Krembil Research Institute, Vision Division, Krembil Discovery Tower, Toronto, Ontario, Canada.
Department of Physiology, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada.
Nat Chem Biol. 2019 Nov;15(11):1035-1042. doi: 10.1038/s41589-019-0345-z. Epub 2019 Aug 26.
Until recently, the existence of extracellular kinase activity was questioned. Many proteins of the central nervous system are targeted, but it remains unknown whether, or how, extracellular phosphorylation influences brain development. Here we show that the tyrosine kinase vertebrate lonesome kinase (VLK), which is secreted by projecting retinal ganglion cells, phosphorylates the extracellular protein repulsive guidance molecule b (RGMb) in a dorsal-ventral descending gradient. Silencing of VLK or RGMb causes aberrant axonal branching and severe axon misguidance in the chick optic tectum. Mice harboring RGMb with a point mutation in the phosphorylation site also display aberrant axonal pathfinding. Mechanistic analyses show that VLK-mediated RGMb phosphorylation modulates Wnt3a activity by regulating LRP5 protein gradients. Thus, the secretion of VLK by projecting neurons provides crucial signals for the accurate formation of nervous system circuitry. The dramatic effect of VLK on RGMb and Wnt3a signaling implies that extracellular phosphorylation likely has broad and profound effects on brain development, function and disease.
直到最近，细胞外激酶活性的存在还受到质疑。许多中枢神经系统的蛋白质都是靶向的，但尚不清楚细胞外磷酸化是否以及如何影响大脑发育。在这里，我们表明，由投射性视网膜神经节细胞分泌的脊椎动物孤独激酶（VLK）是一种酪氨酸激酶，它在背-腹下降梯度中磷酸化细胞外蛋白排斥性导向分子 b（RGMb）。VLK 或 RGMb 的沉默会导致小鸡视顶盖中轴突分支异常和严重的轴突误导。携带磷酸化位点点突变的 RGMb 的小鼠也表现出异常的轴突寻路。机制分析表明，VLK 介导的 RGMb 磷酸化通过调节 LRP5 蛋白梯度来调节 Wnt3a 活性。因此，投射神经元分泌的 VLK 为神经系统回路的精确形成提供了关键信号。VLK 对 RGMb 和 Wnt3a 信号的显著影响意味着细胞外磷酸化可能对大脑发育、功能和疾病有广泛而深远的影响。
