Abnormalities of cellular polarity underlie the primary substrate in a genetic form of atrial fibrillation

Atrial fibrillation (AF) is the most common clinical arrhythmia and is associated with heart failure and stroke. The primary substrate for AF is poorly understood due to limited access to primary human tissue and the lack of mechanistically faithful in vitro or in vivo models. We used an MYH6:mCherry knock-in reporter line to generate and purify human pluripotent stem cell-derived cardiomyocytes displaying electrophysiological and molecular characteristics of atrial cells (hPSC-atrial cells). We modeled human MYL4 mutants, one of the few definitive genetic causes of AF. Single cell transcriptomics on hPSC-atrial cells (WT and MYL4 mutant) was performed to study changes in gene expression among the cell types that exist in atrial lineage. D60 hES-atrial cells derived from MYL4+/+ , MYL4+/- and MYL4-/- (two biological replicates of each) lines were dissociated with Accutase. Following centrifugation, cells were resuspended in sorting medium (RPMI with 0.5%BSA) and cells were sorted with a FACS machine into mCherry+ and mCherry- and combined in 2/3(mCherry+) and 1/3(mCherry-) ratio. Next, individual cells were captured and barcoded using the inDrop platform.