Altered CALR-ERp57-STIM1 binding in presence of CALR mutations. (A) Statistical analysis of the percentage of Mks presenting periodic Ca²⁺ spikes. Box plots depict the upper and lower values (lowest and highest horizontal line, respectively), lower and upper quartile with median value (box), and outside values (dots). Overall, data derive from 6 samples per subgroup (P < .05). (B) Representative analysis of spontaneous Ca²⁺ spikes in MPN Mk cultured in physiological Ca²⁺ concentration (1.5 mM) without addition of rhTPO. Samples were recorded for a minimum of 15 minutes. (C) Analysis of CALR localization in mature Mks from healthy controls (Ctrl) and MPN patients (CALR [green stain]; nuclei [blue stain]; scale bar, 15 μm; original magnification, ×60/NA1.2). (D) In situ PLA of STIM1 and CALR interaction. Quantification of dot number per single Mk (overall, data derive from 402 measurements; P < .05). (E) In situ PLA of STIM1 and ERp57 interaction. Quantification of dot number per single Mk (overall, data derive from 412 measurements; P < .05). Overall, data derive from 5 samples per subgroup.