Brain Health Research Centre, Department of Anatomy, University of Otago, Dunedin, New Zealand.
Department of Pathology, University of Otago, Dunedin, New Zealand.
Sci Rep. 2017 Jan 6;7:39823. doi: 10.1038/srep39823.
Mutations in RAD51 have recently been linked to human Congenital Mirror Movements (CMM), a developmental disorder of the motor system. The only gene previously linked to CMM encodes the Netrin-1 receptor DCC, which is important for formation of corticospinal and callosal axon tracts. Thus, we hypothesised that Rad51 has a novel role in Netrin-1-mediated axon development. In mouse primary motor cortex neurons, Rad51 protein was redistributed distally down the axon in response to Netrin-1, further suggesting a functional link between the two. We next manipulated Rad51 expression, and assessed Netrin-1 responsiveness. Rad51 siRNA knockdown exaggerated Netrin-1-mediated neurite branching and filopodia formation. RAD51 overexpression inhibited these responses, whereas overexpression of the CMM-linked R250Q mutation, a predicted loss-of-function, had no effect. Thus, Rad51 appears to negatively regulate Netrin-1 signalling. Finally, we examined whether Rad51 might operate by modulating the expression of the Unc5 family, known negative regulators of Netrin-1-responsiveness. Unc5b and Unc5c transcripts were downregulated in response to Rad51 knockdown, and upregulated with RAD51 overexpression, but not R250Q. Thus, Rad51 negatively regulates Netrin-1 signalling, at least in part, by modulating the expression of Unc5s. Imbalance of positive and negative influences is likely to lead to aberrant motor system development resulting in CMMs.
RAD51 突变最近与人类先天性镜像运动（CMM）有关，CMM 是一种运动系统的发育障碍。之前与 CMM 相关的唯一基因编码 Netrin-1 受体 DCC，它对皮质脊髓和胼胝体轴突束的形成很重要。因此，我们假设 Rad51 在 Netrin-1 介导的轴突发育中有一个新的作用。在小鼠原代运动皮层神经元中，Rad51 蛋白在 Netrin-1 的作用下重新分布到轴突的远端，这进一步表明两者之间存在功能联系。接下来，我们操纵 Rad51 的表达，并评估 Netrin-1 的反应性。Rad51 siRNA 敲低使 Netrin-1 介导的神经突分支和丝状伪足形成加剧。RAD51 过表达抑制了这些反应，而与 CMM 相关的 R250Q 突变（预测的功能丧失）的过表达则没有影响。因此，Rad51 似乎负调控 Netrin-1 信号。最后，我们研究了 Rad51 是否可以通过调节已知的 Netrin-1 反应性负调控因子 Unc5 家族的表达来发挥作用。Rad51 敲低后，Unc5b 和 Unc5c 转录本下调，RAD51 过表达后上调，但 R250Q 没有作用。因此，Rad51 通过调节 Unc5s 的表达来负调控 Netrin-1 信号，至少部分如此。正、负影响的失衡可能导致运动系统发育异常，从而导致 CMM。
