Showing papers by "Masatoshi Hagiwara published in 2007"

Spliceostatin A targets SF3b and inhibits both splicing and nuclear retention of pre-mRNA.

Abstract: The removal of intervening sequences from transcripts is catalyzed by the spliceosome, a multicomponent complex that assembles on the newly synthesized pre-mRNA. Pre-mRNA translation in the cytoplasm leads to the generation of aberrant proteins that are potentially harmful. Therefore, tight control to prevent undesired pre-mRNA export from the nucleus and its subsequent translation is an essential requirement for reliable gene expression. Here, we show that the natural product FR901464 (1) and its methylated derivative, spliceostatin A (2), inhibit in vitro splicing and promote pre-mRNA accumulation by binding to SF3b, a subcomplex of the U2 small nuclear ribonucleoprotein in the spliceosome. Importantly, treatment of cells with these compounds resulted in leakage of pre-mRNA to the cytoplasm, where it was translated. Knockdown of SF3b by small interfering RNA induced phenotypes similar to those seen with spliceostatin A treatment. Thus, the inhibition of pre-mRNA splicing during early steps involving SF3b allows unspliced mRNA leakage and translation.

The Fox-1 Family and SUP-12 Coordinately Regulate Tissue-Specific Alternative Splicing In Vivo

Abstract: Many pre-mRNAs are alternatively spliced in a tissue-specific manner in multicellular organisms. The Fox-1 family of RNA-binding proteins regulate alternative splicing by either activating or repressing exon inclusion through specific binding to UGCAUG stretches. However, the precise cellular contexts that determine the action of the Fox-1 family in vivo remain to be elucidated. We have recently demonstrated that ASD-1 and FOX-1, members of the Fox-1 family in Caenorhabditis elegans, regulate tissue-specific alternative splicing of the fibroblast growth factor receptor gene, egl-15, which eventually determines the ligand specificity of the receptor in vivo. Here we report that another RNA-binding protein, SUP-12, coregulates the egl-15 alternative splicing. By screening for mutants defective in the muscle-specific expression of our alternative splicing reporter, we identified the muscle-specific RNA-binding protein SUP-12. We identified juxtaposed conserved stretches as the cis elements responsible for the regulation. The Fox-1 family and the SUP-12 proteins form a stable complex with egl-15 RNA, depending on the cis elements. Furthermore, the asd-1; sup-12 double mutant is defective in sex myoblast migration, phenocopying the isoform-specific egl-15(5A) mutant. These results establish an in vivo model that coordination of the two families of RNA-binding proteins regulates tissue-specific alternative splicing of a specific target gene.

Introns play an essential role in splicing-dependent formation of the exon junction complex

Abstract: Pre-mRNA splicing specifically deposits the exon junction complex (EJC) onto spliced mRNA, which is important for downstream events. Here, we show that EJC components are primarily recruited to the spliceosome by association with the intron via the intron-binding protein, IBP160. This initial association of EJC components occurs in the absence of the final EJC-binding site on the exon. RNA interference (RNAi) knockdown of IBP160 arrested EJC association with cytoplasmic RNAs following nonsense-mediated decay. We propose that the intron has a crucial role in the early steps of EJC formation and is indispensable for the subsequent formation of a functional EJC.

Cross-talks between Transcription and Post-transcriptional Events within a ‘mRNA Factory’

Abstract: Eukaryotic gene expression is controlled in multi steps. Pre-messenger RNAs (pre-mRNAs) transcribed by RNA polymerase II (RNAPII) are capped at 5' end, spliced to remove introns and polyadenylated at 3' end. These processes are followed by other post-transcriptional steps that include mRNA export, translation and mRNA degradation. Recent studies have shown that individual events occurring during eukaryotic gene expression are coupled together under more elaborate regulatory controls. In this review, the molecular and functional cross-talks between transcription and the post-transcriptional events are overviewed.

Shortened life spans of biotech pioneer patents in Japan: a lesson from the DNA chip

Abstract: Strict examinations have resulted in drastically shortened life spans for a broad range of biotech 'pioneer' patents in Japan.

Transgenic reporter system that reveals expression profiles and regulation mechanisms of alternative splicing in nematodes

Abstract: An object of the present invention is to develop a new alternative splicing reporter system and to provide a method for detecting alternative splicing patterns in a multicellular organism more precisely, a method for identifying efficiently substances and gene regions that affect alternative splicing in a multicellular organism, and the like by utilizing the alternative splicing reporter system. Specifically, the present invention relates to a method for detecting alternative splicing in a multicellular organism, and a method for identifying substances and gene regions that affect alternative splicing in a multicellular organism, which use a DNA construct in which at least two different reporter genes are inserted into a specific gene that undergoes alternative splicing, or a combination of DNA constructs (a combination of at least two different DNA constructs) in which DNA construct a reporter gene is inserted into a specific gene that undergoes alternative splicing.