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

The Na-G ion channel, previously cloned from a rat astroglia cDNA library, belongs to a new family of ion channels, related to but distinct from the predominant brain and muscle fast voltage-gated Na(+) channels. In vivo, the corresponding transcripts are widely expressed in peripheral nervous system neurons and glia, but only in selected subpopulations of neuronal and glia-like cells of the central nervous system. In the present report, we show that Na-G messenger RNA level in astrocyte and Schwann cell cultures is modulated in a cell-specific manner by several growth factors, hormones, and intracellular second messengers pathways.

The Na-G ion channel is transcribed from a single promoter controlled by distinct neuron- and Schwann cell-specific DNA elements.

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 tissue-specific expression of this channel, we isolated the 5' 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 beta-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 -6,500 and -1,050 bp upstream of the main transcription initiation sites.

In vitro assembly of Neurospora assimilatory nitrate reductase from protein subunits of a Neurospora mutant and the xanthine oxidizing or aldehyde oxidase systems of higher animals.

In vitro assembly or complementation of a hybrid assimilatory nitrate reductase was attained by mixing a preparation of nitrate-induced N. crassa mutant nit-1 specifically with acid-treated (pH 2.5) bovine milk or intestinal xanthine oxidase, rabbit liver aldehyde oxidase, or chicken liver xanthine dehydrogenase.