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.
Highlights
The organ of Corti, the sense organ of hearing in mammals, develops from relatively simple epithelial cells into a complex group of highly polarized hair cells (HCs) and their surrounding supporting cells (SCs) (Fig. 1A) (Kelly and Chen, 2009; Rida and Chen, 2009)
Summary Dramatic 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
We discovered that marshalin is abundantly expressed in both sensory hair cells and supporting cells
Summary
The organ of Corti, the sense organ of hearing in mammals, develops from relatively simple epithelial cells into a complex group of highly polarized hair cells (HCs) and their surrounding supporting cells (SCs) (Fig. 1A) (Kelly and Chen, 2009; Rida and Chen, 2009). The apical portions of IHCs, OHCs, IPCs, IPs, OPs, and the phalangeal processes of DCs are connected through tight junctions to form the reticular lamina, which separates endolymph from perilymph. OHC basal portions are secured within Deiters’ cups Various intercellular structures, such as tight junctions, adhesive junctions, desmosomes, and gap junctions are found within the organ of Corti (Slepecky, 1996; Nunes et al, 2006). Even though both HCs and SCs are highly polarized, MT arrangements in these cell types differ (Fig. 1B). Packed MT bundles in SCs provide the architectural support required to convey mechanical signals to mechano-sensitive hair cells (Patuzzi, 1996).
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