One of the most exciting findings in RNA biology is the discovery of numerous circular RNAs （circRNA） in mammalian genome. Once being considered as low abundance splicing byproducts, circRNAs are surprisingly abunda...One of the most exciting findings in RNA biology is the discovery of numerous circular RNAs （circRNA） in mammalian genome. Once being considered as low abundance splicing byproducts, circRNAs are surprisingly abundant and can be generated by multiple pathways. The majority of circRNAs are generated from the RNA backsplicing in which an upstream 3＇ splicing site （ss） is joined with a downstream 5＇ ss. Several groups have independently demonstrated that the complementary paring of intronic sequences is sufficient to promote the biogenesis of circRNA via backsplicing. In addition, intronic circRNAs can also be generated through partial degradation of lariat RNAs that are splicing byproduct.展开更多
Major histocompatibility complex （MHC） is a family of highly polymorphic genes activating adaptive immunity in vertebrates. However, the underlying mecha- nism of MHC evolution is still not fully understood. In this...Major histocompatibility complex （MHC） is a family of highly polymorphic genes activating adaptive immunity in vertebrates. However, the underlying mecha- nism of MHC evolution is still not fully understood. In this study, we investigated genetic variation of three classical MHC class I genes in the giant panda （Ailuropoda mela- noleuca） and tested for selection effect and recombination event across exonic and intronic sequences to understand maintenance mechanism of polymorphism at Aime-MHC class I genes. In total, we isolated 21 MHC class I haplotypes （exon 2-intron 2-exon 3） from 46 captive giant pandas, of which eight were for Aime-C, seven for Aime-I and six for Aime-L; however, we only identified six unique sequences from these haplotypes. The subsequent maximum-likeli- hood and Chi-square analyses both detected evidence of recombination acting on the 21 haplotypes. These results indicate that the giant panda still retains a relatively high adaptive variation at Aime-MHC-I genes, and that the intronic segments have been homogenized along evolu- tionary time by recombination and subsequent genetic drift.We calculated nucleotide substitution rates of the antigen- binding regions （exons 2 and 3） and the noncoding intron 2, and found two pieces of evidence supporting the presence of balancing selection in the giant panda： an excess of nonsynonymous over synonymous substitutions at the antigen-binding sites, and an obviously higher synonymous substitutions in the exons than nucleotide substitutions in the intron. Thus, this study reveals that balancing selection and recombination together shape the diversity pattern at Aime- MHC-I loci of the giant panda.展开更多
Pre-mRNA splicing is a fundamental process required for the expression of most metazoan genes. It is carried out by the spliceosome, which catalyzes the removal of non-coding intronic sequences to assemble exons into ...Pre-mRNA splicing is a fundamental process required for the expression of most metazoan genes. It is carried out by the spliceosome, which catalyzes the removal of non-coding intronic sequences to assemble exons into mature mRNAs prior to export and translation. Defects in splicing lead to many human genetic diseases [ 1 ], and splicing mutations in a number of genes involved in growth control have been implicated in multiple types of cancer [2].展开更多
文摘One of the most exciting findings in RNA biology is the discovery of numerous circular RNAs （circRNA） in mammalian genome. Once being considered as low abundance splicing byproducts, circRNAs are surprisingly abundant and can be generated by multiple pathways. The majority of circRNAs are generated from the RNA backsplicing in which an upstream 3＇ splicing site （ss） is joined with a downstream 5＇ ss. Several groups have independently demonstrated that the complementary paring of intronic sequences is sufficient to promote the biogenesis of circRNA via backsplicing. In addition, intronic circRNAs can also be generated through partial degradation of lariat RNAs that are splicing byproduct.
基金supported by a special grant(SG1411)for the giant panda from the State Forestry Administration of China
文摘Major histocompatibility complex （MHC） is a family of highly polymorphic genes activating adaptive immunity in vertebrates. However, the underlying mecha- nism of MHC evolution is still not fully understood. In this study, we investigated genetic variation of three classical MHC class I genes in the giant panda （Ailuropoda mela- noleuca） and tested for selection effect and recombination event across exonic and intronic sequences to understand maintenance mechanism of polymorphism at Aime-MHC class I genes. In total, we isolated 21 MHC class I haplotypes （exon 2-intron 2-exon 3） from 46 captive giant pandas, of which eight were for Aime-C, seven for Aime-I and six for Aime-L; however, we only identified six unique sequences from these haplotypes. The subsequent maximum-likeli- hood and Chi-square analyses both detected evidence of recombination acting on the 21 haplotypes. These results indicate that the giant panda still retains a relatively high adaptive variation at Aime-MHC-I genes, and that the intronic segments have been homogenized along evolu- tionary time by recombination and subsequent genetic drift.We calculated nucleotide substitution rates of the antigen- binding regions （exons 2 and 3） and the noncoding intron 2, and found two pieces of evidence supporting the presence of balancing selection in the giant panda： an excess of nonsynonymous over synonymous substitutions at the antigen-binding sites, and an obviously higher synonymous substitutions in the exons than nucleotide substitutions in the intron. Thus, this study reveals that balancing selection and recombination together shape the diversity pattern at Aime- MHC-I loci of the giant panda.
文摘Pre-mRNA splicing is a fundamental process required for the expression of most metazoan genes. It is carried out by the spliceosome, which catalyzes the removal of non-coding intronic sequences to assemble exons into mature mRNAs prior to export and translation. Defects in splicing lead to many human genetic diseases [ 1 ], and splicing mutations in a number of genes involved in growth control have been implicated in multiple types of cancer [2].
