Regulation of protein abundance in pluripotent cells undergoing commitment to the neural lineage.

The P19 cell line is a widely studied model of neural differentiation When pluripotent P19 cells are cultured as aggregates in the presence of retinoic acid for 4 days, the cells commit to the neural fate, but have not yet undergone overt differentiation. Two-dimensional polyacrylamide gel electrophoresis was used to analyze cellular protein expression during this induction. Approximately 500 abundant polypeptides were analyzed. Seventeen polypeptides were upregulated during induction; several of these were significantly regulated 48 h after the addition of retinoic acid. No downregulations were observed. Fifteen of the 17 polypeptides continued to be expressed throughout terminal differentiation. The upregulation of 14 of the 17 polypeptides requires both retinoic acid and aggregation, which alone do not induce neural differentiation. Furthermore, these regulated polypeptides are expressed in neural tissue, suggesting they are associated with neural function in vivo. Embryonic stem cells, a totipotent line, also neurally differentiate in response to retinoic acid and aggregation. Comparison of embryonic stem cells to P19 cells shows that the two systems regulate a similar set of polypeptides and are thus likely to utilize a similar pathway. These studies are a step toward determining the full extent of regulation involved in the commitment of pluripotent cells to the neural fate.