刺激黄雀新纹状体前部大细胞核外侧部对发声和呼吸的影响

实验材料为乌拉坦麻醉的鸣禽黄雀（Ｃａｒｄｕｅｌｉｓ ｓｐｉｎｕｓ）。观察了电及化学刺激新纹状体前部大细胞核外侧部（１ＭＡＮ）对发声和呼吸的影响。结果如下：（１）电刺激１ＭＡＮ的不同区域都引起鸣叫反应。（２）长串电脉冲刺激１ＭＡＮ使呼吸频率增加,呼吸幅度降低。（３）短串电脉冲刺激１ＭＡＮ,落位于吸气相,产生吸气要断效应;落位于呼气相,可使呼气时程延长,以冲刺激１ＭＡＮ,落位于吸气相,产生吸气切断效应     

细胞对机械刺激感知的生物力学机制

细胞作为机体的基本单位,始终处于一个受力环境中。微环境中的细胞不仅受化学信号的影响,还受基质刚度、外界力载荷及胞外基质(ECM)结构的调控,这些都能影响细胞分化、迁移、形态发生、增殖等方面的生物学反应。目前,部分学者致力于细胞生物力学的应用和机制方面的探索,但对于细胞力学感知机理的认知仍无法形成一个完整的定论。本文将就整合素、G蛋白耦联受体、张力活化通道(SAC)、细胞核等介导的细胞生物力学感知通路作一综述。     

Centrosome positioning in polarized cells: Common themes and variations

The centrosome position is tightly regulated during the cell cycle and during differentiated cellular functions. Because centrosome organizes the microtubule network to coordinate both intracellular organization and cell signaling, centrosome positioning is crucial to determine either the axis of cell division, the direction of cell migration or the polarized immune response of lymphocytes. Since alteration of centrosome positioning seems to promote cell transformation and tumor spreading, the molecular mechanisms controlling centrosome movement in response to extracellular and intracellular cues are under intense investigation. Evolutionary conserved pathways involving polarity proteins and cytoskeletal rearrangements are emerging as common regulators of centrosome positioning in a wide variety of cellular contexts.     

Song ranging by incubating male Blue-headed Vireos: the importance of song representation in repertoires and implications for song delivery patterns and local/foreign dialect discrimination

ABSTRACT.   Mechanisms used by birds to range their distance from singing conspecifics are being debated. In particular, the idea that an incoming song must be in a bird's repertoire for it to be ranged accurately is controversial, but important to our appreciation of the role ranging plays in song evolution. We tested the relation between ranging accuracy and songs in repertoires in playback experiments to male Blue-headed Vireos ( Vireo solitarius ) whose precise locations were known because they were incubating eggs. Males ranged songs heard while incubating and, when their mates relieved them at the nest, flew directly to the silent playback sites, suggesting that they remembered the locations of simulated intruders. Male vireos approached playback sites of local songs, likely in their own repertoires, more precisely than foreign songs recorded 95–645 km from our study site. Songs included in local and foreign playback tapes differed primarily in frequency modulation, but were similar in other measurements. These results support ranging theory as described by Morton (1986) . If the songs within an individual's repertoire are ranged with greater accuracy, we discuss how the stability of neighborhoods becomes a factor as to whether or not selection will favor repertoire sharing in song evolution. As well, singing style is affected by ranging. Because Blue-headed Vireos present their songs in a stereotyped order, a listener can compare ordered sequential changes in signal degradation. Comparing degradation in a sequence of songs adds a temporal element that should result in more accurate ranging of the singer's location.     

Active uptake of cyst nematode parasitism proteins into the plant cell nucleus

Cyst nematodes produce parasitism proteins that contain putative nuclear localisation signals (NLSs) and, therefore, are predicted to be imported into the nucleus of the host plant cell. The in planta localisation patterns of eight soybean cyst nematode (Heterodera glycines) parasitism proteins with putative NLSs were determined by producing these proteins as translational fusions with the GFP and GUS reporter proteins. Two parasitism proteins were found to be imported into the nuclei of onion epidermal cells as well as Arabidopsis protoplasts. One of these two parasitism proteins was further transported into the nucleoli. Mutations introduced into the NLS domains of these two proteins abolished nuclear import and caused a cytoplasmic accumulation. Furthermore, we observed active nuclear uptake for three additional parasitism proteins, however, only when these proteins were synthesised as truncated forms. Two of these proteins were further transported into nucleoli. We hypothesise that nuclear uptake and nucleolar localisation are important mechanisms for H. glycines to modulate the nuclear biology of parasitised cells of its host plant.     

The instructive role of binocular vision in the Xenopus tectum

This review presents the fascinating neurobiology underlying the development of the frog optic tectum, the brain structure where the two separate inputs from the two eye are combined into a single, integrated map. In the species Xenopus laevis, binocular visual information has a dramatic impact on axon growth and connectivity, and the formation of binocular connections in this system provides a rich basis for both theoretical and experimental investigations.     

The nuclear proteasome and the degradation of oxidatively damaged proteins

Summary. The accumulation of oxidized proteins is known to be linked to some severe neurodegenerative diseases like Alzheimer’s, Parkinson’s and Huntington’s disease. Furthermore, the aging process is also accompanied by an ongoing aggregation of misfolded and damaged proteins. Therefore, mammalian cells have developed potent degradation systems, which selectively degrade damaged and misfolded proteins. The proteasomal system is largely responsible for the removal of oxidatively damaged proteins form the cellular environment. Not only cytosolic proteins are prone to oxidative stress, also nuclear proteins are readily oxidized. The nuclear proteasomal system is responsible for the degradation of these proteins. This review is focused on the specific degradation of oxidized nuclear proteins, the role of the proteasome in this process and the regulation of the nuclear proteasomal system under oxidative conditions.     

In vitro nuclear egress of herpes simplex virus type 1 capsids

During their life cycles, viruses typically undergo many transport events throughout the cell. These events depend on a variety of both viral and host proteins and are often not fully understood. Such studies are often complicated by asynchronous infections and the concurrent presence of various viral intermediates in the cells, making it difficult to molecularly define each step. In the case of the herpes simplex virus type 1, the etiological agent of cold sores and many other illnesses, the viral particles undergo an intricate series of transport steps during its life cycle. Upon entry by fusion with a cellular membrane, they travel to the host cell nucleus where the virus replicates and assembles new viral particles. These particles then travel across the two nuclear envelopes and transit through the trans-Golgi network before finally being transported to and released at the cell surface. Though viral components and some host proteins modulating these numerous transport events have been identified, the details of these processes remain to be elucidated. To specifically address how the virus escapes the nucleus, we set up an in vitro model that reproduces the unconventional route used by herpes simplex type 1 virus to leave nuclei. This has not only allowed us to clarify the route of capsid egress of the virus but is now useful to define it at the molecular level.     

Kinetics and subunit composition of NMDA receptors in respiratory-related neurons

NMDA receptors are involved in a variety of brainstem functions. The excitatory postsynaptic NMDA currents of pre-Botzinger complex interneurons and hypoglossal motoneurons, which are located in the medulla oblongata, show remarkably fast deactivation kinetics of approximately 30 ms compared with NMDA receptors in other types of neurons. Because structural heterogeneity might be the basis for physiological properties, we examined the expression of six NMDA receptor subunits (NMDAR1, NR2A-2D, and NR3A) plus eight NMDR1 splice variants in pre-Botzinger complex, hypoglossal and, for comparison, neurons from the nucleus of the solitary tract in young rats using single cell multiplex RT-PCR. Expression of NR2A, NR2B, and NR2D was observed in all three cell types while NR3A was much more abundant in pre-Botzinger complex interneurons, which belong to the rhythm generator of respiratory activity. In hypoglossal neurons, the NMDAR1 splice variants NMDAR1-4a and NMDAR1-4b were found. In neurons of the nucleus of the solitary tract, instead of NMDAR1-4b, the NMDAR1-2a splice variant was detected. This differential expression of modulatory splice variants might be the molecular basis for the characteristic functional properties of NMDA receptors, as neurons expressing a special NMDAR1 splice variant at the mRNA level show fast kinetics compared with neurons lacking this splice variant.     

Conformation-specific antibodies reveal distinct actin structures in the nucleus and the cytoplasm

For many years the existence of actin in the nucleus has been doubted because of the lack of phalloidin staining as well as the failure to document nuclear actin filaments by electron microscopy. More recent findings reveal actin to be a component of chromatin remodeling complexes and of the machinery involved in RNA synthesis and transport. With distinct functions for nuclear actin emerging, the quest for its conformation and oligomeric/polymeric structure in the nucleus has resumed importance. We used chemically cross-linked 'lower dimer' (LD) to generate mouse monoclonal antibodies specific for different actin conformations. One of the resulting antibodies, termed 1C7, recognizes an epitope that is buried in the F-actin filament, but is surface-exposed in G-actin as well as in the LD. In immunofluorescence studies with different cell lines, 1C7 selectively reacts with non-filamentous actin in the cytoplasm. In addition, it detects a discrete form of actin in the nucleus, which is different from the nuclear actin revealed by the previously described 2G2 [Gonsior, S.M., Platz, S., Buchmeier, S., Scheer, U., Jockusch, B.M., Hinssen, H., 1999. J. Cell Sci. 112, 797]. Upon latrunculin-induced disassembly of the filamentous cytoskeleton in Rat2 fibroblasts, we observed a perinuclear accumulation of the 1C7-reactive actin conformation. In addition, latrunculin treatment led to the assembly of phalloidin-staining actin structures in chromatin-free regions of the nucleus in these cells. Our results indicate that distinct actin conformations and/or structures are present in the nucleus and the cytoplasm of different cell types and that their distribution varies in response to external signals.