Biology subjects

Takeichi, M.

Publications and source records attributed to Takeichi, M..

4 recordsLinked to original sources

bioRxiv2021

CAMSAP2 organizes a γ-tubulin-independent microtubule nucleation centre

Microtubules are dynamic polymers consisting of {beta}-tubulin heterodimers. The initial polymerization process, called microtubule nucleation, occurs spontaneously via {beta}-tubulin. Since a large energy barrier prevents microtubule nucleation in cells, the {gamma}-tubulin ring complex is recruited to the centrosome to overcome the nucleation barrier. However, detachment of a considerable number of microtubules from the centrosome is known to contribute to fundamental processes in cells. Here, we present evidence that minus-end-binding calmodulin-regulated spectrin-associated protein 2 (CAMSAP2) serves as a strong nucleator for microtubule formation from soluble {beta}-tubulin independent of {gamma}-tubulin. CAMSAP2 significantly reduces the nucleation barrier close to the critical concentration for microtubule polymerization by stabilizing the longitudinal contacts among {beta}-tubulins. CAMSAP2 clusters together with {beta}-tubulin to generate nucleation intermediates, from which numerous microtubules radiate, forming aster-like structures. Our findings suggest that CAMSAP2 supports microtubule growth by organizing a nucleation centre as well as by stabilizing microtubule nucleation intermediates.

cell biology↗

bioRxiv2020

Celsr1 and CAMSAP3 differently regulate intercellular and intracellular cilia orientation in oviduct multiciliated cells

The molecular mechanisms by which cilia orientation is coordinated within and between multiciliated cells (MCCs) is not fully understood. By observing the orientation of basal bodies (BB) in MCCs of mouse oviducts, here, we show that Celsr1, a planar cell polarity (PCP) factor involved in tissue polarity regulation, is dispensable for determining BB orientation in individual cells, whereas CAMSAP3, a microtubule minus-end regulator, is critical for this process but not for PCP. MCCs exhibit a characteristic BB orientation and microtubule gradient along the tissue axis, and these intracellular polarities were maintained in the cells lacking Celsr1, although the intercellular coordination of the polarities was partly disrupted. On the other hand, CAMSAP3 regulated the assembly of microtubules interconnecting BBs by localizing at the BBs, and its mutation led to disruption of intracellular coordination of BB orientation, but not affecting PCP factor localization. Thus, both Celsr1 and CAMSAP3 are responsible for BB orientation but in distinct ways; and therefore, their cooperation should be critical for generating functional multiciliated tissues.

cell biology↗

bioRxiv2020

CAMSAP3 is required for mTORC1-dependent ependymal cell growth and lateral ventricle shaping in mouse brains

Microtubules (MTs) regulate numerous cellular processes, but their roles in brain morphogenesis are not well known. Here we show that CAMSAP3, a non-centrosomal microtubule regulator, is important for shaping the lateral ventricles. In differentiating ependymal cells, CAMSAP3 became concentrated at the apical domains, serving to generate MT networks at these sites. Camsap3-mutated mice showed abnormally narrow lateral ventricles, in which excessive stenosis or fusion was induced, leading to a decrease of neural stem cells at the ventricular and subventricular zones. This defect was ascribed at least in part to a failure of neocortical ependymal cells to broaden their apical domain, a process necessary for expanding the ventricular cavities. mTORC1 was required for ependymal cell growth but its activity was downregulated in mutant cells. Lysosomes, which mediate mTORC1 activation, tended to be reduced at the apical regions of the mutant cells, along with disorganized apical MT networks at the corresponding sites. These findings suggest that CAMSAP3 supports mTORC1 signaling required for ependymal cell growth via MT network regulation, and, in turn, shaping of the lateral ventricles. Summary statementCAMSAP3, which mediates non-centrosomal microtubule assembly, is required for mTORC1-dependent maturation of ependymal cells at the neocortex of developing mouse brains. Loss of CAMSAP3 causes deformation of the lateral ventricles.

developmental biology↗

bioRxiv2020

Adherens junction serves to generate cryptic lamellipodia required for collective migration of epithelial cells

Collective migration of epithelial cells plays crucial roles in various biological processes such as cancer invasion. In migrating epithelial sheets, leader cells form lamellipodia to advance, and follower cells also form similar motile apparatus at cell-cell boundaries, which are called cryptic lamellipodia (c-lamellipodia). Using adenocarcinoma-derived epithelial cells, we investigated how c-lamellipodia are generated, and found that they sporadically grew from Ecadherin-based adherens junctions (AJs). WAVE and Arp2/3 complexes were localized along the AJs, and silencing them not only interfered with c-lamellipodia formation but also prevented follower cells from trailing the leaders. Disruption of AJs by removing E-catenin resulted in uncontrolled c-lamellipodia growth, and this was brought about by myosin II activation and the resultant contraction of AJ-associated actomyosin cables. Additional observations indicated that c-lamellipodia tended to grow at mechanically weak sites of the junction. We conclude that AJs not only tie cells together but also generate c-lamellipodia by recruiting actin regulators, enabling epithelial cells to undergo ordered collective migration.

cell biology↗