Knockdown of Nav 1.6a Na+ channels affects zebrafish motoneuron development

Abstract

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.

Prdm1a directly activates foxd3 and tfap2a during zebrafish neural crest specification

“…DIG-conjugated antisense probes were synthesized from full-length transcript sequences in the pCS2+ plasmid to the following genes: snai1b (primers 5Ј-GCTAGGGATCCGCCGCCA -CCATGCCACGCTCATTTC TTGTCA-3Ј and 5Ј-GAATTCTAGATG -TGTGTCCACTAGAGCGCC-3Ј); foxd3 (see above); sox10 (Olesnicky et al, 2010); crestin (Rubinstein et al, 2000); and tfap2a (from T. Williams). Fluorescent ISH was performed as described (Pineda et al, 2006) and used the TSA Biotin System (Perkin Elmer, NEL700A001KT) followed by streptavidin Alexa Fluor 488 antibody (Invitrogen, S11223) to develop FITC-labeled antisense probes and the Fast Red Kit (Sigma, F4648) to develop DIG-labeled probes.…”

Biogenesis of GPI-anchored proteins is essential for surface expression of sodium channels in zebrafish Rohon-Beard neurons to respond to mechanosensory stimulation

“…siRNA-mediated knockdown of cyclin-dependent kinase 5 (Cdk5) promotes the programmed cell death of RB neurons, whereas overexpression of Cdk5 decreases the RB cell death (Kanungo et al, 2006). Interestingly, a reduction in sodium currents either by an inhibitor of voltage-gated sodium channels or by antisense-mediated knockdown of an  subunit of voltage-gated sodium channels (Nav1.6a) also decreases the RB cell death (Svoboda et al, 2001;Pineda et al, 2006), thereby suggesting that neurotrophic inputs, kinase regulations and electrical activity provide signals that are required for the normal elimination of RB neurons.…”

Modulation of potassium channel function confers a hyperproliferative invasive phenotype on embryonic stem cells

“…It is now clear that ion currents, electric fields, and endogenous voltage gradients are an endogenous system for cellular communication (1,2). Roles for bioelectric signals have been uncovered in galvanotaxis of migratory cells, mitotic regulation, and control of differentiation, as well as in complex morphogenetic events, such as wound healing, limb development, left-right patterning, neurogenesis, vertebrate tail regeneration, and cancer (3)(4)(5)(6)(7)(8).…”