中国南部亚热带森林地表植被动态变化

系统研究了南方5个亚热带森林生态系统地表植被的动态变化情况.研究方法是:在每个研究区域内,按照地形梯度分别布设50个1m2 的样方,记录样方内所有物种的频度及相关的环境变量,5个研究区域共设250个样方,每个样方分别调查两次.通过单元及多元统计方法分析表明:维管植物物种频度在一个区域明显下降,另二个区域显著增加;苔藓物种频度在一个区域有明显下降,另一个区域明显增加;苔藓物种数量在3个区域显著增加,另二个区域显著下降;维管植物物种数量显著增加在二个区域;物种组成沿着第一个植被梯度轴DCA 1没有显著变化,沿着第二个植被梯度轴DCA 2在二个区域有显著变化.综合分析表明,苔藓对气候变化及其波动反映敏感,是较好的气候变化及气候波动生物指示因子,而管植物数量及频度的变化没有明显证据显示与土壤酸化和大气污染有紧密关系.     

Preinfection Human Immunodeficiency Virus (HIV)-Specific Cytotoxic T Lymphocytes Failed To Prevent HIV Type 1 Infection from Strains Genetically Unrelated to Viruses in Long-Term Exposed Partners

Understanding the mechanisms underlying potential altered susceptibility to human immunodeficiency virus type 1 (HIV-1) infection in highly exposed seronegative (ES) individuals and the later clinical consequences of breakthrough infection can provide insight into strategies to control HIV-1 with an effective vaccine. From our Seattle ES cohort, we identified one individual (LSC63) who seroconverted after over 2 years of repeated unprotected sexual contact with his HIV-1-infected partner (P63) and other sexual partners of unknown HIV-1 serostatus. The HIV-1 variants infecting LSC63 were genetically unrelated to those sequenced from P63. This may not be surprising, since viral load measurements in P63 were repeatedly below 50 copies/ml, making him an unlikely transmitter. However, broad HIV-1-specific cytotoxic T-lymphocyte (CTL) responses were detected in LSC63 before seroconversion. Compared to those detected after seroconversion, these responses were of lower magnitude and half of them targeted different regions of the viral proteome. Strong HLA-B27-restricted CTLs, which have been associated with disease control, were detected in LSC63 after but not before seroconversion. Furthermore, for the majority of the protein-coding regions of the HIV-1 variants in LSC63 (except gp41, nef, and the 3′ half of pol), the genetic distances between the infecting viruses and the viruses to which he was exposed through P63 (termed the exposed virus) were comparable to the distances between random subtype B HIV-1 sequences and the exposed viruses. These results suggest that broad preinfection immune responses were not able to prevent the acquisition of HIV-1 infection in LSC63, even though the infecting viruses were not particularly distant from the viruses that may have elicited these responses.Understanding the mechanisms of altered susceptibility or control of human immunodeficiency virus type 1 (HIV-1) infection in highly exposed seronegative (ES) persons may provide invaluable information aiding the design of HIV-1 vaccines and therapy (9, 14, 15, 33, 45, 57, 58). In a cohort of female commercial sex workers in Nairobi, Kenya, a small proportion of individuals remained seronegative for over 3 years despite the continued practice of unprotected sex (12, 28, 55, 56). Similarly, resistance to HIV-1 infection has been reported in homosexual men who frequently practiced unprotected sex with infected partners (1, 15, 17, 21, 61). Multiple factors have been associated with the resistance to HIV-1 infection in ES individuals (32), including host genetic factors (8, 16, 20, 37-39, 44, 46, 47, 49, 59, 63), such as certain HLA class I and II alleles (41), as well as cellular (1, 15, 26, 55, 56), humoral (25, 29), and innate immune responses (22, 35).Seroconversion in previously HIV-resistant Nairobi female commercial sex workers, despite preexisting HIV-specific cytotoxic T-lymphocyte (CTL) responses, has been reported (27). Similarly, 13 of 125 ES enrollees in our Seattle ES cohort (1, 15, 17) have become late seroconverters (H. Zhu, T. Andrus, Y. Liu, and T. Zhu, unpublished observations). Here, we analyze the virology, genetics, and immune responses of HIV-1 infection in one of the later seroconverting subjects, LSC63, who had developed broad CTL responses before seroconversion.     

Structure and Functional Implications of the Human Rad9-Hus1-Rad1 Cell Cycle Checkpoint Complex

Cellular DNA lesions are efficiently countered by DNA repair in conjunction with delays in cell cycle progression. Previous studies have demonstrated that Rad9, Hus1, and Rad1 can form a heterotrimeric complex (the 9-1-1 complex) that plays dual roles in cell cycle checkpoint activation and DNA repair in eukaryotic cells. Although the 9-1-1 complex has been proposed to form a toroidal structure similar to proliferating cell nuclear antigen (PCNA), which plays essential roles in DNA replication and repair, the structural basis by which it performs different functions has not been elucidated. Here we report the crystal structure of the human 9-1-1 complex at 3.2 Å resolution. The crystal structure, together with biochemical assays, reveals that the interdomain connecting loops (IDC loop) of hRad9, hHus1, and hRad1 are largely divergent, and further cocrystallization study indicates that a PCNA-interacting box (PIP box)-containing peptide derived from hFen1 binds tightly to the interdomain connecting loop of hRad1, providing the molecular basis for the damage repair-specific activity of the 9-1-1 complex in contrast to PCNA. Furthermore, structural comparison with PCNA reveals other unique structural features of the 9-1-1 complex that are proposed to contribute to DNA damage recognition.Cellular DNA damage triggers the activation of the cell cycle checkpoint, leading to a delay or arrest in cell cycle progression to prevent replication and inducing DNA damage repair (1, 2). In response to DNA damage, the 9-1-1³ complex can be loaded onto DNA lesion sites by Rad17-RFC2–5 (which consists of one large subunit, Rad17, and four small subunits, RFC2–5), where it triggers the activation of the cell cycle checkpoint (3, 4). Moreover, the 9-1-1 complex can also directly participate in DNA repair via physical association with many factors involved in base excision repair (BER), translesion synthesis, homologous recombination, and mismatch repair pathways (5–9).Although both the 9-1-1 and the PCNA complexes perform critical functions in eukaryotic cells with predicted similar structures (10), their specific roles are distinct. First, the 9-1-1 complex is a DNA damage sensor in the cell cycle checkpoint but does not function as a scaffold for the major DNA replication factors; however, PCNA plays exactly the opposite role (1, 11). Second, although both the complexes function in DNA repair, their specific activities are different. Previous observations indicated that some BER enzymes, such as MYH (MutY glycosylate homolog) (12), TDG (thymine DNA glycosylate) (7), and NEIL (Nei-like glycosylate) (8), interact with the 9-1-1 complex via motifs that are located outside the conserved PCNA-interacting box (the PIP box), implying that the 9-1-1 complex functions as a damage repair-specific clamp, in contrast to PCNA. However, the structural basis for this hypothesis remains unclear. Another important unresolved issue concerns the damage-sensing mechanism of the 9-1-1 complex. During the DNA replication process, the PCNA·RFC clamp·clamp loader specifically recognizes the primer-template junction (13). However, the molecular basis by which the 9-1-1·Rad17-RFC2–5 clamp·clamp loader specifically recognizes the damaged DNA is little known. To address these questions, we performed structural and biochemical studies on the 9-1-1 complex.     

Synthesis and biological evaluation of 3-ethylidene-1,3-dihydro-indol-2-ones as novel checkpoint 1 inhibitors

Chk1 inhibitors have emerged as a novel class of neoplastic agents for abrogating the G2 DNA damage checkpoint arrest. Analogs of the Chk1 inhibitor, 3-ethylidene-1,3-dihydro-indol-2-one, were synthesized and tested in vitro for their inhibitory activities. The most promising compound identified from this series is analog 28, which possesses potent enzymatic and cellular activities.     

Affinity maturation of anti-TNF-alpha scFv with somatic hypermutation in non-B cells

Activation-induced cytidine deaminase (AID) is required for the generation of antibody diversity through initiating both somatic hypermutation (SHM) and class switch recombination. A few research groups have successfully used the feature of AID for generating mutant libraries in directed evolution of target proteins in B cells in vitro. B cells, cultured in suspension, are not convenient for transfection and cloning. In this study, we established an AID-based mutant accumulation and sorting system in adherent human cells. Mouse AID gene was first transfected into the human non-small cell lung carcinoma H1299 cells, and a stable cell clone (H1299-AID) was selected. Afterwards, anti-hTNF-αscFv (ATscFv) was transfected into H1299-AID cells and ATscFv was displayed on the surface of H1299-AID cells. By 4-round amplification/flow cytometric sorting for cells with the highest affinities to hTNF-alpha, two ATscFv mutant gene clones were isolated. Compared with the wild type ATscFv, the two mutants were much more efficient in neutralizing cytotoxicity of hTNF-alpha. The results indicate that directed evolution by somatic hypermutation can be carried out in adherent non-B cells, which makes directed evolution in mammalian cells easier and more efficient.     

Involvement of Nox2 and Nox4 NADPH oxidases in early brain injury after subarachnoid hemorrhage

Oxidative stress is responsible for a poor prognosis of subarachnoid hemorrhage (SAH) patients. Nox2 has been shown to participate in SAH-induced early brain injury (EBI). Nox4 is another major subtype of Nox family widely expressed in central nervous system (CNS). Here, we investigated the role of Nox4 and whether there was a synergistic effect of Nox2 and Nox4 in SAH-induced EBI. Clinical brain biopsies of four patients with traumatic brain injury (TBI) and perihematomal brain tissue from six subjects with SAH were examined. Gp91ds-tat (a specific inhibitor of Nox2), GKT137831 (a specific inhibitor of Nox4), and apocynin (a non-specific Nox inhibitor) were used to test the role of Nox2 and Nox4. The protein levels of Nox2 and Nox4 were elevated in rat neurons and astrocytes at 12?h after SAH, and in cultured brain microvascular endothelial cells at 24?h after exposure to OxyHb. Similarly, there were higher Nox2 and Nox4 protein levels in perihematomal neurons and astrocytes in SAH patients than that in brain tissue from subjects with TBI. In SAH rat model, gp91ds-tat and GKT137831 could reduce SAH-induced neuronal death and degeneration, whereas apocynin did not induce a more intense neuroprotection. Consistently, in in vitro SAH model, siRNA-mediated silencing of Nox2 and Nox4 suppressed the OxyHb-induced neuronal apoptosis, whereas Nox2 and Nox4 co-knockdown also did not show a remarkable overlay effect. In conclusion, Nox4 should contribute to the pathological processes in SAH-induced EBI, and there was not an overlay effect of Nox2 inhibition and Nox4 inhibition on preventing SAH-induced EBI.     

Geometry-Dependent Surface Plasmonic Properties and Dielectric Sensitivity of Bimetallic Au@Pd Nanorods

Plasmonics - Bimetallic nanoparticles have attracted increasing interest because of their unique optical, electronic, magnetic, and catalytic properties which are different from that of their...     

麻竹花药培养及再生植株的获得

以麻竹(Dendrocalamus latiflorus Munro)花药为材料, 于M₈+2 mg·L^–1 NAA +0.5 mg·L^–1 6-BA+15 mg·L^–1 PAA+7.5 mg·L^–1 STS+500 mg·L^–1 CH+100 mg·L^–1 proline+100 mg·L^–1 glutamin+5.4% maltose+0.8% agar的诱导培养基上成功诱导出胚性愈伤组织, 在此培养基上继代可形成体胚并分化成苗, 初步建立了麻竹花药一步成苗的再生体系。