SUMMARY The ocular motility disorder “Congenital fibrosis of the extraocular muscles type 1″ (CFEOM1) results from heterozygous mutations altering the motor and 3rd coiled-coil stalk of the anterograde kinesin, KIF21A. We demonstrate that Kif21a knock-in mice harboring the most common human mutation develop CFEOM. The developing axons of the oculomotor nerve’s superior division stall in the proximal nerve; the growth cones enlarge, extend excessive filopodia, and assume random trajectories. Inferior division axons reach the orbit but branch ectopically. We establish a gain-of-function mechanism and find that human motor or stalk mutations attenuate Kif21a autoinhibition, providing in vivo evidence for mammalian kinesin autoregulation. We identify Map1b as a Kif21a interacting protein and report that Map1b−/− mice develop CFEOM. The interaction between Kif21a and Map1b is likely to play a critical role in the pathogenesis of CFEOM1, and highlights a selective vulnerability of the developing oculomotor nerve to perturbations of the axon cytoskeleton.

The stereotypical projection of retinal ganglion cell (RGC) axons to the optic disc has served as a good model system for studying axon guidance. By both in vitro and in vivo experiments, we show that a secreted molecule, Sonic hedgehog (Shh), may play a critical role in the process. It is expressed in a dynamic pattern in the ganglion cell layer with a relatively higher expression in the center of the retina. Through gel culture and stripe assays, we show that Shh has a dual effect on RGC axonal growth, acting as a positive factor at low concentrations and a negative factor at high concentrations. Results from time-lapse video microscopic and stripe assay experiments further suggest that the effects of Shh on axons are not likely attributable to indirect transcriptional regulation by Shh. Overexpression of Shh protein or inhibition of Shh function inside the retina resulted in a complete loss of centrally directed projection of RGC axons, suggesting that precise regulation of Shh level inside the retina is critical for the projection of RGC axons to the optic disc.

Spinal muscular atrophy (SMA), an inherited disease of motor neuron dysfunction, results from insufficient levels of the survival motor neuron (SMN) protein. Movement of the SMN protein as granules within cultured axons suggests that the pathogenesis of SMA may involve defects in neuronal transport, yet the nature of axon transport vesicles remains enigmatic. Here we show that SMN directly binds to the α-subunit of the coat protein I (COPI) vesicle coat protein. The α-COP protein co-immunoprecipitates with SMN, small nuclear ribonucleoprotein-associated assembly factors and β-actin mRNA. Although typically Golgi associated, in neuronal cells α-COP localizes to lamellipodia and growth cones and moves within the axon, with a subset of these granules traveling together with SMN. Depletion of α-COP resulted in mislocalization of SMN and actin at the leading edge at the lamellipodia. We propose that neurons utilize the Golgi-associated COPI vesicle to deliver cargoes necessary for motor neuron integrity and function.

Macropinocytosis is a type of poorly characterized fluid-phase endocytosis that results in formation of relatively large vesicles. We report that Sonic hedgehog (Shh) protein induces macropinocytosis in the axons through activation of a noncanonical signaling pathway, including Rho GTPase and nonmuscle myosin II. Macropinocytosis induced by Shh is independent of clathrin-mediated endocytosis but dependent on dynamin, myosin II, and Rho GTPase activities. Inhibitors of macropinocytosis also abolished the negative effects of Shh on axonal growth, including growth cone collapse and chemorepulsive axon turning but not turning per se. Conversely, activation of myosin II or treatment of phorbol ester induces macropinocytosis in the axons and elicits growth cone collapse and repulsive axon turning. Furthermore, macropinocytosis is also induced by ephrin-A2, and inhibition of dynamin abolished repulsive axon turning induced by ephrin-A2. Macropinocytosis can be induced ex vivo by high Shh, correlating with axon retraction. These results demonstrate that macropinocytosis-mediated membrane trafficking is an important cellular mechanism involved in axon chemorepulsion induced by negative guidance factors.

Background: The NCOA7 gene product is an estrogen receptor associated protein that is highly similar to the human OXR1 gene product, which functions in oxidation resistance. OXR genes are conserved among all sequenced eukaryotes from yeast to humans. In this study we examine if NCOA7 has an oxidation resistance function similar to that demonstrated for OXR1. We also examine NCOA7 expression in response to oxidative stress and its subcellular localization in human cells, comparing these properties with those of OXR1.

Axon pathfinding is essential for the establishment of proper neuronal connections during development. Advances in neuroimaging and genomic technologies, coupled with animal modeling, are leading to the identification of an increasing number of human disorders that result from aberrant axonal wiring. In this review, we summarize the recent clinical, genetic and molecular advances with regard to three human disorders of axon guidance: Horizontal gaze palsy with progressive scoliosis, Congenital mirror movements, and Congenital fibrosis of the extraocular muscles, Type III.

The function and mechanism of macropinocytosis in cells outside of the immune system remain poorly understood. We used a neuroblastoma cell line, Neuro-2a, to study macropinocytosis in neuronal cells. We found phorbol 12-myristate 13-acetate (PMA) and insulin-like growth factor 1 (IGF-1) induced two dinstinct types of macropinocytosis in the Neuro-2a cells. IGF-1-induced macropinocytosis occurs mostly around the cell bodies and requires phosphoinositide 3-kinase (PI3K), while PMA-induced macropinocytosis occurs predominantly in the neurites and is independent of PI3K. Both types of macropinocytosis were inhibited by a specific inhibitor of non-muscle myosin II, blebbistatin. siRNA knock-down of nonmuscle myosin II isoforms, -IIA and –IIB, resulted in opposite effects on macropinocytosis induced by PMA or IGF. Myosin IIA knock-down significantly increased, whereas myosin IIB knock-down significantly decreased, macropinocytosis with correlating changes in membrane ruffle formation.

Risk is not a simple phenomenon; contrary to the arguments of frustrated scientists who claim evidentiary support for the development and release of genetically modified organisms (GMOs), opponents of these organisms claim that the risks associated with their release are unacceptable. Obviously, the evaluation of risk is often contentious and ambiguous, and yet the phenomenon of how people actually evaluate risk is not widely known among scientists. Hence, we present a review of the literature on risk that underscores its complexity. Scholars argue the merits of different types of risk assessment, but most agree that the process is far more complex than simple cost/benefit analyses. Indeed, the literature presents a plethora of theories, ranging from economic and actuarial assessment to psychological and social assessments. We agree with the social constructionist view, and argue that opponents of GMOs have amplified the socially derived feelings of risk that the various stakeholders and publics harbour towards GMOs. We likewise conclude that GMO opponents are amplifying the factors of control and unknown risk.