EFFECTS OF THYROID-HORMONE ON EMBRYONIC OLIGODENDROCYTE PRECURSOR CALL DEVELOPMENT IN-VIVO AND IN-VITRO

The oligodendrocyte precursor cell divides a limited number of times b efore terminal differentiation. The timing of differentiation depends on both intracellular mechanisms and extracellular signals, including mitogens that stimulate proliferation and signals such as thyroid horm one (TH) and retinoic acid (RA) that help trigger the cells to stop di viding and differentiate. We show here that, both ira vivo and in vitr o, TH is required for the normal development of rodent optic nerve oli godendrocytes, although in its absence some oligodendrocyte developmen t still occurs, perhaps promoted by signals from axons. We also demons trate that TH from both mother and pup plays a part in oligodendrocyte development in vivo. Finally, we show that precursors in embryonic ne rve cultures differ from those in postnatal cultures in two ways: they respond much better Po TH than to RA, and they respond more slowly to TH, suggesting that oligodendrocyte precursor cells mature during the ir early development.