Multiple elements regulate Mash1 expression in the developing CNS.

Mash1, a transcription factor of the basic helix-loop-helix class, is expressed during embryogenesis in restricted regions of the nervous system. An essential role for Mash1 in neural development was demonstrated previously in mice carrying a targeted disruption of the Mash1 gene. Regulation of the precise temporal and spatial expression of Mash1 is thus likely to be important for proper neural development. In this study, sequences that regulate Mash1 expression in the central nervous system were characterized by assaying the expression of lacZ reporter genes in transgenic embryos. A 1158-bp enhancer localized approximately 7 kb upstream of the Mash1 coding region was identified. Deletions within this enhancer region reveal the presence of both positive and negative cis-acting elements. Analysis of multiple sequences within the enhancer demonstrate that different elements preferentially function in different regions within the Mash1-specific CNS expression domain. In addition, a role for sequences 3' of the Mash1 coding region is revealed, providing evidence for posttranscriptional control of Mash1 expression in multiple CNS domains.

Identification of an achaete-scute homolog, Fash1, from Fugu rubripes.

Proteins of the achaete-scute family of transcription factors play important roles in neurogenesis in both invertebrates and vertebrates. Here, we report the cloning and characterization of a Japanese pufferfish, Fugu rubripes achaete-scute homolog 1, Fash1. Sequence alignment of the predicted amino acid sequence of Fash1 with other vertebrate homologs of the achaete scute homolog 1 subclass shows that the carboxyl 2/3 of the protein, including the basic helix-loop-helix, a putative nuclear localization signal and several consensus phosphorylation sites, is highly conserved. Strikingly, the similarity in this region between eight vertebrate species is close to 90%.

Regional and cellular expression patterns of four K+ channel mRNAs in the adult rat brain.

Potassium (K+) channels are involved in the modulation and fine tuning of the excitable properties of neurons and glia in the nervous system. In the present report, in situ hybridization histochemistry was used to determine the regional and cellular distribution patterns in the adult rat brain of four mRNAs encoding subunits of voltage-gated K+ channels. These are Kv1.1, Kv1.6, K13 and IK8. All K+ channels examined showed distinct yet overlapping expression patterns. Expression of Kv1.1 mRNA was high in cells of certain motor-related structures of the brainstem. Kv1.6 mRNA expression was observed in cerebellar Purkinje cells and in various olfactory and amygdaloid structures. K13 was the only mRNA expressed in both neuronal and non-neuronal cell populations, including the cells of choroid plexus and pia. IK8 expression was observed only in the forebrain structures. In many brain regions, mRNAs for Kv1.1 and Kv1.6, both encoding K+ channel subunits belonging to the Shaker subfamily, were co-expressed, a necessary condition for heteromultimer formation.

Lineage-specific regulation of the neural differentiation gene MASH1.

Mash1 is a transcription factor required during embryogenesis for the development of multiple neural lineages. It is expressed in restricted domains at specific stages in the developing central and peripheral nervous systems and in the developing olfactory epithelium. We have investigated the regulation of Mash1 expression during embryogenesis using transgenic mice containing Mash1/lacZ reporter constructs. Cis-acting regulatory elements controlling Mash1 expression in the central nervous system are located within an 8-kb sequence upstream of the Mash1 coding region. This 8-kb sequence does not contain elements directing expression to the peripheral nervous system, olfactory epithelium, or retina. Sequences outside this 8 kb but within 36 kb of the Mash1 locus contain elements responsible for expression in the autonomic division of the peripheral nervous system. However, transgene expression in embryos containing the 36-kb sequence was never detected in the olfactory epithelium and retina. Thus, regulatory elements driving expression in these lineages may be at even greater distances from the Mash1 coding region. These data provide evidence for complex regulation of Mash1 expression in which multiple lineage-specific cis-acting regulatory regions span greater than 36 kb of the Mash1 locus. Further characterization of these regions will facilitate the study of factors that regulate the temporal and spatial expression of Mash1 during development. In addition, the regulatory sequences identified here can direct expression of heterologous genes to developing neural lineages that normally express Mash1, thus providing an important tool for examining the function of candidate regulatory genes in mammalian nervous system development.