Significant role of laminin-1 in branching morphogenesis of mouse salivaryepithelium cultured in basement membrane matrix

Mouse submandibular epithelium shows branching morphogenesis in mesenchyme- free conditions when covered with a basement membrane matrix (Matrigel) in medium supplemented with epidermal growth factor. In the present study, the role of laminin-1 (LN1), a major glycoprotein of Matrigel, in this culture system was defined. When the epithelium was cultured in a LN1-nidogen gel, the epithelium showed much branching, comparable to that observed with Mat rigel. By electron microscopy, only a felt-like matrix was formed on the ep ithelial surface in the LN1-nidogen gel cultures, while an organized basal lamina structure was formed on the epithelial surface in direct or transfil ter recombination cultures with mesenchyme. Next, the epithelium covered wi th Matrigel was cultured in medium containing either biologically active pe ptides from LN1, IKVAV-including peptide (2097-2108), AG10 (2183-2194), AG3 2 (2370-2381) or AG73 (2719-2730) from the alpha 1 chain, or YIGSR-includin g peptide (926-933) from the beta 1 chain. Only AG73 (RKRLQVQLSIRT from the alpha 1 chain carboxyl-terminal globular domain) inhibited the epithelial branching in Matrigel. These results suggest that LN1-nidogen can support t he branching morphogenesis of submandibular epithelium even if LN1-nidogen is not assembled into an intact basal lamina, and that the AG73 sequence is an important site on LN1, which interacts with submandibular epithelial ce lls.