Aberrant condensation and localization of the RNA-binding protein (RBP) fused in sarcoma (FUS) occur in variants of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Changes in RBP function are commonly associated with changes in axonal cytoskeletal organization and branching in neurodevelopmental disorders. Here, we asked whether branching defects also occur in vivo in a model of FUS-associated disease. We use two reported Xenopus models of ALS/FTD (of either sex), the ALS-associated mutant FUS(P525L) and a mimic of hypomethylated FUS, FUS(16R). Both mutants strongly reduced axonal complexity in vivo. We also observed an axon looping defect for FUS(P525L) in the target area, which presumably arises due to errors in stop cue signaling. To assess whether the loss of axon complexity also had a cue-independent component, we assessed axonal cytoskeletal integrity in vitro. Using a novel combination of fluorescence and atomic force microscopy, we found that mutant FUS reduced actin density in the growth cone, altering its mechanical properties. Therefore, FUS mutants may induce defects during early axonal development.

肉瘤 (FUS) 中融合的 RNA 结合蛋白 (RBP) 的异常浓缩和定位发生在肌萎缩侧索硬化症 (ALS) 和额颞叶痴呆 (FTD) 的变异体中。 RBP 功能的变化通常与神经发育障碍中轴突细胞骨架组织和分支的变化有关。在这里，我们询问 FUS 相关疾病模型中是否也会在体内发生分支缺陷。我们使用两种报道的 ALS/FTD非洲爪蟾模型（无论性别），即 ALS 相关突变体 FUS(P525L) 和低甲基化 FUS 的模拟物 FUS(16R)。两种突变体都强烈降低了体内轴突的复杂性。我们还在目标区域观察到 FUS(P525L) 的轴突循环缺陷，这可能是由于停止提示信号传导错误而产生的。为了评估轴突复杂性的丧失是否也具有与线索无关的成分，我们在体外评估了轴突细胞骨架的完整性。使用荧光和原子力显微镜的新颖组合，我们发现突变体 FUS 降低了生长锥中的肌动蛋白密度，改变了其机械性能。因此，FUS 突变体可能会在早期轴突发育过程中诱发缺陷。