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author:("Koike, chieo")
1.  A role for nyctalopin, a small leucine rich repeat protein, in localizing the TRPM1 channel to retinal depolarizing bipolar cell dendrites 
Expression of channels to specific neuronal sites can critically impact their function and regulation. Currently, the molecular mechanisms underlying this targeting and intracellular trafficking of TRP channels remains poorly understood and identifying proteins involved in these processes will provide insight into underlying mechanisms. Vision is dependent on the normal function of retinal depolarizing bipolar cells (DBCs), which couple a metabotropic glutamate receptor 6 (mGluR6) to the TRP melastatin 1 (TRPM1) channel to transmit signals from photoreceptors. We report that the extracellular membrane attached protein, nyctalopin, is required for the normal expression of TRPM1 on the dendrites of DBCs in mus musculus. Biochemical and genetic data indicate that nyctalopin and TRPM1 interact directly suggesting that nyctalopin is acting as an accessory TRP channel subunit critical for proper channel localization to the synapse.
PMCID: PMC3139999  PMID: 21734298
TRPM1; nyctalopin; depolarizing bipolar cell; dendritic targeting; retina
2.  TRPM1 mutations are associated with the complete form of congenital stationary night blindness 
Molecular Vision  2010;16:425-437.
To identify human transient receptor potential cation channel, subfamily M, member 1 (TRPM1) gene mutations in patients with congenital stationary night blindness (CSNB).
We analyzed four different Japanese patients with complete CSNB in whom previous molecular examination revealed no mutation in either nyctalopin (NYX) or glutamate receptor, metabotropic 6 (GRM6). The ophthalmologic examination included best-corrected visual acuity, refraction, biomicroscopy, ophthalmoscopy, fundus photography, Goldmann kinetic perimetry, color vision tests, and electroretinography (ERG). Exons 2 through 27 and the exon-intron junction regions of human TRPM1 were sequenced.
Five different mutations in human TRPM1 were identified. Mutations were present in three unrelated patients with complete CSNB. All three patients were compound heterozygotes. Fundus examination revealed no abnormalities other than myopic changes, and the single bright-flash, mixed rod-cone ERG showed a “negative-type” configuration with a reduced normal a-wave and a significantly reduced b-wave amplitude. Our biochemical and cell biologic analyses suggest that the two identified IVS mutations lead to abnormal TRPM1 protein production, and imply that the two identified missense mutations lead to the mislocalization of the TRPM1 protein in bipolar cells (BCs).
Human TRPM1 mutations are associated with the complete form of CSNB in Japanese patients, suggesting that TRPM1 plays an essential role in mediating the photoresponse in ON BCs in humans as well as in mice.
PMCID: PMC2838739  PMID: 20300565
3.  Functional Roles of Otx2 Transcription Factor in Postnatal Mouse Retinal Development▿ † 
Molecular and Cellular Biology  2007;27(23):8318-8329.
We previously reported that Otx2 is essential for photoreceptor cell fate determination; however, the functional role of Otx2 in postnatal retinal development is still unclear although it has been reported to be expressed in retinal bipolar cells and photoreceptors at postnatal stages. In this study, we first examined the roles of Otx2 in the terminal differentiation of photoreceptors by analyzing Otx2; Crx double-knockout mice. In Otx2+/−; Crx−/− retinas, photoreceptor degeneration and downregulation of photoreceptor-specific genes were much more prominent than in Crx−/− retinas, suggesting that Otx2 has a role in the terminal differentiation of the photoreceptors. Moreover, bipolar cells decreased in the Otx2+/−; Crx−/− retina, suggesting that Otx2 is also involved in retinal bipolar-cell development. To further investigate the role of Otx2 in bipolar-cell development, we generated a postnatal bipolar-cell-specific Otx2 conditional-knockout mouse line. Immunohistochemical analysis of this line showed that the expression of protein kinase C, a marker of mature bipolar cells, was significantly downregulated in the retina. Electroretinograms revealed that the electrophysiological function of retinal bipolar cells was impaired as a result of Otx2 ablation. These data suggest that Otx2 plays a functional role in the maturation of retinal photoreceptor and bipolar cells.
PMCID: PMC2169187  PMID: 17908793
4.  Cloning and characterization of mr-s, a novel SAM domain protein, predominantly expressed in retinal photoreceptor cells 
Sterile alpha motif (SAM) domains are ~70 residues long and have been reported as common protein-protein interaction modules. This domain is found in a large number of proteins, including Polycomb group (PcG) proteins and ETS family transcription factors. In this work, we report the cloning and functional characterization of a novel SAM domain-containing protein, which is predominantly expressed in retinal photoreceptors and the pineal gland and is designated mouse mr-s (major retinal SAM domain protein).
mr-s is evolutionarily conserved from zebrafish through human, organisms through which the mechanism of photoreceptor development is also highly conserved. Phylogenetic analysis suggests that the SAM domain of mr-s is most closely related to a mouse polyhomeotic (ph) ortholog, Mph1/Rae28, which is known as an epigenetic molecule involved in chromatin modifications. These findings provide the possibility that mr-s may play a critical role by regulating gene expression in photoreceptor development. mr-s is preferentially expressed in the photoreceptors at postnatal day 3–6 (P3-6), when photoreceptors undergo terminal differentiation, and in the adult pineal gland. Transcription of mr-s is directly regulated by the cone-rod homeodomain protein Crx. Immunoprecipitation assay showed that the mr-s protein self-associates mainly through the SAM domain-containing region as well as ph. The mr-s protein localizes mainly in the nucleus, when mr-s is overexpressed in HEK293T cells. Moreover, in the luciferase assays, we found that mr-s protein fused to GAL4 DNA-binding domain functions as a transcriptional repressor. We revealed that the repression activity of mr-s is not due to a homophilic interaction through its SAM domain but to the C-terminal region.
We identified a novel gene, mr-s, which is predominantly expressed in retinal photoreceptors and pineal gland. Based on its expression pattern and biochemical analysis, we predict that mr-s may function as a transcriptional repressor in photoreceptor cells and in pinealocytes of the pineal gland.
PMCID: PMC1435744  PMID: 16539743

Results 1-4 (4)