaN 和树突成熟之间形成了一个关键联系。CaN 通过促进 NFATc4 与晚期表达基因的结合来抑制不成熟 CGN 中的该程序和 NFI 占据。随着成熟 CGN 变得更加超极化，NFATc4 结合下降，导致 NFI 时间结合和 NFI 开关程序的开始。
