We have used an indirect method to compare the dynamic properties of microtubules (MTs) in the main shaft and distal regions of the axon. Individual MTs are staggered along the length of the axon and consist of a labile domain situated at the plus end of a stable domain (Baas and Black, 1990). As a result of this organization and the plus-end- distal orientation of axonal MTs, the most distal region of the axon consists entirely of labile domains, while the main shaft consists of a mixture of labile and stable domains. In this study, we wished to determine whether the labile domains extending into the distal axon differ in their dynamic properties from the labile domains terminating in the main shaft. To address this issue, we used immunoelectron microscopy to compare the tyrosination state of the labile domains terminating in these 2 axon regions. Because detyrosination is a polymerspecific modification of alpha-tubulin that accumulates with time, the levels of tyrosinated alpha-tubulin will be a reflecti...

Microtubules are a primary cytoskeletal constituent of axons and growth cones. In addition to serving as a scaffolding for axon assembly, they also provide a means of transport of organelles that are essential for outgrowth and maintenance of synaptic function. Pharmacological manipulations that disrupt net assembly of microtubules also interfere with growth cone advance and axon extension. Less is known about the effects of disrupting microtubule dynamics without affecting net assembly. To investigate this, we studied the effects of low doses of nocodazole on axon extension and microtubule organization in rat superior cervical ganglion neurons. We report that 165–330 nm nocodazole significantly reduces axon extension rate and increases axon diameter without affecting the rate of production of axoplasm or microtubule polymer, and without decreasing the average length or number of microtubules. Two observations suggested that microtubule dynamics were depressed by this dose of nocodazole. First, this treatm...

Alterations in mitochondrial dynamics (fission, fusion, and movement) are implicated in many neurodegenerative diseases, from rare genetic disorders such as Charcot-Marie-Tooth disease, to common conditions including Alzheimer's disease. However, the relationship between altered mitochondrial dynamics and neurodegeneration is incompletely understood. Here we show that disease associated MFN2 proteins suppressed both mitochondrial fusion and transport, and produced classic features of segmental axonal degeneration without cell body death, including neurofilament filled swellings, loss of calcium homeostasis, and accumulation of reactive oxygen species. By contrast, depletion of Opa1 suppressed mitochondrial fusion while sparing transport, and did not induce axonal degeneration. Axon degeneration induced by mutant MFN2 proteins correlated with the disruption of the proper mitochondrial positioning within axons, rather than loss of overall mitochondrial movement, or global mitochondrial dysfunction. We also f...

Doublecortin-like kinase 1 (DCLK1) is a neuronal serine-threonine protein kinase that is a closely related family protein of Doublecortin (DCX) originally identified as a causative gene product of human cortical malformation. DCLK1 contains the microtub...

During development, neuronal activity is essential for axon guidance and wiring. However, its function in axonal regeneration in the mature CNS remains elusive. We found that overexpression of the light-sensitive GPCR melanopsin in the retina enhanced n...

Spinal cord injury results in permanent disruption of axonal pathways that leads to loss of motor and sensory function. The long-term goal of our work is to develop neuron-specific polymeric micelle nanoparticles for combinatorial delivery of bioactive ...

Although mature CNS neurons do not spontaneously regenerate injured axons, conditioning injury (CI) to the peripheral branches of DRG sensory neurons can robustly upregulate regeneration-associated genes (RAGs) and thereby enhance central axon regenerat...

Intra-axonal protein synthesis plays an important role in axon growth during development, in peripheral nerve regeneration and in vitro. Previous studies showed axons contain hundreds to thousands of mRNAs in their growth cones by microarray or next-gen...

Neurons in the adult central nervous system (CNS) are unable to regenerate after spinal cord injury (SCI) due to an inhibitory environment and a decreased intrinsic growth capacity. Modulating environmental inhibitors and their neuronal receptors such a...

Canonical and noncanonical Wnt signaling pathways are essential for development and maintenance of the CNS. Whereas the roles of canonical Wnt pathways in neuronal survival and axonal regeneration in adult CNS have been described, the functions of noncanonical Wnt pathways are not well understood. Furthermore, the role of noncanonical Wnt ligands in the adult retina has not been investigated. Noncanonical Wnt signaling shares receptors with canonical Wnt ligands but functions through calcium and c-Jun N-terminal kinase (JNK) signaling pathways. Noncanonical ligands, such as the prototypic ligand Wnt5a, have varying effects in the developing CNS, including inhibiting or promoting axonal growth. To identify a role for noncanonical Wnt signaling in the developed retina after injury, we characterized the effect of Wnt5a on neurite outgrowth in cultured retinal ganglion cell (RGC) neurons and on axonal regeneration in the injured optic nerve in the mouse. Endogenous Wnt5a was upregulated after injury and exogen...