The preservation of specialization by dispersed steer thyroidal cells in long-term culture

Serially propagated cells derived from the steer thyroid gland preserve several specialized characteristics, some demonstrable for as long as 8 months (over 15 passes). For about 5 passes (3 months), follicular-like arrays of cells develop. Thyroid-stimulating hormone (TSH) or thyrotropin (1 and 10 mu./ml) induces the formation of supernumerary nucleoli, and promotes at the ultrastructural level the prompt (within 10 min) appearance of microvilli, pseudopodia, and intracytoplasmic droplets. These cells have a mean plating efficiency (PE) of 16·5 ±4·5 % (standard deviation) and with 3 × 104 cells as the standard inoculum, a mean doubling time (Td) of 43·7± 1·2 h. The linear variation of Td with the number of cells seeded probably signifies strong cell-cell interactions. TSH (1–50 mu./ml) influences both PE and Td, with 1 mu./ml producing the maximum stimulation. TSH (0·001–100 mu./ml) also induces the discharge of incorporated radio-iodide from the cultured thyroid cells, achieving a peak by 2–4 h, titres of 0·1–1 mu./ml being most potent. Long-acting thyroid stimulator (LATS) (0·2 u./ml) likewise effects release of 131I into growth medium (1 experiment), but over a more protracted period. After labelling with [3H]leucine, radioautographs demonstrate that the synthesis of proteins is stimulated by exposure to TSH (1 mu./ml). Precipitation with trichloro acetic acid indicates that these cells persist in synthesizing 131I-tagged iodoproteins, an activity optimally stimulated by 1 mu./ml TSH and marked by 3 h. Hence, such thyroidal cell lines afford a useful model for studying differentiation and hormonal effects.