Pluripotent stem cells and livestock genetic engineering

The unlimited proliferative ability and capacity to contribute to germline chimeras make pluripotent embryonic stem cells (ESCs) perfect candidates for complex genetic engineering. The utility of ESCs is best exemplified by the numerous genetic models that have been developed in mice, for which such cells are readily available. However, the traditional systems for mouse genetic engineering may not be practical for livestock species, as it requires several generations of mating and selection in order to establish homozygous founders. Nevertheless, the self-renewal and pluripotent characteristics of ESCs could provide advantages for livestock genetic engineering such as ease of genetic manipulation and improved efficiency of cloning by nuclear transplantation. These advantages have resulted in many attempts to isolate livestock ESCs, yet it has been generally concluded that the culture conditions tested so far are not supportive of livestock ESCs self-renewal and proliferation. In contrast, there are numerous reports of derivation of livestock induced pluripotent stem cells (iPSCs), with demonstrated capacity for long term proliferation and in vivo pluripotency, as indicated by teratoma formation assay. However, to what extent these iPSCs represent fully reprogrammed PSCs remains controversial, as most livestock iPSCs depend on continuous expression of reprogramming factors. Moreover, germline chimerism has not been robustly demonstrated, with only one successful report with very low efficiency. Therefore, even 34 years after derivation of mouse ESCs and their extensive use in the generation of genetic models, the livestock genetic engineering field can stand to gain enormously from continued investigations into the derivation and application of ESCs and iPSCs.     

Resistance to fluoroquinolones in Salmonella: emerging mechanisms and resistance prevention strategies

We review the current state of knowledge about the genetic and biochemical mechanisms that mediate quinolone resistance in Salmonella. They include modifications of topoisomerase targets, increased efflux activity and the recently described topoisomerase protection by the plasmid-encoded Qnr protein. We discuss what factors may determine the order of implementation of these various mechanisms in a particular strain, and what strategies could be used to combat resistance, from the inhibition of mutagenesis mechanisms to counteracting, during fluoroquinolone treatment, of resistance mechanisms already set in the infecting strain.     

Making transgenic livestock: genetic engineering on a large scale.

The feasibility of introducing foreign genes into the genomes of cattle, goats, pigs, and sheep has only recently been demonstrated. Studies have thus far focused on improving growth efficiency or directing expression of pharmaceutical proteins to the mammary glands of these species. The general strategy for producing transgenic livestock and mice is similar. In addition to the obvious difference in scale between mice and livestock experiments, there are noteworthy obstacles that significantly reduce the efficiency of producing transgenic livestock. Low embryo viability, low transgene integration rates, and high animal costs contribute to project costs that can easily exceed hundreds of thousands of dollars. A better understanding of the mechanisms that govern transgene integration should lead to improved efficiencies. But, the full potential of the transgenic livestock system will not be fully realized until: 1) gene constructs can be designed that function in a reproducible, predictable manner; and 2) the genetic control of physiological processes are more clearly elucidated. Newly emerging approaches may resolve at least some of these issues within the next decade.     

酿酒酵母乙醇耐性的分子机制及基因工程改造

提高工业微生物对毒性代谢产物及高温等环境胁迫因素的耐受性对工业生产具有重要的意义。发酵过程中产生的乙醇对酵母细胞的生长和代谢都具有较强的抑制作用,是酿酒酵母的重要环境胁迫因素之一。对酿酒酵母乙醇耐性的分子机制的研究可为选育具有较强乙醇耐受性的酵母菌种提供理论基础。近年来,通过细胞全局基因转录分析和基因功能分析,对酿酒酵母乙醇耐性的分子机制有了更多新的认识,揭示了很多新的与乙醇耐性相关的基因,并在此基础上,通过对相关基因进行过量表达或敲除,成功提高了酵母菌的乙醇耐性。以下综述了近年来酵母菌乙醇耐性的生物化学与分子生物学机制的研究进展,以及构建具有较高乙醇耐性的酵母菌的基因工程操作。这些研究不仅加深了对酿酒酵母乙醇耐性的机理认识,也可为高效进行生物转化生产生物质能源奠定理论基础。     

Genetic elements of plant viruses as tools for genetic engineering.

Viruses have developed successful strategies for propagation at the expense of their host cells. Efficient gene expression, genome multiplication, and invasion of the host are enabled by virus-encoded genetic elements, many of which are well characterized. Sequences derived from plant DNA and RNA viruses can be used to control expression of other genes in vivo. The main groups of plant virus genetic elements useful in genetic engineering are reviewed, including the signals for DNA-dependent and RNA-dependent RNA synthesis, sequences on the virus mRNAs that enable translational control, and sequences that control processing and intracellular sorting of virus proteins. Use of plant viruses as extrachromosomal expression vectors is also discussed, along with the issue of their stability.     

Evolving strategies for the genetic engineering of herbicide resistance in plants

Developments in plant genetic engineering technology will shortly permit the commercial introduction of transgenic crop varieties resistant to a number of non-selective herbicides. High levels of tolerance have been achieved both by overexpression of a target protein and by modification of that target to an insensitive form. However the results of preliminary trials suggest that in some instances the yield penalty for such genetic alterations will be prohibitive. An alternative strategy, based on the transfer and expression of a gene encoding a herbicide-detoxifying enzyme, appears to offer high resistance levels at low metabolic cost and is expected to assume increasing importance, although it may not prove suitable for all herbicides.     

Current genetic engineering strategies for the production of antihypertensive ACEI peptides

Hypertension is a major and highly prevalent risk factor for various diseases. Among the most frequently prescribed antihypertensive first-line drugs are synthetic angiotensin I-converting enzyme inhibitors (ACEI). However, since  their use in hypertension therapy has been linked to various side effects, interest in the application of food-derived ACEI peptides (ACEIp) as antihypertensive agents is rapidly growing. Although promising, the industrial production of ACEIp through conventional methods such as chemical synthesis or enzymatic hydrolysis of food proteins has been proven troublesome. We here provide an overview of current antihypertensive therapeutics, focusing on ACEI, and illustrate how biotechnology and bioengineering can overcome the limitations of ACEIp large-scale production. Latest advances in ACEIp research and current genetic engineering-based strategies for heterologous production of ACEIp (and precursors) are also presented. Cloning approaches include tandem repeats of single ACEIp, ACEIp fusion to proteins/polypeptides, joining multivariate ACEIp into bioactive polypeptides, and producing ACEIp-containing modified plant storage proteins. Although bacteria have been privileged ACEIp heterologous hosts, particularly when testing for new genetic engineering strategies, plants and microalgae-based platforms are now emerging. Besides being generally safer, cost-effective and scalable, these “pharming” platforms can perform therelevant posttranslational modifications and produce (and eventually deliver) biologically active protein/peptide-based antihypertensive medicines.     

Biochemical and genetic engineering strategies to enhance hydrogen production in photosynthetic algae and cyanobacteria

As an energy carrier, hydrogen gas is a promising substitute to carbonaceous fuels owing to its superb conversion efficiency, non-polluting nature, and high energy content. At present, hydrogen is predominately synthesized via chemical reformation of fossil fuels. While various biological methods have been extensively explored, none of them is justified as economically feasible. A sustainable platform for biological production of hydrogen will certainly impact the biofuel market. Among a selection of biological systems, algae and cyanobacteria have garnered major interests as potential cell factories for hydrogen production. In conjunction with photosynthesis, these organisms utilize inexpensive inorganic substrates and solar energy for simultaneous biosynthesis and hydrogen evolution. However, the hydrogen yield associated with these organisms remains far too low to compete with the existing chemical systems. This article reviews recent advances of biochemical, bioprocess, and genetic engineering strategies in circumventing technological limitations to hopefully improve the applicative potential of these photosynthetic hydrogen production systems.     

Cell death in mammalian cell culture: molecular mechanisms and cell line engineering strategies

Cell death is a fundamentally important problem in cell lines used by the biopharmaceutical industry. Environmental stress, which can result from nutrient depletion, by-product accumulation and chemical agents, activates through signalling cascades regulators that promote death. The best known key regulators of death process are the Bcl-2 family proteins which constitute a critical intracellular checkpoint of apoptosis cell death within a common death pathway. Engineering of several members of the anti-apoptosis Bcl-2 family genes in several cell types has extended the knowledge of their molecular function and interaction with other proteins, and their regulation of cell death. In this review, we describe the various modes of cell death and their death pathways at molecular and organelle level and discuss the relevance of the growing knowledge of anti-apoptotic engineering strategies to inhibit cell death and increase productivity in mammalian cell culture.     

Studies on DNA-related enzymes to elucidate molecular mechanisms underlying genetic information processing and their application in genetic engineering

ABSTRACT

Recombinant DNA technology, in which artificially “cut and pasted” DNA in vitro is introduced into living cells, contributed extensively to the rapid development of molecular biology over the past 5 decades since the latter half of the 20^th century. Although the original technology required special experiences and skills, the development of polymerase chain reaction (PCR) has greatly eased in vitro genetic manipulation for various experimental methods. The current development of a simple genome-editing technique using CRISPR-Cas9 gave great impetus to molecular biology. Genome editing is a major technique for elucidating the functions of many unknown genes. Genetic manipulation technologies rely on enzymes that act on DNA. It involves artificially synthesizing, cleaving, and ligating DNA strands by making good use of DNA-related enzymes present in organisms to maintain their life activities. In this review, I focus on key enzymes involved in the development of genetic manipulation technologies.     

Molecular-genetic mechanisms of plant resistance to viruses

This paper gives a brief overview of the recent ideas about molecular and genetic mechanisms of plant resistance to viruses. Two plant antiviral strategies (R-gene-mediated mechanism and RNA-silencing) are considered. Examples of engineered virus resistance are presented.     

Perspectives of genomics for genetic conservation of livestock

Genomics provides new opportunities for conservation genetics. Conservation genetics in livestock is based on estimating diversity by pedigree relatedness and managing diversity by choosing those animals that maximize genetic diversity. Animals can be chosen as parents for the next generation, as donors of material to a gene bank, or as breeds for targeting conservation efforts. Genomics provides opportunities to estimate diversity for specific parts of the genome, such as neutral and adaptive diversity and genetic diversity underlying specific traits. This enables us to choose candidates for conservation based on specific genetic diversity (e.g. diversity of traits or adaptive diversity) or to monitor the loss of diversity without conservation. In wild animals direct genetic management, by choosing candidates for conservation as in livestock, is generally not practiced. With dense marker maps opportunities exist for monitoring relatedness and genetic diversity in wild populations, thus enabling a more active management of diversity.     

丝状真菌降解转化纤维素的机制与遗传改良前景简

丝状真菌可以分泌大量纤维素酶及辅助酶来降解纤维素底物,也是目前工业上纤维素酶的主要生产者。回顾并综述了丝状真菌降解转化纤维素的酶系和机制进展,详细总结了组学研究在纤维素酶研究上的新成果,并探讨了提高丝状真菌酶系效率和产量的遗传改良策略。