CRISPR/Cas9-mediated generation of a tyrosine hydroxylase reporter iPSC line for live imaging and isolation of dopaminergic neurons

Patient-specific induced pluripotent stem cells (iPSCs) are a powerful tool to investigate the molecular mechanisms underlying Parkinson’s disease (PD), and might provide novel platforms for systematic drug screening. Several strategies have been developed to generate iPSC-derived tyrosine hydroxylase (TH)-positive dopaminergic neurons (DAn), the clinically relevant cell type in PD; however, they often result in mixed neuronal cultures containing only a small proportion of TH-positive DAn. To overcome this limitation, we used CRISPR/Cas9-based editing to generate a human iPSC line expressing a fluorescent protein (mOrange) knocked-in at the last exon of the TH locus. After differentiation of the TH-mOrange reporter iPSC line, we confirmed that mOrange expression faithfully mimicked endogenous TH expression in iPSC-derived DAn. We also employed calcium imaging techniques to determine the intrinsic functional differences between dopaminergic and non-dopaminergic ventral midbrain neurons. Crucially, the brightness of mOrange allowed direct visualization of TH-expressing cells in heterogeneous cultures, and enabled us to isolate live mOrange-positive cells through fluorescence-activated cell sorting, for further differentiation. This technique, coupled to refined imaging and data processing tools, could advance the investigation of PD pathogenesis and might offer a platform to test potential new therapeutics for PD and other neurodegenerative diseases.
Research from the authors’ laboratories is supported by the European Research Council-ERC (2012-StG-311736-PD-HUMMODEL), the European Union’s Horizon 2020 Program (MESOBRAIN project; grant agreement No 713140), the Spanish Ministry of Economy and Competitiveness-MINECO (SAF2015-69706-R; BFU2017-83066-P; and BFU2016-80870-P), Instituto de Salud Carlos III-ISCIII/FEDER (Red de Terapia Celular - TerCel RD16/0011/0003 and RD16/0011/0024; PIE12/00061), AGAUR (2017-SGR-899 and 2017-SGR-1061), and CERCA Program/Generalitat de Catalunya. C.C. is supported by the PD-HUMMODEL European Research Council (ERC)- Ideas PhD fellowship. G.C. is partially supported by pre-doctoral fellowship from Spanish Economy and Competitiveness-MINECO (BES-2014-069603).