Department of Neuroscience, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
The Children's Hospital of Philadelphia, Division of Protective Immunity, 3615 Civic Center Boulevard, Philadelphia, PA 19104, USA; Department of Pathology and Laboratory Medicine, Perelman School of Medicine, University of Pennsylvania, 3400 Civic Center Boulevard, Building 421, Philadelphia, PA 19104, USA.
Cell Rep. 2019 Mar 19;26(12):3298-3312.e4. doi: 10.1016/j.celrep.2019.02.080.
Commissural axons initially respond to attractive signals at the midline, but once they cross, they become sensitive to repulsive cues. This switch prevents axons from re-entering the midline. In insects and mammals, negative regulation of Roundabout (Robo) receptors prevents premature response to the midline repellant Slit. In Drosophila, the endosomal protein Commissureless (Comm) prevents Robo1 surface expression before midline crossing by diverting Robo1 into late endosomes. Notably, Comm is not conserved in vertebrates. We identified two Nedd-4-interacting proteins, Ndfip1 and Ndfip2, that act analogously to Comm to localize Robo1 to endosomes. Ndfip proteins recruit Nedd4 E3 ubiquitin ligases to promote Robo1 ubiquitylation and degradation. Ndfip proteins are expressed in commissural axons in the developing spinal cord and removal of Ndfip proteins results in increased Robo1 expression and reduced midline crossing. Our results define a conserved Robo1 intracellular sorting mechanism between flies and mammals to avoid premature responsiveness to Slit.
连合纤维轴突最初对中线的吸引信号作出反应，但一旦它们穿过中线，就会对排斥信号敏感。这种转变阻止了轴突重新进入中线。在昆虫和哺乳动物中，Roundabout（Robo）受体的负调控可防止其过早对中线排斥物 Slit 作出反应。在果蝇中，内体蛋白 Commissureless（Comm）在中线交叉之前通过将 Robo1 转移到晚期内体中来防止 Robo1 表面表达。值得注意的是，Comm 在脊椎动物中并不保守。我们鉴定了两个与 Comm 类似的 Nedd-4 相互作用蛋白，Ndfip1 和 Ndfip2，它们将 Robo1 定位到内体中。Ndfip 蛋白募集 Nedd4 E3 泛素连接酶来促进 Robo1 的泛素化和降解。Ndfip 蛋白在发育中的脊髓中的连合纤维轴突中表达，去除 Ndfip 蛋白会导致 Robo1 表达增加和中线穿越减少。我们的结果定义了一个在苍蝇和哺乳动物之间保守的 Robo1 细胞内分拣机制，以避免对 Slit 的过早反应。
