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排序方式: 共有937条查询结果,搜索用时 15 毫秒
41.
Harris D Orme C Kramer J Namba L Champion M Palladino MJ Natzle J Hawley RS 《Genetics》2003,165(2):637-652
In Drosophila oocytes, euchromatic homolog-homolog associations are released at the end of pachytene, while heterochromatic pairings persist until metaphase I. A screen of 123 autosomal deficiencies for dominant effects on achiasmate chromosome segregation has identified a single gene that is haplo-insufficient for homologous achiasmate segregation and whose product may be required for the maintenance of such heterochromatic pairings. Of the deficiencies tested, only one exhibited a strong dominant effect on achiasmate segregation, inducing both X and fourth chromosome nondisjunction in FM7/X females. Five overlapping deficiencies showed a similar dominant effect on achiasmate chromosome disjunction and mapped the haplo-insufficient meiotic gene to a small interval within 66C7-12. A P-element insertion mutation in this interval exhibits a similar dominant effect on achiasmate segregation, inducing both high levels of X and fourth chromosome nondisjunction in FM7/X females and high levels of fourth chromosome nondisjunction in X/X females. The insertion site for this P element lies immediately upstream of CG18543, and germline expression of a UAS-CG18543 cDNA construct driven by nanos-GAL4 fully rescues the dominant meiotic defect. We conclude that CG18543 is the haplo-insufficient gene and have renamed this gene matrimony (mtrm). Cytological studies of prometaphase and metaphase I in mtrm hemizygotes demonstrate that achiasmate chromosomes are not properly positioned with respect to their homolog on the meiotic spindle. One possible, albeit speculative, interpretation of these data is that the presence of only a single copy of mtrm disrupts the function of whatever "glue" holds heterochromatically paired homologs together from the end of pachytene until metaphase I. 相似文献
42.
Kolker DE Losee Olson S Dutton-Boilek J Bennett KM Wallen EP Horton TH Turek FW 《American journal of physiology. Regulatory, integrative and comparative physiology》2002,282(5):R1382-R1388
Aging alters many aspects of circadian rhythmicity, including responsivity to phase-shifting stimuli and the amplitude of the rhythm of melatonin secretion. As melatonin is both an output from and an input to the circadian clock, we hypothesized that the decreased melatonin levels exhibited by old hamsters may adversely impact the circadian system as a whole. We enhanced the diurnal rhythm of melatonin by feeding melatonin to young and old hamsters. Animals of both age groups on the melatonin diet showed larger phase shifts than control-fed animals in response to an injection with the benzodiazepine triazolam at a circadian time known to induce phase advances in the activity rhythm of young animals. Thus melatonin treatment can increase the sensitivity of the circadian timing system of young animals to a nonphotic stimulus, and the ability to increase this sensitivity persists into old age, indicating exogenous melatonin might be useful in reversing at least some age-related changes in circadian clock function. 相似文献
43.
44.
Engineered CD4- and CXCR4-using simian immunodeficiency virus from African green monkeys is neutralization sensitive and replicates in nonstimulated lymphocytes
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König RR Flory E Steidl S Neumann J Coulibaly C Holznagel E Holzammer S Norley S Cichutek K 《Journal of virology》2002,76(21):10627-10636
During human immunodeficiency virus type 1 (HIV-1) infection, disease progression correlates with the occurrence of variants using the coreceptor CXCR4 for cell entry. In contrast, apathogenic simian immunodeficiency virus (SIV) from African green monkeys (SIVagm), specifically the molecular virus clone SIVagm3mc, uses CCR5, Bob, and Bonzo as coreceptors throughout the course of infection. The influence of an altered coreceptor usage on SIVagm3mc replication was studied in vitro and in vivo. The putative coreceptor binding domain, the V3 region of the surface envelope (SU) glycoprotein, was replaced by the V3 loop of a CD4- and CXCR4-tropic HIV-1 strain. The resulting virus, termed SIVagm3-X4mc, exclusively used CD4 and CXCR4 for cell entry. Consequently, its in vitro replication was inhibited by SDF-1, the natural ligand of CXCR4. Surprisingly, SIVagm3-X4mc was able to replicate in vitro not only in interleukin-2- and phytohemagglutinin-stimulated but also in nonstimulated peripheral blood mononuclear cells (PBMCs) from nonhuman primates. After experimental infection of two pig-tailed macaques with either SIVagm3-X4mc or SIVagm3mc, the coreceptor usage was maintained during in vivo replication. Cell-associated and plasma viral loads, as well as viral DNA copy numbers, were found to be comparable between SIVagm3mc and SIVagm 3-X4mc infections, and no pathological changes were observed up to 14 months postinfection. Interestingly, the V3 loop exchange rendered SIVagm3-X4mc susceptible to neutralizing antibodies present in the sera of SIVagm3-X4mc- and SIVagm3mc-infected pig-tailed macaques. Our study describes for the first time a successful exchange of a V3 loop in nonpathogenic SIVagm resulting in CD4 and CXCR4 usage and modulation of virus replication in nonstimulated PBMCs as well as sensitivity toward neutralization. 相似文献
45.
Asymmetric divisions are key to regulating the number and patterning of stomata in Arabidopsis thaliana (L.) Heynh. Many formative asymmetric divisions take place in neighbor cells (NCs), cells adjacent to a stoma or stomatal precursor. TOO MANY MOUTHS is a receptor-like protein required for the correct plane of NC division, resulting in the placement of the new precursor distal to the pre-existing stoma. Because plant cells usually become polarized before asymmetric division, we studied whether NCs display a cytological asymmetry as a function of cell stage and of possible division behavior. Cells that divided in the developing leaf epidermis were smaller than 400 micro m(-2) in area and included NCs as well as isolated cells. All NCs in the youngest complexes divided with comparable frequencies, but divisions became restricted to the smaller and most recently produced NCs as the stomatal complex matured. The majority of developing NCs had distally located nuclei, suggesting that nuclear position is actively regulated in NCs. NC stages exhibiting distally located nuclei were the likeliest to divide asymmetrically. However, a distal nucleus did not necessarily predict an asymmetric division, because more NCs had distal nuclei than were likely to divide. No defect was detected in nuclear distribution in tmm NCs. These data suggest that TMM uses intercellular signals to control the plane of asymmetric division after or independently of nuclear positioning. 相似文献
46.
Neuropilin-2 regulates the development of selective cranial and sensory nerves and hippocampal mossy fiber projections 总被引:12,自引:0,他引:12
Chen H Bagri A Zupicich JA Zou Y Stoeckli E Pleasure SJ Lowenstein DH Skarnes WC Chédotal A Tessier-Lavigne M 《Neuron》2000,25(1):43-56
Neuropilin-1 and neuropilin-2 bind differentially to different class 3 semaphorins and are thought to provide the ligand-binding moieties in receptor complexes mediating repulsive responses to these semaphorins. Here, we have studied the function of neuropilin-2 through analysis of a neuropilin-2 mutant mouse, which is viable and fertile. Repulsive responses of sympathetic and hippocampal neurons to Sema3F but not to Sema3A are abolished in the mutant. Marked defects are observed in the development of several cranial nerves, in the initial central projections of spinal sensory axons, and in the anterior commissure, habenulo-interpeduncular tract, and the projections of hippocampal mossyfiber axons in the infrapyramidal bundle. Our results show that neuropilin-2 is an essential component of the Sema3F receptor and identify key roles for neuropilin-2 in axon guidance in the PNS and CNS. 相似文献
47.
48.
Opposing Contributions of NR1 and NR2 to Protein Kinase C Modulation of NMDA Receptors 总被引:4,自引:1,他引:3
Elfrida R. Grant Brian J. Bacskai Norifusa J. Anegawa †David E. Pleasure † David R. Lynch 《Journal of neurochemistry》1998,71(4):1471-1481
Abstract: N -Methyl- d -aspartate (NMDA) receptors mediate increases in intracellular calcium that can be modulated by protein kinase C (PKC). As PKC modulation of NMDA receptors in neurons is complex, we studied the effects of PKC activation on recombinant NMDA receptor-mediated calcium rises in a nonneuronal mammalian cell line, human embryonic kidney 293 (HEK-293). Phorbol 12-myristate 13-acetate (PMA) pretreatment of HEK-293 cells enhanced or suppressed NMDA receptor-mediated calcium rises based on the NMDA receptor subunit composition. NR2A or NR2B, in combination with NR1011 , conveyed enhancement whereas NR2C and NR2D conveyed suppression. The PKC inhibitor bisindolylmaleimide blocked each of these effects. The region on NR2A that conveyed enhancement localized to a discrete segment of the C terminus distal to the portion of NR2C that is homologous to NR2A. Calcium-45 accumulation, but not intracellular calcium store depletion, matched PMA effects on NMDA receptor-mediated calcium changes, suggesting that these effects were not due to effects on intracellular calcium stores. The suppression of intracellular calcium transients seen with NR2C was eliminated when combined with NR1 splice variants lacking C-terminal cassette 1. Thus, the intracellular calcium effects of PMA were distinguishable based on both the NR1 splice variant and the NR2 subunit type that were expressed. Such differential effects resemble the diversity of PKC effects on NMDA receptors in neurons. 相似文献
49.
Sabrina Klix Antje Els Katharina Paul Andreas Graessl Celal Oezerdem Oliver Weinberger Lukas Winter Christof Thalhammer Till Huelnhagen Jan Rieger Heidrun Mehling Jeanette Schulz-Menger Thoralf Niendorf 《PloS one》2015,10(1)
Purpose
This study examines the subjective acceptance during UHF-CMR in a cohort of healthy volunteers who underwent a cardiac MR examination at 7.0T.Methods
Within a period of two-and-a-half years (January 2012 to June 2014) a total of 165 healthy volunteers (41 female, 124 male) without any known history of cardiac disease underwent UHF-CMR. For the assessment of the subjective acceptance a questionnaire was used to examine the participants experience prior, during and after the UHF-CMR examination. For this purpose, subjects were asked to respond to the questionnaire in an exit interview held immediately after the completion of the UHF-CMR examination under supervision of a study nurse to ensure accurate understanding of the questions. All questions were answered with “yes” or “no” including space for additional comments.Results
Transient muscular contraction was documented in 12.7% of the questionnaires. Muscular contraction was reported to occur only during periods of scanning with the magnetic field gradients being rapidly switched. Dizziness during the study was reported by 12.7% of the subjects. Taste of metal was reported by 10.1% of the study population. Light flashes were reported by 3.6% of the entire cohort. 13% of the subjects reported side effects/observations which were not explicitly listed in the questionnaire but covered by the question about other side effects. No severe side effects as vomiting or syncope after scanning occurred. No increase in heart rate was observed during the UHF-CMR exam versus the baseline clinical examination.Conclusions
This study adds to the literature by detailing the subjective acceptance of cardiovascular magnetic resonance imaging examinations at a magnetic field strength of 7.0T. Cardiac MR examinations at 7.0T are well tolerated by healthy subjects. Broader observational and multi-center studies including patient cohorts with cardiac diseases are required to gain further insights into the subjective acceptance of UHF-CMR examinations. 相似文献50.
Vallabh O. Shah Casey Carroll Ryan Mals Donica Ghahate Jeanette Bobelu Phillip Sandy Kathleen Colleran Ronald Schrader Thomas Faber Mark R. Burge 《PloS one》2015,10(5)