Role of surface exclusion genes in lethal zygosis in Escherichia coli K12 mating

Summary We find that diaminopimelic acid in the recipient membrane is released into the medium during bacterial matings, indicating that membrane damage was inflicted on the recipient by the donor, probably for forming a channel for DNA transfer. When the damage is extensive, as in matings with an excess of Hfr bacteria, the F^- bacteria are killed (lethal zygosis). The transfer of a large amount of DNA in Hfr matings appears to enhance the killing. In analogous F⁺xF^- (Nal^r) matings, on the other hand, killing of F^- bacteria does not occur unless F plasmid transfer is inhibited by a substance like nalidixic acid. The F^- bacteria are killed, suggesting that F plasmids contain genes that express immunity to lethal zygosis in the recipient. For example, bacteria containing surface exclusion-deficient mutants of F plasmids, such as traS ^- and traT ^-, induce lethal zygosis in F^- bacteria and are susceptible to it. Various tra ^- polar mutants that abolish surface exclusion are also susceptible to lethal zygosis when mated with Hfr bacteria. Kinetic experiments indicate that in F⁺ (wild type) x F^- matings, immunity to lethal zygosis is expressed in the F^- recipient within 1/4 division time, whereas a complete expression of surface exclusion requires more than 1 division time. Thus, a complete change in all receptor sites seems to be required for the expression of surface exclusion.     

云南省香格里拉大峡谷藏族神山在自然保护中的意义

位于云南省西北部迪庆藏族自治州境内的香格里拉大峡谷拥有独特的自然人文景观和丰富的生物多样性。藏族作为当地最重要的原住民族,他们的文化对当地的自然环境具有重要的影响。为了解藏族传统文化中的神山崇拜对香格里拉大峡谷地区自然环境的影响,本文应用民族生态学、植物生态学和文化人类学的研究方法,结合文献资料的分析,对香格里拉大峡谷的藏族神山进行了调查和研究,并对处于不同保护状态下（神山与非神山）的两个典型植物群落即高山松(Pinus densata)群落和云南黄果冷杉(Abies ernestii var. salouenensis)群落进行了比较。结果显示,在相同的样地面积内（20 m×20 m）,神山植物群落在物种数量（20,14）和群落盖度（100%,85%）方面都明显高于非神山植物群落（11,2;70%,60%）。结合入户调查资料,发现广泛分布于香格里拉大峡谷的藏族神山构成了一个“自下而上”的乡土保护体系,它不仅在保护生物多样性、维护当地脆弱的生态环境等方面发挥着重要的作用,而且还可以提供多种非林产品,实现多种生态功能。文章探讨了发挥乡土保护体系的保护功效及应用传统文化知识以促进自然保护的重要性,建议应当尊重和保护原住民的传统文化,发掘其中优秀的自然保护知识和经验,引导其发挥更加有效的自然保护功能,使民族传统保护体系成为现代自然保护体系的有力补充。     

Secondary succession of plant communities in a subtropical mountainous region of SW China

Since 1985, originally forested mountainous areas of China have been allowed to return to their natural state after years of exploitation including agriculture, development, and logging. The reforms began earlier in less accessible locations, so that today the successional process is more advanced there. The vegetation in Luquan, Qiongzhusi, and Xishan near Kunming, central Yunnan, exhibits, in a limited area, a range of stages of plant succession that are widely encountered throughout the broader region, and thus affords a special opportunity for a comprehensive study. We analyzed the successional sequence of these various plant communities. They ranged from pioneer coniferous and/or pioneer deciduous broad-leaved stands to pre-mature semi-humid evergreen broad-leaved stands, through mixed coniferous and broad-leaved or mixed deciduous and evergreen broad-leaved stands. The succession proceeded from pioneer coniferous Pinus and Keteleeria, and deciduous Platycarya and Alnus, to late-successional evergreen broad-leaved Cyclobalanopsis and Castanopsis. Two regeneration types of woody species in either the early successional (15–50 years), the mid-successional (40–80 years), or the late-successional (80–180 years) stage were classified. Relatively high species diversity was found in the seral phase at the three study sites. The late-successional stage was commonest where human disturbance was least evident. Poor soil chemical properties under pioneer Pinus were seen as a limitation to plant growth, while the abundance of Alnus at the early stage led to an improved level of organic matter and nitrogen.     

NMDA受体在海马CA3区习得性TP保持中的作用

The effect of microinjection of 2-amino-5-phosphonovaleric acid (APV), a selective NMDA receptor antagonist, into the rat hippocampal CA3 area on the synaptic efficacy and related conditioned behavior during the acquisition and consolidation of discrimination learning behavior was examined. The results showed: (1) After population spike (PS) amplitude had just increased to the maximum through training i.e. learning-dependent LTP had just formed, APV 1 microliter (2 mmol/L) was injected into CA3 area, then the rats were trained during the time of efficacy of the drug in every experimental block. The result demonstrated that the PS amplitude could not be maintained at the highest level but decreased to the pre-experiment level after 8 blocks. Correct response percentage of rats could not be consolidated with further training but decreased to less than 10%. (2) After the PS amplitude had kept up at the highest level, APV 1 microliter (2 mmol/L) was injected into CA3 area, then the rats were trained during the time of efficacy of the drug in every experimental block, in which case the PS amplitude also could not be maintained at the highest level but decreased to the pre-experiment level after 14 blocks. Correlatively, when the correct response percentage of rats decreased gradually to less than 10%, the conditioned response of the animals extinguished, but its extinction speed was slower than it was in result (1). These results suggest that the NMDA receptor in CA3 area plays an important role in the maintenance of the learning-dependent long-term potentiation.     

Ungulate bocaparvovirus 4 and rodent bocavirus are different genotypes of the same species of virus

Bocaviruses are associated with many human infectious diseases, such as respiratory tract infections, gastroenteritis, and hepatitis. Rats are known to be reservoirs of bocaviruses, including rodent bocavirus and rat bocavirus. Recently, ungulate bocaparvovirus 4, a known porcine bocavirus, has also been found in rats. Thus, investigating bocaviruses in rats is important for determining the origin of the viruses and preventing and controlling their transmission. To the best of our knowledge, no study to date has investigated bocaviruses in the livers of rats. In this report, a total of 624 rats were trapped in southern China between 2014 and 2017. Liver and serum samples from rats were tested for the prevalence of bocaviruses using PCR. Sequences related to ungulate bocaparvovirus 4 and rodent bocavirus were detected in both liver and serum samples. Interestingly, the prevalence of ungulate bocaparvovirus 4 (reference strain:KJ622366.1) was higher than that of rodent bocavirus (reference strain:KY927868.1) in both liver (2.24% and 0.64%, respectively) and serum samples (2.19% and 0.44%, respectively). The NS1 regions of ungulate bocaparvovirus 4 and rodent bocavirus related sequences displayed over 84% and 88% identity at the nucleic acid and amino acid levels, respectively. Furthermore, these sequences had similar genomic structure, genomic features, and codon usage bias, and shared a common ancestor. These viruses also displayed greater adaptability to rats than pigs. Our results suggested that ungulate bocaparvovirus 4 and rodent bocavirus may originate from rats and may be different genotypes of the same bocavirus species.     

毕赤酵母表达的含前S1、前S2和S表位乙肝表面抗原疫苗的制备和免疫原性研究

整合了乙肝表面抗原嵌合基因SS1和SS2的毕赤酵母工程菌株GS115-SS1S2经高密度发酵培养,甲醇诱导,抗原表达量达到300~600mg/L发酵液。SS1S2抗原经细胞破碎、硅胶吸附、疏水层析和凝胶过滤纯化,纯度达99%以上,每升培养物可收获纯化抗原82mg。纯化的SS1S2抗原经Al(OH)3吸附,在NIH小鼠中进行免疫效果评价。三组NIH雌性小鼠,分别腹腔接种2.5μg、0.625μg和0.156μgSS1S2疫苗或商品化的单S疫苗。部分小鼠在30天时采血,测定各疫苗组的ED50值。在SS1S2疫苗组,前S1、前S2和S抗原的ED50值分别为0.46、0.29和0.84μg,而S疫苗组S抗原的ED50为0.99μg。另一部分小鼠分别在7天和14天时采血,考察抗体阳转率与时间的关系。SS1S2疫苗前S1、前S2抗体阳转率在7d和14d时比S抗体的阳转率为高,提示前S抗体出现的时间较早。上述结果显示SS1S2疫苗比单S疫苗具有更好的免疫原性。     

Perforin and Fas cytolytic pathways coordinately shape the selection and diversity of CD8+-T-cell escape variants of influenza virus

Antigenic variation is a viral strategy exploited to promote survival in the face of the host immune response and represents a major challenge for efficient vaccine development. Influenza viruses are pathogens with high transmissibility and mutation rates, enabling viral escape from immunity induced by prior infection or vaccination. Intense selection from neutralizing antibody drives antigenic changes in the surface glycoproteins, resulting in emergence of new strains able to reinfect hosts immune to previously circulating viruses. CD8+ cytotoxic T cells (CTLs) also provide protective immunity from influenza virus infection and may contribute to the antigenic evolution of influenza viruses. Utilizing mice transgenic for an influenza virus NP366-374 peptide-specific T-cell receptor, we demonstrated that the respiratory tract is a suitable site for generation of escape variants of influenza virus selected by CTL in vivo. In this report the contributions of the perforin and Fas pathways utilized by influenza virus-specific CTLs in viral clearance and selection of CTL escape variants have been evaluated. While transgenic CTLs deficient in either perforin- or Fas-mediated pathways are efficient in initial pulmonary viral control, variant virus emergence was observed in all the mice studied, although the spectrum of viral CTL escape variants selected varied profoundly. Thus, a less-restricted repertoire of escape variants was observed in mice with an intact perforin cytotoxic pathway compared with a limited variant diversity in perforin pathway-deficient mice, although maximal variant diversity was observed in mice having both Fas and perforin pathways intact. We conclude that selection of viral CTL escape variants reflects coordinate action between the tightly controlled perforin/granzyme pathway and the more promiscuous Fas/FasL pathway.     

黄唇鱼(Bahaba flavolabiata)的全基因组测序和基因组特征研究

黄唇鱼(Bahaba flavolabiata)为国家二级重点保护野生动物、IUCN(世界自然保护联盟)红色名录的极度濒危物种(CR)。基于其样本数量极其有限,全基因组研究可以提供大量与重要性状相关的功能基因和分子标记,从而揭示其重要生命现象的遗传机制。采用二代测序技术于2018年5月完成了黄唇鱼基因组精细图的测序,分析结果表明,测序得到约202 Gb的高质量数据,总测序深度约为317×;组装得到的基因组大小为637.43 Mb,Contig N50约为88 Kb,Scaffold N50约为4.65 Mb;重复序列约142.72 Mb,占比22.39%,预测得到23743个基因、920个t RNA、85个rRNA、176个假基因;98.46%的基因可以注释到NR、GO等数据库中;有67个基因家族是黄唇鱼所特有的。本研究从单碱基错误率、核心基因完整性及二代Reads比对分析3个方面对黄唇鱼基因组精细图的组装结果进行了评估,结果显示所组装的基因区的完整性较好。黄唇鱼基因组序列图谱的绘制完成,对于黄唇鱼自然资源的保护和种质资源挖掘具有极其重要的科学意义。     

Hydroxychloroquine-mediated inhibition of SARS-CoV-2 entry is attenuated by TMPRSS2

Hydroxychloroquine, used to treat malaria and some autoimmune disorders, potently inhibits viral infection of SARS coronavirus (SARS-CoV-1) and SARS-CoV-2 in cell-culture studies. However, human clinical trials of hydroxychloroquine failed to establish its usefulness as treatment for COVID-19. This compound is known to interfere with endosomal acidification necessary to the proteolytic activity of cathepsins. Following receptor binding and endocytosis, cathepsin L can cleave the SARS-CoV-1 and SARS-CoV-2 spike (S) proteins, thereby activating membrane fusion for cell entry. The plasma membrane-associated protease TMPRSS2 can similarly cleave these S proteins and activate viral entry at the cell surface. Here we show that the SARS-CoV-2 entry process is more dependent than that of SARS-CoV-1 on TMPRSS2 expression. This difference can be reversed when the furin-cleavage site of the SARS-CoV-2 S protein is ablated or when it is introduced into the SARS-CoV-1 S protein. We also show that hydroxychloroquine efficiently blocks viral entry mediated by cathepsin L, but not by TMPRSS2, and that a combination of hydroxychloroquine and a clinically-tested TMPRSS2 inhibitor prevents SARS-CoV-2 infection more potently than either drug alone. These studies identify functional differences between SARS-CoV-1 and -2 entry processes, and provide a mechanistic explanation for the limited in vivo utility of hydroxychloroquine as a treatment for COVID-19.