Department of Pediatrics.
Department of Human Genetics.
eNeuro. 2018 Apr 17;5(2). doi: 10.1523/ENEURO.0389-17.2018. eCollection 2018 Mar-Apr.
Axon guidance in vertebrates is controlled by genetic cascades as well as by intrinsic activity-dependent refinement of connections. Midline axon crossing is one of the best studied pathfinding models and is fundamental to the establishment of bilaterally symmetric nervous systems. However, it is not known whether crossing requires intrinsic activity in axons, and what controls that activity. Further, a mechanism linking neuronal activity and gene expression has not been identified for axon pathfinding. Using embryonic zebrafish, we found that the NMDA receptor (NMDAR) NR1.1 subunit () is expressed in commissural axons. Pharmacological inhibition of , hypoxia exposure reduction of expression, or CRISPR knock-down of leads to defects in midline crossing. Inhibition of neuronal activity phenocopies the effects of loss on midline crossing. By combining pharmacological inhibition of the NMDAR with optogenetic stimulation to precisely restore neuronal activity, we observed rescue of midline crossing. This suggests that the NMDAR controls pathfinding by an activity-dependent mechanism. We further show that the NMDAR may act, via modulating activity, on the transcription factor (mammalian ), a known regulator of midline pathfinding. These findings uncover a novel role for the NMDAR in controlling activity to regulate commissural pathfinding and identify as a key link between the genetic and activity-dependent regulation of midline axon guidance.
脊椎动物的轴突导向受遗传级联控制，也受连接的内在活性依赖性细化控制。中线轴突交叉是研究得最好的寻路模型之一，是建立双侧对称神经系统的基础。然而，尚不清楚交叉是否需要轴突中的内在活性，以及什么控制这种活性。此外，尚未确定将神经元活动与基因表达联系起来的机制用于轴突寻路。使用胚胎斑马鱼，我们发现 NMDA 受体 (NMDAR) NR1.1 亚基 () 在连合轴突中表达。药理学抑制 、缺氧暴露减少 表达或 CRISPR 敲低 导致中线交叉缺陷。神经元活性的抑制模拟了 损失对中线交叉的影响。通过将 NMDAR 的药理学抑制与光遗传学刺激相结合，精确地恢复神经元活性，我们观察到中线交叉的恢复。这表明 NMDAR 通过一种依赖活性的机制控制寻路。我们进一步表明，NMDAR 可能通过调节活性，作用于转录因子 （哺乳动物 ），这是中线寻路的已知调节剂。这些发现揭示了 NMDAR 在控制活动以调节连合轴突寻路中的新作用，并确定 作为遗传和活性依赖性中线轴突导向调节之间的关键联系。
