Fig. 2

iCMPs are suitable for Myh6/7-molecular-beacon-based selection and capable of long-term propagation. a Myh6/7 molecular beacon principle used to purify iCMPs. (Additional file 1: Fig. S5 for gating strategies) b Schematic outline of the experimental timeline. c Analysis of Myh6/7 mRNA expression in reprogrammed cells by flow cytometry using Cy5-labeled negative control (NEGC, no sequence match, Cy5-BHQ2 label) and Myh6/7 probes (sequence match, Cy5-BHQ2 label) on day 14 or 18 after GMTMy transduction. Shown are contour plots (contour level 5%). d Scatter plot with bar graph presents the proportion of Cy5-positive cells in (c) as mean ± SD (day 14/18, n = 10/4). e Immunofluorescent staining for cTnT, α-actinin, and myosin (magenta) in combination with eGFP (cyan) in GMTMy-transduced cells immediately before and 7 days after fluorescence-activated cell sorting demonstrates successful iCMP enrichment. DAPI (yellow) marks cell nuclei. Scale bars, 100 µm. f iCMP phenotype stability is dependent on expansion medium composition. Flow cytometric analysis of Myh6/7-based Cy5 fluorescence 14 and 21 days after expansion of purified iCMPs in media containing the respective supplements. g,h Cumulative population doubling levels (PDLs) (g) and growth rate as population doublings (PDs) per day h of iCMPs during expansion after sorting. Proliferation data were recorded for 27 days. Line graphs show mean ± SD (n = 4). i Brightfield images taken at indicated points in time during expansion show maintained iCMP morphology. Scale bars, 100 µm Figure 3