Dual and asynchronous deposition of laminin chains at the epithelial-mesenchymal interface in the gut

The production of laminin by 14-day fetal rat intestinal endoderm and mesenchyme was investigated. The amount of neosynthesized laminin was measured after purification using affinity chromatography. Chain composition of laminin was analyzed by immunoblotting and immunofluorescence staining. The data show that both embryonic intestinal tissue components synthesize laminin and that A and B1/B2 chains were detected in both endodermal and mesenchymal cells. The cellular source of laminin found at the epithelial basement membrane has been studied by immunocytochemistry in rat/chick or mouse/chick interspecies hybrid intestines taken at various stages of development. Immunodetection of the whole laminin molecule and of the individual A and B1/B2 chains by rodent-specific polyclonal and monoclonal antibodies at the basement membrane level in these hybrid intestines revealed (a) laminin molecules, which originate from both mesenchymal and endodermal cells; (b) deposition of A and B1/B2 chains by endodermal cells, regardless of the stage of growth of the hybrid intestines; and (c) asynchronous deposition of the various chains of laminin into the basement membrane by the mesenchyme. B1/B2 chains are deposited concomitant with contact with the epithelium, whereas A chains appear only later (13 days after grafting). These data reinforce the suggestion from previous studies that cooperation between epithelium and mesenchyme is necessary for the formation of a complete basement membrane in the developing intestine.