Loss of sensory hair cells in mammals results in permanent deafness because regeneration does not occur. The loss of regenerative ability is tied to the inability of the specialized supporting cells within the organ of Corti to begin dividing in response to hair cell death. We have taken a developmental approach to this problem. Our hope is that by thoroughly understanding the process by which the cells of the organ of Corti stop dividing during embryogenesis, we will gain insight into why regeneration does not occur. In doing so, we hope to provide tools and targets for therapeutic intervention into the problem of deafness. During development of the organ of Corti, control of cell proliferation is tightly coordinated with the process of cell differentiation and patterning (Ruben, 1968). We have shown that the cyclin-dependent kinase inhibitor p27Klp1 is required for timing this coordination. In p27Klp1 mutant mice, cell cycle exit is delayed, leading to supernumerary cells, a disruption of the orderly pattern of hair cell organization, and deafness (Chen and Segil, 1999). Although p27Klp1 abundance is widely believed to be regulated at the post-transcriptional level through control of protein turnover, our results indicate that transcriptional regulation of p27Klp1 is largely, though not entirely, responsible for the determining the number of cells in the mature organ. Additional preliminary data indicates that Notch pathway signaling may be a key player in regulating p27 transcription during organ of Corti formation.
In Specific Aim 1 we analyze the role of Notch signaling in the spatial and temporal regulation of p27Klp1 transcription during embryogenesis of the organ of Corti. In spite of the importance of p27Klp1 transcriptional regulation, we have observed that in Skp2 mutant mice, there is also a defect in cell cycle exit and organ of Corti structure. Skp2 is part of the SCF-ubiquitin ligase complex that is involved in regulating p27Klp1 protein turnover.
In Specific Aim 2 we address the role of post-transcriptional mechanisms in the regulation of p27Klp1. Finally, in Specific Aims 3 and 4 we address the problem of regeneration directly, by studying p27Klp1 regulation in postnatal supporting cells. We have recently developed techniques that allow us to purify postnatal supporting cells and grow them in vitro. In doing so, we have discovered that perinatal supporting cells retain the capacity to reenterthe cell cycle and divide, while supporting cells from P14 mice are unable to do so. Changes in the ability of P14 supporting cells to down-regulate p27Kip1 are partly responsible for the block to cell division that results in the lack of regeneration.
This specific aim i nvestigates the molecular basis for the age-dependent change in p27 regulation that we hypothesize underlies the lack of regeneration in the mammalian innerear.

Agency
National Institute of Health (NIH)
Institute
National Institute on Deafness and Other Communication Disorders (NIDCD)
Type
Research Project (R01)
Project #
5R01DC004189-10
Application #
7991349
Study Section
Auditory System Study Section (AUD)
Program Officer
Freeman, Nancy
Project Start
1999-08-01
Project End
2013-09-30
Budget Start
2010-12-01
Budget End
2013-09-30
Support Year
10
Fiscal Year
2011
Total Cost
$364,308
Indirect Cost
Name
House Research Institute
Department
Type
DUNS #
062076989
City
Los Angeles
State
CA
Country
United States
Zip Code
90057
Abdolazimi, Yassan; Stojanova, Zlatka; Segil, Neil (2016) Selection of cell fate in the organ of Corti involves the integration of Hes/Hey signaling at the Atoh1 promoter. Development 143:841-50
Stojanova, Zlatka P; Kwan, Tao; Segil, Neil (2015) Epigenetic regulation of Atoh1 guides hair cell development in the mammalian cochlea. Development 142:3529-36
White, Patricia M; Stone, Jennifer S; Groves, Andrew K et al. (2012) EGFR signaling is required for regenerative proliferation in the cochlea: conservation in birds and mammals. Dev Biol 363:191-200
Basch, Martín L; Ohyama, Takahiro; Segil, Neil et al. (2011) Canonical Notch signaling is not necessary for prosensory induction in the mouse cochlea: insights from a conditional mutant of RBPjkappa. J Neurosci 31:8046-58
Doetzlhofer, Angelika; Basch, Martin L; Ohyama, Takahiro et al. (2009) Hey2 regulation by FGF provides a Notch-independent mechanism for maintaining pillar cell fate in the organ of Corti. Dev Cell 16:58-69
Radde-Gallwitz, Kristen; Pan, Ling; Gan, Lin et al. (2004) Expression of Islet1 marks the sensory and neuronal lineages in the mammalian inner ear. J Comp Neurol 477:412-21
Doetzlhofer, Angelika; White, Patricia M; Johnson, Jane E et al. (2004) In vitro growth and differentiation of mammalian sensory hair cell progenitors: a requirement for EGF and periotic mesenchyme. Dev Biol 272:432-47
Chen, Ping; Johnson, Jane E; Zoghbi, Huda Y et al. (2002) The role of Math1 in inner ear development: Uncoupling the establishment of the sensory primordium from hair cell fate determination. Development 129:2495-505