*2.1. CRISPR*/*Cas9 Plasmid Construction and Transfection*

The CRISPR/Cas9 with T2A-eGFP co-expression vector pSpCas9(BB)–2A-GFP (PX458) was a gift from Feng Zhang (Addgene plasmid). The exon 1 of *GLA* was selected for guiding RNA design and the sequence (5 -AGGAACCCAGAACTACATCT-3 ) was cloned into PX458 (abbreviated as GLA-Cas9-GFP) as previously described [8]. The *GLA*-specific targeting plasmid was transfected into hESC line (WA09) by electroporation using Nucleofector System (Lonza, Basel, Switzerland) following the manufacturer's protocol. Briefly, hESC cells were cultured to 80–90% confluence, then harvested and washed with PBS without Ca2<sup>+</sup> and Mg2<sup>+</sup>. Approximately 4 <sup>×</sup> 105 cells were resuspended in the pre-mixture solution with 2 μg GLA-Cas9-GFP plasmid, and the optimized protocol (program B016) was used for electroporation. The cells were plated on Matrigel-coated 6-well plate in mTeSR1 medium containing 10 μM Y27632. 48 h later, the proportion of cells expressing EGFP was enriched by flow cytometry using FACSCalibur (BD Biosciences, San Jose, CA, USA). Three days later, cells were detached with TrypLE (Invitrogen, Thermo Fisher Scientific, Waltham, MA, USA), separated into single cells and seeded with a density of 1 cell/well of a 96-well dish.
