Analysis of synonymous codon usage in the UL24 gene of duck enteritis virus

The analysis on codon usage bias of UL24 gene of duck enteritis virus (DEV) may improve our understanding of the evolution and pathogenesis of DEV and provide a basis for understanding the relevant mechanism for biased usage of synonymous codons and for selecting appropriate expression systems to improve the expression of target genes. The codon usage bias of UL24 genes of DEV and 27 reference herpesviruses were analyzed. The results showed that codon of UL24 gene of DEV was strong bias toward the synonymous codons with A and T at the third codon position. A high level of diversity in codon usage bias existed, and the effective number of codons used in a gene plot revealed that the genetic heterogeneity in UL24 gene of herpesviruses was constrained by the G + C content. The phylogentic analysis suggested that DEV was evolutionarily closer to Alphaherpesvirinae and that there was no significant deviation in codon usage in different virus strains. There were 20 codons showing distinct usage differences between DEV and Escherichia coli, 23 between DEV and Homo sapiens, but only 16 codons between DEV and yeast. Therefore the yeast expression system may be more suitable for the expression of DEV genes. Renyong Jia, Anchun Cheng, Mingshu Wang, and Hongyi Xin contributed equally to this work and should be considered as first author.     

A viral regulator of glycoprotein complexes contributes to human cytomegalovirus cell tropism

Viral glycoproteins mediate entry of enveloped viruses into cells and thus play crucial roles in infection. In herpesviruses, a complex of two viral glycoproteins, gH and gL (gH/gL), regulates membrane fusion events and influences virion cell tropism. Human cytomegalovirus (HCMV) gH/gL can be incorporated into two different protein complexes: a glycoprotein O (gO)-containing complex known as gH/gL/gO, and a complex containing UL128, UL130, and UL131 known as gH/gL/UL128-131. Variability in the relative abundance of the complexes in the virion envelope correlates with differences in cell tropism exhibited between strains of HCMV. Nonetheless, the mechanisms underlying such variability have remained unclear. We have identified a viral protein encoded by the UL148 ORF (UL148) that influences the ratio of gH/gL/gO to gH/gL/UL128-131 and the cell tropism of HCMV virions. A mutant disrupted for UL148 showed defects in gH/gL/gO maturation and enhanced infectivity for epithelial cells. Accordingly, reintroduction of UL148 into an HCMV strain that lacked the gene resulted in decreased levels of gH/gL/UL128-131 on virions and, correspondingly, decreased infectivity for epithelial cells. UL148 localized to the endoplasmic reticulum, but not to the cytoplasmic sites of virion envelopment. Coimmunoprecipitation results indicated that gH, gL, UL130, and UL131 associate with UL148, but that gO and UL128 do not. Taken together, the findings suggest that UL148 modulates HCMV tropism by regulating the composition of alternative gH/gL complexes.The lipid bilayer membranes of living cells pose an existential challenge to viruses. In enveloped viruses, viral glycoproteins execute a highly regulated fusion event between virion and cellular membranes, thereby delivering the viral genome and other contents of the virion into the host cell. Antibody responses that block entry are considered neutralizing and represent an important host defense against viral pathogens.In many enveloped viruses, one or two viral glycoproteins suffice to carry out binding and membrane fusion events that mediate entry. In herpesviruses, however, at least four envelope glycoproteins are typically involved. The core machinery for herpesvirus entry comprises three highly conserved viral glycoproteins, glycoprotein B (gB), glycoprotein H (gH), and glycoprotein L (gL), along with one or more accessory glycoproteins necessary for binding to cell surface receptors (reviewed in refs. 1, 2). gB is thought to be the proximal mediator of membrane fusion, whereas gH and gL form a complex, termed gH/gL, which has been found to regulate the fusogenic activity of gB (3–6). In a number of beta and gamma herpesviruses, including the human pathogens human cytomegalovirus (HCMV), human herpesvirus 6 (HHV-6), and Epstein–Barr virus (EBV), two different gH/gL complexes are found on the virion envelope and are necessary for the viruses to enter the full range of cell types that they infect in vivo.Of the two gH/gL complexes expressed in HCMV virions, the gH/gL complex with glycoprotein O (gO), gH/gL/gO, suffices for entry into fibroblasts, a cell type in which fusion events at the plasma membrane initiate infection (7). Infection of several other types of cells, including monocytes, dendritic cells, endothelial cells, and epithelial cells, requires the pentameric complex of gH/gL and three small glycoproteins—UL128, UL130, and UL131 (UL128-131)—and appears to involve fusion at endosomal membranes (8–16). Strains of HCMV, such as AD169 and Towne, that have undergone extensive serial passage in cultured fibroblasts fail to express the pentameric gH/gL/UL128-131 complex on virions and thus are unable to infect epithelial and endothelial cells (12, 13, 15); however, repair of a frameshift mutation in the UL131 gene of strain AD169 restores expression of gH/gL/UL128-131 (11, 12) and expands its cell tropism.Less extensively passaged HCMV strains that retain expression of gH/gL/UL128-131 can efficiently infect epithelial and endothelial cells (13, 17, 18). Nonetheless, several such strains replicate to ∼1,000-fold lower titers on epithelial cells compared with strain AD169 repaired for UL131 (11). AD169 lacks a ∼15-kb region at the end of the unique long genome region, termed the ULb′ (19). We were intrigued by the rather striking differences in cell tropism between laboratory strain AD169 repaired for expression of the pentameric gH/gL/UL128-131 complex, and strains, such as TB40/E, that have largely intact ULb′ regions and maintain expression of gH/gL/UL128-131. We hypothesized the ULb′ region encodes an additional factor involved in HCMV cell tropism. Our studies addressing this hypothesis led us to identify a new function for UL148, a gene within the ULb′. We found that UL148 encodes an endoplasmic reticulum (ER) resident glycoprotein that influences virion cell tropism by regulating the composition of alternative gH/gL complexes.     

When is it safe to exercise mechanically ventilated patients in the intensive care unit? An evaluation of consensus recommendations in a cardiothoracic setting

Rationale

Consensus recommendations have been developed to guide exercise rehabilitation of mechanically ventilated patients in the intensive care unit.

糖尿病大鼠周围神经功能及结构的改变及意义

目的 了解糖尿病状态下周围神经损伤的发展过程.方法 链脲菌素诱导糖尿病,分别在2、4、6、8、12周,通过神经传导速度、热痛阈值、坐骨神经结构改变和腓肠神经定量分析,动态观察糖尿病大鼠周围神经的功能和结构变化特点.结果 糖尿病大鼠2周即可出现神经传导速度减慢、痛觉阈值减低等功能改变,4周出现超微结构改变,并随病程延长逐渐加重.结论 实验性糖尿病大鼠早期即出现神经病变,且功能改变先于结构病变.     

大鼠心肌细胞的肌浆网与闰盘间偶联的电镜观察

本实验对大鼠心房心肌细胞的肌浆网与閏盘间的关系进行了超微结构观察。结果表明,肌浆网与閏盘的非特化肌膜存在偶联,为区别于一般的周围偶联,而将它们之间的偶联称为閏盘偶联。它具有周围偶联及内部偶联的形态结构特征,即(1)在偶联区域内存在胞浆间隙,宽约11～18nm;(2)在胞浆间隙内有连接突或连足;(3)肌浆网腔内含有电子致密物质。在偶联区域,肌浆网膜不仅与閏盘的非特化肌膜形成偶联,而且与线粒体外膜紧密并置。此外,心肌缝隙连接与肌浆网可形成缝隙连接-肌浆网偶联,其超微结构特点与心肌偶联相同。本文对肌浆网与閏盘的偶联的功能意义进行了讨论。     

家兔非吞噬细胞的超微吞噬观察

本文对5只家兔用台盼蓝活体染色-碱性品红整块复染法进行观察。光镜下除各器官的巨噬细胞有强烈的超微吞噬作用外,其他非吞噬细胞如肝细胞、肾近端小管上皮细胞以及成纤维细胞等对无毒的胶体活性染料也具有超微吞噬的能力。表明它们对机体也起防御作用。     

大鼠弓状核损毁后睾丸超微结构的变化

已知初生期大鼠注射谷氨酸一钠(MSG)可引起下丘脑弓状核严重损毁。本研究证实,雄性大鼠生后2及4天经腹腔注射MSG(4mg/g体重),成年后睾丸电镜观察,曲细精管内各级生精细胞发生明显改变,胞质出现空泡,线粒体变性,嵴断裂;核膜缺损,核质疏松,染色体遭到严重破坏。提示:睾丸超微结构变化,可能来自于神经内分泌系统功能变化,与下丘脑弓状核损毁密切相关。     

人尖锐湿疣中乳头瘤病毒形态发生之观察

免疫细胞化学和电镜观察人乳头瘤病毒（ＨＰＶ）形态发生结果表明：该病毒抗原见之于棘层、颗粒层和角质层细胞核内；毒粒则仅见之于颗粒层及角质层。从而提示了棘层以上的细胞层次为ＨＰＶ复制、装配和发育成熟的主要场所。本研究还观察到了ＨＰＶ装配的过渡阶段，宿主细胞的“溶解”及含有ＨＰＶ颗粒的细胞不一定都出现空泡等现象，从而提示了该病毒可因细胞溶解而释放，并造成上皮内扩散和再感染；空泡细胞不能作为诊断该病毒感染的可靠依据。     

大鼠严重烫伤后早期肠道营养对肠粘膜屏障的保护作用

本研究采用光镜、电镜、冷冻蚀刻，观察了大鼠严重烫伤（３０％ＴＢＳＡⅢ°）后２４ｈ内回肠粘膜的病理变化。结果表明：烫伤对照组，伤后３ｈ开始出现各种病理改变：回肠粘膜固有层水肿，中性粒细胞浸润，绒毛顶部上皮下出现囊状空隙，中央乳糜管扩张，粘膜上皮细胞变性坏死脱落；回肠上皮细胞连接分离，微绒毛坏死脱落，线粒体空化、嵴断裂，核周间隙扩张；肠上皮细胞紧密连接的嵴状突起排列紊乱，数量减少，融合或脱节。早期肠道