Cloning and characterization of mr-s, a novel SAM domain protein, predominantly expressed in retinal photoreceptor cells

doi:10.1186/1471-213X-6-15

BMC Developmental Biology
Volume 6

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Inoue T
Terada K
Furukawa A
Koike C
Tamaki Y
Araie M
Furukawa T

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Terada K
Furukawa A
Koike C
Tamaki Y
Araie M
Furukawa T
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Research article

Cloning and characterization of mr-s, a novel SAM domain protein, predominantly expressed in retinal photoreceptor cells

Tatsuya Inoue^*¹^,2^,3 , Koji Terada^*¹ , Akiko Furukawa¹^,4 , Chieko Koike¹ , Yasuhiro Tamaki³ , Makoto Araie³ and Takahisa Furukawa¹^,2

¹Osaka Bioscience Institute; 6-2-4 Furuedai, Suita, Osaka 565-0874, Japan

²PRESTO, Japan Science and Technology Agency; 4-1-8 Honcho, Kawaguchi, Saitama, Japan

³Department of Ophthalmology, Tokyo University School of Medicine; 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan

⁴Department of Ophthalmology, Osaka University Medical School; Yamadaoka, Suita, Osaka 565-0871, Japan

author email corresponding author email* Contributed equally

BMC Developmental Biology 2006, 6:15doi:10.1186/1471-213X-6-15


Published:	16 March 2006

Abstract

Background

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).

Results

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.

Conclusion

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.