■ 第536回支部講演会
日時:2011年2月10日(木)16:00〜17:30 場所:北海道大学理学部5号館8階5-813室
演題:「Germ cells, translational control, and non-coding RNAs」 演者:Norman B. Hecht 先生 University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6080 USA
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Transcriptional, post-transcriptional, translational, and post-translational regulatory mechanisms are used to control the cellular phenotypes of testicular cells. The termination of transcription during spermiogenesis and the haploid genomes of the differentiating spermatids necessitates extensive post-transcriptional control. This requires a large number of RNA-binding proteins in the mammalian testis. In my presentation I will focus on the functions of the nucleic acid -binding protein MSY2 in germ cells. MSY2 is a highly conserved and abundant germ cell-specific DNA/RNA-binding protein that functions as a global stabilizer/translational suppressor of mRNAs. Combining immunoprecipitation and suppressive subtractive hybridization, two distinct populations of germ cell mRNAs bound or not by MSY2 were identified. MSY2 bound mRNAs are enriched for stored or translationally-delayed, male gamete-specific transcripts while the non-bound population is enriched for cell growth and ubiquitously expressed mRNAs. Chromatin precipitation assays revealed that most of the MSY2 target mRNAs were transcribed from genes containing a 12nt Y-box DNA binding motif in their promoters. Thus in the nucleus MSY2 binds to a specific promoter DNA sequence before selectively binding to its mRNA thereby linking transcription with cytoplasmic mRNA stabilization. MSY2 is an essential protein for spermatogenesis, because its deletion by gene targeting leads to phenotypically normal, but infertile male and female mice. This infertility is due to precocious translation and destabilization of germ cell mRNAs. Germ cells contain many transcripts that do not encode proteins. Piwi-family proteins are required for the processing and perhaps stabilization of one class of small non-coding RNA named piRNAs. piRNAs are an extremely abundant (hundreds of thousands) group of small germ cell RNAs of 26- 32nt that usually start with a 5’ uracil and are evolutionarily conserved, but not sequence conserved. They are distinct from microRNAs and believed to be derived from long precursor RNAs by a Dicer independent mechanism. piRNAs have been proposed to have many functions in the male germ line including repression of transposons, regulation of translation, and targeting regions of the genome for epigenetic change. The population of piRNAs in germ cells is highly heterogeneous with a sub-population that selectively binds to MSY2. Applying a cross-linking and immunoprecipitation procedure (the CLIP assay) with an affinity-purified antibody to MSY2, we have recently discovered that the MSY2 protein selectively binds a novel population of small testicular RNAs (MSY-RNAs). MSY-RNAs are ~26-32 nts, often initiate with a 5’ adenine, are expressed throughout germ cell differentiation and in somatic cells, and are mostly derived from the sense strands of annotated genes. Although much remains to be understood regarding non-coding RNA metabolism and functions in eukaryotic cells, possible functions of the MSY-RNAs will be discussed.
座長:春見 達郎 旭川医科大学解剖学教室 出席者:約30名
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