Structured illumination microscopy (SIM) images were acquired using a Zeiss Elyra PS.1 system equipped with a 100X 1.46 NA or 63X 1.4NA objective. Acquisition was performed with PCO edge sCMOS camera and image reconstruction was done with built-in structured illumination model. Confocal microscopy images were acquired using Zeiss LSM800 microcopy with 63X 1.4NA objective or Zeiss LSM780 microcopy with 40X 1.1NA objective. Z stack images were done with a step size of 2.5 um. Further image process was done with Fiji.
Human lymphocytes from healthy subjects and ALS patients were obtained from the NINDS Biorepository at the Coriell Institute for Medical Research and reprogrammed into iPSCs as previously described using episomal vectors61. Briefly, mammalian expression vectors containing Oct4, Sox2, Klf4, L-Myc, Lin28, and a p53 shRNA were introduced into the lymphocytes using the Adult Dermal Fibroblast Nucleofector™ Kit and Nucleofector™ 2b Device (Lonza) according to the manufacturer’s protocol. The cells were then cultured on mouse feeders until iPSC colonies appeared. The colonies were then expanded and maintained on Matrigel (BD) in mTeSR1 medium (Stem Cell Technologies). 
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