INDUCTIVE ROLE OF FIBROBLASTIC CELL-LINES IN DEVELOPMENT OF THE MOUSETHYMUS ANLAGE IN ORGAN-CULTURE

Previously, we have shown that embryonic day 12 thymus anlage cultured alone cannot develop into the mature organ but degenerates. In the pr esent study, we investigated the cause of this insufficient organogene sis of embryonic day 12 thymus anlage in organ culture. We cocultured embryonic day 12 thymus anlages with various cell lines as pellets for med by centrifugation. In coculture with fibroblastic cell lines, but not with thymic epithelial cell lines, embryonic day 12 thymus anlages developed to support full T cell differentiation, and expressed matur e stromal cell markers, Ia and K-b. By pellet culture of thymus anlage s and fibroblastic cell lines transfected with a beta-galactosidase ex pression vector, we analyzed the distribution of added fibroblastic ce lls in pellets. The added fibroblastic cells constituted neither thymi c capsule nor septa but disappeared after about 2 weeks in culture. Mo reover, immunohistochemical studies indicated that added fibroblastic cells were adjacent to mesenchymal cells of thymus anlage. Our results strongly suggest that added fibroblastic cells support the developmen t of the thymus anlage through interaction with its mesenchymal cells. (C) 1998 Academic Press.