A Combinatorial MAP Code Dictates Polarized Microtubule Transport

Abstract

Many eukaryotic cells distribute their intracellular components through asymmetrically regulated active transport driven by molecular motors along microtubule tracks. While intrinsic and extrinsic regulation of motor activity exists, what governs the overall distribution of activated motor-cargo complexes within cells remains unclear. Here, we utilize in vitro reconstitution of purified motor proteins and non-enzymatic microtubule-associated proteins (MAPs) to demonstrate that these MAPs exhibit distinct influences on the motility of the three main classes of transport motors: kinesin-1, kinesin-3, and cytoplasmic dynein. Further, we dissect how combinations of MAPs affect motors, and reveal how transient interactions between MAPs and motors may promote these effects. From these data, we propose a general "MAP code" that has the capacity to strongly bias directed movement along microtubules and helps elucidate the intricate intracellular sorting observed in highly polarized cells such as neurons.kinesin-1 carries cargoes into the axon, but is largely excluded from the dendrites 6-10 . Posttranslational modifications of tubulin have been proposed to act as a "tubulin-code" that can be read out by activated motor proteins to direct their movement to specific cellular compartments 9 .However, other than the effect of tyrosination on dynein landing rate 11 , the reported biophysical effects of certain tubulin modifications, such as acetylation, on kinesin motor movement are relatively modest 12 , raising questions about how such effects could directly result in guiding transport in vivo. A large variety of other proteins bind to microtubules, and as such, transport motors must encounter a number of non-enzymatic microtubule-associated proteins (MAPs) that decorate the microtubule cytoskeleton 13 . Disruption of this bidirectional transport system due to mutations in motor complexes or MAPs leads to a wide range of neurodevelopmental and neurodegenerative disorders [13][14][15][16][17] , highlighting the interplay between these classes of proteins.Since the identification of "structural" MAPs that co-purified with polymerized brain tubulin 18 , such as MAP1, MAP2, tau, MAP7, and doublecortin (DCX), MAPs have been described as stabilizers, nucleation-promoting factors, and bundlers of microtubules 19-24 .However, recent work suggests that these MAPs may also function to direct motor transport 6,[25][26][27] . Perhaps the most well-studied MAP with regards to its effects on motors is the Alzheimer's disease-associated MAP, tau, which was originally thought to be axon-specific, but can also be observed in mature dendrites ( Figure S1) 27,28 . Tau inhibits kinesin-1 and kinesin-3 to varying degrees 25,26,29-31 , but does not strongly impede processive dynein motility 27 . These differential effects are due to a steric clash between tau and the relatively large kinesin motor domain, which does not exist for the smaller dynein microtubule-binding domain 27,32,33 . MAP2 is localized to dendrites and the axon initial segment ...

Crowd Control: Effects of Physical Crowding on Cargo Movement in Healthy and Diseased Neurons

“…However, the extent to which each MAP competes with MT motors can differ (Gumy et al, 2017). Since MAPs may be distributed differentially on the minus and plus end of a given MT (Qiang et al, 2018), movement of MT motors may vary depending on their location on the MT (Dixit et al, 2008; Monroy et al, 2019). As an example, the plus TIP complex that forms at the plus end of MTs may physically compete with MT motor binding, forcing the release of MT motors and associated cargo from the MT plus end (Akhmanova and Steinmetz, 2015).…”

Autoregulatory control of microtubule binding in the oncogene, doublecortin-like kinase 1

“…Although the roles of DCLK1 and DCX in neurodevelopment have been phenotypically described in vivo, the molecular basis for these observations remains ill-defined. Prior studies have shown that DCLK1 and DCX may act as microtubule stabilizers, nucleators, and regulators of microtubule-based transport (29)(30)(31)(32)(33)(34)(35)(36). Dissecting the mechanisms by which DCLK1 binds to the microtubule can therefore provide insight into the microtubule-binding behaviors of other DCX family members and how they may be subverted in disease.…”

DYRK1A role in microtubule-based axonal transport regulates the retrograde dynamics of APP vesicles in human neurons

“…Interestingly, upon an obstacle encounter, cargoes transported by dynein-dynactins often remain attached to the microtubule and undergo microtubule sliding 77 . Moreover, differential effects are exerted on kinesin and dynein motors by microtubule protein decoration 57 78 79 . DYRK1A appears to selectively modify the retrograde component due to changes in microtubule decoration and/or the regulation of active dynein motors in distal axonal loaded vesicles.…”