Emerging strategies for engineering microbial communities

From biosynthesis to bioremediation, microbes have been engineered to address a variety of biotechnological applications. A promising direction in these endeavors is harnessing the power of designer microbial consortia that consist of multiple populations with well-defined interactions. Consortia can accomplish tasks that are difficult or potentially impossible to achieve using monocultures. Despite their potential, the rules underlying microbial community maintenance and function (i.e. the task the consortium is engineered to carry out) are not well defined, though rapid progress is being made. This limited understanding is in part due to the greater challenges associated with increased complexity when dealing with multi-population interactions. Here, we review key features and design strategies that emerge from the analysis of both natural and engineered microbial communities. These strategies can provide new insights into natural consortia and expand the toolbox available to engineers working to develop novel synthetic consortia.     

Emerging strategies of lignin engineering and degradation for cellulosic biofuel production

Ethanol and other biofuels produced from lignocellulosic biomass represent a renewable, more carbon-balanced alternative to both fossil fuels and corn-derived or sugarcane-derived ethanol. Unfortunately, the presence of lignin in plant cell walls impedes the breakdown of cell wall polysaccharides to simple sugars and the subsequent conversion of these sugars to usable fuel. Recent advances in the understanding of lignin composition, polymerization, and regulation have revealed new opportunities for the rational manipulation of lignin in future bioenergy crops, augmenting the previous successful approach of manipulating lignin monomer biosynthesis. Furthermore, recent studies on lignin degradation in nature may provide novel resources for the delignification of dedicated bioenergy crops and other sources of lignocellulosic biomass.     

Emerging intra-articular drug delivery systems for the temporomandibular joint

Temporomandibular joint (TMJ) disorders are a heterogeneous group of diseases that cause progressive joint degeneration leading to chronic pain and reduced quality of life. Both effective pain reduction and restoration of TMJ function remain unmet challenges. Intra-articular injections of corticosteroids and hyaluronic acid are currently used to treat chronic pain, but these methods require multiple injections that increase the risk of iatrogenic joint damage and other complications. The small and emerging field of TMJ tissue engineering aims to reduce pain and disability through novel strategies that induce joint tissue regeneration. Development of methods for sustained, intra-articular release of growth factors and other pro-regenerative signals will be critical for the success of TMJ tissue engineering strategies. This review discusses methods of intra-articular drug delivery to the TMJ, as well as emerging injectable controlled release systems with potential to improve TMJ drug delivery, to encourage further research in the development of sustained release systems for both long-term pain management and to enhance tissue engineering strategies for TMJ regeneration.     

同种异体骨移植治疗大段骨缺损的研究进展

同种异体骨已成为临床上治疗创伤、感染、先天性骨病及肿瘤切除所致的大段骨缺损的重要材料.本文主要从同种异体骨愈合机制、制备保存、临床应用效果、排斥反应及预防方法四个方面就同种异体骨移植治疗大段骨缺损的研究进展作一综述,为临床骨缺损治疗提供理论支持.     

Polypeptide factors regulating osteogenesis and bone marrow repair

Osteogenic growth polypeptides regulate bone cell function in vitro and may act in vivo in an autocrine, paracrine, or endocrine manner. Several of these polypeptides are present in the blood in an inactive form. During postablation bone marrow regeneration these factors may be activated, released from the blood clot, and together with locally produced polypeptides mediate the initial intramedullary/systemic osteogenic phase of this process. Then, the same and/or other polypeptides expressed by stromal cells have the potential to promote the second phase of regeneration that consists of osteoclastogenesis, resorption of the transient intramedullary bone, and hemopoiesis. This may be an indirect influence since these polypeptides can regulate the stromal cell expression of some of the hemopoietic factors. Clinically, the osteogenic growth polypeptides that regulate osteogenesis and hemopoiesis have a potential role in osteoporosis therapy, implant bone surgery, and bone marrow transplantation. © 1994 Wiley-Liss, Inc.     

Baculovirus display strategies: Emerging tools for eukaryotic libraries and gene delivery.

Recombinant baculoviruses have been extensively used as vectors for abundant expression of a large variety of foreign proteins in insect cell cultures. The appeal of the system lies essentially in easy cloning techniques and virus propagation combined with the eukaryotic post-translational modification machinery of the insect cell. Recently, a novel molecular biology tool was established by the development of baculovirus surface display, using different strategies for presentation of foreign peptides and proteins on the surface of budded virions. This eukaryotic display system enables presentation of large complex proteins on the surface of baculovirus particles and has thereby become a versatile system in molecular biology. Surface display strategies play an important role, as they may be used to enhance the efficiency and specificity of viral binding and entry to mammalian cells. In addition, baculovirus surface display vectors have been engineered to contain mammalian promoter elements designed for gene delivery both in vitro and in vivo. Moreover, baculovirus capsid display has recently been developed; this holds promise for intracellular targeting of the viral capsid and subsequent cytosolic delivery of desired protein moieties. Finally, the viruses can accommodate large insertions of foreign DNA and replicate only in insect cells. Together, these are attributes that are very likely to make them important tools in functional genomics and proteomics.     

Protein- and gene-based tissue engineering in bone repair

A tissue engineering approach to bone regeneration includes the use of a scaffold, cells and bioactive factors alone or in various combinations. Several investigators have demonstrated enhanced bone formation when the tissue-engineered construct possesses traits inherent to autogenic bone grafts, namely osteoconductivity, osteoinductivity and osteogenicity. Use of the biodegradable polymer poly(lactide-co-glycolide) in combination with bone morphogenetic protein or primary cells genetically modified to release osteogenic protein have demonstrated the ability to induce osteogenic differentiation of, and subsequent mineralization by, muscle-derived cells and mesenchymal stem cells in both in vitro and in vivo applications.     

Protein-based tissue engineering in bone and cartilage repair

Bioactive proteins signal host or transplanted cells to form the desired tissue type. Matrix systems are utilized to locally deliver the proteins and to maintain effective protein concentrations. For some indications, a matrix is required to define the physical form of the regenerated tissue. Substantial progress has been made in bone tissue engineering in recent years, based on the results of controlled clinical studies using bone morphogenetic proteins. Ongoing research in this area centers on the design of additional delivery matrices to expand the clinical indications, using synthetic delivery systems that mimic biological qualities of the natural materials currently in use. Although a similar rationale exists for the regeneration of articular cartilage with bioactive factors, advancement in this area has not been as substantial.     

热对成骨和破骨细胞影响及热休克蛋白和因子参与调节的研究进展

热物理因素在骨疾病的治疗、骨再生修复过程中的应用及对成骨细胞影响重要性的认识不断被深化,一定温度热处理可促进成骨细胞分化,热休克蛋白及热休克因子参与细胞保护与分化.但目前尚未阐明热对成骨细胞与破骨细胞偶联关系的影响及热休克蛋白70(HSP70)和热休克因子2(HSF2)对成骨细胞RANKL的调节机制.探明该影响及调节机制可能成为揭示热物理干预影响骨转化的关键所在之一.     

Small RNAs: Emerging key players in DNA double-strand break repair

DNA double-strand break (DSB) is the most deleterious form of DNA damage and poses great threat to genome stability. Eukaryotes have evolved complex mechanisms to repair DSBs through coordinated actions of protein sensors, transducers, and effectors. DSB-induced small RNAs (diRNAs) or Dicer/Drosha-dependent RNAs (DDRNAs) have been recently discovered in plants and vertebrates, adding an unsuspected RNA component into the DSB repair pathway. DiRNAs/DDRNAs control DNA damage response (DDR) activation by affecting DDR foci formation and cell cycle checkpoint enforcement and are required for efficient DSB repair. Here, we summarize the findings of diRNAs/DDRNAs and discuss the possible mechanisms through which they act to facilitate DSB repair.     

Trabecular bone structure and strength - remodelling and repair

The strength of the spinal trabecular bone declines by a factor of 4-5 from the age of 20 to 80 years. At the same time, the volumetric (apparent) density declines by a factor of only 2. This discrepancy can be explained by the known power relationship between density and strength; this power relationship is based on the fact that trabecular bone is a porous material. To date, it has not been possible to determine or quantify the influence other factors may have in determining the strength of a loadbearing trabecular network. However, it is known that with age: 1) There is a loss of connectivity through osteoclastic perforations of horizontal struts. 2) There is an increase in anisotropy - again due to loss of horizontal struts, and perhaps also due to micro-modelling drift or to thickening of some vertical trabeculae. 3) The changes in the network can lead to the slenderness ratio between vertical and horizontal struts reaching a certain magnitude and thereby inducing buckling under compression. 4) Microdamage and microfractures will occur - mainly in these very loaded vertical struts. The microfractures will be repaired by microcallus formation, and these calluses will later be removed by the remodelling process. 5) Bone material quality will slightly change, leading to a decrease in collagen content and a relative increase in the degree of mineralisation. But, it is not known how these factors will influence the power relationship between density and strength. Nor is it known how different treatment regimens will affect the 'natural' power relationship: will the same curve be followed, but in the opposite direction? Or will the curve be less or more steep? Will the gain in bone strength be larger if treatment is started early - on the steep part of the curve? Furthermore, as trabecular bone can never be isolated in vivo, other factors need to be investigated: The interplay between the cortical shell and the trabecular network; transmission of load; the interplay between soft tissues (cartilage, connective tissue, muscle) and bone; the shock absorbing capacity of the discs; and the hydraulic effect of the bone marrow. In order to answer these questions, more in vitro and in vivo studies on human bone in relation to aging, to immobilisation, to exercise and in relation to different treatment regimens are needed.     

Development of joint application strategies for two microbial gene finders

MOTIVATION: As a starting point in annotation of bacterial genomes, gene finding programs are used for the prediction of functional elements in the DNA sequence. Due to the faster pace and increasing number of genome projects currently underway, it is becoming especially important to have performant methods for this task. RESULTS: This study describes the development of joint application strategies that combine the strengths of two microbial gene finders to improve the overall gene finding performance. Critica is very specific in the detection of similarity-supported genes as it uses a comparative sequence analysis-based approach. Glimmer employs a very sophisticated model of genomic sequence properties and is sensitive also in the detection of organism-specific genes. Based on a data set of 113 microbial genome sequences, we optimized a combined application approach using different parameters with relevance to the gene finding problem. This results in a significant improvement in specificity while there is similarity in sensitivity to Glimmer. The improvement is especially pronounced for GC rich genomes. The method is currently being applied for the annotation of several microbial genomes. AVAILABILITY: The methods described have been implemented within the gene prediction component of the GenDB genome annotation system.     

Biomolecular strategies of bone augmentation in spinal surgery

Autologous bone grafts and allografts are the most accepted procedures for achieving spinal fusion. Recently, breakthroughs in understanding bone biology have led to the development of novel approaches to address the clinical problem of bone regeneration in an unfavorable environment, while bypassing the drawbacks of traditional treatments, including limited availability, donor site morbidity, risk of disease transmission and reduced osteogenicity. These approaches have also been studied for their effectiveness in reaching successful spinal fusion. This review focuses on the cellular and molecular mechanisms explaining the rationale behind these methods, including bone marrow aspirate and mesenchymal stem cells, platelet-rich plasma, bone morphogenetic proteins and gene therapy, which have opened a promising perspective in the field of bone formation in spinal surgery.