(A) Schematic of MISR2 signaling pathway and luciferase reporter. (B) Luciferase reporter optimization by transfection of combinations of type I receptors (ALK2/3/6) and receptor SMADs (SMAD1/5/9) with BRE-luc and MISR2v1 constructs. Luminosity was measured 24 h following treatment with MIS (0.5 µg/mL) or SP600125 (12.5 µM) and plotted relative to vehicle control (n = 3 per treatment, mean ± SD, *P < 0.05, ***P < 0.005, ****P < 0.001). (C) Comparison of luciferase induction in COS7 transiently transfected with BRE-luc, ALK2, SMAD1, and MISR2v1 or MISR2v3 and treated with MIS (10 µg/mL), SP600125 (12.5 µM), DMH1 (10 µM) + MIS (10 µg/mL), or equivalent volume of mock-purified MIS (MOCK) as a control for MIS or vehicle control (DMSO) for SP600125 (n = 5 per group, mean ± SD). (D) Scatterplot of luciferase intensity values across two replicates. Right quadrant identifies hits with 3 SD induction across both replicates. (E) Active hits identified across two replicates ranked by median activity score (n = 2 replicates, mean ± SD).