Immunohistochemical study on a macrophage calcium-type lectin in mouse embryos: transient expression in chondroblasts during endochondral ossification.

We investigated expression of mouse macrophage galactose/N-acetylgalactosamine-specific calcium-type lectin (MMGL) in mouse embryos using a rat monoclonal antibody (mAb) LOM-14 that we previously developed. Immunoblot analysis revealed that a significant expression of MMGL was first detected in detergent extracts of whole embryos of 11 days post coitus (dpc) and the level of its expression increased during further fetal development (examined up to 18-dpc embryos). Tissue sections of 12, 14, 16, and 18-dpc embryos, newborn and adult mice were investigated by immunohistochemical staining. In embryos of 12-dpc and later stages, mesenchymal cells (typically distributed in the embryonic skin) exhibited positive signals for MMGL. Interestingly, a conspicuous staining was observed during endochondral ossification in temporary cartilage tissue, in which chondroblasts were transiently positive for MMGL. The staining intensity for the chondroblasts peaked in 14-dpc embryos and then gradually decreased. The staining was diminished while hypertrophy and maturation of chondrocytes proceeded, and was eliminated in areas with calcification. Immunoelectron microscopic study demonstrated the presence of MMGL in rough endoplasmic reticulum in the chondroblasts in the temporary cartilage tissue in 14-dpc embryos. These results provide first evidence showing the expression of MMGL in cells other than macrophages.