Although many similarities in arthropod central nervous systems (CNS) development exist, differences in midline cell formation and ventral nerve cord axonogenesis have been noted in arthropods. It is possible that cha...
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Although many similarities in arthropod central nervous systems (CNS) development exist, differences in midline cell formation and ventral nerve cord axonogenesis have been noted in arthropods. It is possible that changes in the expression of axon guidance molecules such as Netrin, which functions during commissural axon guidance in Drosophila and many other organisms, may parallel these differences. In this investigation, we analyze this hypothesis by examining Netrin accumulation during development of the brine shrimp Artemia franciscana, a branchiopod crustacean. An Artemia franciscana netrin (afrnet) orthologue was cloned. An antibody to the afrNet protein was generated and used to examine the pattern of afrNet accumulation during Artemia development. Despite differences between Drosophila and Artemia nerve cord development, examination of afrNet accumulation suggests that this protein functions to regulate commissure formation during Artemia CNS development. However, detection of afrNet at the midline and on commissural axons occurs at a relatively later time point in Artemia as compared with Drosophila. Detection of afrNet in a subset of midline cells that closely resemble Netrin-expressing cells at the Drosophila midline provides evidence for homology of midline cells in arthropods. Expression of Netrins in many other tissues is comparable, suggesting that Netrin proteins may play many conserved roles during arthropod development.
Delta-like 4 (Dll4) is a transmembrane ligand for Notch receptors that is expressed in arterial blood vessels and sprouting endothelial cells. Here we show that Dll4 regulates vessel branching during development by in...
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Delta-like 4 (Dll4) is a transmembrane ligand for Notch receptors that is expressed in arterial blood vessels and sprouting endothelial cells. Here we show that Dll4 regulates vessel branching during development by inhibiting endothelial tip cell formation. Heterozygous deletion of dll4 or pharmacological inhibition of Notch signaling using gamma-secretase inhibitor revealed a striking vascular phenotype, with greatly increased numbers of filopodia-extending endothelial tip cells and increased expression of tip cell marker genes compared with controls. Filopodia extension in dll(+/-) retinal vessels required the vascular growth factor VEGF and was inhibited when VEGF signaling was blocked. Although VEGF expression was not significantly altered in dll4(+/-) retinas, dll4(+/-) vessels showed increased expression of VEGF receptor 2 and decreased expression of VEGF receptor 1 compared with wildtype, suggesting they could be more responsive to VEGF stimulation. in addition, expression of dll4 in wild-type tip cells was itself decreased when VEGF signaling was blocked, indicating that dll4 may act downstream of VEGF as a "brake" on VEGF-mediated angiogenic sprouting. Taken together, these data reveal Dll4 as a negative regulator of vascular sprouting and vessel branching that is required for normal vascular network formation during development.
Eph receptor tyrosine kinases and their ephrin ligands participate in the control of neuronal growth and migration in a variety of contexts, but the mechanisms by which they guide neuronal motility are still incomplet...
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Eph receptor tyrosine kinases and their ephrin ligands participate in the control of neuronal growth and migration in a variety of contexts, but the mechanisms by which they guide neuronal motility are still incompletely understood. By using the enteric nervous system (ENS) of the tobacco hornworm Manduca sexta as a model system, we have explored whether Manduca ephrin (MsEphrin;a GPI-linked ligand) and its Eph receptor (MsEph) might regulate the migration and outgrowth of enteric neurons. During formation of the Manduca ENS, an identified set of similar to 300 neurons (EP cells) populates the enteiric plexus of the midgut by migrating along a specific set of muscle bands forming on the gut, but the neurons strictly avoid adjacent interband regions. By determining the mRNA and protein expression patterns for MsEphrin and the MsEph receptor and by examining their endogenous binding patterns within the ENS, we have demonstrated that the ligand and its receptor are distributed in a complementary manner: MsEphrin is expressed exclusively by the migratory EP cells, whereas the MsEph receptor is expressed by midline interband cells that are normally inhibitory to migration. Notably, MsEphrin could be detected on the filopodial processes of the EP cells that extended up to but not across the midline cells expressing the MsEph receptor. These results suggest a model whereby MsEphrin-dependent signaling regulates the response of migrating neurons to a midline inhibitory boundary, defined by the expression of MsEph receptors in the developing ENS.
The atypical protein kinase C (aPKC) in complex with PAR3 and PAR6 is required for axon-dendrite differentiation, but the upstream factors responsible for regulating its activity are largely unknown. Here, we report t...
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The atypical protein kinase C (aPKC) in complex with PAR3 and PAR6 is required for axon-dendrite differentiation, but the upstream factors responsible for regulating its activity are largely unknown. Here, we report that in cultured hippocampal neurons aPKC is directly regulated by Dishevelled (Dvl), an immediate downstream effector of Wnt. We found that downregulation of Dvl abrogated axon differentiation, whereas Dvl overexpression resulted in multiple axon formation. Interestingly, Dvl was associated with aPKC and this interaction resulted in aPKC stabilization and activation. Furthermore, the multiple axon formation resulting from Dvl overexpression was attenuated by expressing a dominant-negative aPKC in these neurons and overexpression of aPKC prevented the loss of axon caused by Dvl downregulation. Finally, Wnt5a, a noncanonical Wnt, activated aPKC and promoted axon differentiation. The Wnt5a effect on axon differentiation was attenuated by downregulating Dvl or inhibiting aPKC. Thus, Dvl-aPKC interaction can promote axon differentiation mediated by the PAR3-PAR6-aPKC complex.
Plant protection products with active micro-organisms are allegedly less hazardous to the environment and wildlife than synthetic chemical pesticides. Nevertheless, they need a proper pre-marketing environmental safet...
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Plant protection products with active micro-organisms are allegedly less hazardous to the environment and wildlife than synthetic chemical pesticides. Nevertheless, they need a proper pre-marketing environmental safety evaluation because of their potential toxicity and pathogenicity. Scientific and technical guidance on such a safety evaluation for regulatory purposes is scarce. Therefore, a risk decision tree is proposed to provide such guidance and to discern the acceptable from the unacceptable environmental risks. The decision tree is based on the risk criteria of the European Union. It takes integrally into account the characterisation, identification and efficacy and also emission, exposure, environmental effects and, finally, the environmental risk assessment. Case by case expert judgement remains necessary in view of limited knowledge of microbial ecology, limited experience with regulatory test protocols and taxonomic difficulties in relation to the indigenousness of active micro-organisms. The decision tree offers regulatory guidance on the environmental safety evaluation of microbial plant protection products.
Autonomous vehicles with an ability to trace chemical plumes can be instrumental in tasks such as detection of unexploded ordnance, search for undersea wreckage and environmental monitoring. As a consequence, use of a...
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Autonomous vehicles with an ability to trace chemical plumes can be instrumental in tasks such as detection of unexploded ordnance, search for undersea wreckage and environmental monitoring. As a consequence, use of autonomous vehicles to perform chemical plume tracing has received an increasing interest from the research community in recent years. Owing to the diversity of applications and ambient fluid environment of the plumes, there are numerous plume tracing strategies and approaches. This paper reviews two main approaches and a number of strategies that have been successfully implemented to track air or water borne plumes in order to locate odour sources using autonomous vehicles. The first strategy considered is the biomimetic approach that offers excellent models for the development of robotic systems. Strategies inspired by lobsters and bacterium are the main focus in this study. The second scheme considers parallelization of the search procedure by employing a multi-robot approach. This approach has the advantage of utilising a group of smaller and simpler communicating robots which are capable of performing a collaborative search of the plume.
While initially thought to be essentially a developmental characteristic observed in artificial in vitro models, local protein synthesis in growth cones has been described in the adult, and more interestingly, during ...
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While initially thought to be essentially a developmental characteristic observed in artificial in vitro models, local protein synthesis in growth cones has been described in the adult, and more interestingly, during nerve regeneration. This emerging field is under intense investigation, revealing new functions of localized protein synthesis that include axon guidance, growth cone adaptation and sensitivity modulation at intermediate targets or axon regeneration. Here, we will review these functions and provide a short survey of the current knowledge on mechanisms of mRNA transport and regulation of localized protein synthesis. In addition, we will consider what lessons can be learned from localized protein synthesis in dendrites and what developments can be expected next in the field. This latter question relates to the crucial point of which technical strategy to adopt for an ideal and pertinent analysis of the phenomenon.
Adult neural progenitor cells (aNPCs) exhibit limited migration in vivo with the exception of the rostral migratory stream and injury-induced movement. Surprisingly little is known regarding those signals regulating a...
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Adult neural progenitor cells (aNPCs) exhibit limited migration in vivo with the exception of the rostral migratory stream and injury-induced movement. Surprisingly little is known regarding those signals regulating attraction or inhibition of the aNPC. These studies demonstrate that aNPCs respond principally to a repulsive cue expressed at the embryonic floor plate (FIR) and also the injured adult CNS. Adult spinal cord progenitor cells (aSCPs) were seeded onto organotypic slice preparations of the intact embryonic or injured adult spinal cord. Cell migration assays combined with genetic and molecular perturbation of FP-derived migration cues or aSCP receptors establish netrin-1 (Ntn-1) but not Slit-2, Shh, or Ephrin-B3 as the primary FP-derived repellant. When slices were prepared from injured spinal cord, aSCP migration away from the injury core was Ntn-1-dependent. These studies establish Ntn-1 as a critical regulator of aSCP migration in the intact and injured CNS.
In flowering plants, signaling between the male pollen tube and the synergid cells of the female gametophyte is required for fertilization. In the Arabidopsis thaliana mutant feronia ( fer), fertilization is impaired;...
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In flowering plants, signaling between the male pollen tube and the synergid cells of the female gametophyte is required for fertilization. In the Arabidopsis thaliana mutant feronia ( fer), fertilization is impaired;the pollen tube fails to arrest and thus continues to grow inside the female gametophyte. FER encodes a synergid-expressed, plasma membrane-localized receptor-like kinase. We found that the FER protein accumulates asymmetrically in the synergid membrane at the filiform apparatus. Interspecific crosses using pollen from Arabidopsis lyrata and Cardamine flexuosa on A. thaliana stigmas resulted in a fer-like phenotype that correlates with sequence divergence in the extracellular domain of FER. Our findings show that the female control of pollen tube reception is based on a FER-dependent signaling pathway, which may play a role in reproductive isolation barriers.
We herein describe the application of a new guiding system designed for percutaneous biopsies. The guiding system set is composed of a 0.41 mm (27G) stainless steel guide stylet and a 22G Chiba needle. Following the i...
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We herein describe the application of a new guiding system designed for percutaneous biopsies. The guiding system set is composed of a 0.41 mm (27G) stainless steel guide stylet and a 22G Chiba needle. Following the initial insertion of the Chiba needle, the stylet is advanced via the needle toward the lesion. The stylet serves either as a guide for the Chiba needle or as an exchange wire for the introduction of larger or cutting biopsy needles. The stylet can also be curved prior to its insertion to facilitate access to lesions which require needle redirection. The technique was applied to 117 cases (54 thoracic, 31 abdominal, 21 pelvic, and 11 vertebral lesions.) The main advantage of the stylet is its small diameter, rendering it atraumatic and permitting multiple punctures for the successful final targeting of the lesion. With this guiding set we achieved targeting of difficult lesions. Furthermore, larger needles were more easily introduced in locations that posed technical difficulties. No major complications were observed. The complication rate was comparable to that of the conventional biopsy technique. The technique using the guide stylet was easily performed and could be applied to almost all organs.
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