Within cells, motor and non-motor microtubule-associated proteins (MAPs) simultaneously converge on the microtubule. How the binding activities of non-motor MAPs are coordinated and how they contribute to the balance and distribution of motor transport is unknown. Here, we examine the relationship between MAP7 and tau owing to their antagonistic roles in vivo. We find that MAP7 and tau compete for binding to microtubules, and determine a mechanism by which MAP7 displaces tau from the lattice. MAP7 promotes kinesin-based transport in vivo and strongly recruits kinesin-1 to the microtubule in vitro, providing evidence for direct enhancement of motor motility by a MAP. Both MAP7 and tau strongly inhibit kinesin-3 and have no effect on cytoplasmic dynein, demonstrating that MAPs differentially control distinct classes of motors. Overall, these results reveal a general principle for how MAP competition dictates access to the microtubule to determine the correct distribution and balance of motor activity.

Highlights d Microtubule-associated proteins (MAPs) act as modulators of motor movement d Dendrite-localized DCX, DCLK1, and MAP9 inhibit kinesin-1 but not kinesin-3 d MAP9 enhances kinesin-3 motility in vitro and in vivo via the motor's K-loop d MAP9 inhibits the dynein-dynactin complex by blocking the p150-tubulin interaction

2 Within cells, numerous motor and non-motor microtubule-associated proteins (MAPs)simultaneously converge on the microtubule lattice. How the binding activities of nonmotor MAPs are coordinated and how they contribute to the balance and distribution of microtubule motor transport is unknown. Here, we examine the relationship between MAP7 and tau due to their antagonistic effects on neuronal branch formation and kinesin motility in vivo 1-8 . We find that MAP7 and tau compete for binding to microtubules, and determine a mechanism by which MAP7 displaces tau from the lattice. In striking contrast to the inhibitory effect of tau, MAP7 promotes kinesin-based transport in vivo and strongly enhances kinesin-1 binding to the microtubule in vitro, providing evidence for direct enhancement of motor motility by a MAP. In contrast, both MAP7 and tau strongly inhibit kinesin-3 and have no effect on cytoplasmic dynein, demonstrating that MAPs exhibit differential control over distinct classes of motors. Overall, these results reveal a general principle for how MAP competition dictates access to the microtubule to determine the correct distribution and balance of molecular motor activity.The balance of intracellular transport is essential for the structural and functional organization of a cell. The microtubule motors, kinesin-1 and cytoplasmic dynein, drive cellular cargoes towards microtubule plus-ends and minus ends, respectively. Mutations in either motor pathway disrupt the balance of transport and cause a range of diseases 9,10 . Motors must navigate a crowded microtubule lattice that is decorated with non-motor MAPs. These MAPs play various roles in regulating microtubule dynamics, turnover, and stability, as well as in influencing molecular motor transport 3,[11][12][13] . The Alzheimer's disease related MAP, tau (MAPT), is highly enriched in neuronal axons and inhibits kinesin-1 motility in vivo and in vitro, but has less of an effect on dynein-based movement [3][4][5][6][7][8] . How plus-end directed transport is accomplished in the tau-3 rich axonal environment is therefore an outstanding question, though the effects of tau on other classes of kinesin motors have not been tested. One MAP that appears to be antagonistic to tau is MAP7 ensconsin) 14,15 . The knockdown of MAP7 or tau in neurons produces opposite axonal branching phenotypes 1,2 . In addition, MAP7 is important for kinesin-based cargo transport and nuclear positioning in vivo [16][17][18] ; however, the molecular mechanism underlying this relationship is unclear. How tau and MAP7 activities are coordinated on the surface of individual microtubules in cells, and the functional consequence of MAP distributions on microtubule motor motility remain open questions.To approach this problem, we first examined the localization patterns of MAP7 and tau in mature Drosophila peripheral nervous system neurons in vivo and DIV4 primary mouse neuronal cultures. In both systems, we found that MAP7 localized within both dendrites and axons, while tau was predominantl...

Drosophila Ensconsin (also known as MAP7) controls spindle length, centrosome separation in brain neuroblasts (NBs) and asymmetric transport in oocytes. The control of spindle length by Ensconsin is Kinesin-1 independent but centrosome separation and oocyte transport require targeting of Kinesin-1 to microtubules by Ensconsin. However, the molecular mechanism used for this targeting remains unclear. Ensconsin contains a microtubule (MT)binding domain (MBD) and a Kinesin-binding domain (KBD). Rescue experiments show that only full-length Ensconsin restores the spindle length phenotype. KBD expression rescues ensc centrosome separation defects in NBs, but not the fast oocyte streaming and the localization of Staufen and Gurken. Interestingly, the KBD can stimulate Kinesin-1 targeting to MTs in vivo and in vitro. We propose that a KBD and Kinesin-1 complex is a minimal activation module that increases Kinesin-1 affinity for MTs. Addition of the MBD present in full-length Ensconsin allows this process to occur directly on the MT and triggers higher Kinesin-1 targeting. This dual regulation by Ensconsin is essential for optimal Kinesin-1 targeting to MTs in oocytes, but not in NBs, illustrating the importance of adapting Kinesin-1 recruitment to different biological contexts.

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 ...