PDF(Pubmed)
Abstract：
In both vertebrates and invertebrates, commissural neurons prevent premature responsiveness to the midline repellant Slit by downregulating surface levels of its receptor Roundabout1 (Robo1). In Drosophila, Commissureless (Comm) plays a critical role in this process; however, there is conflicting data on the underlying molecular mechanism. Here, we demonstrate that the conserved PY motifs in the cytoplasmic domain of Comm are required allow the ubiquitination and lysosomal degradation of Robo1. Disruption of these motifs prevents Comm from localizing to Lamp1 positive late endosomes and to promote axon growth across the midline in vivo. In addition, we conclusively demonstrate a role for Nedd4 in midline crossing. Genetic analysis shows that nedd4 mutations result in midline crossing defects in the Drosophila embryonic nerve cord, which can be rescued by introduction of exogenous Nedd4. Biochemical evidence shows that Nedd4 incorporates into a three-member complex with Comm and Robo in a PY motif-dependent manner. Finally, we present genetic evidence that Nedd4 acts with Comm in the embryonic nerve cord to downregulate Robo1 levels. Taken together, these findings demonstrate that Comm promotes midline crossing in the nerve cord by facilitating Robo ubiquitination by Nedd4, ultimately leading to its degradation.
摘要：
在脊椎动物和无脊椎动物中，连合神经元通过下调其受体Roundabout1（Robo1）的表面水平来防止对中线排斥剂Slit的过早反应。在果蝇中,无委托(Comm)在这一过程中发挥着关键作用；然而，关于潜在的分子机制有相互矛盾的数据。这里,我们证明Comm的细胞质结构域中保守的PY基序是允许Robo1的泛素化和溶酶体降解所必需的。这些基序的破坏阻止了Comm定位到Lamp1阳性晚期内体，并促进了体内中线的轴突生长。此外,我们最终证明了Nedd4在中线穿越中的作用。遗传分析表明，nedd4突变导致果蝇胚胎神经索中线交叉缺陷，可以通过引入外源Nedd4来拯救。生化证据表明，Nedd4以依赖PY基序的方式与Comm和Robo结合为三成员复合物。最后,我们提供了遗传证据，表明Nedd4在胚胎神经索中与Comm一起作用以下调Robo1水平。一起来看,这些发现表明，Comm通过促进Nedd4的Robo泛素化来促进神经索的中线穿越，最终导致其降解。
