Alginate gel culture allows the retention of extracellular matrix and follicular structure of rat thyroid tissue but does not lead to the formation of follicles by FRTL-5 cells.

Extracellular matrix (ECM) and basement membrane (BM) components were studied by immunohistological methods in native rat thyroid tissue, and in rat thyroid tissue and FRTL-5 cells cultured in a three-dimensional alginate bead system. In all three situations, the presence of collagen IV, laminin, perlecan, and fibronectin was demonstrated. There were marked differences between rat thyroid tissue and FRTL-5 cells in culture. Rat thyroid tissue maintained a follicular structure, whereas FRTL-5 cells did not form follicles. Rat thyroid cells multiplied more slowly than FRTL-5 cells and thyroglobulin (Tg) was visible in the follicular lumen, while in FRTL-5 cells Tg was only seen intracellularly. Tg iodination was much lower in FRTL-5 cells than in rat cells. In rat thyroid cells, positive staining for collagen IV, laminin, and perlecan was seen in thin membranes around individual follicles, and for fibronectin around groups of follicles. In FRTL-5 cells, these ECM/BM components could be identified, but were ...