Fig 1: LSMEM2 is a previously uncharacterized protein on the surface of cardiomyocytes.a, Pie chart visualizing the number of proteins restrictive to cardiomyocytes within the heart or restrictive to cardiomyocytes when compared to 68 other non-cardiac cell types. b, log2 intensity values for LSMEM2, APOM, CFHR2 and ITIH1 for pooled LA and RA samples (six pooled donors for each LA and RA) and three matched donors for LV and RV. Scatter plots are shown with mean and s.d. Proteins are reported by UniProt accession and gene name. c, Protter11 image of LSMEM2 visualizing the epitope used to develop an mAb against LSMEM2 and the N-glycopeptide identified by CellSurfer. d, CIRFESS9 output showing the conflicting prediction of the extracellular domain of LSMEM2 by Phobius and TMHMM. e, Representative confocal immunofluorescence images of human cardiac tissue stained for LSMEM2 (purple), cardiac troponin I (TNNI3, green) and nuclei (blue). f, Representative confocal immunofluorescence images of human cardiac tissue stained for LSMEM2 (purple), vimentin (green) and nuclei (blue). Scale bars, 20 µm (top panel) and 5 µm (bottom panel). g, Representative confocal immunofluorescence images of cardiac tissue stained for LSMEM2 (purple), KCNJ2 (green) and nuclei (blue). Intercalated discs are marked by asterisks. Cell membrane is marked by arrows. Scale bars, 20 µm (top panel) and 5 µm (middle and bottom panel). h, Representative confocal immunofluorescence images of cardiac tissue stained for LSMEM2 (purple), SCN5A (green) and nuclei (blue). Intercalated discs are marked by asterisks. Scale bars, 20 µm (top panel) and 5 µm (bottom panel). i, Representative confocal immunofluorescence images of cardiac tissue stained for LSMEM2 (purple), connexin 43 (Cx43, green) and nuclei (blue). Scale bar, 5 µm. j, Flow cytometry contour plots depicting live cell flow cytometry of LSMEM2 on HeLa, Jurkat and U-2 OS cells. e–i, 10, 3, 3, 2 and 6 biological replicates for LSMEM2, KCNJ2, SCN5A, vimentin and CX43, respectively. j, Three biological replicates for each cell line.