NADPH oxidases are important for neuronal function but detailed subcellular localization studies have not been performed. Here, we provide the first evidence for the presence of functional NOX2-type NADPH oxidase complex in neuronal growth cones and its bidirectional relationship with the actin cytoskeleton. NADPH oxidase inhibition resulted in reduced F-actin content, retrograde F-actin flow, and neurite outgrowth. Stimulation of NADPH oxidase via protein kinase C activation increased levels of hydrogen peroxide in the growth cone periphery. The main enzymatic NADPH oxidase subunit NOX2/gp91phox localized to the growth cone plasma membrane and showed little overlap with the regulatory subunit p40phox. p40phox itself exhibited co-localization with filopodial actin bundles. Differential subcellular fractionation revealed preferential association of NOX2/gp91phox and p40phox with the membrane and the cytoskeletal fraction, respectively. When neurite growth was evoked with beads coated with the cell adhesion molecule apCAM, we observed a significant increase in co-localization of p40phox with NOX2/gp91phox at apCAM adhesion sites. Together, these findings suggest a bidirectional functional relationship between NADPH oxidase activity and the actin cytoskeleton in neuronal growth cones, which contributes to the control of neurite outgrowth.

The measurement of local mechanical properties of living cells by nano/micro indentation relies on the foundational assumption of locally isotropic cellular deformation. As a consequence of assumed isotropy, the cell membrane and underlying cytoskeleton are expected to locally deform axisymmetrically when indented by a spherical tip. Here, we directly observe the local geometry of deformation of membrane and cytoskeleton of different living adherent cells during nanoindentation with the integrated Atomic Force (AFM) and spinning disk confocal (SDC) microscope. We show that the presence of the perinuclear actin cap (apical stress fibers), such as those encountered in cells subject to physiological forces, causes a strongly non-axisymmetric membrane deformation during indentation reflecting local mechanical anisotropy. In contrast, axisymmetric membrane deformation reflecting mechanical isotropy was found in cells without actin cap: cancerous cells MDA-MB-231, which naturally lack the actin cap, and NIH 3T3 cells in which the actin cap is disrupted by latrunculin A. Careful studies were undertaken to quantify the effect of the live cell fluorescent stains on the measured mechanical properties. Using finite element computations and the numerical analysis, we explored the capability of one of the simplest anisotropic models – transverse isotropy model with three local mechanical parameters (longitudinal and transverse modulus and planar shear modulus) – to capture the observed non-axisymmetric deformation. These results help identifying which cell types are likely to exhibit non-isotropic properties, how to measure and quantify cellular deformation during AFM indentation using live cell stains and SDC, and suggest modelling guidelines to recover quantitative estimates of the mechanical properties of living cells.

NADPH oxidase (Nox)-derived reactive oxygen species (ROS) have been linked to neuronal polarity, axonal outgrowth, cerebellar development, regeneration of sensory axons, and neuroplasticity. However, the specific roles that individual Nox isoforms play during nervous system development remain unclear. To address this problem, we investigated the role of Nox activity in the development of retinotectal connections in zebrafish embryos. Zebrafish broadly express four genes (, ,, and ) throughout the CNS during early development. Application of a pan-Nox inhibitor, celastrol, during the time of optic nerve (ON) outgrowth resulted in significant expansion of the ganglion cell layer (GCL), thinning of the ON, and a decrease in retinal axons reaching the optic tectum (OT). With the exception of GCL expansion, these effects were partially ameliorated by the addition of HO, a key ROS involved in Nox signaling. To address isoform-specific Nox functions, we used CRISPR/Cas9 to generate mutations in each zebrafish gene. We found that chimeric mutants displayed ON thinning and decreased OT innervation. Furthermore, homozygous mutants () showed significant GCL expansion and mistargeted retinal axons in the OT. Neurite outgrowth from cultured zebrafish retinal ganglion cells was reduced by Nox inhibitors, suggesting a cell-autonomous role for Nox in these neurons. Collectively, our results show that Nox2/Cybb is important for retinotectal development in zebrafish. Most isoforms of NADPH oxidase (Nox) only produce reactive oxygen species (ROS) when activated by an upstream signal, making them ideal candidates for ROS signaling. Nox enzymes are present in neurons and their activity has been shown to be important for neuronal development and function largely by studies. However, whether Nox is involved in the development of axons and formation of neuronal connections has remained unclear. Using mutant zebrafish embryos, this study shows that a specific Nox isoform, Nox2/Cybb, is important for the establishment of axonal connections between retinal ganglion cells and the optic tectum.

Nicotinamide dinucleotide phosphate oxidases (NOX) control various cellular signaling cascades. In the nervous system, there is recent evidence that NOX-derived reactive oxygen species (ROS) regulate neurite outgrowth, regeneration, and stem cell proliferation; however, a comprehensive NOX gene expression analysis is missing for all major model systems. Zebrafish embryos provide an excellent model system to study neurodevelopment and regeneration because they develop quickly and are well suited for in vivo imaging and molecular approaches. Although the sequences of five NOX genes (nox1, nox2/cybb, nox4, nox5, and duox) have been identified in the zebrafish genome, nothing is known about their expression pattern. Here, we used quantitative polymerase chain reaction combined with in situ hybridization to develop a catalog of nox1, nox2/cybb, nox5, and duox expression in zebrafish during early nervous system development from 12 to 48 hours post fertilization. We found that expression levels of nox1, nox5, and duox are dynamic during the first 2 days of development, whereas nox2/cybb levels remain remarkably stable. By sectioning in situ hybridized embryos, we found a pattern of broad and overlapping NOX isoform expression at 1 and 1.5 days post fertilization. After 2 days of development, a few brain regions displayed increased NOX expression levels. Collectively, these results represent the first comprehensive analysis of NOX gene expression in the zebrafish and will provide a basis for future studies aimed at determining the functions of NOX enzymes in neurodevelopment and regeneration. J. Comp. Neurol. 524:2130-2141, 2016. © 2015 Wiley Periodicals, Inc.