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Parent-of-origin-dependent (epi)genetic factors are important determinants of prenatal development that program adult phenotype. However, data on magnitude and specificity of maternal and paternal genome effects on fetal bone are lacking. We used an outbred bovine model to dissect and quantify effects of parental genomes, fetal sex, and nongenetic maternal effects on the fetal skeleton and analyzed phenotypic and molecular relationships between fetal muscle and bone. Analysis of 51 bone morphometric and weight parameters from 72 fetuses recovered at day 153 gestation (54% term) identified six principal components (PC1-6) that explained 80% of the variation in skeletal parameters. Parental genomes accounted for most of the variation in bone wet weight (PC1, 72.1%), limb ossification (PC2, 99.8%), flat bone size (PC4, 99.7%), and axial skeletal growth (PC5, 96.9%). Limb length showed lesser effects of parental genomes (PC3, 40.8%) and a significant nongenetic maternal effect (gestational weight gain, 29%). Fetal sex affected bone wet weight (PC1, p < 0.0001) and limb length (PC3, p < 0.05). Partitioning of variation explained by parental genomes revealed strong maternal genome effects on bone wet weight (74.1%, p < 0.0001) and axial skeletal growth (93.5%, p < 0.001), whereas paternal genome controlled limb ossification (95.1%, p < 0.0001). Histomorphometric data revealed strong maternal genome effects on growth plate height (98.6%, p < 0.0001) and trabecular thickness (85.5%, p < 0.0001) in distal femur. Parental genome effects on fetal bone were mirrored by maternal genome effects on fetal serum 25-hydroxyvitamin D (96.9%, p < 0.001) and paternal genome effects on alkaline phosphatase (90.0%, p < 0.001) and their correlations with maternally controlled bone wet weight and paternally controlled limb ossification, respectively. Bone wet weight and flat bone size correlated positively with muscle weight (r = 0.84 and 0.77, p < 0.0001) and negatively with muscle H19 expression (r = -0.34 and -0.31, p < 0.01). Because imprinted maternally expressed H19 regulates growth factors by miRNA interference, this suggests muscle-bone interaction via epigenetic factors., (© 2014 American Society for Bone and Mineral Research.)

To determine which genes of the plasminogen activator (PA) system were expressed in osteoclasts, RNA extracted from microisolated mouse osteoclasts was used as template for reverse transcribed polymerase chain reaction (RT-PCR) with gene-specific primer pairs. Using this approach, the expression of RNAs for tissue-type plasminogen activator, urokinase-type plasminogen activator, plasminogen activator inhibitor-1, plasminogen activator inhibitor-2, protease nexin, and urokinase receptor isoform 1 (uPAR1) were detected in mouse osteoclasts. The expression of uPAR RNA in osteoclasts was confirmed by in situ hybridization with a uPAR1 probe. RNA encoding the uPAR isoform 2 was not detected in mouse osteoclasts, but a novel unspliced uPAR RNA variant was detected in these cells. The novel uPAR variant and uPAR1 RNA were also detected in mouse calvarial osteoblasts, kidney, muscle, and the mouse macrophage cell line J774A.1 by RT-PCR. The presence of RNAs for most of the components of the PA system in osteoclasts suggests that it may have a functional role in this cell type.