Mechanisms of Kinesin-1 activation by Ensconsin/MAP7in vivo

Abstract

Centrosome separation in Drosophila larval neuroblasts and asymmetric transport of embryonic determinants in oocytes are both microtubule-dependent processes that require Kinesin-1 activation by Ensconsin/microtubule-associated protein 7 (MAP7). However, the molecular mechanism used by Ensconsin to activate Kinesin-1 remains elusive. Ensconsin/ MAP7 contains an N-terminal microtubule-binding domain (MBD) and a C-terminal Kinesinbinding domain (KBD). Using rescue experiments in live flies, we show that KBD expression alone is sufficient to fully rescue Ensconsin-dependent centrosome separation defects, but not the fast oocyte streaming and the localization patterns of Staufen and Gurken proteins.Interestingly, we show here for the first time that KBD binds and stimulates Kinesin-1 binding to Mts in vivo and in vitro. We propose that the KBD/Kinesin-1 motor represents a minimal activation module that stimulates Kinesin-1 binding to Mts. Addition of the MBD, present in the full length Ensconsin allows this activation to occur directly on the Mt. Our data also suggest that in a very large cell with a complex microtubule network, but not in smaller cells, this dual activation by Ensconsin is essential for optimal Kinesin-1 targeting to the microtubule cytoskeleton.

Microtubule-Associated Proteins: Structuring the Cytoskeleton

“…In a similar manner, other MAPs such as MAP1B [109], MAP2, MAP4 [110,111], MAP6 [112] and MAP7 [113][114][115][116] were shown to influence intracellular transport but perhaps not with the same selectivity (Fig. 3F).…”

MAPs of the neuron

“…To address the functional differences between MAP7D1 and MAP7D2, we expressed truncation as well as chimeric constructs (Figure 2A-D and S2A), as it was recently shown in Drosophila that ensconsin/MAP7 C-terminal kinesin-binding domain was sufficient to rescue several of the mutant phenotype (Metivier et al, 2018). Interestingly, we also observed a partial rescue by overexpressing of MAP7D2-C, however MAP7D1-C could not reverse the knockdown phenotype.…”

“…The microtubule associated protein ensconsin/MAP7 was described as an essential kinesin-1 cofactor by promoting kinesin-1 recruitment to microtubules (Barlan et al, 2013;Sung et al, 2008). Ensconsin/MAP7 is required for all known kinesin-1 dependent processes in polarized Drosophila oocytes (Metivier et al, 2018;Sung et al, 2008) and essential for kinesin-1 mediated myonuclear positioning in mammalian myotubes (Metzger et al, 2012). Moreover, ensconsin/MAP7 cooperates with kinesin-1 to transport cargo (Barlan et al, 2013) and triggers centrosome separation during interphase (Gallaud et al, 2014).…”