DIFFERENTIAL INDUCTION OF HNF-3 TRANSCRIPTION FACTORS DURING NEURONALDIFFERENTIATION

We have investigated the regulation of transcription factors HNF-3 alp ha and HNF-3 beta during the retinoic acid-mediated differentiation of mouse P19 cells. Retinoic acid treatment converts P19 stem cells into neurons and astrocytes and we have clearly shown that gene expression of both HNF-3 alpha and HNF-3 beta is activated during this process. HNF-3 alpha transcription was detected 2 h after addition of retinoic acid and took place in the absence of de novo protein synthesis. This suggests that HNF-3 alpha is a primary target for retinoic acid action . HNF-3 alpha induction displays a biphasic profile and HNF-3 alpha mR NA reaches maximal levels at 2 and 6 days postdifferentiation. Additio nal experiments strongly suggest that the second peak is due to HNF-3 alpha induction in postmitotic neurons. P19 stem cells, on the other h and, do not contain any detectable HNF-3 alpha mRNA. According to our studies, the retinoic acid-mediated induction of HNF-3 alpha occurs at the level of transcriptional initiation and is conferred by distal pr omoter sequences. In comparison to HNF-3 alpha, HNF-3 beta induction i s a subsequent event and detectable levels of HNF-3 beta mRNA material ize approximately 1 day after addition of retinoic acid to P19 stem ce lls. Time course studies firmly demonstrate that HNF-3 beta mRNA peaks at about 2 days postdifferentiation and then declines to virtually un readable levels. This temporal pattern is consistent with HNF-3 beta b eing a secondary target for retinoic acid. In analogy to HNF-3 alpha, HNF-3 beta activation also takes place at the level of transcriptional initiation. Recent studies implicate HNF-3 alpha and HNF-3 beta in ea rly mammalian neurogenesis. The detection of HNF-3 alpha/beta activati on during P19 cell differentiation provides us with a convenient cell culture system to elucidate the induction mechanism and the precise ro le of both transcriptional regulators in the formation of neuronal cel ls. (C) 1997 Academic Press.