Biology subjects

Yajima, J.

Publications and source records attributed to Yajima, J..

4 recordsLinked to original sources

bioRxiv2022

Fission yeast Dis1 is an unconventional TOG/XMAP215 that induces microtubule catastrophe to drive chromosome pulling

The shortening of microtubules attached to kinetochores is the driving force of chromosome movement during cell division. Specific kinesins are believed to shorten microtubules but are dispensable for viability in yeast, implying the existence of additional factors responsible for microtubule shortening. Here, we demonstrate that Dis1, a TOG/XMAP215 ortholog in fission yeast, promotes microtubule shortening to carry attached chromosomes. Although TOG/XMAP215 orthologs are generally accepted as microtubule polymerases, Dis1 promoted microtubule catastrophe in vitro and in vivo. Notably, microtubule catastrophe was promoted when the tip was attached to kinetochores, as they steadily anchored Dis1 at the kinetochore-microtubule interface. Engineered Dis1 oligomers artificially tethered at a chromosome arm region induced the shortening of microtubules in contact, frequently pulling the chromosome arm towards the vicinity of spindle poles in meiocytes. Thus, unlike Alp14 and other TOG/XMAP215 orthologs, Dis1 plays an unconventional role in promoting microtubule catastrophe, thereby driving chromosome movement.

cell biology↗

bioRxiv2021

Torque force in the kinesin stroke drives coupled yaw axis and orbital rotations of kinesin coated gold nanorods

Kinesin motor domains generate impulses of force and movement that have both translational and rotational components, raising the question of how the rotational component contributes to motor functions. We used a new assay in which kinesin-coated gold nanorods (kinesin-GNRs) move on suspended microtubules, for two plus-end-directed and weakly-processive kinesins: single-headed KIF1A, dimeric ZEN-4. Polarization of the light scattered by two types of kinesin-GNRs periodically oscillated as they orbited the microtubule along a left-handed helical trajectory. Our analyses revealed that each kinesin-GNR unidirectionally rotates about its yaw axis as it translocates, and that the period of this yaw-axis rotation corresponds to two periods of its left-handed helical orbit around the microtubule axis. Theoretical analyses suggest that the yaw-axis rotation enhances biased lateral displacement of the kinesin team. Our study reveals biaxial rotation as a new mode of motility in kinesin teams that may help the team to sidestep roadblocks.

biophysics↗

bioRxiv2018

Myosin-driven fragmentation of actin filaments triggers contraction of a disordered actin network

The dynamic cytoskeletal network is responsible for cell shape changes and cell division. The actin-based motor protein myosin II drives the remodeling of a highly disordered actin-based network and enables the network to perform mechanical work such as contraction, migration and adhesion. Myosin II forms bipolar filaments that self-associate via their tail domains. Such myosin minifilaments generate both extensile and compressive forces that pull and push actin filaments, depending on the relative position of myosin and actin filaments in the network. However, it remains unclear how the mechanical properties of myosin II that rely on the energy of ATP hydrolysis spontaneously contract the disordered actin network. Here, we used a minimal in vitro reconstituted experimental system consisting of actin, myosin, and a cross-linking protein, to gain insights into the molecular mechanism by which myosin minifilaments organize disordered actin networks into contractile states. We found that contracted cluster size and time required for the onset of network contraction decreased as ATP concentration decreased. Contraction velocity was negatively correlated with ATP concentrations. Reduction of ATP concentration caused fragmentation of actin filaments by myosin minifilament. We also found that gelsolin, a Ca2+-regulated actin filament-severing protein, induced contraction of a mechanically stable network, implying that fragmentations of actin filaments in the network weaken the intra-network connectivity and trigger contraction. Our findings reveal that the disordered actin network contraction can be controlled by fragmentation of actin filaments, highlighting the molecular mechanism underlying the myosin motor-severing activities, other than the sliding tensile and compressive stress in the disordered actin network.

biophysics↗

bioRxiv2018

Plus-end directionality is present in the catalytic core of kinesin-14 minus-end directed motors.

Molecular motors move along microtubules unidirectionally. However, the origin of directionality is not clear. Here kinesin-14 monomers were engineered such that they could be anchored via either their N- or C-termini, leaving the opposite terminal regions mechanically disconnected from the surface. We find that the conserved catalytic motor core of kinesin-14 has intrinsic plus-end directionality and that the proper function of the neck-helix region is required to achieve minus-end directionality.

biophysics↗