Preferential localization of heat shock protein 47 in dilated endoplasmic reticulum of chicken chondrocytes.

We investigated the distribution of heat shock protein 47 (hsp47) in cultured chicken embryonic chondrocytes and epiphyseal chondrocytes of tibial bones from 1-day-old to 6-week-old chickens. Northern blot and immunoblot analyses revealed that hsp47 exists in epiphyseal cartilage and cultured chondrocytes. Confocal laser immunofluorescence microscopy showed that hsp47 was localized mainly in the many granular structures found in the cytoplasm that contain Type II collagen. Epiphyseal cartilage and cultured chondrocytes were embedded in LR White resin and hsp47 was detected by protein A-immunogold electron microscopy. Gold particles were localized exclusively in the cisternal space of the endoplasmic reticulum (ER), and the labeling density of the cisternal space of the dilated ER was always higher than that of the non-dilated ER. In all the differentiating zones of epiphyseal cartilage, the labeling density was highest in the hypertrophic cells. These findings suggest that hsp47 plays an important role(s) in the synthesis, processing, and assembly of Type II collagen.