Cellular acetylcholine content and neuronal differentiation.

N18TG2 neuroblastoma clone is defective for biosynthetic neurotransmitter enzymes; its inability to establish functional synapses is overcome in the neuroblastoma x glioma 108CC15, where acetylcholine synthesis is also activated. These observations suggest a possible relation between the ability to produce acetylcholine and the capability to advance in the differentiation program and achieve a fully differentiated state. Here, we report the characterization of several clones after transfection of N18TG2 cells with a construct containing a cDNA for rat choline acetyltransferase (ChAT). The ability of these clones to synthesize acetylcholine is demonstrated by HPLC determination on cellular extracts. In the transfected clones, northern blot analysis shows increased expression of mRNAs for a specific neuronal protein associated with synaptic vesicles, synapsin I. Fiber outgrowth of transfected clones is also evaluated to establish whether there is any relation between ChAT levels and morphological differentiation. This analysis shows that the transfected clone 1/2, not expressing ChAT activity, displays a very immature morphology, and its ability to extend fibers also remains rather poor in the presence of "differentiation" agents such as retinoic acid. In contrast, clones 2/4, 3/1, and 3/2, exhibiting high ChAT levels, display higher fiber outgrowth compared with clone 1/2 in both the absence and the presence of differentiating agents.

Characterization of two novel YY1 binding sites in the polyomavirus late promoter.

NF-D is a ubiquitous nuclear factor that has been shown to bind specifically to a DNA element in the polyomavirus regulatory region. In this report, we demonstrate that NF-D is either identical or very similar to a transcription factor that has been variously named YY1, delta, NF-E1, UCRBP, or CF1. Moreover, we show the presence in the polyomavirus genome of a second DNA motif, located 40 bp from the first, which binds YY1/NF-D with high affinity. Both sites lie downstream of the major late transcription initiation sites. By site-directed mutagenesis, we demonstrate that both elements contribute positively to the activity of the late promoter, probably by a cooperative mechanism. We also demonstrate that the requirement of the YY1/NF-D function for late promoter activity varies with the cell line.