Developmental expression patterns of Beta-ig (betaIG-H3) and its function as a cell adhesion protein.

Beta-ig is a secretory protein embodied by fasciclin I-like repeats containing sequences that might bind integrins and glycosaminoglycans in vivo. Expression of Beta-ig is responsive to Transforming Growth Factor-beta and the protein is found to be associated with extracellular matrix (ECM) molecules, implicating Beta-ig as an ECM adhesive protein of developmental processes. The spatiotemporal distribution of Beta-ig during various stages of murine development was examined and its ability to support adhesion of various cell types assessed. In situ hybridization of mouse embryos (E12.5-E18.5) indicated a prominent, distinct expression pattern for Beta-ig message in connective tissue. Beta-ig transcripts were abundantly expressed during mesenchymal cell condensation in areas of axial, craniofacial and appendicular primordial cartilage from E12.5-E14.5. Beginning at E15.5, Beta-ig transcripts appeared in collagen-rich tissues, including dura mater and corneal stroma. During E16.5-E18.5, Beta-ig transcripts were observed in proliferating chondrocytes and areas of endochondral ossification in joint and articular cartilage formation. Connective tissues expressed Beta-ig transcripts within the nasal septum and surrounding cartilage primordia, and in the pericardium, optic cup, kidney, ovary, esophagus, diaphragm, bronchi, trachea and corneal epithelium, and during cardiac valve formation. These patterns of expression indicate that Beta-ig may be involved in tissue morphogenesis. Cells derived from mesenchyme attached onto a substratum comprised of purified recombinant Beta-ig. Taken together, the results indicate that Beta-ig is expressed principally in collagen-rich tissues where it may interact with cells and ECM molecules, perhaps playing a role in tissue morphogenesis.