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Abstract
We used organotypic cultures of the stria vascularis (SV), the organ of Corti (OC) and the modiolus (MOD) of newborn rats to analyze the differential expression levels and responses of cytoskeletal, myelin- and neural growth factor-associated genes following preparatory injury and hypoxia. The transcript mRNA levels of the neurofilaments Nefl , Nefm, the microtubule-associated proteins Mapt, Map1a, Map2, and of the myelin basic protein Mbp decrease during 24 h in a coordinated way across the MOD and OC regions. The increased cell death rate in the MOD region is associated with an increased expression of Nes, the transcript encoding the intermediate filament nestin, and of the neural growth factor receptor Ngfr, the growth-associated protein 43 Gap43 and the Purkinje cell protein Pcp4. The correlation analysis revealed close associations between Nes expression and genes involved in apoptotic and necrotic cell death (caspase Casp3, calpains Capn1, Capn2, Capns1), the glutamate pathway (glutamate receptor NMDA associated protein 1 Grina, glial high affinity glutamate transporter Slc1a3), cytoskeletal genes (Nefm, Map2, Map1a, Mbp), transcription factors (hypoxia inducible factor Hif-1a, jun proto-oncogene Jun, brain expressed myelocytomatosis B-myc, HES family bHLH transcription factor 1 Hes-1, forkhead-box D3 Foxd3) and neural growth factors ( Ngfr, Gap43 and Pcp4 ) . The unique response and the composition of the Nes cluster made us conclude that the expression of cell-death-associated genes and the regeneration-associated genes takes place in a coordinated way, and differs between the MOD and the OC/SV regions.
Highlights
The cochlea consists of three main complex structures, each serving a specific function: the stria vascularis (SV), the organ of Corti (OC) and the modiolus (MOD)[1]
Data from normoxic and hypoxic environments have been combined, because we found no statistical difference in gene expression neither for the numbers of propidium iodide (PI)-stained nuclei nor for the expression of Hif-1a mRNA or that of other genes
The chip used in this study contained sequences for two non-neuronal and three neuron-specific intermediate filaments (IFs), two microtubule proteins (Tubb5, member of the beta family and Tubg1, member of the gamma family), four members of the microtubule-associated protein genes (Map1a, Map1lc3b, Map2 and Mapt) and the myelin-associated transcripts Mbp, Mpz, myelin-associated glycoprotein (Mag) and Cnp (2 ́, 3 ́-cyclic nucleotide phosphodiesterase; Table 1)
Summary
The cochlea consists of three main complex structures, each serving a specific function: the stria vascularis (SV), the organ of Corti (OC) and the modiolus (MOD)[1]. The neuro-sensory outer and inner hair cells (HCs) that transform the mechanical signal into an electrical one are located in the OC. This region contains the non-neural supporting cells that are regarded to be highly specialized forms of the glia cells. The MOD region mainly comprises the bipolar spiral ganglion neurons (SGN) and the Schwann cells (SCs). The SGNs provide the contact between the hair cells and the cochlear nucleus in the brainstem. The Schwann cells myelinate the neurites of the SGNs. The peripheral processes innervate the hair cells in the organ of Corti and the central processes terminate in the cochlear nucleus[1, 2]
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