Transcript Diapositive 1

Supporting cell cytoskeleton during development of the organ of
Corti in rat
JOHNEN Nicolas, THELEN Nicolas, MALGRANGE Brigitte, THIRY Marc
GIGA Neurosciences, CNCM, University of Liège, Belgium
Introduction
In mammals, the perception of sound is mediated by an epithelial sensory patch located in the cochlear region of the inner ear
named the organ of Corti (OC) [Kelley and Bianchi, 2002 ; Kelley, 2006]. The latter is componed of mechanosensory hair cells and
nonsensory supporting cell types. The hair cells are modified epithelial cells that utilise a group of derived microvilli, referred to as
stereocilia, to perceive pressure waves induced through sound. Based on their morphology and physiology, two types of hair cells
can be distinguished: inner and outer hair cells. Likely, at least four types of supporting cells can be identified in the OC: inner pillar
cell, outer pillar cell, inner phalangeal cell and Deiters’ cells. These cells are arranged in a regular mosaic pattern running along the
length of the snail-like cochlea from base to apex. One of the most striking aspects of this mosaic is that specific cell types are
arranged in discreet rows. The edge of the OC located closest to the modiolus is composed of a single row of alternating inner hair
cells and inner phalangeal cells. The edge of the Corti's organ located closest to the stria vascularis is composed of three rows of
outer hair cells and Deiters’cells that are also arranged into a regular alternating mosaic. Finally, the single row of inner hair cells and
the three rows of outer hair cells are separated by the tunnel of Corti that is a space delimited by a single row of inner pillar cells and
a single row of outer pillar cells. The formation of Corti’s tunnel appears after birth in rat [Roth and Bruns, 1992].
Although the structure of the auditory organ in mature mammals, the organ of Corti, is clearly established, its development is far to be elucidated. Using antibodies against different
proteins cytoskeleton (tubulin (tubulin beta IV), cytokeratins pan (CK 1, 4, 5, 6, 8, 10, 13, 18, and 19) and vimentin (V9)),we investigated by confocal microscopy the setting up of
supporting cells' cytoskeleton during the differentiation of the OC in rat from the embryonic day 18 (E18) to postnatal day 15 (P15).
Results
Tubulin beta IV
Figures A-G: Spatiotemporal distribution of tubulin beta IV during the mammalian auditory organ development from E22 to P15 in the basal part of the cochlea. At E22,
small tubulin beta IV could only be detected in the cytoplasm of inner hair cell by confocal microscopy. At P0, moreover the inner hair cell, the inner pillar cell and the inner phallangeal
cell are labelled. At P4-P5, the tubulin beta IV is important within the inner pillar cells and it dissapear of the inner hair cell. At P8 to P14-P15, there is the tubulin beta IV in the pillar
cells and at the periphery of the Deiters' cells. I: Inner hair cell; O: Outer hair cell; Ip: Inner Pillar cell; Op: Outer Pillar cell; D: Deiters' cell. Bar: 10µm. Red: Myosin VI; Green: Tubulin
beta IV; Blue: Dapi.
Cytokeratins pan
Figures A-F: Spatiotemporal distribution of Cytokeratin pan during the mammalian auditory organ development from E22 to P15 in the basal part of the cochlea. At E22,
small cytokeratins could only be detected in the base of the inner inner phalangeal cell, outer pillar cell and Deiters' cells by confocal microscopy. At P0 to P4-P5, it desappear of the
inner phalangeal cell, the inner and outer pillar cell and the Deiter's cells are labelled. At P8 to P10, there is the cytokeratin in the pillar cells, the Deiters' cells and near the phalangeal
and bording cells. At P14-P15, the basal parts of the pillar cell and of the Deiters' cells, and the phalangeal cells are labelled. I: Inner hair cell; O: Outer hair cell; Ip: Inner Pillar cell; Op:
Outer Pillar cell; D: Deiters' cell. Bar: 10µm. Red: Myosin VI; Green: Tubulin beta IV; Blue: Dapi.
Vimentin V9
Figures A-F: Spatiotemporal distribution of vimentin V9 during the mammalian auditory organ development from E22 to P15 in the basal part of the cochlea. At E22, no label
of vimentin is observed. At P0, there are vimentin in the cytoplasm of outer pillar cells and in the basal part of inner pillar cell and Deiters' cells it desappear of the inner phalangeal cell,
the inner and outer pillar cell and the Deiter's cells are labelled. At P10, the vimentin is present in the pillar cells, the Deiters' cells and near the phalangeal and bording cells. At P11-12
to P14-P15, the pillar cells and Deiter's cell are labelled. I: Inner hair cell; O: Outer hair cell; Ip: Inner Pillar cell; Op: Outer Pillar cell; D: Deiters' cell. Bar: 10µm. Red: Myosin VI; Green:
Tubulin beta IV; Blue: Dapi.
Conclusions
We showed that inner pillar cells are labelled with an anti-tubulin beta IV antibody from P0. Using an antibody to cytokeratins, a labelling appeared in Deiters' cells from E22. We also
revealed that during the development of the OC, supporting cells were labelled with anti-vimentin antibody from P0. Surprinsingly, supporting cells, which are epithelial cells, are
labelled with vimentin at P15. Further investigations will be necessary to understand the development of the supporting cell cytoskeleton.