Newly identified gene muscle segment homeobox C may play a role in intermuscular bone development of Hemibarbus labeo

Intermuscular bones, ossified from tendons within the myosepta, occur only in teleost fish. Current understanding of the homology and origins of intermuscular bones in fishes is based mainly on morphological data. To date, there is no published data regarding molecular mechanisms of intermuscular bone formation. In this study, we cloned the gene muscle segment homeobox C (MsxC). MsxC potentially plays a role in intermuscular bone development of Hemibarbus labeo, an important species of cyprinid fish in the Chinese aquaculture industry. Sequence analysis of MsxC revealed motifs characteristic of the homeobox domain family. Whole-mount in situ hybridization showed that MsxC was primarily expressed in the myosepta and brain. MsxC was expressed in the myosepta from 26 to 41 days after hatching (DAH); this coincided with the onset of intermuscular bone ossification, which occurred between 35 and 62 DAH. Evidence for localization of MsxC expression by in situ hybridization correlated with its detection by quantitative real-time PCR. In vertebrates, MsxC plays a role in the regulation of mesenchymal cell differentiation during bone formation. We therefore conclude that MsxC may have a role in epithelium-mesenchyme interactions during intermuscular bone formation in H. labeo.