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11.
The neuronal secretory pathway represents the intracellular route for proteins involved in synaptic transmission and plasticity, as well as lipids required for outgrowth and remodelling of dendrites and axons. Although neurons use the same secretory compartments as other eukaryotic cells, the enormous distances involved, as well as the unique morphology of the neuron and its signalling requirements, challenge canonical models of secretory pathway organization. Here, we review evidence for a distributed secretory pathway in neurons, suggest mechanisms that may regulate secretory compartment distribution, and discuss the implications of a distributed secretory pathway for neuronal morphogenesis and neural-circuit plasticity. 相似文献
12.
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Dmitriev BA Toukach FV Schaper KJ Holst O Rietschel ET Ehlers S 《Journal of bacteriology》2003,185(11):3458-3468
Although the chemical structure and physical properties of peptidoglycan have been elucidated for some time, the precise three-dimensional organization of murein has remained elusive. Earlier published computer simulations of the bacterial murein architecture modeled peptidoglycan strands in either a regular (D. Pink, J. Moeller, B. Quinn, M. Jericho, and T. Beveridge, J. Bacteriol. 182: 5925-5930, 2000) or an irregular (A. Koch, J. Theor. Biol. 204: 533-541, 2000) parallel orientation with respect to the plasma membrane. However, after integrating published experimental data on glycan chain length distribution and the degree of peptide side chain cross-linking into this computer simulation, we now report that the proposed planar network of murein appears largely dysfunctional. In contrast, a scaffold model of murein architecture, which assumes that glycan strands extend perpendicularly to the plasma membrane, was found to accommodate published experimental evidence and yield a viable stress-bearing matrix. Moreover, this model is in accordance with the well-established principle of murein assembly in vivo, i.e., sequential attachment of strands to the preexisting structure. For the first time, the phenomenon of division plane alternation in dividing bacteria can be reconciled with a computer model of the molecular architecture of murein. 相似文献
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15.
Dynamics and regulation of clathrin coats at specialized endocytic zones of dendrites and spines 总被引:19,自引:0,他引:19
Endocytosis is a fundamental mechanism by which neurons control intercellular signaling, nutrient uptake, and synaptic transmission. This process is carried out by the assembly of clathrin coats and the budding of clathrin-coated vesicles from the neuronal plasma membrane. Here, we demonstrate that in young neurons, clathrin assembly and disassembly occur rapidly, locally, and repeatedly at "hot spots" throughout dendrites and at the tips of dendritic filopodia. In contrast, clathrin coats in mature dendrites reside in stable, long-lasting zones at sites of endocytosis, where clathrin undergoes continuous exchange with local cytosolic pools. In dendritic spines, endocytic zones lie lateral to the postsynaptic density (PSD) where they develop and persist independent of synaptic activity, akin to the PSD itself. These results reveal the presence of a novel specialization dedicated to endocytosis near the postsynaptic membrane. 相似文献
16.
Among the most morphologically complex cells, neurons are masters of membrane specialization. Nowhere is this more striking than in the division of cellular labor between the axon and the dendrites. In morphology, signaling properties, cytoskeletal organization, and physiological function, axons and dendrites (or more properly, the somatodendritic compartment) are radically different. Such polarization of neurons into domains specialized for either receiving (dendrites) or transmitting (axons) cellular signals provides the underpinning for all neural circuitry. The initial specification of axonal and dendritic identity occurs early in neuronal life, persists for decades, and is manifested by the presence of very different sets of cell surface proteins. Yet, how neuronal polarity is established, how distinct axonal and somatodendritic domains are maintained, and how integral membrane proteins are directed to dendrites or accumulate in axons remain enduring and formidable questions in neuronal cell biology. 相似文献
17.
The embryonic development of the flatworm Mesostoma lingua was studied using a combination of life observation and histological analysis of wholemount preparations and sections (viewed
by both light and electron microscopy.) We introduce a series of stages defined by easily recognizable morphological criteria.
These stages are also applicable to other platyhelminth taxa that are currently under investigation in our laboratory. During
cleavage (stages 1 and 2), the embryo is located in the center of the egg, surrounded by a layer of yolk cells. After cleavage,
the embryo forms a solid, disc-shaped cell cluster. During stage 3, the embryo migrates to the periphery of the egg and acquires
bilateral symmetry. The side where it contacts the egg surface corresponds to the future ventral surface of the embryo. Stage
4 is the emergence of the first organ primordia, the brain and pharynx. Gastrulation, as usually defined by the appearance
of germ layers, does not exist in Mesos-toma; instead, organ primordia emerge ”in situ” from a mesenchymal mass of cells. Organogenesis takes place during stages 5 and
6. Cells at the ventral surface form the epidermal epithelium; inner cells differentiate into neurons, somatic and pharyngeal
muscle cells, as well as the pharyngeal and protonephridial (excretory) epithelium. A junctional complex, consisting initially
of small septate junctions, followed later by a more apically located zonula adherens, is formed in all epithelial tissues
at stage 6. Beginning towards the end of stage 6 and continuing throughout stages 7 and 8, cytodifferentiation of the different
organ systems takes place. Stage 7 is characterized by the appearance of eye pigmentation, brain condensation and spindle-shaped
myocytes. Stage 8 describes the fully dorsally closed and differentiated embryo. Muscular contraction moves the body in the
egg shell. We discuss Mesostoma embryogenesis in comparison to other animal phyla. Particular attention is given to the apparent absence of gastrulation
and the formation of the epithelial junctional complex.
Received: 10 February 2000 / Accepted: 10 April 2000 相似文献
18.
Activity-dependent mRNA splicing controls ER export and synaptic delivery of NMDA receptors 总被引:12,自引:0,他引:12
Activity-dependent targeting of NMDA receptors (NMDARs) is a key feature of synapse formation and plasticity. Although mechanisms for rapid trafficking of glutamate receptors have been identified, the molecular events underlying chronic accumulation or loss of synaptic NMDARs have remained unclear. Here we demonstrate that activity controls NMDAR synaptic accumulation by regulating forward trafficking at the endoplasmic reticulum (ER). ER export is accelerated by the alternatively spliced C2' domain of the NR1 subunit and slowed by the C2 splice cassette. This mRNA splicing event at the C2/C2' site is activity dependent, with C2' variants predominating upon activity blockade and C2 variants abundant with increased activity. The switch to C2' accelerates NMDAR forward trafficking by enhancing recruitment of nascent NMDARs to ER exit sites via binding of a divaline motif within C2' to COPII coats. These results define a novel pathway underlying activity-dependent targeting of glutamate receptors, providing an unexpected mechanistic link between activity, mRNA splicing, and membrane trafficking during excitatory synapse modification. 相似文献
19.
20.
We have isolated the delta-globin gene of the New-World spider monkey,
Ateles geoffroyi, and compared its nucleotide sequence with those of other
primate delta- and beta-globin genes. Among primate delta-globin genes, the
rate of nonsynonymous substitutions is much less than the rate of
synonymous substitutions. This suggests that primate delta- globin genes
may remain under evolutionary conservation, perhaps because hemoglobin A2
has an as yet unknown physiological importance.
相似文献