Expression of tubulin, GFAP and of their encoding mRNAs during the proliferation and differentiation of cultured astrocytes.

The expression of tubulin, of glial fibrillary acidic protein of their encoding mRNAs were studied in primary cultures of mouse astrocytes. The effects of dibutyryl cyclic AMP on these parameters were also analyzed. (1) The concentration of both ?- and ?-tubulin chains markedly increased (3-fold) between 7 and 12 days of culture and then remained at the same high value at later stages. In contrast ?-tubulin mRNA concentration remained constant throughout the same culture period. (2) Glial fibrillary acidic protein concentration increased steadily reaching a 4-fold higher value at the end of the same culture period. The glial fibrillary acidic protein mRNA increased 3-fold during the first 2 weeks of culture, leveled off at day 18 and then decreased steadily returning to low values (3-fold decrease) at later stages. (3) Addition for 2 days, at day 5 or 19 of the culture, of either dibutyryl cyclic AMP or forskolin remained without effect on tubulin concentration whereas a 50% decrease in ?-tubulin mRNA was observed. In the same conditions the effects of these drugs on glial fibrillary acidic protein and its mRNA were not significant. These results suggest that the increase in tubulin concentration seen between days 7 and 12, as well as that of glial fibrillary acidic protein observed during the last weeks of the culture, are not secondary to an increase either of the rate of transcription or of the stability of their encoding mRNAs.