The role of HIV replicative fitness in perinatal transmission of HIV

Perinatal transmission of Human immunodeficiency virus(HIV),also called mother-to-child transmission(MTCT),accounts for 90% of infections in infants worldwide and occurs in 30%-45% of children born to untreated HIV-1 infected mothers.Among HIV-1 infected mothers,some viruses are transmitted from mothers to their infants while others are not.The relationship between virologic properties and the pathogenesis caused by HIV-1 remains unclear.Previous studies have demonstrated that one obvious source of selective pressure in the perinatal transmission of HIV-1 is maternal neutralizing antibodies.Recent studies have shown that viruses which are successfully transmitted to the child have growth advantages over those not transmitted,when those two viruses are grown together.Furthermore,the higher fitness is determined by the gp120 protein of the virus envelope.This suggests that the selective transmission of viruses with higher fitness occurred exclusively,regardless of transmission routes.There are many factors contributing to the selective transmission and HIV replicative fitness is an important one that should not be neglected.This review summarizes current knowledge of the role of HIV replicative fitness in HIV MTCT transmission and the determinants of viral fitness upon MTCT.     

Specific binding of activated Vip3Aa10 to Helicoverpa armigera brush border membrane vesicles results in pore formation

Helicoverpa armigera is one of the most harmful pests in China. Although it had been successfully controlled by Cry1A toxins, some H. armigera populations are building up resistance to Cry1A toxins in the laboratory. Vip3A, secreted by Bacillus thuringiensis, is another potential toxin against H. armigera. Previous reports showed that activated Vip3A performs its function by inserting into the midgut brush border membrane vesicles (BBMV) of susceptible insects. To further investigate the binding of Vip3A to BBMV of H. armigera, the full-length Vip3Aa10 toxin expressed in Escherichia coli was digested by trypsin or midgut juice extract, respectively. Among the fragments of digested Vip3Aa10, only a 62 kDa fragment (Vip3Aa10-T) exhibited binding to BBMV of H. armigera and has insecticidal activity. Moreover, this interaction was specific and was not affected by the presence of Cry1Ab toxin. Binding of Vip3Aa10-T to BBMV resulted in the formation of an ion channel. Unlike Cry1A toxins, Vip3Aa10-T was just slightly associated with lipid rafts of BBMV. These data suggest that although activated Vip3Aa10 specifically interacts with BBMV of H. armigera and forms an ion channel, the mode of action of it may be different from that of Cry1A toxins.     

Panicle Water Potential, a Physiological Trait to Identify Drought Tolerance in Rice

Two upland rice varieties （IRAT109, IAPAR9） and one lowland rice variety （Zhenshan 97B） were planted in summer and treated with both normal （full water） and drought stress in the reproductive stage. Panicle water potential （PWP） and leaf water potential （LWP） were measured every 1.0-1.5 h over 24 h on sunny days. Both PWP and LWP of upland varieties started to decrease later, maintained a higher level and recovered more quickly than that of the lowland variety. The results show that PWP can be used as an indicator of plant water status based on the parallel daily changes, and the high correlation between PWP and LWP. Similar correlations were also observed between PWP, LWP and eight traits related to plant growth and grain yield formation. PWP seemed to be more effective for distinguishing the upland rice varieties with different drought-tolerant ability. Differences in PWP and LWP between upland and lowland rice varieties were also observed at noon even under normal water conditions, implying the incorporation of the drought-tolerant mechanism to improve the photosynthesis and yield of traditional paddy rice.     

Chemical compounds and pharmacological effects of Rabdosia excisa

Many kinds of diterpenoids have been isolated from Rabdosia spp.Some of them have anti-microbial effects,counteract inflammation,and inhibit tumor progression activities.We conducted the present study in order to look for bioactive compounds in the medicinal plant Rabdosia excisa.In this study,five compounds were isolated from R.excisa;they were oridonin,isokamebakaurin,oleanolie acid,ursolic acid,and β-sitosterol.In order to identify the function of the extracts,the activity of antibiotics,antioxidation,and immunity test were carried out against these functions.Prospective results were observed in all of the tested items.     

Mre11 and Ku regulation of double-strand break repair by gene conversion and break-induced replication

The yeast Mre11-Rad50-Xrs2 (MRX) and Ku complexes regulate single-strand resection at DNA double-strand breaks (DSB), a key early step in homologous recombination (HR). A prior plasmid gap repair study showed that mre11 mutations, which slow single-strand resection, reduce gene conversion tract lengths and the frequency of associated crossovers. Here we tested whether mre11Delta or nuclease-defective mre11 mutations reduced gene conversion tract lengths during HR between homologous chromosomes in diploid yeast. We found that mre11 mutations reduced the efficiency of HR but did not reduce tract lengths or crossovers, despite substantially reduced end-resection at the test (ura3) locus. End-resection is increased in yku70Delta, but this change also had no effect on tract lengths. Thus, heteroduplex formation and tract lengths are not regulated by the extent of end-resection during DSB repair in a chromosomal context. In a plasmid-chromosome DSB repair assay, tract lengths were again similar in wild-type and mre11Delta, but they were reduced in mre11Delta in a gap repair assay. These results indicate that tract lengths are not affected by the extent of end processing when broken ends can invade nearby sites, perhaps because MRX coordination of the two broken ends is dispensable when ends invade nearby sites. Although HR outcome was largely unaffected in mre11 mutants, break-induced replication (BIR) and chromosome loss increased, suggesting that Mre11 function in mitotic HR is limited to early HR stages. Interestingly, yku70Delta suppressed BIR in mre11 mutants. BIR is also elevated in rad51 mutants, but yku70Delta did not suppress BIR in a rad51 background. These results indicate that Mre11 functions in Rad51-independent BIR, and that Ku functions in Rad51-dependent BIR.     

点叶绵枣叶片培养及器官分化的研究

点叶绵枣叶外植体培养于MS 6-BA 1 PPm IBA 0.5 ppm培养基中,一月后不定芽仅从近轴面的叶表面产生。组织学的观察表明,不定芽起源于表皮细胞。     

A parallel coiled-coil tetramer with offset helices

Specific helix-helix interactions are fundamental in assembling the native state of proteins and in protein-protein interfaces. Coiled coils afford a unique model system for elucidating principles of molecular recognition between alpha helices. The coiled-coil fold is specified by a characteristic seven amino acid repeat containing hydrophobic residues at the first (a) and fourth (d) positions. Nonpolar side chains spaced three and four residues apart are referred to as the 3-4 hydrophobic repeat. The presence of apolar amino acids at the e or g positions (corresponding to a 3-3-1 hydrophobic repeat) can provide new possibilities for close-packing of alpha-helices that includes examples such as the lac repressor tetramerization domain. Here we demonstrate that an unprecedented coiled-coil interface results from replacement of three charged residues at the e positions in the dimeric GCN4 leucine zipper by nonpolar valine side chains. Equilibrium circular dichroism and analytical ultracentrifugation studies indicate that the valine-containing mutant forms a discrete alpha-helical tetramer with a significantly higher stability than the parent leucine-zipper molecule. The 1.35 A resolution crystal structure of the tetramer reveals a parallel four-stranded coiled coil with a three-residue interhelical offset. The local packing geometry of the three hydrophobic positions in the tetramer conformation is completely different from that seen in classical tetrameric structures yet bears resemblance to that in three-stranded coiled coils. These studies demonstrate that distinct van der Waals interactions beyond the a and d side chains can generate a diverse set of helix-helix interfaces and three-dimensional supercoil structures.     

CRSBP-1/LYVE-l-null mice exhibit identifiable morphological and functional alterations of lymphatic capillary vessels

CRSBP-1, a membrane glycoprotein, can mediate cell-surface retention of secreted growth factors containing CRS motifs such as PDGF-BB. CRSBP-1 has recently been found to be identical to LYVE-1, a specific marker for lymphatic capillary endothelial cells. The in vivo role of CRSBP-1/LYVE-1 is unknown. CRSBP-1-null mice are overtly normal and fertile but exhibit identifiable morphological and functional alterations of lymphatic capillary vessels in certain tissues, marked by the constitutively increased interstitial-lymphatic flow and lack of typical irregularly-shaped lumens. The CRSBP-1 ligands PDGF-BB and HA enhance interstitial-lymphatic flow in wild-type mice but not in CRSBP-1-null animals.     

Insulin reverses growth hormone-induced homologous desensitization

Growth hormone (GH) is secreted in a pulsatile pattern to promote body growth and metabolism. GH exerts its function by activating several signaling pathways, including JAK2/STAT and MEK/ERK. ERK1/2 activation by GH plays important roles in gene expression, cell proliferation, and growth. We previously reported that in rat H4IIE hepatoma cells after an initial GH exposure, a second GH exposure induces STAT5 phosphorylation but not ERK1/2 phosphorylation (Ji, S., Frank, S. J., and Messina, J. L. (2002) J. Biol. Chem. 277, 28384-28393). In this study the mechanisms underlying GH-induced homologous desensitization were investigated. A second GH exposure activated the signaling intermediates upstream of MEK/ERK, including JAK2, Ras, and Raf-1. This correlated with recovery of GH receptor levels, but was insufficient for GH-induced phosphorylation of MEK1/2 and ERK1/2. Insulin restored the ability of a second GH exposure to induce phosphorylation of MEK1/2 and ERK1/2 without altering GH receptor levels or GH-induced phosphorylation/activation of JAK2 and Raf-1. GH and insulin synergized in promoting cell proliferation. Further investigation suggested that insulin increased the amount of MEK bound to KSR (kinase suppressor of Ras) and restored GH-induced tyrosine phosphorylation of KSR. Previous GH exposure also induced desensitization of STAT1 and STAT3 phosphorylation, but this desensitization was not reversed by insulin. Thus, insulin-regulated resensitization of GH signaling may be necessary to reset the complete response to GH after a normal, physiologic pulse of GH.