In addition to rapid signaling, electrical activity provides important cues to developing neurons. Electrical activity relies on the function of several different types of voltage-gated ion channels. Whereas voltage-gated Ca2+ channel activity regulates several aspects of neuronal differentiation, much less is known about developmental roles of voltage-gated Na+ channels, essential mediators of electrical signaling. Here, we focus on the zebrafish Na+ channel isotype, Nav1.6a,which is encoded by the scn8a gene. A restricted set of spinal neurons, including dorsal sensory Rohon-Beard cells, two motoneuron subtypes with different axonal trajectories, express scn8a during embryonic development. CaP, an early born primary motoneuron subtype with ventrally projecting axons expresses scn8a, as does a class of secondary motoneurons with axons that project dorsally. To test for developmental roles of scn8a, we knocked down Nav1.6a protein using antisense morpholinos. Na+ channel protein and current amplitudes were reduced in neurons that express scn8a. Furthermore,Nav1.6a knockdown altered axonal morphologies of some but not all motoneurons. Dorsally projecting secondary motoneurons express scn8aand displayed delayed axonal outgrowth. By contrast, CaP axons developed normally, despite expression of the gene. Surprisingly, ventrally projecting secondary motoneurons, a population in which scn8a was not detected,displayed aberrant axonal morphologies. Mosaic analysis indicated that effects on ventrally projecting secondary motoneurons were non cell-autonomous. Thus,voltage-gated Na+ channels play cell-autonomous and non cell-autonomous roles during neuronal development.

Abstract.Voltage-gated sodium channels underlie action potential generation in excitable tissue.To establish the evolutionary mechanisms that shaped the vertebrate sodium channel a-subunit (SCNA) gene family and their encoded Na v 1 proteins, we identified all SCNA genes in several teleost species. Molecular cloning revealed that teleosts have eight SCNA genes, comparable to the number in another vertebrate lineage, mammals.Prior phylogenetic analyses had indicated that teleosts and tetrapods share four monophyletic groups of SCNA genes and that tandem duplications selectively expanded the number of genes in two of the four mammalian groups. However, the number of genes in each group varies between teleosts and tetrapods suggesting different evolutionary histories in the two vertebrate lineages. Our findings from phylogenetic analysis and chromosomal mapping of Danio rerio genes indicate that tandem duplications are an unlikely mechanism for generation of the extant teleost SCNA genes. Instead, analysis of other closely mapped genes in D. rerio supports the hypothesis that a whole genome duplication was involved in expansion of the SCNA gene family in teleosts. Interestingly, despite their different evolutionary histories, mRNA analyses demonstrated a conservation of expression patterns for SCNA orthologues in teleosts and tetrapods, suggesting functional conservation.

Whereas it is known that voltage-gated calcium channels play important roles during development, potential embryonic roles of voltage-gated sodium channels have received much less attention. Voltagegated sodium channels consist of pore-forming ␣-subunits (Na v 1) and auxiliary ␤-subunits. Here, we report the embryonic and larval expression patterns for all eight members of the gene family (scna) coding for zebrafish Na v 1 proteins. We find that each scna gene displays a distinct expression pattern that is temporally and spatially dynamic during embryonic and larval stages. Overall, our findings indicate that scna gene expression occurs sufficiently early during embryogenesis to play developmental roles for both muscle and nervous tissues.

No abstract

Two methods are presented here that allow clear visualization of antibody localization in zebrafish whole mount preparations, both for immunocytochemistry (ICC) alone and in combination with in situ hybridization (ISH). The first protocol describes ICC performed using a modified permeabilization technique and the chromogen AEC (3-Amino-9-ethylcarbazole). The second protocol describes the co-localization of transcriptional and translational products using a combined ISH/ICC protocol. A fluorescing chromogen (Fast Red, FR) is used to detect mRNA transcripts by ISH, and is combined with ICC that uses a secondary antibody conjugated to a different fluorescent molecule (Alexa 488). These procedures allow the identification of gene expression patterns in cell types identifiable with known antibodies.

No abstract

No abstract