Marshalin, a microtubule minus-end binding protein, regulates cytoskeletal structure in the organ of Corti

Abstract

SummaryDramatic structural changes in microtubules (MT) and the assembly of complicated intercellular connections are seen during the development of the cellular matrix of the sense organ for hearing, the organ of Corti. This report examines the expression of marshalin, a minus-end binding protein, during this process of cochlear development. We discovered that marshalin is abundantly expressed in both sensory hair cells and supporting cells. In the adult, prominent marshalin expression is observed in the cuticular plates of hair cells and in the noncentrosomal MT organization centers (MTOC) of Deiters' and pillar cells. Based upon differences in marshalin expression patterns seen in the organ of Corti, we identified eight isoforms ranging from 863 to 1280 amino acids. mRNAs/proteins associated with marshalin's isoforms are detected at different times during development. These isoforms carry various protein–protein interacting domains, including coiled-coil (CC), calponin homology (CH), proline-rich (PR), and MT-binding domains, referred to as CKK. We, therefore, examined membranous organelles and structural changes in the cytoskeleton induced by expressing two of these marshalin isoforms in vitro. Long forms containing CC and PR domains induce thick, spindle-shaped bundles, whereas short isoforms lacking CC and PR induce more slender variants that develop into densely woven networks. Together, these data suggest that marshalin is closely associated with noncentrosomal MTOCs, and may be involved in MT bundle formation in supporting cells. As a scaffolding protein with multiple isoforms, marshalin is capable of modifying cytoskeletal networks, and consequently organelle positioning, through interactions with various protein partners present in different cells.

Microtubule Minus-End-Targeting Proteins

“…CAMSAP3 possesses another microtubule-interacting helical domain between CC3 and CKK, which makes it the most potent microtubule stabilizer and minus-end growth inhibitor among the three mammalian CAMSAPs [38] ( Figure 1A). Interestingly, CAMSAP3 is expressed as multiple splice isoforms, some of which lack CC1, CC2 and MBD [46] and thus likely have reduced microtubule affinity.…”

“…CAMSAP3 was found to be prominently expressed in the organ of Corti, where it was named Marshalin [46]. The supporting cells of the organ of Corti are a specialized type of epithelial cell and contain extremely dense microtubule bundles that originate from both centrosomal as well as non-centrosomal, cortical microtubule-organizing centers [46,66].…”

“…The supporting cells of the organ of Corti are a specialized type of epithelial cell and contain extremely dense microtubule bundles that originate from both centrosomal as well as non-centrosomal, cortical microtubule-organizing centers [46,66]. CAMSAP3/Marshalin was enriched at all non-centrosomal microtubule-organizing sites, suggesting that it might be required for their formation.…”

“…CAMSAP3/Marshalin was enriched at all non-centrosomal microtubule-organizing sites, suggesting that it might be required for their formation. Interestingly, microtubules in these cells are composed of 15 protofilaments: it would be interesting to know whether the expression of specific isoforms of CAMSAP3 contributes to this unusual microtubule structure [46].…”

Control of apico-basal epithelial polarity by the microtubule minus-end binding protein CAMSAP3 and spectraplakin ACF7

“…CAMSAP3 is also very abundant in supporting cells of the organ of Corti, a specialized type of epithelial cell with extremely dense microtubule bundles that are anchored at centrosomal and non-centrosomal microtubuleorganizing centers at the cell cortex (Takahashi et al, 2016;Zheng et al, 2013). Similar to other CAMSAP/Patronin-family members, CAMSAP3 has a C-terminal conserved domain, the CKK, as well as several coiled-coil regions and an N-terminal calponin homology domain, the function of which is currently unknown (Akhmanova and Hoogenraad, 2015;Baines et al, 2009).…”