Inoue Tatsuya, Terada Koji, Furukawa Akiko, Koike Chieko, Tamaki Yasuhiro, Araie Makoto, Furukawa Takahisa
Osaka Bioscience Institute, 6-2-4 Furuedai, Suita, Osaka 565-0874, Japan.
BMC Dev Biol. 2006 Mar 16;6:15. doi: 10.1186/1471-213X-6-15.
Sterile alpha motif (SAM) domains are approximately 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.
无菌α基序（SAM）结构域长度约为70个氨基酸残基，据报道是常见的蛋白质 - 蛋白质相互作用模块。该结构域存在于大量蛋白质中，包括多梳蛋白家族（PcG）蛋白和ETS家族转录因子。在本研究中，我们报道了一种新型含SAM结构域蛋白的克隆及功能特性，该蛋白主要在视网膜光感受器和松果体中表达，被命名为小鼠mr-s（主要视网膜SAM结构域蛋白）。
从斑马鱼到人类，mr-s在进化上是保守的，而光感受器发育机制在这些生物中也高度保守。系统发育分析表明，mr-s的SAM结构域与小鼠多同源蛋白（ph）直系同源物Mph1/Rae28关系最为密切，后者是一种参与染色质修饰的表观遗传分子。这些发现提示mr-s可能通过调节光感受器发育中的基因表达发挥关键作用。mr-s在出生后第3 - 6天（P3 - 6）光感受器进行终末分化时以及成年松果体的光感受器中优先表达。mr-s的转录直接受视锥 - 视杆同源结构域蛋白Crx调控。免疫沉淀分析表明，mr-s蛋白主要通过含SAM结构域的区域以及ph进行自我结合。当mr-s在HEK293T细胞中过表达时，mr-s蛋白主要定位于细胞核。此外，在荧光素酶测定中，我们发现与GAL4 DNA结合结构域融合的mr-s蛋白起转录抑制作用。我们揭示，mr-s的抑制活性并非因其SAM结构域的同源相互作用，而是由于其C末端区域。
我们鉴定了一个新基因mr-s，它主要在视网膜光感受器和松果体中表达。基于其表达模式和生化分析，我们预测mr-s可能在光感受器细胞和松果体的松果体细胞中作为转录抑制因子发挥作用。
