For decades, numerous studies have proposed that fast muscles contribute to quick movement, while slow muscles underlie locomotion requiring endurance. By generating mutant zebrafish whose fast muscles are synaptically silenced, we examined the contribution of fast muscles in both larval and adult zebrafish. In the larval stage, mutants lacked the characteristic startle response to tactile stimuli: bending of the trunk (C-bend) followed by robust forward propulsion. Unexpectedly, adult mutants with silenced fast muscles showed robust C-bends and forward propulsion upon stimulation. Retrograde labeling revealed that motor neurons genetically programmed to form synapses on fast muscles are instead rerouted and innervate slow muscles, which led to partial conversion of slow and intermediate muscles to fast muscles. Thus, extended silencing of fast muscle synapses changed motor neuron innervation and caused muscle cell type conversion, revealing an unexpected mechanism of locomotory adaptation.

数十年来，许多研究提出，快速的肌肉有助于快速的运动，而缓慢的肌肉是需要耐力的运动的基础。通过生成突变的斑马鱼，其快肌被突触沉默，我们检查了幼虫和成年斑马鱼中快肌的贡献。在幼虫阶段，突变体缺乏对触觉刺激的特征性惊吓反应：躯干弯曲（C形弯曲），然后进行稳固的前向推进。出乎意料的是，具有沉默的快速肌肉的成年突变体在刺激后表现出强劲的C形弯曲和正向推进。逆行标记显示，通过基因编程在快肌上形成突触的运动神经元会被重新布线，并支配慢肌，这导致慢肌和中肌部分转化为快肌。从而，