A molecular brake that modulates spliceosome pausing at detained introns contributes to neurodegeneration

Emerging evidence suggests that intron-detaining transcripts (IDTs) are a nucleus-detained and polyadenylated mRNA pool for cell to quickly and effectively respond to environmental stimuli and stress. However, the underlying mechanisms of detained intron (DI) splicing are still largely unknown. Here, we suggest that post-transcriptional DI splicing is paused at the Bact state, an active spliceosome but not catalytically primed, which depends on Smad Nuclear Interacting Protein 1 (SNIP1) and RNPS1 (a serine-rich RNA binding protein) interaction. RNPS1 and Bact components preferentially dock at DIs and the RNPS1 docking is sufficient to trigger spliceosome pausing. Haploinsufficiency of Snip1 attenuates neurodegeneration and globally rescues IDT accumulation caused by a previously reported mutant U2 snRNA, a basal spliceosomal component. Snip1 conditional knockout in the cerebellum decreases DI splicing efficiency and causes neurodegeneration. Therefore, we suggest that SNIP1 and RNPS1 form a molecular brake to promote spliceosome pausing, and that its misregulation contributes to neurodegeneration.

Effects of GYP mRNA alternative splicing on cell surface localization of MNS blood group glycoprotein GPA and GPB / 中国输血杂志

【Objective】 To analyze the polymorphisms of GYPA and GYPB mRNA spliceosomes associated with MNS blood group, and to explore the mechanism of subcellular localization of GPA and GPB protein isomerism encoded by various spliceosomes as well as the expression of MNS blood group antigen. 【Methods】 Ten blood samples of voluntary blood donors were randomly selected. The total mRNA of peripheral blood was extracted and reversed into cDNA. Nested PCR was used to amplify reading open frame of GYPA and GYPB gene, and sequencing was performed by Sanger. The base sequence obtained was compared with GYPA(NCBI: NM_002099) and GYPB(NCBI: Nm_002100.5). After the wild type and various splicing isomer of the open reading frame of GYPA and GYPB had been obtained, they were fused with the encoding gene of green fluorescent protein (GFP) by fusion PCR technology, then cloned and transfected into HEK293 cells for over expression. The subcellular localization of GPA-GFP and GPB-GFP fused fluorescent proteins was monitored by focusing laser scanning microscope. 【Results】 Exon-1 and Exon-2 were missing in GYPA mRNA of the 2 samples, and 2~26 amino acids were missing in the predicted GPA isomer, and the full length sequence of GYPB mRNA was complete. GYPA mRNA was intact in 6 samples, exon-2 was missing in GYPB mRNA, 13~45 amino acids were missing in the predicted GPB protein isomer, and other exon sequences were intact. One sample had intact GYPA mRNA, and 364~385 bases in exon-5 of GYPB mRNA were replaced by AG, indicating truncation of amino acid signal peptide. The GYP mRNA sequences of other samples were complete. The fluorescence signal of GP-GFP fusion protein showed that all GPA and GPB glycoprotein isomers, cloned according to various RNA splicing, could demonstrate the orientation distribution on the cell membrane surface, while some alternative splicing leaded to different degrees of protein dispersion in the cell, and affected the distribution speed and proportion of protein on the cell surface, which might be one of the reasons for the strength variation of MNS antigen. 【Conclusion】 The GYP mRNA spliceosome is obviously polymorphic, but the partial deletion of GYP mRNA fragment does not affect the localization and distribution of the protein isomers encoded by GYP mRNA on the cell surface, which can ensure the expression of MNS antigen characteristics.

Expression and Significance of ACIN1 mRNA in Platelets of Lung Cancer / 中国肺癌杂志

BACKGROUND@#During the occurring and developing of tumor, tumor-educated platelets mRNA profiles were altered. Since platelets are anuclear, the level of mRNAs is probably post-transcriptional regulated by the splicing maturation of pre-mRNA and alternative splicing. Apoptotic chromatin condensation inducer 1 (ACIN1) has been shown to be a component of a splicing-dependent multiprotein exon junction complex (EJC) and was involved in mRNA metabolism associated with splicing. This study analyzed the expression of ACIN1 mRNA in platelets, and explored its potential as a biomarker of lung cancer.@*METHODS@#156 patients with lung cancer and 58 healthy controls in Shandong Cancer Hospital were collected. We isolated platelet pellets by low-speed centrifugation and extracted total RNA. The expression of ACIN1 mRNA in platelets was detected by RT-PCR, the results were analyzed statistically. And the relationship between expression of ACIN1 mRNA and clinical factors were also analyzed.@*RESULTS@#The expression level of ACIN1 mRNA in platelets of patients with lung cancer was significantly higher than that in platelets of healthy controls (P=0.015). The ROC curve showed that the area under the curve of ACIN1 mRNA for detecting lung cancer were 0.608. The expression of ACIN1 mRNA in platelets of lung cancer has no significant relationship with age, gender, pathological type and metastasis or not (P>0.05).@*CONCLUSIONS@#ACIN1 mRNA was highly expressed in platelets of lung cancer patients, and the detection of its expression level might have potential clinical value for the diagnosis of lung cancer.

Update on mutations of precursor mRNA splicing factor genes linked to retinitis pigmentosa / 中华实验眼科杂志

Retinitis pigmentosa (RP),one of the common forms of hereditary retinal dystrophies (HRD),is typified by significant genetic heterogeneities.Executed by the spliceosome,precursor mRNA (pre-mRNA) splicing is a highly regulated process by which introns are removed and exons are ligated together.To date,more than 80 genes have been involved in RP etiology.Specially,8 of these genes (PRPF3,PRPF8,PRPF31,PRPF6,PRPF4,SNRNP200,RP9 and DHX38) encode proteins essential for pre-mRNA splicing and are expressed ubiquitously.However,mutations of these RP causative pre-mRNA splicing genes exclusively result in only retinal phenotypes,and the mechanism remains unknown.In this review,we recapitulate splicing process,summarize the mutations identified in pre-mRNA splicing genes related to RP and discuss conceivable hypothesis explaining for the consequent retinaspecific phenotypes.

Research progress on spliceosome mutations in myelodysplastic syndromes / 中国肿瘤临床

Spliceosomal dysfunction plays a major role in pathogenesis of myelodysplastic syndrome (MDS). Splicing factor somatic mutations, including SF3B1, U2AF1 (U2AF35), SRSF2, ZRSR2, PRPF40B, SF1, SF3A1, and U2AF2, comprise a common (45%–85%) class of mutated genes in MDS. These genes exist in a mutually exclusive manner at the 3'splice site of mRNA processing and are predomi-nantly heterozygous and missense. RNA splicing might have therapeutic and prognosis values in MDS. This review mainly describes the pathogenesis of common splicing factor gene mutations in MDS and discusses possible therapeutic implications, clinical analysis, and prognosis.

Identification of SL addition trans-splicing acceptor sites in the internal transcribed spacer I region of pre-rRNA in Leishmania (Leishmania) amazonensis

Trypanosomatidae is a family of early branching eukaryotes harbouring a distinctive repertoire of gene expression strategies. Functional mature messenger RNA is generated via the trans-splicing and polyadenylation processing of constitutively transcribed polycistronic units. Recently, trans-splicing of pre-small subunit ribosomal RNA in the 5' external transcribed spacer region and of precursor tRNAsec have been described. Here, we used a previously validated semi-nested reverse transcription-polymerase chain reaction strategy to investigate internal transcribed spacer (ITS) I acceptor sites in total RNA from Leishmania (Leishmania) amazonensis. Two distinct spliced leader-containing RNAs were detected indicating that trans-splicing reactions occur at two AG acceptor sites mapped in this ITS region. These data provide further evidence of the wide spectrum of RNA molecules that act as trans-splicing acceptors in trypanosomatids.

Footprints of a trypanosomatid RNA world: pre-small subunit rRNA processing by spliced leader addition trans-splicing

The addition of a capped mini-exon [spliced leader (SL)] through trans-splicing is essential for the maturation of RNA polymerase (pol) II-transcribed polycistronic pre-mRNAs in all members of the Trypanosomatidae family. This process is an inter-molecular splicing reaction that follows the same basic rules of cis-splicing reactions. In this study, we demonstrated that mini-exons were added to precursor ribosomal RNA (pre-rRNA) are transcribed by RNA pol I, including the 5' external transcribed spacer (ETS) region. Additionally, we detected the SL-5'ETS molecule using three distinct methods and located the acceptor site between two known 5'ETS rRNA processing sites (A' and A1) in four different trypanosomatids. Moreover, we detected a polyadenylated 5'ETS upstream of the trans-splicing acceptor site, which also occurs in pre-mRNA trans-splicing. After treatment with an indirect trans-splicing inhibitor (sinefungin), we observed SL-5'ETS decay. However, treatment with 5-fluorouracil (a precursor of RNA synthesis that inhibits the degradation of pre-rRNA) led to the accumulation of SL-5'ETS, suggesting that the molecule may play a role in rRNA degradation. The detection of trans-splicing in these molecules may indicate broad RNA-joining properties, regardless of the polymerase used for transcription.

Pre-mRNA splicing and retinitis pigmentosa / 中华实验眼科杂志

Retinitis pigmentosa (RP) is a large group of common hereditary eye diseases with highlyheterogeneous genetic background. Over forty genes with diverse functionalities are associated with RP and they include a set of ubiquitously expressed genes. These include five genes involved in the precursor messenger RNA( premRNA) splicing. Recent progress in disease gene identification for RP has established the involvement of pre-mRNA splicing as one important mechanism in the disease etiology and has shed light on the splicing process itself, a fundamental biological process. To this date, studies in this field have been focused on two major issues. First, how do the mutations of the adRP associated splicing factors (adRP-SF) affect the splicing function? Second, how do the mutations in these ubiquitously expressed genes lead to specific retinopathy? The two topics fit with the two continuous important steps of the disease pathogenesis. Recently, researchers have made a dramatic progress in the first topic. The identification of the SNRNP200 gene,the fifth adRP-SF and its relevant functional study has shown significance to the progress in the study of RP. Numerous investigations are also being carried out in addressing the second issue.Generation of a variety of models led to a better description of the pathological process of the disease. However, in respect to the key pathogenic mechanism,researchers are still puzzled with a number of confusing questions. In this commentary,the results from the latest investigations were summarized, and in particular,the difficulties in studying the molecular mechanism by which the pre-mRNA splicing deficiency causes RP were detailed.

Short nucleotide sequences signal spliceosomal binding in nucleic acids.

We have explored the region around the splice sites of the human intron and exons from the exon-intron database (EID) and located a number of short 6-nucleotide and 7-nucleotide sequences that are relatively common in the regions. These short sequences, we expect play an important role in the selection of the appropriate splicing process. We propose that the external signals via short recognition sequences play the deterministic role in the actual splicing process. We have obtained 50 such sequences each from the exon and intron from the beginning and from the ending and noted a number of common features.