The Na‐G Ion Channel Is Transcribed from a Single Promoter Controlled by Distinct Neuron‐ and Schwann Cell‐Specific DNA Elements

Abstract

Na-G is a putative sodium (or cationic) channel expressed in neurons and glia of the PNS, in restricted neuronal subpopulations of the brain, and in several tissues outside the nervous system, like lung and adrenal medulla. To analyze the mechanisms underlying tissuespecific expression of this channel, we isolated the 5Ј region of the corresponding gene and show that Na-G mRNA transcription proceeds from a single promoter with multiple initiation sites. By transgenic mice studies, we demonstrate that 600 bp containing the Na-G proximal promoter region and the first exon are sufficient to drive the expression of a ␤-galactosidase reporter gene in neurons of both CNS and PNS, whereas expression in Schwann cells depends on more remote DNA elements lying in the region between Ϫ6,500 and Ϫ1,050 bp upstream of the main transcription initiation sites. Crucial elements for lung-specific expression seem to be located in the region between Ϫ1,050 and Ϫ375 bp upstream of the promoter. Using in vivo footprint experiments, we demonstrate that several sites of the Na-G proximal promoter region are bound specifically by nuclear proteins in dorsal root ganglion neurons, as compared with nonexpressing hepatoma cells.

Genetic and epigenetic control of the Na-G ion channel expression in glia

“…This discrepancy may reflect the existence of strong inhibitory cues that operate in vivo but are lacking in our ex vivo experimental system. In line with this hypothesis are the results of our previous studies in transgenic mice (Poiraud et al, 1999), showing that the same Na‐G constructs are unable to drive the β‐galactosidase reporter expression in astroglia in situ.…”

“…In a recent work, we characterized the 5′ region of the Na‐G gene and have shown that, irrespective of their tissue or cell‐type origin, Na‐G mRNAs originate from a single promoter (the nucleotide sequence for the 11.7 kilobase Na‐G genomic fragment has been deposited in the Genbank database under accession number AF125160). By studies in transgenic mice, some of the genomic regions controlling the tissue and cell‐type specificity of Na‐G transcript expression were identified (Poiraud et al, 1999). In the present article, we provide further information on the cellular and transcriptional mechanisms that control the Na‐G gene expression in astrocytes and Schwann cells.…”

Identification and functional characterization of the promoter of the mouse sodium‐activated sodium channel Nax gene (Scn7a)

“…The mouse basal promoter of Na x sodium channel is 91% homologous to the rat Na x promoter sequence, although the TSSs are not at the same position (Poiraud et al, 1999). We found that NGFI-C and Ebox sites are conserved in both promoters, suggesting the possibility that these elements are also important for promoter activity in rat.…”

“…The GATA1 site, which has no significant contribution to promoter activity in mouse, is not conserved in rat. Poiraud et al (1999) suggested that a 600-bp fragment of the Na x rat promoter from position -375 nt to the end of exon 1, is sufficient to drive specific transcription in CNS neurons as much as PNS neurons in transgenic mice. Contrary to their proposal, the results derived from our functional analysis experiments using mouse Na x suggest that Na x basal promoter is active in all cells and that its tissue-specific expression is regulated by repression.…”

Identification of the sensory neuron specific regulatory region for the mouse gene encoding the voltage‐gated sodium channel NaV1.8

“…1998, 1999). Finally, the tissue specific gene promoter for the NAG channel (Poiraud et al. 1999) is somewhat similar to the Scn10a promoter.…”