后生动物非编码保守元件

生物体基因组中除了编码序列之外, 还存在大量的非编码调控序列。比较基因组学研究发现：脊椎动物、尾索动物、头索动物、果蝇、线虫等基因组中存在保守的非编码调控序列。这些非编码保守元件通常分布在与转录调控发育相关的基因上下游区域, 作为基因调控网络核心的一部分, 常常在基因表达过程中扮演转录增强子的角色。文章总结了近年来有关后生动物非编码保守元件的发现和主要特点, 并进一步就非编码保守元件在大规模基因组倍增之后的演化及其在生物躯体图式进化过程中的影响进行了综述。     

转座元件在不同人类基因组数据库中分布情况的研究

在人类基因组中,大多数的基因都含有转座元件,但是转座元件在蛋白质编码区所占的比例大约只有1%。1%这个比例很可能是被低估的。我们系统分析了转座元件在不同的人类基因组注释数据库中的变化情况。在Ref Seq数据库中,0.43%的蛋白质编码序列被转座元件覆盖,但在Ensembl数据库中,这一比例达到了1.30%。对于Ensembl特有的蛋白质编码区,转座元件的覆盖率达到了15.3%,远远高于在Ref Seq中所对应的比例(0.43%)。这些结果表明,未被识别出的蛋白质编码序列比现有的蛋白质编码序列含有更多的转座元件,这也预示着这些蛋白质编码序列将会更加难以被识别出来。     

真核生物基因组中的非编码序列

真核生物基因组绝大部分是非编码序列;绝大部分非编码序列以高度重复序列的形式存在,如卫星、小卫星、微卫星、长散布元件、短散布元件等;内含子、３’不译区作为结构基因的一部分被一同转录;ＲＮＡ基因转录具有明确功能的ＲＮＡ分子;顺式作用元件是目前已知的具有重要调控功能的非编码序列;非编码序列的存在与真核生物基因表达调控密切相关;目前非编码序列的研究已引起广泛的科学关注,利用数理方法研究其遗传信息的储存方式     

新城疫病毒非编码序列的遗传演化趋势

【目的】探讨新城疫病毒全基因序列中非编码序列的分子演化规律。【方法】结合本研究室2012年自产蛋下降鸭群中分离测序的一株鸭源新城疫病毒全序列,从GenBank下载35株不同基因型新城疫病毒全长cDNA序列,获取非编码序列,分别绘制引导序列、尾随序列、F-HN及HN-L基因间隔序列(IGS)的遗传进化树,比较编码基因内5’及3’UTR序列核苷酸序列替代特点。【结果】非编码序列的长度及位置高度保守,而其核苷酸基因序列在不断发生变异,且变异趋势与编码基因序列相一致。【结论】新城疫病毒在整个基因组上编码和非编码序列同步发生变异。     

长非编码RNA

人类基因组序列的约5%～10%被稳定转录,蛋白质编码基因仅约占1%,其余4%～9%的序列虽能转录,但转录物功能尚不明确。尽管如此,已确证在非蛋白质编码转录物中,含有具备调节功能的非编码RNA(noncoding RNA,ncRNA)。与具有调节功能的短链非编码RNA[如微RNA(microRNA)、小干扰RNA(siRNA),、Piwi-RNA]相比,长非编码RNA(long noncoding RNA,lncRNA)在数量上占大多数。lncRNA通过多种方式产生,以多种途径调节靶基因表达,参与调控生物体生长、发育、衰老、死亡等过程;lncRNA功能异常往往导致疾病发生。本文综述了lncRNA的起源、分类、作用分子机制及lncRNA异常与疾病的相关性等内容,旨在充分了解这一重要新型调控分子。     

长链非编码RNA作为潜在药物靶点的研究进展

随着生命科学的不断发展,2012年DNA元件百科全书（ENCODE）项目进一步丰富了人类基因组功能元件的相关信息。该项目 发现人类基因组超过80%的序列会被转录,其中大部分转录本是非编码RNA（ncRNA）。目前,在这些非编码RNA中,小RNA的研究 相对深入,而长链非编码RNA（lncRNA）的研究相对较少。越来越多研究表明,很多lncRNA参与到人类重大疾病的发生、发展过程之 中,并且一些动物实验证实lncRNA可作为药物靶点。因此,从lncRNA角度筛选新的药物靶点也越来越受到研究者的关注。重点总结了 lncRNA的生物学功能及作为潜在药物靶点的研究进展。     

长链非编码RNA及其与肿瘤关系

人类基因组DNA信息分析显示,基因组中编码序列不超过2％,其余为非编码序列,其中能够稳定转录的部分称之为非编码RNA(noncoding RNA,ncRNA)基因.依据ncRNA长度将其分为长非编码RNA(lncRNA,碱基数＞200nt)和短非编码RNA (sncRNA).在人体内,lncRNAs分布广泛,数目众多,并且大多数是由RNA聚合酶Ⅱ转录的,且有5'端帽子结构以及3 '端的多聚腺苷酸.就lncRNA的特征及其在肿瘤细胞中的功能进行阐述.     

编者按: 非编码RNA——有待挖掘的生物宝库

进入21世纪以来,非编码RNA和非编码基因的研究越来越引起人们的关注。2010年12月7日的《科学》杂志(Science)在评选本世纪前10年的十大科学突破时,首先提到的就是基因组中的暗物质(the genome's "dark matter")。近10年非编码RNA领域发展如此迅速,首先源于20世纪90年代开展的基因组研究和随后的比较基因组研究。海量的基因组序列数据证实：DNA上编码蛋白质的区域(也就是通常说的基因)只占人类和其他高等动、植物基因组的极小部分,在人类不会超过整个基因组的3%,其余部分都不编码蛋白质或多肽。而且,随着生物从简单到复杂、从低级到高级,非编码序列在基因组中所占的比例也单调地增加,说明非编码序列是有功能的;近年来大量转录组的新实验结果表明,基因组中的非编码序列是可以表达的,其表达产物就是非编码RNA,转录组的研究说明基因组中的非编码序列是有信息发放的;此后,越来越多的事实证明非编码RNA具有重要的生物功能,microRNA(miRNA)的研究就是最突出的例子。上述的进展明确地告诉我们数量巨大的非编码RNA是有待挖掘的生物宝库。当今,非编码序列、非编码基因和非编码RNA的研究已成为生物学领域的研究热点,重新唤起了科学家们对“RNA世界”的重视及对“生命起源于RNA分子”这一命题的兴趣。目前,这一领域值得关注的问题很多,比如： 1 长非编码RNA系统发现和功能研究 尽管长度小于50个碱基的非编码RNA(如microRNA和piRNA等)的研究已取得突破性进展,但长度大于100个碱基的非编码RNA,还有数以万计功能尚未发现。长非编码RNA不仅数量巨大,更为重要的是它们能折叠为特定的空间结构,因此它们与其他生物分子相互作用的方式是不同于microRNA的。虽然到目前为止,才知道了几百个长非编码RNA的功能,但已涉及到：转录调控、转录后调控、翻译调控、表观遗传调控、基因印迹以及端粒系统等。近年来还发现了一些新类型的长非编码RNA,如ceRNA和环RNA等。所以,进一步开展非编码序列、非编码基因和非编码RNA的研究,系统发现新的长非编码RNA,研究它们的空间结构与功能,可能为我们带来更多的创新机会。 2 非编码RNA是生物网络的元件 近年来的大量新研究成果表明非编码RNA是许多生命过程中富有活力的参与者。一些科学家认为成千上万非编码RNA分子组成了巨大的分子网络调节着细胞中的生命活动,它们与蛋白质网络相对应,同时这两类网络必然有紧密的相互作用,从而构成更复杂的网络。所以未来的网络至少是双色的才更符合生命活动的实际。 3 非编码RNA调节的多样性 非编码RNA在发挥生物学功能时的作用方式是多种多样的,以miRNA为例：它的负调控作用不仅存在于靶mRNA的3'UTR区,也可发生在5'UTR区;miRNA不仅具有负调控作用,在特定条件下也可以激活基因的表达;最近的研究表明,miRNA不仅可通过调节mRNA的表达发挥生物作用,还可以通过调节蛋白来发挥生物功能。 miRNA的作用方式尚且如此复杂,其他非编码RNA行使功能的途径可能更为多样。 4 非编码RNA与疾病紧密相关 非编码RNA,特别是miRNA,与疾病相关的研究已数不胜数。长非编码RNA也和人类疾病紧密相关,仅以肿瘤为例：PCGEM1与前列腺癌有关;His-1是白血病致病因素,而且参与了癌变代谢通路和细胞周期调控; MALAT-1的转录本是一条8000多个碱基长度的非编码RNA,该基因与非小细胞肺癌有关。上述一些成果正逐渐走向临床。非编码RNA研究是一个紧密结合实际,又可迅速用于实际的领域,应特别关注从基础到应用的转化。 为了让广大读者了解非编码RNA领域的进展,本刊特意组织了这个专辑。邀请国内RNA研究领域的5位知名专家对该领域当前的进展与挑战作了综述。屈良鹄教授介绍了microRNA和细胞信号通路间的相互作用及其对两者功能发挥的关键作用,并探讨了其生物学意义;邵宁生教授的综述介绍了在不同细胞或同一细胞的不同状态下microRNA发挥生物学功能的时序特异性和组织特异性,说明microRNA在机体内工作的复杂性;张辰宇教授结合自己多年的研究实践叙述了人体体液中microRNA的起源与功能,对分泌RNA和循环RNA概念作了论述,并探讨了它们在临床医学领域的潜在诊断功能;施蕴渝教授从结构生物学出发综述了RNA分子伴侣Hfq是如何促进sRNA和mRNA相互配对的;鲁志教授介绍了长非编码RNA研究中的各种生物信息学的工具与方法。希望大家对这些文章感兴趣,也希望它们能给大家带来知识与帮助。     

长链非编码RNA研究进展

基因组计划研究表明, 在组成人类基因组的30亿个碱基对中, 仅有1.5%的核酸序列用于蛋白质编码, 其余98.5%的基因组为非蛋白质编码序列。这些序列曾被认为是在进化过程中累积的“垃圾序列”而未予以关注, 但在随后启动的ENCODE研究计划中却发现, 75%的基因组序列能够被转录成RNA, 其中近74%的转录产物为非编码RNA(Non-coding RNA, ncRNA)。在非编码RNA中, 绝大多数转录本的长度大于200个碱基, 这些“长链非编码RNA(Long non-coding RNA, lncRNA)”能够在转录及转录后水平上调节蛋白编码基因的表达, 从而广泛地参与包括细胞分化、个体发育在内的重要生命过程, 其异常表达还与多种人类重大疾病的发生密切相关。文章综述了长链非编码RNA的发现、分类、表达、作用机制以及其在个体发育和人类疾病中的作用。     

非编码序列发生基因突变可能引起性状变化

非编码序列包括原核细胞基因的非编码区、真核细胞基因的非编码区和编码区的内含子,非编码序列虽然不能够编码蛋白质,但是对遗传信息的表达具有调控作用,如果非编码序列发生基因突变,可能会影响遗传信息的表达,从而引起性状的变化。     

Ancient vertebrate conserved noncoding elements have been evolving rapidly in teleost fishes

Vertebrate genomes contain thousands of conserved noncoding elements (CNEs) that often function as tissue-specific enhancers. In this study, we have identified CNEs in human, dog, chicken, Xenopus, and four teleost fishes (zebrafish, stickleback, medaka, and fugu) using elephant shark, a cartilaginous vertebrate, as the base genome and investigated the evolution of these ancient vertebrate CNEs (aCNEs) in bony vertebrate lineages. Our analysis shows that aCNEs have been evolving at different rates in different bony vertebrate lineages. Although 78-83% of CNEs have diverged beyond recognition ("lost") in different teleost fishes, only 24% and 40% have been lost in the chicken and mammalian lineages, respectively. Relative rate tests of substitution rates in CNEs revealed that the teleost fish CNEs have been evolving at a significantly higher rate than those in other bony vertebrates. In the ray-finned fish lineage, 68% of aCNEs were lost before the divergence of the four teleosts. This implicates the "fish-specific" whole-genome duplication in the accelerated evolution and the loss of a large number of both copies of duplicated CNEs in teleost fishes. The aCNEs are rich in tissue-specific enhancers and thus many of them are likely to be evolutionarily constrained cis-regulatory elements. The rapid evolution of aCNEs might have affected the expression patterns driven by them. Transgenic zebrafish assay of some human CNE enhancers that have been lost in teleosts has indicated instances of conservation or changes in trans-acting factors between mammals and fishes.     

Defining a genomic radius for long-range enhancer action: duplicated conserved non-coding elements hold the key

Many conserved non-coding elements (CNEs) in vertebrate genomes have been shown to function as tissue-specific enhancers. However, the target genes of most CNEs are unknown. Here we show that the target genes of duplicated CNEs can be predicted by considering their neighbouring paralogous genes. This enables us to provide the first systematic estimate of the genomic range for distal cis-regulatory interactions in the human genome: half of CNEs are >250 kb away from their associated gene.     

Striking nucleotide frequency pattern at the borders of highly conserved vertebrate non-coding sequences

In a recent study, 1373 highly conserved non-coding elements (CNEs) were detected by aligning the human and Takifugu rubripes (Fugu) genomes. The remarkable degree of sequence conservation in CNEs compared with their surroundings suggested comparing the base composition within CNEs with their 5' and 3' flanking regions. The analysis reveals a novel, sharp and distinct signal of nucleotide frequency bias precisely at the border between CNEs and flanking regions.     

Early Evolution of Conserved Regulatory Sequences Associated with Development in Vertebrates

Comparisons between diverse vertebrate genomes have uncovered thousands of highly conserved non-coding sequences, an increasing number of which have been shown to function as enhancers during early development. Despite their extreme conservation over 500 million years from humans to cartilaginous fish, these elements appear to be largely absent in invertebrates, and, to date, there has been little understanding of their mode of action or the evolutionary processes that have modelled them. We have now exploited emerging genomic sequence data for the sea lamprey, Petromyzon marinus, to explore the depth of conservation of this type of element in the earliest diverging extant vertebrate lineage, the jawless fish (agnathans). We searched for conserved non-coding elements (CNEs) at 13 human gene loci and identified lamprey elements associated with all but two of these gene regions. Although markedly shorter and less well conserved than within jawed vertebrates, identified lamprey CNEs are able to drive specific patterns of expression in zebrafish embryos, which are almost identical to those driven by the equivalent human elements. These CNEs are therefore a unique and defining characteristic of all vertebrates. Furthermore, alignment of lamprey and other vertebrate CNEs should permit the identification of persistent sequence signatures that are responsible for common patterns of expression and contribute to the elucidation of the regulatory language in CNEs. Identifying the core regulatory code for development, common to all vertebrates, provides a foundation upon which regulatory networks can be constructed and might also illuminate how large conserved regulatory sequence blocks evolve and become fixed in genomic DNA.     

Hundreds of conserved non-coding genomic regions are independently lost in mammals

Conserved non-protein-coding DNA elements (CNEs) often encode cis-regulatory elements and are rarely lost during evolution. However, CNE losses that do occur can be associated with phenotypic changes, exemplified by pelvic spine loss in sticklebacks. Using a computational strategy to detect complete loss of CNEs in mammalian genomes while strictly controlling for artifacts, we find >600 CNEs that are independently lost in at least two mammalian lineages, including a spinal cord enhancer near GDF11. We observed several genomic regions where multiple independent CNE loss events happened; the most extreme is the DIAPH2 locus. We show that CNE losses often involve deletions and that CNE loss frequencies are non-uniform. Similar to less pleiotropic enhancers, we find that independently lost CNEs are shorter, slightly less constrained and evolutionarily younger than CNEs without detected losses. This suggests that independently lost CNEs are less pleiotropic and that pleiotropic constraints contribute to non-uniform CNE loss frequencies. We also detected 35 CNEs that are independently lost in the human lineage and in other mammals. Our study uncovers an interesting aspect of the evolution of functional DNA in mammalian genomes. Experiments are necessary to test if these independently lost CNEs are associated with parallel phenotype changes in mammals.     

Highly conserved regulatory elements around the SHH gene may contribute to the maintenance of conserved synteny across human chromosome 7q36.3

Comparative genomic analysis reveals an exceptionally large section of conserved shared synteny between the human 7q36 chromosomal region and the pufferfish (Fugu rubripes) genome. Remarkably, this conservation extends not only to gene order across 16 genes, but also to the position and orientation of a number of prominent conserved noncoding elements (CNEs). A functional assay using zebrafish has shown that most of the CNEs have reproducible and specific enhancer activity. This enhancer activity is often detected in a subset of tissues which reflect the endogenous expression pattern of a proximal gene, though some CNEs may act over a long range. We propose that the distribution of CNEs, and their probable association with a number of genes throughout the region, imposes a critical constraint on genome architecture, resulting in the maintenance of such a large section of conserved synteny across the vertebrate lineage.     

Computational methods to detect conserved non-genic elements in phylogenetically isolated genomes: application to zebrafish

Many important model organisms for biomedical and evolutionary research have sequenced genomes, but occupy a phylogenetically isolated position, evolutionarily distant from other sequenced genomes. This phylogenetic isolation is exemplified for zebrafish, a vertebrate model for cis-regulation, development and human disease, whose evolutionary distance to all other currently sequenced fish exceeds the distance between human and chicken. Such large distances make it difficult to align genomes and use them for comparative analysis beyond gene-focused questions. In particular, detecting conserved non-genic elements (CNEs) as promising cis-regulatory elements with biological importance is challenging. Here, we develop a general comparative genomics framework to align isolated genomes and to comprehensively detect CNEs. Our approach integrates highly sensitive and quality-controlled local alignments and uses alignment transitivity and ancestral reconstruction to bridge large evolutionary distances. We apply our framework to zebrafish and demonstrate substantially improved CNE detection and quality compared with previous sets. Our zebrafish CNE set comprises 54 533 CNEs, of which 11 792 (22%) are conserved to human or mouse. Our zebrafish CNEs (http://zebrafish.stanford.edu) are highly enriched in known enhancers and extend existing experimental (ChIP-Seq) sets. The same framework can now be applied to the isolated genomes of frog, amphioxus, Caenorhabditis elegans and many others.     

Positive and negative selection in murine ultraconserved noncoding elements

There are many more selectively constrained noncoding than coding nucleotides in the mammalian genome, but most mammalian noncoding DNA is subject to weak selection, on average. One of the most striking discoveries to have emerged from comparisons among mammalian genomes is the hundreds of noncoding elements of more than 200 bp in length that show absolute conservation among mammalian orders. These elements represent the tip of the iceberg of a much larger class of conserved noncoding elements (CNEs). Much evidence suggests that CNEs are selectively constrained and not mutational cold-spots, and there is evidence that some CNEs play a role in the regulation of development. Here, we quantify negative and positive selection acting in murine CNEs by analyzing within-species nucleotide variation and between-species divergence of CNEs that we identified using a phylogenetically independent comparison. The distribution of fitness effects of new mutations in CNEs, inferred from within-species polymorphism, suggests that CNEs receive a higher number of strongly selected deleterious mutations and many fewer nearly neutral mutations than amino acid sites of protein-coding genes or regulatory elements close to genes. However, we also show that CNEs experience a far higher proportion of adaptive substitutions than any known category of genomic sites in murids. The absolute rate of adaptation of CNEs is similar to that of amino acid sites of proteins. This result suggests that there is widespread adaptation in mammalian conserved noncoding DNA elements, some of which have been implicated in the regulation of crucially important processes, including development.