In pursuit of a molecular mechanism for adaptive gene amplification

"Adaptive" or "stationary-phase" mutation is a collection of apparent stress responses in which cells exposed to a growth-limiting environment generate genetic changes, some of which can allow resumption of rapid growth. In the well-characterized Lac system of Escherichia coli, reversions of a lac frameshift allele give rise to adaptive point mutations. Also in this system, adaptive gene amplification has been documented as a separate and parallel response that allows growth on lactose medium without acquisition of a compensatory frameshift mutation. In amplification, the DNA region containing the weakly functional lac allele becomes amplified to multiple copies, which produce sufficient enzyme activity to allow growth on the otherwise growth-limiting lactose medium. The amplifications are "adaptive" in that they occur after cells encounter the growth-limiting environment. Adaptive amplification is a reversible genetic change that allows adaptation and growth. It may be similar to chromosomal instability observed in the origins and progression of many cancers. We explore possible molecular mechanisms of adaptive amplification in the bacterial system and note parallels to chromosomal instability in other systems.     

In vivo gene therapy for diabetes mellitus

Gene therapy has been hyped as a possible 'cure' for diabetes mellitus in the near future ever since insulin was first cloned and expressed in cultured cells in the late 1970s. In the past decade, however, the bar for gene therapy for diabetes has been raised because of recent advances in the clinical management of diabetes. Although current treatment modalities fall far short of a cure, they produce greatly improved, if imperfect, glycemic control. In this context, we review the latest advances in in vivo gene therapy and conclude that the most widely applied strategy of insulin gene transfer does not measure up to the existing treatment options, whereas the recently proved concept of induced islet neogenesis has the potential of bettering the currently available therapy. Much work remains to be done, however, before this regimen can be taken from the bench to the bedside.     

Artificial and engineered chromosomes: developments and prospects for gene therapy

At the gene therapy session of the ICCXV Chromosome Conference (2004), recent advances in the construction of engineered chromosomes and de novo human artificial chromosomes were presented. The long-term aims of these studies are to develop vectors as tools for studying genome and chromosome function and for delivering genes into cells for therapeutic applications. There are two primary advantages of chromosome-based vector systems over most conventional vectors for gene delivery. First, the transferred DNA can be stably maintained without the risks associated with insertion, and second, large DNA segments encompassing genes and their regulatory elements can be introduced, leading to more reliable transgene expression. There is clearly a need for safe and effective gene transfer vectors to correct genetic defects. Among the topics discussed at the gene therapy session and the main focus of this review are requirements for de novo human artificial chromosome formation, assembly of chromatin on de novo human artificial chromosomes, advances in vector construction, and chromosome transfer to cells and animals.     

In pursuit of ecotourism

Ecotourism is expected, by the tourism industry and academics, to grow rapidly over the next 20 years. Much has been written about ecotourism, often with missionary zeal, but there is little consensus about its definition. It is argued here that conservationists and protected area managers should adopt a definition of ecotourism which contributes to the maintenance of biodiversity and an appropriate definition is suggested.Ecotourism is not merely an alternative to mass tourism, nor is it the only alternative. The literature on nature tourism and the environmental impacts of the industry dates back to the late 1970s. Tourism is now the world's largest industry and it has an increasing impact on protected areas. Our understanding of these mechanisms, their ecological impacts and our capacity to manage tourism in protected areas lags behind the growth of tourism to protected areas.A rapid growth in nature tourism and tourism to protected areas has coincided with a shift in protected area management strategies towards integrated development. Tourism is one means available to protected area managers seeking to increase the economic value of a protected area and to offer sustainable opportunities for economic development to local people.This paper argues that potentially conflicting commercial, protected area and development interests all contribute to the emergence of ecotourism and have been doing so for many years. Ecotourism needs to be tightly defined if it is to benefit conservation. Protected area managers should consider how they can take control of nature tourism to the parks they manage and convert it into ecotourism for the benefit of conservation and the livelihoods of local people.     

Possibility of transkingdom gene therapy for complex I diseases

Defects of complex I are involved in many human mitochondrial diseases, and therefore we have proposed to use the NDI1 gene encoding a single subunit NADH dehydrogenase of Saccharomyces cerevisiae for repair of respiratory activity. The yeast NDI1 gene was successfully introduced into mammalian cell lines. The expressed NDI1 protein was correctly targeted to the matrix side of the inner mitochondrial membranes, was fully functional and restored the NADH oxidase activity to the complex I-deficient cells. The NDI1-transduced cells were more resistant to complex I inhibitors and diminished production of reactive oxygen species induced by rotenone. It was further shown that the NDI1 protein can be functionally expressed in tissues such as skeletal muscles and the brain of rodents, which scarcely induced an inflammatory response. The use of NDI1 as a potential molecular therapy for complex I-deficient diseases is briefly discussed, including the proposed animal model.     

Promising developments bringing prion diseases closer to therapy and prophylaxis

Prion diseases are fatal, infectious, neurodegenerative disorders, and there are no available therapeutic or prophylactic regimens. The potential of immune system components in combating peripheral prion infection has long been underestimated, but recent studies have suggested that such molecules could be effective. For example, promising results have been reported from a passive vaccination study in prion-infected mice. In addition, elegant transgenic mouse studies have shown the inhibitory effect on prion propagation of a soluble immunoglobulin G (IgG)-like dimeric prion protein. This type of molecule might represent a new class of anti-prion compounds.     

In pursuit of effective toxicogenomics

Biological systems exhibit complex responses to xenobiotics varying from generic stress responses to very specific changes closely associated with the mechanism of toxicity. Until recently our view of this complexity was obscured by the simplicity of available analysis tools which allowed determination of only a few genes in any one study. Then genome sequencing and high throughput library screening projects delivered data on the genome sequence of many organisms, and clones were collected and made available to researchers in a previously unparalleled quantity. To exploit this new resource the microarray was developed from its predecessor the dot blot. Further development has expanded the number of clones contained on any one microarray to a point where the expression of many tens of thousands of genes in a biological system can be determined in a short period of time. What these data are revealing is the full complexity of the gene expression response to stimuli such as xenobiotic exposure. Toxicogenomics seeks to use the complexity of this response as a fingerprint or signature characteristic of that xenobiotic exposure. There are though two major experimental challenges that need to be dealt with for toxicogenomics to be successful. The first is technical and relates to the intrinsic difficulties associated with the accurate measurement of gene expression. For microarrays, this problem is multiplied by the number of genes on the microarray itself. To overcome this technical variability correct experimental design is critical. The second challenge concerns the biological system used. What genetic background, time point and dose of xenobiotic should be chosen? For in vitro systems should cell lines or primary cells be used? These factors, and more, could affect the gene expression profile obtained in response to the same xenobiotic exposure. Using both our data and data from public databases these issues are explored in this paper.     

非侵入性基因治疗在中枢神经系统疾病中的应用

非侵入性地将具有治疗作用的基因通过血脑屏障输送至脑内,以治疗中枢神经系统疾病,是生物学领域研究的难点和热点,而应用适宜的转运载体是解决这一难题的有效途径。使用病毒载体或非病毒载体,已成功进行非侵入性基因治疗的中枢神经系统疾病有实验性运动神经疾病、脑部肿瘤和帕金森病等。随着对脑微血管内皮细胞上的受体的研究和新型载体的开发,应用非侵入性基因治疗中枢神经系统疾病将会更为广泛。     

Engineering human chromosomes for gene therapy studies

We now have the capability to engineer human chromosomes that could be used to deliver therapeutic genes in gene therapy studies. These vectors have the advantages of being non-disruptive to the genome, non-immunogenic and are capable of carrying very large genes with all their regulatory sequences. What challenges lie ahead, and what future does this technology hold for gene therapy?     

A new colloidal lipidic system for gene therapy

A novel type of liposomal vector for gene therapy is described (Artificial Virus Particles; AVPs). This vector is based on the composition of retroviral envelopes, serum-resistant and non-toxic and smaller than 200 nm in size. The DNA is condensed using low molecular weight branched PEI. Equipment of these particles with a cyclic RGD peptide ligand as targeting device renders them selective for tumor endothelial and melanoma cells expressing high levels of alphavbeta3-integrins, and allows for an efficient delivery of the enclosed genetic material. The specificity of the vector system for melanoma cells could be further improved by using a melanocyte-specific tyrosinase promoter to drive transgene expression.     

线粒体治疗：一种新型的线粒体相关疾病的生物疗法

线粒体是细胞内的一种多功能细胞器,主要负责能量产生、细胞凋亡等生命过程。线粒体缺陷与临床上百种疾病相关。越来越多的研究已表明,细胞外的线粒体可被细胞内吞,进入到细胞内,然后以完整的形态发挥作用。研究发现,线粒体是对氧含量和酸碱度极为敏感的细胞器,细胞内环境可影响线粒体的功能。外源线粒体进入到生理环境中的细胞后,将提高细胞能量供应、促进细胞存活;但线粒体进入到缺氧和酸性的肿瘤组织后,将大量产生氧自由基、诱发细胞死亡。线粒体这种环境响应性的药理特性,可应用于清除肿瘤细胞、恢复受损组织的功能。目前线粒体已用于治疗中枢神经系统疾病(帕金森氏病、抑郁症、精神分裂症等)、外周系统疾病(缺血性心肌损伤、脂肪肝、肺气肿等)和肿瘤等,为线粒体相关疾病的治疗提供了新的方法。文中对这种新型生物治疗方法的研究进展、医学应用和存在的挑战进行综述。