Localization of the glucocorticoid receptor mRNA in cartilage and bone cells of the rat. An in situ hybridization study

The in vivo localization of glucocorticoid receptor (GR) mRNA expression was studied in the cartilage and bone cells of the femur of young adult rats to compare its distribution with that of the GR protein, which had previously been shown histochemically in the same areas. To achieve this, we used a synthetic oligodeoxynucleotide as a probe, in line with the published human GR (hGR) cDNA sequence. The probe was coupled to fluorescein (FL), applying a rapid Fast-Tag TM FL nucleic acid labeling method. Negative controls were achieved by using sense sequences of the hGR oligoprobe, similarly coupled by using the Fast-Tag TM FL labeling kit. Dewaxed sections were treated for in situ hybridization (ISH) histochemistry with the antisense and sense oligoprobes. The ISH reaction product was more intense in the cytoplasm of proliferative and maturative chondrocytes of the growth plate cartilage than in that shown in the hypertrophic ones. In the metaphyseal secondary ossification zone, osteoblasts (OBs) and osteocytes (OCs) were variably labeled, whereas osteoclasts (OCLs) were always intensely stained. The labeling was also visible in some bone marrow cells, in articular chondrocytes, in the cells of tendon-bone junctions, and in the perichondrium and periosteal cells. Our results confirm a cellular co-location of GR protein and mRNA. In agreement with GR immunolocalization, the variability of labeling appeared to be related to the cell cycle, the stage of differentiation and cell-type differences.