Differential gene expression of bgp and mgp in trabecular and compact bone of Atlantic salmon (Salmo salar L.) vertebrae

The tissue-specific gene expression of the vitamin K-dependent proteins bone gamma-carboxyglutamate-protein (BGP) and matrix gamma-carboxyglutamate-protein (MGP) in Atlantic salmon (Salmo salar L.) was investigated. In previous studies, BGP, the most abundant non-collagenous protein of bone, was almost exclusively associated with bone, whereas the non-structural protein MGP has a more widespread tissue distribution. In-situ hybridization of juvenile Atlantic salmon (similar to 40 g, fresh water) vertebrae demonstrated expression of bgp and mgp mRNA in osteoblasts lining the trabecular bone, whereas no staining was observed in the compact bone. By separating the trabecular and compact bone of both juvenile (similar to 40 g, fresh water) and adult (similar to 1000 g, sea water) Atlantic salmon, we observed that the two vertebral bone compartments displayed different levels of bgp, whereas no such differences were seen for mgp. Measurements of the mineral content and Ca/P molar ratio in adult salmon revealed no significant differences between trabecular and compact bone. In conclusion, the osteoblasts covering the salmon vertebrae have unique gene expression patterns and levels of bgp and mgp. Further, the study confirms the presence of mRNA from the vitamin K-dependent proteins BGP and MGP in the vertebrae, fin and gills of Atlantic salmon.