Tissue recombinants to study extracellular matrix targeting to basement membranes.

Several techniques have been used to study the expression of basement membranes molecules but none of them allow distinguishing the cellular origin of the deposition of a single molecule at the subepithelial basement membrane. For this purpose, we designed an experimental model using recombinants between chick and mouse embryonic intestines. Following constructions of interspecies endodermal/mesenchymal associations in culture, developmental growth was achieved by in vivo transplantation in the chick embryo. Immunocytochemistry, using species-specific antibodies recognizing either chick or mouse basement membrane molecules, was then performed on cryosections made through the developed hybrid intestines.The use of this experimental design permits determination of the precise expression/secretion in the intestinal basement membrane region of the individual constituents: interestingly some of them are strictly of epithelial or of mesenchymal origin, while others are of dual origin. Furthermore, we could show that each of these molecules is expressed in a peculiar development-dependent pattern. Such interspecies as well as heterotopic recombinants (from different levels of the gastrointestinal tract) can also be used successfully to approach the regulation of the expression of functional markers, i.e., digestive enzymes.