The deposition of intestinal heparan sulfate proteoglycan (HSPG) at the epithelial-mesenchymal interface and its cellular source have been studied by immunocytochemistry at various developmental stages and in rat/chick interspecies hybrid intestines. Polyclonal heparan sulfate antibodies were produced by immunizing rabbits with HSPG purified from the Engelbreth-Holm-Swarm mouse tumor; these antibodies stained rat intestinal basement membranes. A monoclonal antibody (mAb 4C1) produced against lens capsule of 11-d-old chick embryo reacted with embryonic or adult chick basement membranes, but did not stain that of rat tissues. Immunoprecipitation experiments indicated that mAb 4C1 recognized the chicken basement membrane HSPG. Immunofluorescent staining with these antibodies allowed us to demonstrate that distribution of HSPG at the epithelial-mesenchymal interface varied with the stages of intestinal development, suggesting that remodeling of this proteoglycan is essential for regulating cell behavior during morphogenesis. The immunofluorescence pattern obtained with the two species-specific HSPG antibodies in rat/chick epithelial/mesenchymal hybrid intestines developed as grafts (into the coelomic cavity of chick embryos or under the kidney capsule of adult mice) led to the conclusion that HSPG molecules located in the basement membrane of the developing intestine were produced exclusively by the epithelial cells. These data emphasize the notion already gained from previous studies, in which type IV collagen has been shown to be produced by mesenchymal cells (Simon-Assmann, P., F. Bouziges, C. Arnold, K. Haffen, and M. Kedinger. 1988. Development (Camb.). 102:339-347), that epithelial-mesenchymal interactions play an important role in the formation of a complete basement membrane.

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