In vivo imaging of endogenous neural stem cells in the adult brain

The discovery of endogenous neural stem cells (eNSCs) in the adult mammalian brain with their ability to self-renew and differentiate into functional neurons, astrocytes and oligodendrocytes has raised the hope for novel therapies of neurological diseases. Experimentally, those eNSCs can be mobilized in vivo, enhancing regeneration and accelerating functional recovery after, e.g., focal cerebral ischemia, thus constituting a most promising approach in stem cell research. In order to translate those current experimental approaches into a clinical setting in the future, non-invasive imaging methods are required to monitor eNSC activation in a longitudinal and intra-individual manner. As yet, imaging protocols to assess eNSC mobilization non-invasively in the live brain remain scarce, but considerable progress has been made in this field in recent years. This review summarizes and discusses the current imaging modalities suitable to monitor eNSCs in individual experimental animals over time, including optical imaging, magnetic resonance tomography and-spectroscopy, as well as positron emission tomography (PET). Special emphasis is put on the potential of each imaging method for a possible clinical translation, and on the specificity of the signal obtained. PET-imaging with the radiotracer 3’-deoxy-3’-[¹⁸F]fluoro-L-thymidine in particular constitutes a modality with excellent potential for clinical translation but low specificity; however, concomitant imaging of neuroinflammation is feasible and increases its specificity. The non-invasive imaging strategies presented here allow for the exploitation of novel treatment strategies based upon the regenerative potential of eNSCs, and will help to facilitate a translation into the clinical setting.     

The Pteridine Pathway in Zebrafish: Regulation and Specification during the Determination of Neural Crest Cell‐Fate

This review describes pteridine biosynthesis and its relation to the differentiation of neural crest derivatives in zebrafish. During the embryonic development of these fish, neural crest precursor cells segregate into neural elements, ectomesenchymal cells and pigment cells; the latter then diversifying into melanophores, iridophores and xanthophores. The differentiation of neural cells, melanophores, and xanthophores is coupled closely with the onset of pteridine synthesis which starts from GTP and is regulated through the control of GTP cyclohydrolase I activity. De novo pteridine synthesis in embryos of this species increases during the first 72‐h postfertilization, producing H₄biopterin, which serves as a cofactor for neurotransmitter synthesis in neural cells and for tyrosine production in melanophores. Thereafter, sepiapterin (6‐lactoyl‐7,8‐dihydropterin) accumulates as yellow pigment in xanthophores, together with 7‐oxobiopterin, isoxanthopterin and 2,4,7‐trioxopteridine. Sepiapterin is the key intermediate in the formation of 7‐oxopteridines, which depends on the availability of enzymes belonging to the xanthine oxidoreductase family. Expression of the GTP cyclohydrolase I gene (gch) is found in neural cells, in melanoblasts and in early xanthophores (xanthoblasts) of early zebrafish embryos but steeply declines in xanthophores by 42‐h postfertilization. The mechanism(s) whereby sepiapterin branches off from the GTP‐H₄biopterin pathway is currently unknown and will require further study. The surge of interest in zebrafish as a model for vertebrate development and its amenability to genetic manipulation provide powerful tools for analysing the functional commitment of neural crest‐derived cells and the regulation of pteridine synthesis in mammals.     

Comparison of floristic changes on vegetation affected by different levels of soil erosion in Miocene clays and Eocene marls from Northeast Spain

Increased soil erosion on Eocene marls from N Aragón (NE Spain) tends to reduce vegetation cover and plant species number, but little is known about its effect in the neighbouring Miocene clays. In this study, the vegetation of strongly eroded areas on Miocene clays was analysed in terms of erosion intensity and compared with Eocene marls. Relevés were carried out on uniform patches of vegetation affected by different levels of erosion. The degeneration of vegetation cover explained 34% of the variation in species number as opposed to 48% in marls, and a clear pattern of species replacement through the destruction of the vegetation cover was not observed. Approximately 25% of the species decreased significantly and 4% increased, as opposed to 47% and 0% in marls, respectively. Erosion on marls may be more severe (more disturbance) and less stressing for vegetation (more water availability) than on clays. The few species that colonized intermediate degeneration stages and highly eroded sites were more common in non-eroded areas in drier bioclimatic belts. Thus, the degeneration of vegetation by soil erosion favoured the establishment of xeric species. The ecological range of erosion-resistant species was not wider than non-resistant species. Overall, increased soil erosion selected for different plant species in marls than in clays.     

分支位点在真核基因受体位点识别中的作用

真核基因受体位点识别是剪接位点识别的一部分,也是基因识别中的重要环节,一直受到研究人员的关注。已有的研究结果显示受体位点的识别与分支位点有关,然而关于分支位点和受体位点识别的关系问题,目前还无人将其作为专门的问题予以深入研究。从受体位点识别出发,选取不同的受体位点序列长度,以神经网络为识别工具,对分支位点在受体位点识别中的作用做了深入研究和分析。实验结果表明,受体位点序列的特征信息集中在分支位点一例,因此分支位点在受体位点识别中具有重要作用。研究结果为受体位点识别问题中序列特征提取提供了依据。     

Establishment by an Original Single‐cell Cloning Method and Characterization of an Immortal Mouse Melanoblast Cell Line (NCCmelb4)

We devised a unique new single‐cell cloning method which uses microscope cover glasses and established a melanoblast cell line derived from mouse neural crest cells. A microscope cover glass was nicked and broken into small pieces and put on a dish. Culture medium and a suspension of 20–30 cells/ml were dropped in the dish. After 1–3 d, a piece of glass to which only one cell was adhered was picked up and transferred to another dish containing culture medium. The greatest advantage of this method is that the derivation of a colony from a single cell can be directly confirmed by microscopy and there is no risk of migratory cells being contaminated by other colonies. Using this single‐cell cloning method, in this study we established a cell line derived from a neural crest cell line (NCC‐S4.1) and designated it as NCCmelb4. When the culture medium was supplemented with stem cell factor (SCF) alone, NCCmelb4 cells were KIT‐positive and tyrosinase‐negative melanocyte precursors; they remained at an immature and undifferentiated stage. When the medium was supplemented with phorbol 12‐o‐tetradecanoyl‐13‐acetate (TPA) + cholera toxin (CT), the cell morphology changed and became l ‐3,4‐dihydroxyphenylalanine (DOPA)‐positive. This observation indicates that the NCCmelb4 cells are capable of further differentiation with suitable stimulation. NCCmelb4 cells derived from the mouse neural crest has characteristics of melanocyte precursors (melanoblasts), and is a cell line which can be utilized to study differentiation‐inducing factors and growth factors without the effects of feeder cells.     

小鼠胚胎神经干细胞的分离培养及其鉴定

且的探索小鼠胚胎神经干细胞的体外培养方法,并获取高纯度的神经干细胞,为神经干细胞的深入研究提供实验材料。方法无菌条件下分离E15天小鼠胚脑皮质,制成单细胞悬液,在bFGF和B27存在的培养基中培养扩增,通过免疫细胞化学染色鉴定神经干细胞及其子代细胞的分化方向。结果培养的部分细胞在B27和bFGF存在的无血清培养基中可以在体外分裂增殖,同时表达神经干细胞特异性抗原nestin,并在撤出B27和bFGF的有血清培养基中向神经细胞和胶质细胞分化。结论小鼠胚脑皮质存在具有多向分化潜能的神经干细胞,这些细胞可以在体外稳定培养、传代并自然分化,为细胞替代治疗提供了理想的细胞来源。     

Deciphering apicoplast targeting signals – feature extraction from nuclear-encoded precursors of Plasmodium falciparum apicoplast proteins

The malaria causing protozoan Plasmodium falciparum contains a vestigal, non-photosynthetic plastid, the apicoplast. Numerous proteins encoded by nuclear genes are targeted to the apicoplast courtesy of N-terminal extensions. With the impending sequence completion of an entire genome of the malaria parasite, it is important to have software tools in place for prediction of subcellular locations for all proteins. Apicoplast targeting signals are bipartite; containing a signal peptide and a transit peptide. Nuclear-encoded apicoplast protein precursors were analyzed for characteristic features by statistical methods, principal component analysis, self-organizing maps, and supervised neural networks. The transit peptide contains a net positive charge and is rich in asparagine, lysine, and isoleucine residues. A novel prediction system (PATS, predict apicoplast-targeted sequences) was developed based on various sequence features, yielding a Matthews correlation coefficient of 0.91 (97% correct predictions) in a 40-fold cross-validation study. This system predicted 22% apicoplast proteins of the 205 potential proteins on P. falciparum chromosome 2, and 21% of 243 chromosome 3 proteins. A combination of the PATS results with a signal peptide prediction yields 15% potentially nuclear-encoded apicoplast proteins on chromosomes 2 and 3. The prediction tool will advance P. falciparum genome analysis, and it might help to identify apicoplast proteins as drug targets for the development of novel anti-malaria agents.     

Intrinsic and extrinsic influences on cardiac rhythms in crustaceans

Several factors cause predictable changes in heart rate of crustaceans thus affecting basic heart rhythms. In decapod crustaceans these consist of: many internal factors including influences from neural and neurohormonal systems and chemosensory influences; many external factors including startling stimuli and other disturbance; ventilatory (scaphognathite) reversals; tail flips and other postural movements including locomotor activity; and variations in environmental factors such as oxygen level, temperature and air-exposure. In many cases the initial response involves temporary bradycardia or cardiac arrest. These responses may quickly facilitate to sustained low level stimuli although maintained strong stimulation will eventually be associated with cardio-acceleration and escape responses. Measurement of change in heart rate alone is rarely a sensible monitor of cardiac performance in crustaceans since simultaneous changes in cardiac stroke volume occur which may confound diagnosis. Hypoxia for instance causes decrease in heart rate of adult crustaceans but the apparent decrease in cardiac output is offset or reversed by increase in stroke volume. Concomitant changes occur in cardiac output and in the proportion of cardiac output which is delivered to particular tissues. In fact change in heart rhythm is only one factor in a complex suite of responses involving several physiological systems which compensate uniquely for changes in environmental or other stimuli. Both neural and neuro-hormonal factors are known to play a role in control of these complex responses.     

Cardiac reflexes and their neural pathways in lepidopterous insects

Previously described salines for lepidoptera did not maintain a constant heart rate for a very long. We have been successful in maintaining a normal heartbeat for many hours in a newly designed saline. This saline was also suitable for maintaining normal neuromuscular junctional potentials. The cardiac reflexes studied in larvae of Bombyx and Agrius were five types of cardiac responses induced by mechanical stimuli to sensillar setae. The cardiac responses were caused by electrical stimulation of nerves in the reflex pathways. The antidromic heartbeat was triggered even in larvae before the 5th instar by stimulation of axons in the visceral nerve arising from the frontal ganglion and terminating at the aorta, while spontaneous heartbeat reversal started to occur in wandering larvae. Other axons in the visceral nerve terminate at the rear end of the heart. Electrical stimuli to the nerves caused cardiac inhibition of the orthodromic heartbeat. Nerves extending from the visceral nerve to the alary muscles of the 2nd abdominal segment contain axons to increase the tone of the muscles. Nerves extending from the 7th abdominal ganglion to the most posterior alary muscles also contain axons to increase the tone of the muscles, and were responsible for acceleration of the antidromic and orthodromic heartbeat, respectively.