Department of Molecular Neurobiology, Max Planck Institute of Neurobiology, Am Klopferspitz 18, 82152 Martinsried, Germany.
J Neurosci. 2012 Apr 11;32(15):5209-15. doi: 10.1523/JNEUROSCI.5707-11.2012.
Repulsive Eph forward signaling from limb-derived ephrins guides the axons of lateral motor column (LMC) motor neurons. LMC axons also express ephrinAs, while their EphA receptors are expressed in the limb mesenchyme. In vitro studies have suggested that reverse signaling from limb-derived EphA4 to axonal ephrinAs might result in attraction of LMC axons. However, genetic evidence for this function is lacking. Here we use the Dunn chamber turning assay to show that EphA proteins are chemoattractants and elicit fast turning responses in LMC neurons in vitro. Moreover, ectopic expression of EphA4 in chick hindlimb changes the limb trajectory of LMC axons. Nervous system-specific deletion of EphA4 in mice resulted in fewer LMC axon projection errors than the ubiquitous deletion of EphA4. Additionally, a signaling-incompetent EphA4 mutant partially rescued guidance errors in the hindlimb, suggesting that limb-derived EphA4 contributes to the establishment of LMC projections. In summary, we provide evidence for a role of EphA:ephrinA attractive reverse signaling in motor axon guidance and in vivo evidence of in-parallel forward Eph and reverse ephrin signaling function in the same neuronal population.
排斥性 Eph 向前信号从肢体衍生的 Ephrins 引导侧向运动柱 (LMC) 运动神经元的轴突。LMC 轴突也表达 EphrinAs，而它们的 EphA 受体则在肢体间质中表达。体外研究表明，来自肢体衍生的 EphA4 到轴突 EphrinAs 的反向信号可能导致 LMC 轴突的吸引。然而，这种功能的遗传证据是缺乏的。在这里，我们使用 Dunn 室转弯测定法表明 EphA 蛋白是趋化因子，在体外引起 LMC 神经元的快速转弯反应。此外，EphA4 在鸡后肢中的异位表达改变了 LMC 轴突的肢体轨迹。在小鼠中特异性地删除 EphA4 会导致较少的 LMC 轴突投射错误，而 EphA4 的普遍缺失则会导致更多的错误。此外，信号缺陷 EphA4 突变体能部分挽救后肢中的引导错误，表明肢体衍生的 EphA4 有助于建立 LMC 投射。总之，我们提供了 EphA:ephrinA 吸引性反向信号在运动轴突导向中的作用的证据，并提供了 Eph 和反向 Ephrin 信号在同一神经元群体中平行作用的体内证据。
