Microtubule-associated protein 6 mediates neuronal connectivity through Semaphorin 3E-dependent signalling for axonal growth (original) (raw)
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MAP6 is an intraluminal protein that induces neuronal microtubules to coil
Science Advances
Neuronal activities depend heavily on microtubules, which shape neuronal processes and transport myriad molecules within them. Although constantly remodeled through growth and shrinkage events, neuronal microtubules must be sufficiently stable to maintain nervous system wiring. This stability is somehow maintained by various microtubule-associated proteins (MAPs), but little is known about how these proteins work. Here, we show that MAP6, previously known to confer cold stability to microtubules, promotes growth. More unexpectedly, MAP6 localizes in the lumen of microtubules, induces the microtubules to coil into a left-handed helix, and forms apertures in the lattice, likely to relieve mechanical stress. These features have not been seen in microtubules before and could play roles in maintaining axonal width or providing flexibility in the face of compressive forces during development.
Molecular Brain, 2019
The growth cone is a specialized structure that forms at the tip of extending axons in developing and regenerating neurons. This structure is essential for accurate synaptogenesis at developmental stages, and is also involved in plasticity-dependent synaptogenesis and axon regeneration in the mature brain. Thus, understanding the molecular mechanisms utilized by growth cones is indispensable to understanding neuronal network formation and rearrangement. Phosphorylation is the most important and commonly utilized protein modification in signal transduction. We previously identified microtubule-associated protein 1B (MAP 1B) as the most frequently phosphorylated protein among ~ 1200 phosphorylated proteins. MAP 1B has more than 10 phosphorylation sites that were present more than 50 times among these 1200 proteins. Here, we produced phospho-specific antibodies against phosphorylated serines at positions 25 and 1201 of MAP 1B that specifically recognize growing axons both in cultured n...
The EMBO Journal, 2013
MAP1B, a structural microtubule (MT)-associated protein highly expressed in developing neurons, plays a key role in neurite and axon extension. However, not all molecular mechanisms by which MAP1B controls MT dynamics during these processes have been revealed. Here, we show that MAP1B interacts directly with EB1 and EB3 (EBs), two core 'microtubule plus-end tracking proteins' (þ TIPs), and sequesters them in the cytosol of developing neuronal cells. MAP1B overexpression reduces EBs binding to plus-ends, whereas MAP1B downregulation increases binding of EBs to MTs. These alterations in EBs behaviour lead to changes in MT dynamics, in particular overstabilization and looping, in growth cones of MAP1Bdeficient neurons. This contributes to growth cone remodelling and a delay in axon outgrowth. Together, our findings define a new and crucial role of MAP1B as a direct regulator of EBs function and MT dynamics during neurite and axon extension. Our data provide a new layer of MT regulation: a classical MAP, which binds to the MT lattice and not to the end, controls effective concentration of core þ TIPs thereby regulating MTs at their plus-ends.
The microtubule-severing protein Spastin is essential for axon outgrowth in the zebrafish embryo
Human Molecular Genetics, 2006
Hereditary spastic paraplegia (HSP) is a collection of neurological disorders characterized by developmental failure or degeneration of motor axons in the corticospinal tract and progressive lower limb spasticity. SPG4 mutations are the most common cause of autosomal dominant HSP and Spastin (the SPG4 gene product) is a microtubule severing protein that shares homology with katanin, the microtubule severing activity of which promotes axon growth in cultured neurons. Given the sequence and functional similarity between spastin and katanin, we hypothesized that spastin promotes the dynamic disassembly and remodelling of microtubules required for robust, properly directed motor axon outgrowth. To investigate this hypothesis, we cloned the zebrafish spg4 orthologue and used morpholino antisense oligonucleotides directed against the translation start site and the intron 7-8 splice donor site to knock down spastin function in the developing zebrafish embryo. Reduced spg4 function caused dramatic defects in motor axon outgrowth without affecting the events driving the initial specification of motor neurones. Other neuronal subtypes also exhibited a requirement for spg4 function, since spg4 knock down caused both widespread defects in neuronal connectivity and extensive CNS-specific apoptosis. Our results reveal a critical requirement for spastin to promote axonal outgrowth during embryonic development, and they validate the zebrafish embryo as a novel model system to dissect the pathogenetic mechanisms underlying HSP. Taken together with other recent studies, our findings suggest that axon outgrowth defects may be a common feature of childhood SPG3A and SPG4 cases.
Brain Research, 2002
Neuronal process extension is dependent on the reorganisation of the cytoskeleton, in particular microtubules and microfilaments, and one of the ways in which microtubules are regulated is by a group of microtubule-associated proteins called MAPs. MAP1B, the first MAP to be expressed in developing neurons, has been shown to play an important role during axonogenesis. Previously, we have shown that a phosphorylated isoform of MAP1B is involved in maintaining growth cone microtubules in a dynamically unstable state. In order to further investigate the role of MAP1B during axonogenesis we have cultured dorsal root ganglion (DRG) neurons from a MAP1B deficient mutant mouse. These mice express only trace amounts of MAP1B, have defects in the development of their nervous system and die perinatally. Cultured DRG neurons from MAP1B deficient mice show a reduction in axon elongation and an increase in growth cone area. The reduction in axon elongation is most likely to occur due to an inhibition in the early stages of axonogenesis. Using time-lapse video we have verified that during the first 2 h after plating, MAP1B deficient neurones extend their axons with an average speed that is half the speed of control neurones. These results support the participation of MAP1B during the initial stages of axonogenesis.
Developmental neurobiology, 2016
Doublecortin-like kinase 1 (DCLK1) is a member of the neuronal microtubule-associated doublecortin (DCX) family and functions in multiple stages of neural development including radial migration and axon growth of cortical neurons. DCLK1 is suggested to play the roles in part through its protein kinase activity, yet the kinase substrates of DCLK1 remain largely unknown. Here we have identified MAP7D1 (microtubule-associated protein 7 domain containing 1) as a novel substrate of DCLK1 by using proteomic analysis. MAP7D1 is expressed in developing cortical neurons, and knockdown of MAP7D1 in layer 2/3 cortical neurons results in a significant impairment of callosal axon elongation, but not of radial migration, in corticogenesis. We have further defined the serine 315 (Ser 315) of MAP7D1 as a DCLK1-induced phosphorylation site and shown that overexpression of a phosphomimetic MAP7D1 mutant in which Ser 315 is substituted with glutamic acid (MAP7D1 S315E), but not wild-type MAP7D1, fully...
Neuronal abnormalities in microtubule-associated protein 1B mutant mice
Proceedings of the National Academy of Sciences, 1996
Microtubules play an important role in establishing cellular architecture. Neuronal microtubules are considered to have a role in dendrite and axon formation. Different portions of the developing and adult brain microtubules are associated with different microtubule-associated proteins (MAPs). The roles of each of the different MAPs are not well understood. One of these proteins, MAPIB, is expressed in different portions of the brain and has been postulated to have a role in neuronal plasticity and brain development. To ascertain the role of MAPIB, we generated mice which carry an insertion in the gene by gene-targeting methods. Mice which are homozygous for the modification die during embryogenesis. The heterozygotes exhibit a spectrum of phenotypes including slower growth rates, lack of visual acuity in one or both eyes, and motor system abnormalities.
Microtubule dynamics in axon guidance
Neuroscience bulletin, 2014
Precise modulation of the cytoskeleton is involved in a variety of cellular processes including cell division, migration, polarity, and adhesion. In developing post-mitotic neurons, extracellular guidance cues not only trigger signaling cascades that act at a distance to indirectly regulate microtubule distribution, and assembly and disassembly in the growth cone, but also directly modulate microtubule stability and dynamics through coupling of guidance receptors with microtubules to control growth-cone turning. Microtubule-associated proteins including classical microtubule-associated proteins and microtubule plus-end tracking proteins are required for modulating microtubule dynamics to influence growth-cone steering. Multiple key signaling components, such as calcium, small GTPases, glycogen synthase kinase-3β, and c-Jun N-terminal kinase, link upstream signal cascades to microtubule stability and dynamics in the growth cone to control axon outgrowth and projection. Understanding ...
Semaphorin junction: making tracks toward neural connectivity
Current Opinion in Neurobiology, 2003
Semaphorins constitute one of the largest families of repulsive and attractive growth cone guidance proteins. They affect the growth cone's actin cytoskeleton through interactions with receptor complexes composed of ligand-binding, signal-transducing, and modulatory subunits. Our understanding of the intracellular signal transduction machinery linking semaphorins to actin dynamics is limited; however, recent advances provide a more comprehensive view of the molecular basis of neuronal semaphorin signaling.