蚊虫Wolbachia 野外试验的研究进展

沃尔巴克氏体(Wolbachia),该共生菌利用引起宿主产生细胞质不亲和(cytoplasmic incompatibility)而快速入侵野生宿主种群,或压制种群数量,或干扰 RNA 病毒在宿主体内复制,对人类、动物、环境和生物链没有影响,从而运用到防治登革热,这已被越来越多的科学家所认可。本文就近年来蚊虫 Wolbachia 野外试验技术条件、生物安全情况和存在问题与展望作一综述。     

A single mutation in the first transmembrane domain of yeast COX2 enables its allotopic expression

During the course of evolution, a massive reduction of the mitochondrial genome content occurred that was associated with transfer of a large number of genes to the nucleus. To further characterize factors that control the mitochondrial gene transfer/retention process, we have investigated the barriers to transfer of yeast COX2, a mitochondrial gene coding for a subunit of cytochrome c oxidase complex. Nuclear-recoded Saccharomyces cerevisiae COX2 fused at the amino terminus to various alternative mitochondrial targeting sequences (MTS) fails to complement the growth defect of a yeast strain with an inactivated mitochondrial COX2 gene, even though it is expressed in cells. Through random mutagenesis of one such hybrid MTS-COX2, we identified a single mutation in the first Cox2 transmembrane domain (W56 → R) that (i) results in the cellular expression of a Cox2 variant with a molecular mass indicative of MTS cleavage, which (ii) supports growth of a cox2 mutant on a nonfermentable carbon source, and that (iii) partially restores cytochrome c oxidase-specific respiration by the mutant mitochondria. COX2^W56R can be allotopically expressed with an MTS derived from S. cerevisiae OXA1 or Neurospora crassa SU9, both coding for hydrophobic mitochondrial proteins, but not with an MTS derived from the hydrophilic protein Cox4. In contrast to some other previously transferred genes, allotopic COX2 expression is not enabled or enhanced by a 3′-UTR that localizes mRNA translation to the mitochondria, such as yeast ATP2^3′-UTR. Application of in vitro evolution strategies to other mitochondrial genes might ultimately lead to yeast entirely lacking the mitochondrial genome, but still possessing functional respiratory capacity.     

Pregnancy-associated venous thromboembolism (VTE) in combined heterozygous factor V Leiden (FVL) and prothrombin (FII) 20210 A mutation and in heterozygous FII single gene mutation alone

The risk of venous thromboembolism (VTE) in the absence of prophylaxis was evaluated in a retrospective study of 47 women (84 pregnancies) with combined thrombophilia [heterozygous factor V Leiden (FVL) plus prothrombin (FII) 20210A mutation (group I)] and in 82 women (193 pregnancies) with the FII alone (group II). VTE was more frequent in group I than in group II [17.8% versus 6.2%, P = 0.003, relative risk (RR) 2.9, 95% confidence interval (CI) 1.4-5.9], ante partum (7.1% and 2.1%) and post partum (11.5% and 4.2%). The risk was higher in index cases than in family members (RR 2.5, 95% CI 1.2-5.2 and RR 2.1, 95% CI 0.2-22.3 respectively) Even women who had no history of VTE before pregnancy had an increased risk (RR 2.2, 95% CI 1.0-4.8). Our results suggest that, during ante partum, prophylaxis is indicated in women with combined thrombophilia and with a VTE before pregnancy. In those without VTE before pregnancy, prophylaxis might be decided for each individual case, taking into consideration all risk factors. In women with the FII mutation alone, the low risk may not justify prophylaxis in the absence of previous VTE. In post partum, prophylaxis is indicated in all cases.     

RET原癌基因点突变所致多发性内分泌腺瘤病2B型一例家系研究

目的：研究1例中国家系中RET原癌基因点突变与多发性内分泌腺瘤病2B型（MEN－2B）发病的相互关系及其遗传特征。方法：收集1例MEN－2B患者术后甲状腺髓样癌肿瘤组织和外周血DNA标本及其父母外周血DNA标本运用PCR和逆转录PCR技术以及直接基因测序技术对上述标本中RET原癌基因16号外显子区域进行分子检测。结果：在患者肿瘤组织（c)DNA及其外周血DNA中均检测到RET原癌基因16号外显子918密码子处基因点突变,即：918Met(ATG）→Thr(ACG).且由基因测序图示,该突变为杂合子错义突变。而患者父母外周血DNA样本中均未发现上述RET原癌基因突变。结论：与国外报道相似,在中国MEN－2B患者中,也找到了RET原癌基因16号外显子基因点突变918Met(ATG)→Thr(ACG)。虽然其发病具有遗传倾向,但同样存在散发病例。MEN－2B发病的基因检测应成为该病的诊断治疗以及患者一级亲属早期诊断和临床干预的分子基础。     

Influence of the type of F8 gene mutation on inhibitor development in a single centre cohort of severe haemophilia A patients

Summary. The development of neutralizing antibodies against factor VIII (FVIII) is a major complication of treatment with FVIII in patients with severe haemophilia A. This study was designed to describe the relationship between the type and location of the factor 8 (F8) gene mutation and the development of clinically relevant inhibitors in patients with severe haemophilia A. We conducted a single centre cohort study among 318 consecutive patients (baseline FVIII activity level <0.01 IU mL^?1) born between 1934 and 2007 who were treated with FVIII on at least 50 exposure days. The primary outcome was clinically relevant inhibitor development, defined as the occurrence of at least two positive inhibitor titres and a decreased recovery. Clinically relevant inhibitors were diagnosed in 14% (43) of patients (30 high‐titre). The cumulative incidence of inhibitor development was 18% (35 of 200) in high‐risk gene defects (67% in patients with large deletions, 30% in patients with nonsense mutations, 15% in patients with intron 1 or 22 inversions) and 7% (8 of 118) in low‐risk gene defects (7% in patients with small deletions and insertions, 6% in patients with missense mutations, 8% in patients with splice site mutations). In patients with point mutations, the cumulative risk of developing inhibitors was highest in patients with mutations in the A3 and C2 domains (13% and 17% respectively). In conclusion, in agreement with earlier observations, the type and location of the F8 gene mutation were important determinants of inhibitor development in patients with severe haemophilia A.     

From the Cover: A bacterial symbiont is converted from an inedible producer of beneficial molecules into food by a single mutation in the gacA gene

Stable multipartite mutualistic associations require that all partners benefit. We show that a single mutational step is sufficient to turn a symbiotic bacterium from an inedible but host-beneficial secondary metabolite producer into a host food source. The bacteria’s host is a “farmer” clone of the social amoeba Dictyostelium discoideum that carries and disperses bacteria during its spore stage. Associated with the farmer are two strains of Pseudomonas fluorescens, only one of which serves as a food source. The other strain produces diffusible small molecules: pyrrolnitrin, a known antifungal agent, and a chromene that potently enhances the farmer’s spore production and depresses a nonfarmer’s spore production. Genome sequence and phylogenetic analyses identify a derived point mutation in the food strain that generates a premature stop codon in a global activator (gacA), encoding the response regulator of a two-component regulatory system. Generation of a knockout mutant of this regulatory gene in the nonfood bacterial strain altered its secondary metabolite profile to match that of the food strain, and also, independently, converted it into a food source. These results suggest that a single mutation in an inedible ancestral strain that served a protective role converted it to a “domesticated” food source.     

The occurrence of Brugada syndrome and isolated cardiac conductive disease in the same family could be due to a single SCN5A mutation or to the accidental association of both diseases.

AIMS: The distinct cardiac arrhythmia diseases, Brugada syndrome (BS) and isolated cardiac conduction disease (ICCD) are caused by heterozygous mutations in the SCN5A gene. Previous studies have demonstrated an intriguing association between ICCD and BS with the same mutation in the SCN5A gene. METHODS AND RESULTS: The proband of a multigenerational family presented BS and a familial history of sudden death. We performed clinical evaluations in family members including drug testing and screening for SCN5A mutations. Based on electrocardiogram features, we identified four individuals with BS, two with ICCD and one compatible with both. For five individuals, one with BS and ICCD, three with BS and one with ICCD, we characterized a heterozygous C- to T- mutation at position 4313 (P1438L) in the SCN5A gene. Expression studies of the P1438L mutation showed non-functional channels. The proband's father with the BS phenotype was not a carrier of the new SCN5A mutation. CONCLUSION: We report the case of a family with BS and/or ICCD and describe a novel mutation, the P1438L SCN5A mutation. In this family, the occurrence of BS and ICCD could be due to this single mutation but also to the accidental association of both diseases.