| Popis: |
P19 embryonal carcinoma cells provide an interesting in vitro model system with which to follow the events involved in neuronal differentiation. After addition of 5 × 10 −7 m retinoic acid to the culture medium, these multipotent stem cells differentiate into neural cells. Expression of the tyrosine kinase-encoding c- src and c- yes protooncogenes was determined at either the level of transcription and/or the level of translation in undifferentiated stem cells and in cells differentiating along a neural lineage. Autophosphorylation studies and Western blot analysis revealed that during neuronal differentiation, activation of pp60 c- src kinase activity is paralleled by an increase in pp60 c- src protein. The activation is not paralleled by decreased tyrosine-specific phosphatase activity. Furthermore, Northern and slot blot analyses showed that the activation is not paralleled by increased amounts of c- src -specific mRNA, suggesting that post-translational modifications and an elevated rate of translation might account for the increased amounts of tyrosine kinase activity and protein. In contrast, the highly related protooncogene c- yes displayed a totally different expression pattern, with increasing amounts of c- yes -specific mRNA correlating with induction of neuronal differentiation. These results suggest that despite their structural similarities, both cellular genes are regulated differently. |
