Moesin KO increases the fusion capacities of mOCs and hOCs. (A) Western blot analysis of activated ERM (P-ERM) expression level during mOC differentiation (days 3, 5, and 7); actin was used as loading control and quantification of P-ERM level was normalized to actin. Each circle represents an independent experiment, means ± SD are shown, n = 5. (B) Same experiment as in A during hOC differentiation (days 3, 6, and 10). Each circle represents a single donor, means ± SDs are shown, n = 9. (A and B) Predicted molecular weight are indicated. n.s. not significant. (C) Reprensentative bright-field microscopy images from a time-lapse movie of control (CTL) and moesin KO mOC (moesin KO) on day 4 of differentiation. Black arrowheads point to multinucleated giant osteoclasts. See Video 6. Scale bar, 100 µm. (D and E) Microscopy analysis of cell fusion in control (CTL) and moesin KO mOC. (D) Representative microscopy images: F-actin (phalloidin, white) and nuclei (DAPI, cyan). Scale bar, 200 µm. (E) Quantification of fusion index (each circle represents an independent experiment, n = 6); and nuclei number per multinucleated osteoclast (150–250 cells/condition, n = 3 independent experiments). (F) Representative western blot analysis of P-ERM expression level in control (CTL), ezrin KO, radixin KO, and moesin KO mOC; actin was used as loading control, n = 2. Predicted molecular weight is indicated. (G and H) Microscopy analysis of hOC fusion after treatment with nontargeting siRNA (siCTL) or siRNA targeting moesin (siMoesin). (G) Representative microscopy images: F-actin (phalloidin, white) and nuclei (DAPI, cyan). Scale bar, 100 µm. (H) Quantification of fusion index (each circle represents a single donor, n = 8) and nuclei number per multinucleated osteoclast (one representative experiment from 8 donors is shown, 100–200 cells/condition). Statistical analyses: (A and B) Friedman and then Dunn’s multiple comparison tests. *P ≤ 0.05; n.s., not significant. Source data are available for this figure: SourceData F2.