CRISPR/Cas系统：RNA靶向的基因组定向编辑新技术

CRISPR/Cas系统广泛存在于细菌及古生菌中, 是机体长期进化形成的RNA指导的降解入侵病毒或噬菌体DNA的适应性免疫系统。对Ⅱ型CRISPR/Cas系统的改造使其成为继锌指核酸酶(ZFNs)和TALE核酸酶(TALENs)以来的另一种对基因组进行高效定点修饰的新技术, 与ZFNs和TALENs相比, CRISPR/Cas系统更简单, 并且更容易操作。文章重点介绍了Ⅱ型CRISPR/Cas系统的基本结构、作用原理及这一技术在基因组定点修饰中的应用, 剖析了该技术可能存在的问题, 展望了CRISPR/Cas系统的应用前景, 为开展这一领域的研究工作提供参考。     

基因编辑新技术最新进展

借助基因编辑技术精准编辑植物基因组,得到性状优良、产量高的农作物种质是目前作物分子育种研究的主要趋势。目前主要的CRISPR/Cas9系统是由产脓链球菌的获得性免疫防御系统改编而来,该系统以其编辑高效、操作方便、成本低廉等明显优势在基因编辑技术中脱颖而出,广受青睐。利用CRISPR/Cas技术编辑作物基因组,能精确引入和改良目标性状,为作物遗传育种提供新途径。当前, CRISPR/Cas9技术在拟南芥、水稻、土豆、玉米等植物中得到普遍应用。该文简要阐述了锌指核酸酶、转录因子激活样效应物核酸酶以及CRISPR/Cas9系统的结构、作用机制及差异,重点综述CRISPR/Cas9系统目前在植物中的应用、其改良的CRISPR/Cpf1技术以及该系统相比于其他核酸酶的优势与局限性。     

新一代精准基因编辑工具CRISPR/Cas9的技术优势与应用局限

CRISPR/Cas9(Clustered regularly interspaced short palindromic repeats/Cas9)是继锌指核酸酶(ZFNs)和类转录激活因子效应物核酸酶(TALENs)基因编辑技术之后的第三代基因编辑技术。CRISPR/Cas9在细菌和古生菌中广泛存在,是细菌在长期进化过程中形成的一种"适应性免疫防御",能够针对噬菌体感染、质粒接合和转化所造成的外源导入基因特异性识别、降解入侵的外源DNA,CRISPR/Cas9通过一段20 bp的短RNA来识别打靶位点的精准编辑技术。CRISPR/Cas9具有设计操作简便、编辑高效和通用性广等优点,是新一代具有革命意义的精准基因编辑技术。从CRISPR/Cas9的发现、作用机理、基因编辑以及应用局限等方面进行归纳总结,旨为理解其工作原理和精准基因编辑技术应用提供参考。     

CRISPR/Cas9:一种新型的基因组定点编辑技术

CRISPR/Cas9系统是原核生物抵御病毒或质粒等外来遗传物质入侵的一种获得性免疫系统,主要由非特异性的Cas9核酸酶和起识别作用的cr RNA所组成。相较于传统的基因组编辑技术,基于CRISPR/Cas9系统的基因组定点编辑技术具有快速、简单、高效等优点,并且几乎可以用于任何物种的基因编辑。尽管CRISPR/Cas9系统的基因组特异性还有待进一步确认,但该系统在基因组编辑方面的简便性和有效性必将促进生物学的研究和人类疾病基因治疗方面的发展。     

CRISPR/Cas9的应用及脱靶效应研究进展

CRISPR/Cas9基因编辑技术在生命科学领域掀起了一场全新的技术革命,该技术可以对基因组特定位点进行靶向编辑,包括缺失、插入、修复等。CRISPR/Cas9比锌指核酸酶 (ZFNs)和转录激活因子样效应物核酸酶(TALENs)技术更易于操作,而且更高效。CRISPR/Cas9系统中的向导RNA(Single guide RNA, sgRNA)是一段与目标DNA片段匹配的RNA序列,指导Cas9蛋白对基因组进行识别。研究发现,设计的sgRNA会与非靶点DNA序列错配,引入非预期的基因突变,即脱靶效应(Off-target effects)。脱靶效应严重制约了CRISPR/Cas9基因编辑技术的广泛应用。为了避免脱靶效应,研究者对影响脱靶效应的因素进行了系统研究并提出了许多降低脱靶效应的方法。文章总结了CRISPR/Cas9系统的应用及脱靶效应研究进展,以期为相关领域的工作提供参考。     

CRISPR/Cas9技术在微生物研究中的应用进展

CRISPR(Clustered regularly interspaced short palindromic repeats)/Cas(CRISPR associated proteins)系统是在细菌和古生菌中发现的一种RNA指导的降解入侵病毒或质粒DNA的适应性免疫系统。由II型CRISPR/Cas系统改造而成的CRISPR/Cas9技术已经被开发成一种强大的基因组编辑和表达调控工具,并且广泛应用于基因功能研究、代谢工程和合成生物学等领域。本文从CRISPR/Cas9系统的发现过程、分类、作用原理、在微生物研究中的应用进展等方面进行总结,并展望了该技术的应用前景。     

Recent advances in the study of Kaposi's sarcoma-associated herpesvirus replication and pathogenesis

It has now been over twenty years since a novel herpesviral genome was identified in Kaposi's sarcoma biopsies. Since then, the cumulative research effort by molecular biologists, virologists, clinicians, and epidemiologists alike has led to the extensive characterization of this tumor virus, Kaposi's sarcoma-associated herpesvirus(KSHV; also known as human herpesvirus 8(HHV-8)), and its associated diseases. Here we review the current knowledge of KSHV biology and pathogenesis, with a particular emphasis on new and exciting advances in the field of epigenetics. We also discuss the development and practicality of various cell culture and animal model systems to study KSHV replication and pathogenesis.     

The structure, reproduction and taxonomy of Vidalia and Osmundaria (Rhodophyta, Rhodomelaceae)

Comprises species occurring mostly in subtidal habitats in tropical, subtropical and warm-temperate areas of the world. An analysis of the type species, V. spiralis (Sonder) Lamouroux ex J. Agardh, a species from Australia, establishes basic characters for distinguishing species in the genus. These characters are (1) branching patterns of thalli, (2) flat blades that may be spiralled on their axis, (3) width of the blade, (4) primary or secondary derivation of sterile and fertile branchlets and (5) position of sterile and fertile branchlets on the thalli. Application of the latter two characters provides an important basic method for separation of species into three major groups. Osmundaria , a genus known only in southern Australia, was studied in relation to Vidalia , and its separation from the Vidalia assemblage is not accepted. Species of Vidalia therefore are transferred to the older genus name, Osmundaria. Two new species, Osmundaria papenfussii and Osmundaria oliveae are described from Natal. Confusion in the usage of the epithet, Vidalia fimbriala Brown ex Turner has been clarified, and Vidalia gregaria Falkenberg, described as an epiphyte on Osmundaria pro/ifera Lamouroux, is revealed to be young branches of the host, Osmundaria prolifera.     

New or rare chromosome counts in Artemisia L. (Asteraceae, Anthemideae) and related genera from Kazakhstan

Fifteen chromosome counts of six Artemisia taxa and one species of each of the genera Brachanthemum, Hippolytia, Kaschgaria, Lepidolopsis and Turaniphytum are reported from Kazakhstan. Three of them are new reports, two are not consistent with previous counts and the remainder are confirmations of very scarce (one to four) earlier records. All the populations studied have the same basic chromosome number, x = 9, with ploidy levels ranging from 2x to 6x. Some correlations between ploidy level, morphological characters and distribution are noted.     

肝癌中HBV和HCV基因和抗原的分布及意义

采用原位分子杂交方法检测HCV RNA及HBV X基因;采用免疫组织化学方法研究HCV核心抗原,非结构区C33c抗原及HBxAg在肝细胞肝癌中的定位及分布.结果表明(1)HCV RNA、HBV X基因在肝细胞肝癌组织检出率分别为40%(55/136)和82%(112/136).HCV RNA定位于癌细胞的胞浆内,阳性细胞呈散在、灶状及弥漫分布三种形式;HBV X基因在肝癌细胞中的分布呈胞浆型、核型及核浆型,阳性细胞也呈上述三种分布形式;(2)HCV C33c抗原、核心抗原在肝细胞肝癌中的阳性率为81%(133/164)及86%(141/164).C33c抗原定位于癌细胞及肝细胞的胞浆内;核心抗原既定位于癌细胞核中,又可定位于胞浆中.C33c抗原阳性细胞以灶状分布为主;而核心抗原阳性细     

Selection with two alleles and complete dominance

For a plant selection model with frequency-independent viabilities, fertilities and selfing rates, it is shown that apart from global fixation, for certain parameter combinations a protected polymorphism and facultative fixation (either allele may become fixed according to initial frequencies) may both occur. Facultative fixation requires different selling rates for the dominant and recessive type. Protection of the polymorphism requires resource allocation for male and female function. In this connection the problem of purely genetically caused population extinction is discussed.
For general frequency dependence and regular segregation, the chances for establishment of a completely recessive gene are compared to those of a completely dominant gene. It is proven that the process of establishment of the recessive gene, despite a fitness advantage, may be considerably endangered by drift effects if random mating prevails. The recessive gene may reach the same effectivity in establishment as a dominant gene, only if the recessive homozygote mates exclusively with its own type during the period of establishment.