Fig. 5: Position-dependent EC diversity in endocardial cushion-derived structures.

a, UMAPs displaying six coarse-grained EC clusters and the TMSB10^high_C_2 clusters, divided into 18 fine-grained cell states representing endocardial (Endoc_EC_1–4) and endocardial cushion-related cells (OF_VEC, IF_VEC, AtrSept_EC), endothelium of great arteries and large veins (Atr_EC_1, Ven_EC) and consecutive segments of the coronary vasculature, including arterial (Art_EC_2), arteriolar (Arteriol_EC), capillary (Cap_EC_1–2) and venular (Venul_EC) endothelial cells. Additionally, proliferating (Prol_EC) and lymphatic endothelial cells (LEC^fg), and refined populations of thymosin-enriched (TMSB10^high_C_2^fg) and PDE4C-enriched endothelial cells (PDE4C^high_EC^fg) are also present. b, Spatial mapping of IF_VECs (green) and OF_VECs (red) to opposite sides of the atrioventricular (ROI A) and semilunar valves (ROIs B–D), presented in 8 PCW (upper) and 12 PCW (lower) heart sections. c, Side-specific spatial enrichment of selected IF_VEC and OF_VEC markers in atrioventricular and semilunar valves in a 9 PCW heart section detected by ISS (left). White arrows mark the direction of blood flow. Heatmap displaying per-gene scaled expression of the same genes across EC, MC and CM states enriched in the valves (outlined in Fig. 7d) (right). d, Spatial mapping of AtrSept_ECs (blue) to the atrial septum between Right_aCM-dominated (green) and Left_aCM-dominated (red) areas in an 8 PCW heart section. e, Gene regulatory network of AtrSept_ECs, including transcription factors enriched compared to IF_VECs and OF_VECs, and their associated target genes. f, Violin plots illustrating regulon enrichment of selected transcription factors in AtrSept_ECs, IF_VECs and OF_VECs across three age groups (5.5–6, 7–8 and 9–14 PCW). slv, semilunar valve; avv, atrioventricular valve; lv, left ventricle; pa, pulmonary artery; as, atrial septum; arrowhead or if, inflow side of valve; asterisk or of, outflow side of valve.