Changes in integrin expression during chondrogenesis in vitro: an immunomorphological study.

Integrins are receptors composed of ligand-specific alpha-chains and cell type-specific beta-chains which are involved in cell-cell and cell-matrix interactions. The distribution of alpha 1- and alpha 3-integrins as well as collagen Types I and II, was investigated by immunofluorescence and immunoelectron microscopy during chondrogenesis in organ culture after various culture periods. Mesenchymal cells from limb buds of Day 12 mouse embryos were grown at high density. Within the first 2 days of the culture period, only alpha 1-integrin could be detected. Formation of cartilage-specific matrix on Day 3 was accompanied by the occurrence of alpha 3-integrin. On Day 7, alpha 3 was present only in cartilage nodules, whereas alpha 1 was strongly expressed in the perichondrium and was more or less homogeneously distributed in the surrounding mesenchyme. On Day 14, alpha 1-integrin was again detectable in cartilage. We suggest that the change in collagen formation from Type I to Type II during chondrogenesis is accompanied by a change in integrin expression from alpha 1 to alpha 3. Conversely, dedifferentiation of chondrocytes in aging cartilage is accompanied by the occurrence of collagen Type I and alpha 1-integrin. Therefore, a strict correlation between the collagen type synthesized by the cells and the appropriate receptor presented by the cells is suggested.