FXIIIA deficiency results in significantly reduced osteoclastogenesis in vitro. (A) Representative images of TRAP staining of splenocyte cultures harvested from fXIIIA^+/+ and fXIIIA^−/− mice and cultured in the presence of 30 ng/mL monocyte colony stimulating factor (M-CSF) and 100 ng/mL RANKL for 8 days. Note the presence of numerous large, multinucleated, TRAP+ (purple) osteoclasts in fXIIIA^+/+ cultures, whereas fXIIIA^−/− splenocyte cultures produced visibly fewer TRAP+/multinucleated cells. (B) Quantification of osteoclast number in 10 random high-powered fields per culture from each of 3 mice. TRAP+ cells that contained >3 nuclei were counted as osteoclasts. Data are represented as mean ± standard error of the mean. (C) Quantitative RT-PCR analysis of TRAP gene expression in osteoclast cultures (n = 3 mice per genotype). Data are expressed as average fold change over wild-type with error bars denoting standard error of the mean. Data were analyzed by the Student t test.