Excess lunatic fringe causes cranial neural crest over-proliferation.

Lunatic fringe is a vertebrate homologue of Drosophila fringe, which plays an important role in modulating Notch signaling. This study examines the distribution of chick lunatic fringe at sites of neural crest formation and explores its possible function by ectopic expression. Shortly after neural tube closure, lunatic fringe is expressed in most of the neural tube, with the exception of the dorsal midline containing presumptive neural crest. Thus, there is a fringe/non-fringe border at the site of neural crest production. Expression of excess lunatic fringe in the cranial neural tube and neural crest by retrovirally mediated gene transfer resulted in a significant increase ( approximately 60%) in the percentage of cranial neural crest cells 1 day after infection. This effect was mediated by an increase in cell division as assayed by BrdU incorporation. Infected embryos had an up-regulation of Delta-1 in the dorsal neural tube and redistribution of Notch-1 to the lumen of the neural tube, confirming that excess fringe modulates Notch signaling. These findings point to a novel role for lunatic fringe in regulating cell division and/or production of neural crest cells by the neural tube.     

Neural crests are actively precluded from the anterior neural fold by a novel inhibitory mechanism dependent on Dickkopf1 secreted by the prechordal mesoderm

It is known the interactions between the neural plate and epidermis generate neural crest (NC), but it is unknown why the NC develops only at the lateral border of the neural plate and not in the anterior fold. Using grafting experiments we show that there is a previously unidentified mechanism that precludes NC from the anterior region. We identify prechordal mesoderm as the tissue that inhibits NC in the anterior territory and show that the Wnt/beta-catenin antagonist Dkk1, secreted by this tissue, is sufficient to mimic this NC inhibition. We show that Dkk1 is required for preventing the formation of NC in the anterior neural folds as loss-of-function experiments using a Dkk1 blocking antibody in Xenopus as well as the analysis of Dkk1-null mouse embryos transform the anterior neural fold into NC. This can be mimicked by Wnt/beta-catenin signaling activation without affecting the anterior posterior patterning of the neural plate, or placodal specification. Finally, we show that the NC cells induced at the anterior neural fold are able to migrate and differentiate as normal NC. These results demonstrate that anterior regions of the embryo lack NC because of a mechanism, conserved from fish to mammals, that suppresses Wnt/beta-catenin signaling via Dkk1.     

On-line estimation of biomass concentration using a neural network and information about metabolic state

This paper deals with the design of a neural network-based biomass concentration estimation system. This system is enhanced by the incorporation of information about the actual metabolism of the microorganism cultivated, which is taken from an on-line knowledge-based system. Two different design approaches have been investigated using the fed-batch cultivation of bakers yeast as the model process. In the first, metabolic state (MS) data were passed as additional input to the neural network; in the second, these data were used to select a neural network suitable for the specific MS. Two neural network types—feed-forward (Levenberg-Marquardt) and cascade correlation—were applied to this system and tested, and the performances of these neural networks were compared.     

Nonlinear system modelling via optimal design of neural trees

This paper introduces a flexible neural tree model. The model is computed as a flexible multi-layer feed-forward neural network. A hybrid learning/evolutionary approach to automatically optimize the neural tree model is also proposed. The approach includes a modified probabilistic incremental program evolution algorithm (MPIPE) to evolve and determine a optimal structure of the neural tree and a parameter learning algorithm to optimize the free parameters embedded in the neural tree. The performance and effectiveness of the proposed method are evaluated using function approximation, time series prediction and system identification problems and compared with the related methods.     

命运决定子Numb在神经干/祖细胞不对称分裂及分化中的调控作用 

不对称分裂是干/祖细胞发育分化中的基本过程,膜相关蛋白Numb在其中发挥重要作用.Numb极性分布于细胞一侧,在干/祖细胞有丝分裂时不对等分配至两个子代细胞,使子代细胞产生不同分化命运.如一个保持在干/祖细胞状态,而另一个发育为神经元,这一过程主要通过抑制Notch信号通路发挥作用.近年在哺乳动物中的研究中发现,高强度Notch信号又能够反馈抑制Numb活性.Numb具有维持神经干/祖细胞增殖与促进分化的双重作用,Numb的命运决定作用还与Shh信号通路和p53蛋白等相关.另外,Numb参与调控细胞的粘连、迁移以及神经元轴突的分支与延长.本文主要对Numb在果蝇及哺乳动物神经干/祖细胞中的定位以及其在决定细胞命运和分化中的调控作用进行综述.     

The Ectomesenchymal-Endodermal Interaction-System (EEIS) of Triturus alpestris in Tissue Culture

A piece of head neural fold tissue from behind the prospective ear region of a Triturus alpestris neurula was cultivated, together with a piece of ventrolateral pharynx endoderm from the same neurula, in hanging drop cultures. This system, referred to as the Ectomesenchymal-Endodermal Interaction-System (EEIS), offers insight into the visible processes of attachment, migration and differentiation of neural crest cells emigrating from the piece of neural fold.
The neural crest cells were not found to move preferably in the direction of the pharynx endoderm. Therefore, instead of chemotaxis, the concept of contact inhibition¹ provides a more satisfactory explanation for the distribution pattern of emigrating neural crest cells.
During culture, the neural crest cells differentiate into neuroblasts, pigment cells, myoblasts, chondroblasts and, after about 11 days, into perichondrial cells. After 6 days, a large number of neural crest cells, now called mesenchymal cells, persist without any visible differentiation throughout the culture.
Chondroblasts only develop from neural crest cells which have been in contact with the pharynx endoderm, as opposed to all other crest cells differentiating in the EEIS.     

Assay for Neural Induction in the Chick Embryo

The chick embryo is a valuable tool in the study of early embryonic development. Its transparency, accessibility and ease of manipulation, make it an ideal tool for studying the formation and initial patterning of the nervous system. This video demonstrates how to graft organizer tissue into a host, a method by which Hensen s node (the organizer in the chick embryo) is grafted to a host competent ectoderm. The organizer graft instructs overlying na ve tissue to adopt a neural fate via neural inducing signals. This mechanism is referred to as neural induction, and constitutes the initial step in the formation of brain and spinal cord in amniotes. This method is essentially used for the characterization of putative neural inducing molecules in chick. This video demonstrates the different steps in the assay for neural induction; First, the donnor embryo is explanted and pinned on a dish. Then, the host embryo is prepared for New culture. The graft is excised and transplanted to the host area pellucida margin. The host is cultured for 18-22 hrs. The assembly is fixed and processed for further applications (e.g. in situ hybridization). This method was originally devised by Waddington ^1,2 and Gallera ^3,4.Open in a separate windowClick here to view.^{(67M, flv)}     

Xenopus neural crest cell migration in an applied electrical field

Xenopus neural crest cells migrated toward the cathode in an applied electrical field of 10 mV/mm or greater. This behavior was observed in relatively isolated cells, as well as in groups of neural crest cells; however, the velocity of directed migration usually declined when a cell made close contact with other cells. Melanocytes with a full complement of evenly distributed melanosomes did not migrate of their own accord, but could be distorted and pulled by unpigmented neural crest cells. Incompletely differentiated melanocytes and melanocytes with aggregated melanosomes displayed the same behavior as undifferentiated neural crest cells, that is, migration toward the cathode. An electrical field of 10 mV/mm corresponded to a voltage drop of less than 1 mV across the diameter of each cell; the outer epithelium of Xenopus embryos drives an endogenous transembryonic current that may produce voltage gradients of nearly this magnitude within high-resistance regions of the embryo. We, therefore, propose that electrical current produced by the skin battery present in these embryos may act as a vector to guide neural crest migration.     

Effect of steady-state response versus excitatory/inhibitory balance on spiking synchronization in neural networks with log-normal synaptic weight distribution

Synchronization of neural activity, especially at the gamma band, contributes to perceptual functions. In several psychiatric disorders, deficits of perceptual functions are reflected in synchronization abnormalities. Plausible cause of this impairment is an alteration in the balance between excitation and inhibition (E/I balance); a disruption in the E/I balance leads to abnormal neural interactions reminiscent of pathological states. Moreover, the local lateral excitatory-excitatory synaptic connections in the cortex exhibit excitatory postsynaptic potentials (EPSPs) that follow a log-normal amplitude distribution. This long-tailed distribution is considered an important factor for the emergence of spatiotemporal neural activity. In this context, we hypothesized that manipulating the EPSP distribution under abnormal E/I balance conditions would provide insights into psychiatric disorders characterized by deficits in perceptual functions, potentially revealing the mechanisms underlying pathological neural behaviors. In this study, we evaluated the synchronization of neural activity with external periodic stimuli in spiking neural networks in cases of both E/I balance and imbalance with or without a long-tailed EPSP amplitude distribution. The results showed that external stimuli of a high frequency lead to a decrease in the degree of synchronization with an increasing ratio of excitatory to inhibitory neurons in the presence, but not in the absence, of high-amplitude EPSPs. This monotonic reduction can be interpreted as an autonomous, strong-EPSP-dependent spiking activity selectively interfering with the responses to external stimuli. This observation is consistent with pathological findings. Thus, our modeling approach has potential to improve the understanding of the steady-state response in both healthy and pathological states.     

Nerve growth factor induces neural differentiation in undifferentiated cell of early chick embryos

Nerve growth factor (NGF) induced differentiation in postnodal pieces (PNPs) of stage 4 chick embryos. This induction was highly selective for neural tissue; no other structures developed in the NGF-treated PNPs. Furthermore, the number of PNPs showing neural differentiation was dependent on the concentration of NGF, but there was no correlation between the concentration of NGF (5-100 ng/ml) and extent of neuralization. The neural inducing capacity of NGF could be abolished by anti-NGF antibody. NGF-induced neural differentiation was accompanied by elevated intracellular levels of cyclic AMP. Exogenous cyclic AMP (175 micrograms/ml) was able to stimulate neural differentiation but, unlike NGF, induced other structures (e.g., notochord and pulsatile tissue). Overall results suggest that cells from chick embryos at developmental stages much earlier than previously thought are responsive to NGF and NGF or a a closely related substance may serve as a neural inducer in the chick embryo.     

Migration and proliferation of cultured neural crest cells in W mutant neural crest chimeras.

Chimeric mice, generated by aggregating preimplantation embryos, have been instrumental in the study of the development of coat color patterns in mammals. This approach, however, does not allow for direct experimental manipulation of the neural crest cells, which are the precursors of melanoblasts. We have devised a system that allows assessment of the developmental potential and migration of neural crest cells in vivo following their experimental manipulation in vitro. Cultured C57Bl/6 neural crest cells were microinjected in utero into neurulating Balb/c or W embryos and shown to contribute efficiently to pigmentation in the host animal. The resulting neural crest chimeras showed, however, different coat pigmentation patterns depending on the genotype of the host embryo. Whereas Balb/c neural crest chimeras showed very limited donor cell pigment contribution, restricted largely to the head, W mutant chimeras displayed extensive pigmentation throughout, often exceeding 50% of the coat. In contrast to Balb/c chimeras, where the donor melanoblasts appeared to have migrated primarily in the characteristic dorsoventral direction, in W mutants the injected cells appeared to migrate in the longitudinal as well as the dorsoventral direction, as if the cells were spreading through an empty space. This is consistent with the absence of a functional endogenous melanoblast population in W mutants, in contrast to Balb/c mice, which contain a full complement of melanocytes. Our results suggest that the W mutation disturbs migration and/or proliferation of endogenous melanoblasts. In order to obtain information on clonal size and extent of intermingling of donor cells, two genetically marked neural crest cell populations were mixed and coinjected into W embryos. In half of the tricolored chimeras, no co-localization of donor crest cells was observed, while, in the other half, a fine intermingling of donor-derived colors had occurred. These results are consistent with the hypothesis that pigmented areas in the chimeras can be derived from extensive proliferation of a few donor clones, which were able to colonize large territories in the host embryo. We have also analyzed the development of pigmentation in neural crest cultures in vitro, and found that neural tubes explanted from embryos carrying wt or weak W alleles produced pigmented melanocytes while more severe W genotypes were associated with deficient pigment formation in vitro.     

Plasminogen activator activity is associated with neural crest cell motility in tissue culture

We have examined the possibility that proteases such as plasminogen activator (PA) contribute to the extraordinary motile capability of neural crest cells. We show that trunk neural crest cells that migrate from isolated neural tubes in vitro produce PA and that the level of cell-associated PA increases dramatically after 8 days in culture. This increase is not the result of differentiation or time in culture, because neural crest cell clusters that form on top of the neural tube and differentiate into pigment cells but are immotile produce very low levels of PA. If these clusters are removed from the neural tube and replated on a plastic substratum where they migrate, the level of PA associated with the cells increases dramatically, suggesting that PA production is associated with motility. Inhibitors of PA/plasmin activity significantly reduce neural crest cell motility in vitro, further supporting the idea that proteases are important in neural crest cell migration.     

The adult hair follicle: cradle for pluripotent neural crest stem cells

This review focuses on the recent identification of two novel neural crest-derived cells in the adult mammalian hair follicle, pluripotent stem cells, and Merkel cells. Wnt1-cre/R26R compound transgenic mice, which in the periphery express beta-galactosidase in a neural crest-specific manner, were used to trace neural crest cells. Neural crest cells invade the facial epidermis as early as embryonic day 9.5. Neural crest-derived cells are present along the entire extent of the whisker follicle. This includes the bulge area, an epidermal niche for keratinocyte stem cells, as well as the matrix at the base of the hair follicle. We have determined by in vitro clonal analysis that the bulge area of the adult whisker follicle contains pluripotent neural crest stem cells. In culture, beta-galactosidase-positive cells emigrate from bulge explants, identifying them as neural crest-derived cells. When these cells are resuspended and grown in clonal culture, they give rise to colonies that contain multiple differentiated cell types, including neurons, Schwann cells, smooth muscle cells, pigment cells, chondrocytes, and possibly other types of cells. This result provides evidence for the pluripotentiality of the clone-forming cell. Serial cloning showed that bulge-derived neural crest cells undergo self-renewal, which identifies them as stem cells. Pluripotent neural crest cells are also localized in the back skin hair of adult mice. The bulge area of the whisker follicle is surrounded by numerous Merkel cells, which together with innervating nerve endings form slowly adapting mechanoreceptors that transduce steady skin indentation. Merkel cells express beta-galactosidase in double transgenic mice, which confirms their neural crest origin. Taken together, our data indicate that the epidermis of the adult hair follicle contains pluripotent neural crest stem cells, termed epidermal neural crest stem cells (eNCSCs), and one newly identified neural crest derivative, the Merkel cell. The intrinsic high degree of plasticity of eNCSCs and the fact that they are easily accessible in the skin make them attractive candidates for diverse autologous cell therapy strategies.     

NFκB signaling regulates embryonic and adult neurogenesis

Both embryonic and adult neurogenesis involves the self-renewal/proliferation,survival,migration and lineage differentiation of neural stem/progenitor cells.Such dynamic process is tightly regulated by...     

Quantitative and phenotypic analysis of bone marrow-derived cells in the intact and inflamed central nervous system

Bone marrow has been proposed as a possible source of cells capable of replacing injured neural cells in diseases such as Multiple Sclerosis (MS). Previous studies have reported conflicting results regarding the transformation of bone marrow cells into neural cells in vivo. This study is a detailed analysis of the fate of bone marrow derived cells (BMDC) in the CNS of C57Bl/6 mice with and without experimental autoimmune encephalomyelitis using flow cytometry to identify GFP-labeled BMDC that lacked the pan-hematopoietic marker, CD45 and co-expressed neural markers polysialic acid-neural cell adhesion molecule or A2B5. A small number of BMDC displaying neural markers and lacking CD45 expression was identified within both the non-inflamed and inflamed CNS. However, the majority of BMDC exhibited a hematopoietic phenotype.     

Temporal control of neural crest lineage generation by Wnt/β-catenin signaling

Wnt/β-catenin signaling controls multiple steps of neural crest development, ranging from neural crest induction, lineage decisions, to differentiation. In mice, conditional β-catenin inactivation in premigratory neural crest cells abolishes both sensory neuron and melanocyte formation. Intriguingly, the generation of melanocytes is also prevented by activation of β-catenin in the premigratory neural crest, which promotes sensory neurogenesis at the expense of other neural crest derivatives. This raises the question of how Wnt/β-catenin signaling regulates the formation of distinct lineages from the neural crest. Using various Cre lines to conditionally activate β-catenin in neural crest cells at different developmental stages, we show that neural crest cell fate decisions in vivo are subject to temporal control by Wnt/β-catenin. Unlike in premigratory neural crest, β-catenin activation in migratory neural crest cells promotes the formation of ectopic melanoblasts, while the production of most other lineages is suppressed. Ectopic melanoblasts emerge at sites of neural crest target structures and in many tissues usually devoid of neural crest-derived cells. β-catenin activation at later stages in glial progenitors or in melanoblasts does not lead to surplus melanoblasts, indicating a narrow time window of Wnt/β-catenin responsiveness during neural crest cell migration. Thus, neural crest cells appear to be multipotent in vivo both before and after emigration from the neural tube but adapt their response to extracellular signals in a temporally controlled manner.     

A requirement for NF-protocadherin and TAF1/Set in cell adhesion and neural tube formation

Neurulation in vertebrates is an intricate process requiring extensive alterations in cell contacts and cellular morphologies as the cells in the neural ectoderm shape and form the neural folds and neural tube. Despite these complex interactions, little is known concerning the molecules that mediate cell adhesion within the embryonic neural plate and neural folds. Here, we demonstrate the requirement for NF-protocadherin (NFPC) and its cytosolic partner TAF1/Set for proper neurulation in Xenopus. Both NFPC and TAF1 function in cell-cell adhesion in the neural ectoderm, and disruptions in either NFPC or TAF1 result in a failure of the neural tube to close. This neural tube defect can be attributed to a lack of proper organization of the cells in the dorsal neural folds, manifested by a loss in the columnar epithelial morphology and apical localization of F-actin. However, the epidermal ectoderm is still able to migrate and cover the open neural tube, indicating that the fusions of the neural tube and epidermis are separate events. These studies demonstrate that NFPC and TAF1 function to maintain proper cell-cell interactions within the neural folds and suggest that NFPC and TAF1 participate in novel adhesive mechanisms that contribute to the final events of vertebrate neurulation.     

The effects of erdosteine, N-acetylcysteine, and vitamin E on nicotine-induced apoptosis of hippocampal neural cells

This study investigated the frequency of apoptosis in rat hippocampal neural cells after intraperitoneal nicotine injection, examining the roles of the inflammatory markers myeloperoxidase (MPO) and tumor necrosis factor alpha (TNF-alpha) in nicotine-induced brain damage and the protective effects of three known antioxidant agents, N-acetylcysteine (NAC), erdosteine, and vitamin E. Female Wistar rats were divided into seven groups, each composed of nine rats: 2 negative control groups, 2 positive control groups, one erdosteine-treated group (500 mg/kg), one NAC-treated group (500 mg/kg), and one vitamin E-treated group (500 mg/kg). Nicotine was intraperitoneally injected at a dosage of 0.6 mg/kg for 21 days. Following nicotine injection, the antioxidants were administered orally; treatment was continued until the rats were killed. Apoptosis level in hippocampal neural cells was determined by using TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick endlabeling) method. Staining of cytoplasmic TNF-alpha in hippocampal neural cells and hippocampus MPO activity were evaluated by immunohistochemistry. Nicotine administration had no effect on local TNF-alpha production, or hippocampal MPO activity. The treatments with erdosteine, NAC and vitamin E significantly reduced the rate of nicotine-induced hippocampal neural cell apoptosis. This findings suggest that erdosteine and NAC can be as effective as vitamin E in protecting against nicotine-induced hippocampal neural cell apoptosis.