The iPSC cell line used in the experiments described herein was obtained from Joseph R. Mazzulli laboratory (Northwestern University, Feinberg School of Medicine, Chicago, Il). This iPSC cell line was produced from primary human fibroblasts by retroviral expression of the reprogramming factors POU5F1, SOX2, MYC/cMYC, and KLF4 (described in [103 (link)]). This cell line has been characterized through the expression of pluripotency markers (i.e. POU5F1, PODXL, SOX2, NANOG) [104 (link)], genomic integrity through G-banding karyotype analysis (described in [105 (link)]), teratoma analysis (described in [106 ]), and RT-PCR analysis of pluripotency markers (described in [106 ]). iPSCs (passage 50–60) were cultured on 6-well plates coated with either Matrigel (VMR, 47743–715) or Vitronectin XF (Stem Cell Technologies, 07180). Medium consisted of mTeSR1 basal medium containing 10% mTeSR1 5× supplement (Stem Cell Technologies, 05825) and was changed every other day. iPSCs were groomed by the manual removal of differentiated cells, passaged en bloc weekly by the manual dissection of iPSC colonies into ~2 mm2 chunks of cells and placement into a Matrigel- or Vitronectin XF-coated 6-well plate. Prior to floor plate induction, iPSCs were grown to 80–90% confluence. iPSC cultures were monitored daily with an in-hood EVOS Core XL cell imaging system (Thermo Fisher Scientific).