Self-incompatibility: insights through microscopy

The contributions of microscopy to our understanding of gametophytic self-incompatibility in the ornamental tobacco Nicotiana alata are reviewed. Self-incompatibility is a genetically based system which prevents self-fertilization and thereby promotes outbreeding in plants. Pollen bearing an S-allele identical to either of the S-alleles in the female sporophytic tissues is rejected. Several S-allele-specific style glycoproteins have been isolated from Solanaceous species. All have ribonuclease activity and are termed S-RNases. The cDNA clones encoding N. alata S-RNases have been used in in situ hybridization experiments which show that the genes are expressed in the transmitting tract of the style and in the epidermis of the placenta. Immunocyto-chemistry using an antibody to S₂-RNase demonstrates extracellular accumulation of the enzyme in the same tissues. These tissues are the pathway through which pollen tubes must grow to reach the ovules. The microscopy data are congruent with a model in which self-pollenation is susceptible to an allele-specific cytotoxin produced by the sporophyte.     

Effect of conversion of functional layout to a cellular layout on the queue time performance: some new insights

Transition from a functional system to a cellular system involves partitioning the machine and part populations. Partitioning the machine population degrades the queue time performance. This paper investigates whether splitting the part population into part families can offset the effect of partitioning the machine population on queue time. Queue times are obtained for both cellular and functional systems through queueing theory for single stage production and by simulation for multistage production under identical factor settings of process time, setup time, batch size and part arrival. Unlike past research, this study identifies certain situations where a cellular system without getting benefits in factor settings outperforms a functional system.     

Blood flow: insights from ultrasound

Ultrasonic pulse-echo systems can provide range-finding, time-position and real-time two-dimensional images of soft-tissue structures within the body. The Doppler effect can be used to study motion and blood flow. Continuous wave Doppler instruments provide information about velocity and direction of flow; depth discrimination can be obtained by pulsing the ultrasound. Two-dimensional Doppler flow imaging can be achieved by manual scanning of a probe over the skin surface. The combination of real-time pulse-echo imaging with pulsed Doppler blood flow detection in the duplex scanner makes it possible to localize the anatomical position of the Doppler sample volume. Real-time Doppler colour flow imaging combines traditional ultrasonic scanning with a two-dimensional flow map. Using appropriate ultrasonic instruments, blood flow volume rates, blood flow velocity profiles, pressure gradients, orifice areas, flow disturbances, jets, characteristics of blood vessels and the circulatory system, and tissue perfusion can all be investigated. These investigations have clinical applications in the study of cardiac, cerebral and peripheral blood flow, blood flow in the female pelvis, the fetus, the abdomen, the neonate, and in malignant tumours. Contemporary ultrasonic diagnosis employs exposure levels that are apparently free from biological risk, but other factors need to be taken into account in considering the prudent use of ultrasonic methods. Promising research is being carried out into the mechanism of ultrasonic scattering by blood, Doppler speckle, time-domain processing for blood flow imaging, methods for increasing the scanning speed, Doppler flow microscopy and contrast agents. The new technology that will result from this research should lead to further substantial progress in ultrasonic blood flow studies.     

提高常规色谱分析的速度,应对新法规的需求

珀金埃尔默公司新推出的Clarus 600型GC和GCMS采用全新柱温箱设计，能够缩短每次分析循环的时间，在有限的时间内可以完成更多的分析测试，从而提高分析效率和仪器的投资回报率。特别适合于需要大批量分析检测的实验室和需要测定挥发性有机物的分析工作。     

Mechanobiology of bone healing and regeneration: in vivo models

Mechanical boundary conditions are well known to influence the regeneration of bone and mechanobiology is the study of how mechanical or physical stimuli regulate biological processes. In vivo models have been applied over many years to investigate the effects of mechanics on bone healing. Early models have focused on the influence of mechanical stability on healing outcome, with an interest in parameters such as the magnitude of interfragmentary movement, the rate and timing of application of micromotion and the number of loading cycles. As measurement techniques have been refined, there has been a shift in orders of magnitude from investigations targeted at the organ level to those targeted at the tissue level and beyond. An understanding of how mechanics influences tissue differentiation during repair and regeneration crucially requires spatial and temporal knowledge of both the local mechanical environment in the healing tissue and a characterization of the tissues formed over the course of regeneration. Owing to limitations in the techniques available to measure the local mechanical conditions during repair directly, simulation approaches, such as the finite element method, are an integral part of the mechanobiologist's toolkit, while histology remains the gold standard in the characterization of the tissue formed. However, with rapid advances occurring in imaging modalities and methods to characterize tissue properties, new opportunities exist to better understand the role of mechanics in the biology of bone regeneration. Combined with developments in molecular biology, mechanobiology has the potential to offer exciting, new regenerative treatments for bone healing.     

Base-induced 1,4-elimination: insights from theory and mass spectrometry

Experimental and theoretical studies on gas-phase base-induced 1,4-elimination reactions are summarized and discussed. The emphasis is on the synergy that is achieved by combining the complementary data from mass spectrometry and theoretical chemistry. The scope and applications of 1,4-eliminations are discussed and compared with other elementary reactions; e.g., 1,2-elimination and aliphatic (S(N)2) and allylic (S(N)2') nucleophilic substitution. Furthermore, the syn versus anti stereochemistry of 1,4-elimination reactions and the effect of E versus Z stereochemistry of the substrate are examined. Particular attention is paid to the mechanistic nature of 1,4-elimination, i.e., E2 or E1cb, as well as special features such as the single-well E2 and E1cb mechanism. Also, new results from density functional theory computations (BP86/TZ2P) are presented.     

Regulatory mechanisms of periodontal regeneration

The periodontal ligament, located between the cementum and the alveolar bone, has a width ranging from 0.15 to 0.38 mm. Regeneration and homeostasis of the periodontal ligament are highly significant functions in relation to periodontal therapy, tooth transplantation or replantation, and orthodontic tooth movement. The purpose of this review is to discuss the regulatory mechanisms of regenerative and homeostatic functions in the periodontal ligament based on currently published studies and also on our own experimental data. We consider the capability of the ligament tissue to promote or to suppress calcification in connection with bone and cementum formation and the maintenance of the periodontal ligament space. Also discussed are the involvement of the periodontal ligament tissue in the regenerative ability, cell proliferation, growth and differentiation factors, extracellular matrix proteins, homeostatic phenomena, function of Malassez epithelial rests, tooth movement, or occlusal loading. Regulatory mechanisms for regeneration and homeostasis of the periodontal ligament are hypothetically proposed.     

MSCs-exosomes in regeneration medicine: Current evidence and future perspectives

Exosomes, especially from mesenchymal stem cells, have attracted extensive attention in regeneration medicine. Mesenchymal stem cells derived exosomes (MSCs-exosomes) have shown anti-inflammatory, anti-oxidant, anti-apoptosis and tissue regeneration effects in a variety of tissue injury repair models. MSCs-exosomes hold many excellent properties such as low immunogenicity, biocompatibility, and targeting capability. With the in-depth study on the generation and function of exosomes, MSCs-exosomes are considered to be the bright stars in the field of regenerative medicine. However, there are still many obstacles to overcome in terms of exosomes isolation, clinical trials and safety evaluation. In this article, what we should focus on about MSCs-exosomes in regeneration medicine will be discussed.     

Microscopic overview of crinoid regeneration.

Crinoids are well known for their striking regenerative potential and can rapidly and completely regenerate arms lost following self-induced or traumatic amputation. Thus they provide a valuable experimental model for investigation of the regenerative process from the macroscopic to the molecular level. In these last years we have studied in detail the overall process of arm regeneration in the comatulid Antedon mediterranea. This phenomenon can be described on the whole as a typical blastemal regeneration in which new structures develop from migratory pluripotential, actively proliferating cells in the presence of presumptive regulatory factors. The overall process can be subdivided into three main phases: a repair phase, an early regenerative phase, and an advanced regenerative phase, whose crucial aspects are related to common fundamental mechanisms such as cell migration and proliferation, intervention of stem cells and/or dedifferentiated cells, contribution of putative growth factors, particularly in terms of specific neurally derived factors, and mechanisms of pattern formation. This article focuses on the main aspects of the phenomenon and gives a brief account of the most recent and relevant results. Our approach employs classical methods of light (LM) and electron (TEM and SEM) microscopy, immunocytochemistry, and histofluorescence on experimentally induced arm regenerations of standard or abnormal type obtained in significantly different experimental conditions, including extreme mutilations (explants) or exposure to pseudo-estrogenic environmental contamination.     

Prospects for tooth regeneration in the 21st century: a perspective

The prospects for tooth regeneration in the 21st century are compelling. Using the foundations of experimental embryology, developmental and molecular biology, the principles of biomimetics (the mimicking of biological processes), tooth regeneration is becoming a realistic possibility within the next few decades. The cellular, molecular, and developmental "rules" for tooth morphogenesis are rapidly being discovered. The knowledge gained from adult stem cell biology, especially associated with dentin, cartilage, and bone tissue regeneration, provides additional opportunities for eventual tooth organogenesis. The centuries of tooth development using xenotransplantation, allotransplantation, and autotransplantation have resulted in many important insights that can enhance tooth regeneration. In considering the future, several lines of evidence need to be considered: (1) enamel organ epithelia and dental papilla mesenchyme tissues contain stem cells during postnatal stages of life; (2) late cap stage and bell stage tooth organs contain stem cells; (3) odontogenic adult stem cells respond to mechanical as well as chemical "signals"; (4) presumably adult bone marrow as well as dental pulp tissues contain "odontogenic" stem cells; and (5) epithelial-mesenchymal interactions are pre-requisite for tooth regeneration. The authors express "guarded enthusiasm," yet there should be little doubt that adult stem cell-mediated tooth regeneration will be realized in the not too distant future. The prospects for tooth regeneration could be realized in the next few decades and could be rapidly utilized to improve the quality of human life in many nations around the world.     

Pliable polylactide plates for guided bone regeneration: manufacturing and in vitro

Three different types of pliable and bioabsorbable plates, 0.4 mm thick, were developed for guided bone regeneration to cover cranial defects. The processing (extrusion, melt-spinning, knitting and heat pressing) and in vitro degradation of the materials were studied. Materials used were poly-L,DL-lactide with an L/DL ratio of 70/30 (PLA70) and poly-L,D-lactide with an L/D ratio of 96/4 (PLA96). The initial tensile strengths of gamma-sterilized PLA96, PLA70 and the PLA70-PLA96 composite plates were 45.7 +/- 3.8, 51.2 +/- 3.6 and 24.7 +/- 5.1 MPa respectively. The composite plates were the stiffest and lasted for more than 24 weeks. The glass transition temperature (Tg) of both polymers decreased in vitro. The crystallinity of PLA96 increased tenfold within 18 weeks. For initially amorphous PLA70 the highest melting enthalpy was 89 J/g at 60 weeks. PLA70 became partially crystalline and the plates changed from transparent to white and swollen. Extrusion and sterilization decreased the initially different molecular weight (Mw) values to the same level. After 18 weeks of hydrolysis, Mw was 15,000 Da for PLA96 and 12,000 Da for PLA70. For the components of the composite plate Mw was 15,000 Da for the PLA70 plate and 27,000 Da for the PLA96 mesh. Morphologically, all the hydrolysed plates retained, for a long period, a solid surface layer under which a porous structure formed. Crystalline branches and some single crystals were seen. The composite plates had the slowest degradation rate and they remained intact the longest.     

Degeneration and regeneration of ganglion cell axons

The retino-tectal system has been used to study developmental aspects of axon growth, synapse formation and the establishment of a precise topographic order as well as degeneration and regeneration of adult retinal ganglion cell (RGC) axons after axonal lesion. This paper reviews some novel findings that provide new insights into the mechanisms of developmental RGC axon growth, pathfinding, and target formation. It also focuses on the cellular and molecular cascades that underlie RGC degeneration following an axonal lesion and on some therapeutic strategies to enhance survival of axotomized RGCs in vivo. In addition, this review deals with problems related to the induction of regeneration after axonal lesion in the adult CNS using the retino-tectal system as model. Different therapeutic approaches to promote RGC regeneration and requirements for specific target formation of regenerating RGCs in vitro and in vivo are discussed.     

Skin regeneration stimulation: the role of PCL‐platelet gel nanofibrous scaffold

Skin is the largest organ of the human body. Thus far, tissue engineering of skin has developed rapidly and has used many types of growth factors and nanofibrous scaffolds. In this study, we differentiated neonate keratinocytes for epithelialization on the polycaprolactone‐Platelet gel (PCL‐PG) scaffold. Fabricated PCL nanofibers prepared by electrospinning technology and coated by platelet gel. Subsequently, the structure of the scaffold was evaluated by SEM, FTIR‐ATR, contact angle and tensile test assays. After seeding the neonate keratinocytes on neat PCL and PCL‐PG scaffolds, the epidermal maturation was tested by detecting cytokeratin 10 and loricrin determinants by immunocytochemistry; moreover, keratinocyte genes such as keratin 14, keratin 10, and Involucrin were investigated by real‐time PCR. The results of MTT assay indicated an increase in cell viability and cell proliferation of neonate keratinocytes on PCL‐PG nanofiber scaffolds compared with PCL. RT‐PCR and immunocytochemical analysis showed better cell differentiation on the PCL‐PG scaffolds than neat PCL. Furthermore, SEM microscopy images demonstrated that neo‐keratinocytes enhance adhesion and proliferation on PCL‐PG nanofiber scaffolds. We found that PG increases biocompatibility and wettability of scaffold, cell adhesion, and expression of keratinocyte markers. Overall, this procedure is recommended to be employed in skin tissue engineering and wounds healing.     

供暖系统的调整

论述供暖系统调整及效果,施工中供暖系统的质量控制管理对供暖系统调整的影响.     

Skeletal stem cells and bone regeneration: translational strategies from bench to clinic

Clinical imperatives for new bone to replace or restore the function of traumatized or bone lost as a consequence of age or disease has led to the need for therapies or procedures to generate bone for skeletal applications. Tissue regeneration promises to deliver specifiable replacement tissues and the prospect of efficacious alternative therapies for orthopaedic applications such as non-union fractures, healing of critical sized segmental defects and regeneration of articular cartilage in degenerative joint diseases. In this paper we review the current understanding of the continuum of cell development from skeletal stem cells, osteoprogenitors through to mature osteoblasts and the role of the matrix microenvironment, vasculature and factors that control their fate and plasticity in skeletal regeneration. Critically, this review addresses in vitro and in vivo models to investigate laboratory and clinical based strategies for the development of new technologies for skeletal repair and the key translational points to clinical success. The application of developmental paradigms of musculoskeletal tissue formation specifically, understanding developmental biology of bone formation particularly in the adult context of injury and disease will, we propose, offer new insights into skeletal cell biology and tissue regeneration allowing for the critical integration of stem cell science, tissue engineering and clinical applications. Such interdisciplinary, iterative approaches will be critical in taking patient aspirations to clinical reality.     

New insights into the morphology of Trypanosoma cruzi reservosome

Reservosomes are late endosomes present only in members of the Schizotrypanum subgenus of the Trypanosoma genus and are defined as the site of storage of endocytosed macromolecules and lysosomal enzymes. They have been extensively described in Trypanosoma cruzi epimastigote: are bounded by a membrane unit, present an electron-dense protein matrix with electron-lucent lipid inclusions, being devoid of inner membranes. Here we performed a detailed ultrastructural analysis of these organelles using a variety of electron microscopy techniques, including ultrathin sectioning, uranyl acetate stained preparations, and freeze fracture, either in intact epimastigotes or in isolated reservosomes. New informations were obtained. First, both isolated and in situ reservosomes presented small profiles of inner membranes that are morphologically similar to the membrane surrounding the organelle. In uranyl acetate stained preparations, internal membrane profiles turned out to be longer than they appeared in ultrathin section images and traversed the organelle diameter. Internal vesicles were also found. Second, endocytosed cargo are not associated with internal vesicles and reach reservosomes on board of vesicles that fuse with the boundary membrane, delivering cargo directly into reservosome lumen. Third, electron-lucent bodies with saturated lipid core surrounded by a membrane monolayer and with unusual rectangular shape were also observed. Fourth, it was possible to demonstrate the presence of intramembranous particles on the E face of both internal vesicles and the surrounding membrane. Collectively, these results indicate that reservosomes have a complex internal structure, which may correlate with their multiple functions.