Major microtubules in epithelial cells are not anchored to the centrosome, in contrast to the centrosomal radiation of microtubules in other cell types. It remains to be discovered how these epithelial microtubules are generated and stabilized at noncentrosomal sites. Here, we found that Nezha [also known as calmodulin-regulated spectrin-associated protein 3 (CAMSAP3)] and its related protein, CAMSAP2, cooperate in organization of noncentrosomal microtubules. These two CAMSAP molecules coclustered at the minus ends of noncentrosomal microtubules and thereby stabilized them. Depletion of CAMSAPs caused a marked reduction of microtubules with polymerizing plus ends, concomitantly inducing the growth of microtubules from the centrosome. In CAMSAP-depleted cells, early endosomes and the Golgi apparatus exhibited irregular distributions. These effects of CAMSAP depletion were maximized when both CAMSAPs were removed. These findings suggest that CAMSAP2 and -3 work together to maintain noncentrosomal microtubules, suppressing the microtubule-organizing ability of the centrosome, and that the network of CAMSAP-anchored microtubules is important for proper organelle assembly.

The cadherins Fat and Dachsous regulate cell polarity and proliferation via their heterophilic interactions at intercellular junctions. Their ectodomains are unusually large because of repetitive extracellular cadherin (EC) domains, which raises the question of how they fit in regular intercellular spaces. Cadherins typically exhibit a linear topology through the binding of Ca 2+ to the linker between the EC domains. Our electron-microscopic observations of mammalian Fat4 and Dachsous1 ectodomains, however, revealed that, although their N-terminal regions exhibit a linear configuration, the C-terminal regions are kinked with multiple hairpin-like bends.

Animal cells contain two populations of microtubules: one radiating from the centrosome and the other growing from non‐centrosomal sites. Whether or not they have differing roles in cellular architecture and function remains not fully understood. The cytoplasmic protein Nezha (also known as CAMSAP3) stabilizes non‐centrosomal microtubules by attaching to their minus ends. Here, we found that depletion of CAMSAP3 in HeLa cells resulted in a relative increase in centrosomal microtubules, and this change was accompanied by accelerated actin stress fiber formation. In these cells, RhoA activity was upregulated, and the soluble fraction of GEF‐H1, a RhoGEF whose activity is inhibited by binding to microtubules, increased, explaining why stress fiber formation was promoted. We further found that CAMSAP3 depletion led to an increase in detyrosinated microtubules, and these microtubules did not interact with GEF‐H1. These findings suggest that CAMSAP3‐anchored non‐centrosomal microtubules capture GEF‐H1 more efficiently than other microtubules do and that a balance between these microtubules is important to maintain proper actin organization.

Cadherins constitute a superfamily of cell-cell interaction molecules that participate in morphogenetic processes of animal development. Fat cadherins are the largest members of this superfamily, with 34 extracellular cadherin repeats. Classic Fat, identified in Drosophila, is known to regulate cell proliferation and planar cell polarity. Although 4 subtypes of Fat cadherin, Fat1, Fat2, Fat3, and Fat4/Fat-J, have been identified in vertebrates, their protein localization remains largely unknown. Here we describe the mRNA and protein distributions of Fat3 during mouse development. We found that Fat3 expression was restricted to the nervous system. In the brain, Fat3 was expressed in a variety of regions and axon fascicles. However, its strongest expression was observed in the olfactory bulb and retina. Detailed analysis of Fat3 in the developing olfactory bulb revealed that Fat3 mRNA was mainly expressed by mitral cells and that its proteins were densely localized along the dendrites of these cells as well as in their axons to some extent. Fat3 transcripts in the retina were expressed by amacrine and ganglion cells, and its proteins were concentrated in the inner plexiform layer throughout development. Based on these observations, we suggest that Fat3 plays a role in the interactions between neurites derived from specific subsets of neurons during development. Developmental Dynamics 236:534 -543, 2007.

KIFC3, a minus end–directed kinesin motor, recruits the ubiquitin-specific protease USP47, a protease that removes ubiquitin chains from substrates, to epithelial adherens junctions. This process suppresses the ubiquitination and resultant degradation of E-cadherin, thereby maintaining stable cell–cell adhesion in epithelial sheets.