Fig. 5: EMOs present improved signals of ventricle myocardium maturation in comparison with CM aggregates only.

a Representative IF staining of EMOs sections after 15 days of co-culture for the mature ventricle CM marker MLC2V, the atrial/immature ventricle CM marker MLC2A and for connexin 43 (CX43) gap junction, highlighting the more intense staining of the mentioned markers near the edges of the EMO, which are in contact with the WT1⁺ cells. IF staining of CM aggregates is also presented as controls for the key mentioned markers. Scale bars, 100 µm. b Representative transmission electron microscopy (TEM) images showing sarcomeres in EMOs and control CM aggregate sections after 15 days of co-culture. ID intercalated disks. Scale bars, 1 µm. c, Quantification of sarcomere length in EMOs and respective control (n > 10 sarcomere measurements from n = 5 organoids and n = 4 CM aggregates; exact p = value <0.0001). d Calcium transient profiles of EMOs after 15 days of co-culture before and after drug stimulation with isoproterenol, verapamil and E-4031. Data are represented as mean ± SEM of n = 3 independent experiments. EMOs epicardium-myocardium organoids, O organoid, BPM beats per minute, DT decay time, TBP time between peak. Ox nomenclature identifies different organoids obtained from at least three independent experiments. Source data are provided with this paper.