Antibodies against domain E3 of laminin-1 and integrin α6 subunit perturb branching epithelial morphogenesis of submandibular gland, but by different modes

Abstract

Branching epithelial morphogenesis requires interactions between the surrounding mesenchyme and the epithelium, as well as interactions between basement membrane components and the epithelium. Embryonic submandibular gland was used to study the roles of two mesenchymal proteins, epimorphin and tenascin-C, as well as the epithelial protein laminin-1 and one of its integrin receptors on branching morphogenesis. Laminin-1 is a heterotrimer composed of an cd chain and two smaller chains (β1 and γ1). Immunofluorescence revealed a transient expression of laminin α1 chain in the epithelial basement membrane during early stages of branching morphogenesis. Other laminin-1 chains and α6, β1, and β4 integrin subunits seemed to be expressed constitutively. Expression of epimorphin, but not tenascin-C, was seen in the mesenchyme during early developmental stages, but a mAb against epimorphin did not perturb branching morphogenesis of this early epithelium. In contrast, inhibition of branching morphogenesis was seen with a mAb against the carboxy terminus of laminin α1 chain, the E3 domain. An inhibition of branching was also seen with a mAb against the integrin α6 subunit. The antibodies against laminin α1 chain and integrin α6 subunit perturbed development in distinct fashions. Whereas treatment with the anti- E3 resulted in discontinuities of the basement membrane at the tips of the branching epithelium, treatment with the mAb against α6 integrin subunit seemed to leave the basement membrane intact. We suggest that the laminin E3 domain is involved in basement membrane formation, whereas α6β1 integrin binding to laminin-1 may elicit differentiation signals to the epithelial cells.