CRISPR/Cas9介导的疾病模型构建与基因修复研究进展

近年来,可编程核酸酶介导的基因编辑技术迅猛发展。CRISPR/Cas9技术源于细菌和古生菌的适应性免疫系统,主要由Cas9内切酶和向导RNA（guide RNA,gRNA）组成。Cas9内切酶在gRNA的指导下造成DNA的双链断裂,从而使研究人员能够精准高效地操纵特定基因组位点。同时,该系统可以揭示基因在疾病进程中所扮演的未知角色,在临床治疗中有应用潜能。现总结了CRISPR/Cas9技术在疾病模型构建与基因修复领域应用的研究进展。     

生态系统服务价值的生态区位修正方法——以北京市为例

生态系统服务价值评估是当前生态经济学和环境经济学的研究热点和焦点,生态区位是影响生态系统服务价值的重要因子。以北京市为例,对北京市进行生态区位的划分,遵循资源稀缺性原理,将不同生态区位赋予不同的生态区位系数,并以北京市1980年、1995年和2000年土地利用图为例,以生态区位系数对北京市用地类型的生态服务价值进行修正,以体现不同生态区位单位面积生态系统服务价值的不同。研究得到了北京市3期土地利用单位面积生态系统服务价值分布图。分析发现:北京市的生态系统服务价值组成中,水田、有林地、灌木林和水体的生态系统服务价值占的比重较高;各生态区位生态系统服务总价值从城区到近郊平原区到近郊半山区到远郊山区依次增加;从1980年到1995年,北京市的生态系统服务价值减少了1.21×107元,而且各生态区位的生态系统服务价值也大都减少;从1995年到2000年,北京市的生态系统服务价值有所提高,但与1980年相比还是减少了3.07×106元。     

A new revision of the sequence of plasmid pBR322

A revised sequence in the region immediately upstream from the rop gene of pBR322 is reported. Two base pairs in the accepted sequence do not exist in the plasmid DNA. Specifically, a TA base pair is missing at sequence coordinate 1893 [Sutcliffe, Cold Spring Harbor Symp. Quant. Biol. 43 (1979) 77–90] and an AT base pair is missing at position 1915, giving a total size for pBR322 of 4361 bp. These changes are in a potential translation initiation sequence and probably reflect errors in the original sequence rather than recent evolution of the plasmid.     

植物叶片解剖结构的量化及其在C4植物高粱中的应用

测量切片内所有细胞或细胞器的总周长,并乘以切片厚度和校正因子是一种量化植物叶片解剖结构的常用方法。前人在使用该方法时因忽视了细胞大小、切片厚度等影响估算精确度的因素,从而导致计数样本偏少并产生较大误差。通过分析该方法误差产生的原因及其与精确度的关系,明确了该方法在实际应用中不同精确度所要求对应的切片数量。在此基础上,将该方法用于C4植物高粱(Sorghum bicolor)叶片结构的量化,提出叶肉细胞与维管束鞘细胞接触面积(CABM)等参数,发展并完善了植物叶片解剖结构的量化方法。     

黄芪复合体（豆科）核型研究补充材料

本文首次报道了民和黄芪的染色体数目及核型。发现该种与黄芪复合体其它类群的染色体数目相同,但核型有别,其核型公式为２ｎ＝１６＝８ｍ（２ＳＡＴ）＋８ｓｍ。这种核型变异与它的形态变异一致。在黄芪复合体内,每一类群的染色体至少具１对随体,且附着在最后１对染色体的短臂上（除蒙古黄芪具２对随体外）,而Ｔｏｈ（１９７１）报道采自Ｋｙｕｎｇｉ和Ｍｔ．Ｈａｒｌａ膜荚黄芪和高山膜荚黄芪（新拟）的染色体不具随体,可能观察有误。     

Efficient gene correction of an aberrant splice site in β‐thalassaemia iPSCs by CRISPR/Cas9 and single‐strand oligodeoxynucleotides

β‐thalassaemia is a prevalent hereditary haematological disease caused by mutations in the human haemoglobin β (HBB) gene. Among them, the HBB IVS2‐654 (C > T) mutation, which is in the intron, creates an aberrant splicing site. Bone marrow transplantation for curing β‐thalassaemia is limited due to the lack of matched donors. The clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR‐associated protein 9 (Cas9), as a widely used tool for gene editing, is able to target specific sequence and create double‐strand break (DSB), which can be combined with the single‐stranded oligodeoxynucleotide (ssODN) to correct mutations. In this study, according to two different strategies, the HBB IVS2‐654 mutation was seamlessly corrected in iPSCs by CRISPR/Cas9 system and ssODN. To reduce the occurrence of secondary cleavage, a more efficient strategy was adopted. The corrected iPSCs kept pluripotency and genome stability. Moreover, they could differentiate normally. Through CRISPR/Cas9 system and ssODN, our study provides improved strategies for gene correction of β‐Thalassaemia, and the expression of the HBB gene can be restored, which can be used for gene therapy in the future.     

Ripley''s K(d)函数分析种群空间分布格局的边缘校正

Ripley’sK(d)函数是分析种群空间分布格局最常用的方法,边缘校正是此方法的关键问题。传统的边缘校正包括3种情形：(i)圆完全包含在样地内;(ii)圆与样地的一条边相交;(iii)圆与样地的两条边相交,并有2个或3个交点。实际上,还存在第(iv)种情形,即圆与样地两条边相交有4个交点的情形。本文从数学上证明,传统边缘校正中,当边缘校正属于第(iv)种情形时,仍按第(iii)种情形进行校正,必然导致权重估计偏大,L(d)值偏高,从而影响结果分析。采用我国东北长白山天然云冷杉林样地资料验证了此结论。结果表明,天然云冷杉林中,3个优势种群林木分布格局特点是：鱼鳞云杉和臭冷杉的分布格局曲线非常相近,而与椴木的差异较大。原因是鱼鳞云杉和臭冷杉具有相似的生态学特性。椴木在小尺度显著聚集,因为椴木常在林隙更新。相比较而言,建群种云冷杉分布的均匀程度要比椴木高。     

Machine learning in quantitative PET: A review of attenuation correction and low-count image reconstruction methods

The rapid expansion of machine learning is offering a new wave of opportunities for nuclear medicine. This paper reviews applications of machine learning for the study of attenuation correction (AC) and low-count image reconstruction in quantitative positron emission tomography (PET). Specifically, we present the developments of machine learning methodology, ranging from random forest and dictionary learning to the latest convolutional neural network-based architectures. For application in PET attenuation correction, two general strategies are reviewed: 1) generating synthetic CT from MR or non-AC PET for the purposes of PET AC, and 2) direct conversion from non-AC PET to AC PET. For low-count PET reconstruction, recent deep learning-based studies and the potential advantages over conventional machine learning-based methods are presented and discussed. In each application, the proposed methods, study designs and performance of published studies are listed and compared with a brief discussion. Finally, the overall contributions and remaining challenges are summarized.     

A second look at bluegill production in Wyland Lake,Indiana

Synopsis An error in the 1962 estimate of bluegill production for Wyland Lake, Indiana, is considered. An approximate corrected value of 625 kg ha^–1 y^–1 is estimated from the original data. This value is approximately six times the original estimate.