CHANGES IN THE SYNTHESIS OF HISTONE H1O AND H1 IN RAT FRTL-5 THYROID CELLS EXPOSED TO THYROTROPIN

In absence of thyrotropin (TSH), FRTL-5 rat thyroid cells stop proliferating and lose the functional characteristics of thyroid tissue. FRTL-5 cells regain their differentiated state and their proliferation activity upon addition of TSH. In this study we investigated the synthesis of histone H1 variants and H1.degree. in FRTL-5 cells exposed to 10-8 M TSH, two days after TSH withdrawal. TSH induced the synthesis of some H1 variants and H1.degree.. This effect was already evident six hours after TSH addition, thus well before proliferation, DNA or thyroglobulin synthesis was induced. These data indicate that the induction of H1.degree. and some H1 variants is an early event after TSH stimulation and may thus be related to the functional differentiation of FRTL-5 cells.