Cell Polarity and Water Transport in Thyroid Epithelial Cells in Separated Follicles in Suspension Culture

Separated thyroid follicles maintained in suspension culture can be used to study the properties of thyroid epithelium in the virtual absence of other cell types and to study the effect of extracellular materials on the follicles. They can be prepared by enzymatic separation of thyroid into single cells followed by reaggregation of the epithelial cells and also by collagenase treatment of thyroids to release follicles and sheets of epithelia that can be separated from other materials by differential filtration. The follicles can exist with normal orientation or inverted (inside out). The follicles are inverted in the presence of high serum concentrations (5%) but can have normal orientation when embedded in a type I collagen gel, even at high serum concentrations. When normally oriented follicles invert, the polarity of the epithelial cells reverses while they are connected to neighbors. During inversion, bipolar cells are observed having microvilli- bearing surfaces at both lumen and medium. Inverted follicles can revert to normal orientation when embedded in collagen gel. Various functional properties of normally oriented follicles are similar to those of follicles in vitro. However, inverted follicles do not concentrate iodide, although they synthesize thyroglobulin and secrete it into the medium. Mutants are available in established cell lines. They have functional and organizational properties that differ from those of normal cells and demonstrate a lack of coupling between functional properties and organization. Inverted follicles transport water from medium into the lumen, although at rates somewhat less than MDCK cells

Histological changes in TSH-dependent tumours of the thyroid gland during serial transplantation in Fischer 344 rats

Transplantable tumours were induced in the thyroids of Fischer 344 rats fed thiouracil (TU) in a moderately low iodine diet for 8–13 months. Pieces of hyperplastic thyroid were implanted subcutaneously into rats fed a TU containing diet. Almost all implants gave rise to very small vascularized transplants but there were three significantly larger, pieces of which were transplanted again and gave rise to the tumour lines. From the third transplantation generation on, pieces of tumours were implanted into rats treated to have elevated circulating thyrotropin and a group fed a high iodine diet. With some exceptions, the implants grew only in rats fed the TU or a low iodine diet and yielded TSH-dependent tumours. Almost all the tumours observed initially were papillary, and most of the remainder had colloid-filled follicles bounded by columnar cells. One line of tumours was of the latter type for eight generations. The others had more complex histories, in which there were sublines that were papillary for eight or nine generations, whereas, others became progressively more cellular or follicular, and more heterogenous with respect to histological types present per section at rates that varied with the subline. The large number of population doublings necessary to make a one gram tumour from a single original tumour cell indicates that the cells of dependent papillary tumours were immortalized