新型免疫抑制剂brasilicardin A的研究进展

Brasilicardin A (BraA)是从致病性放线菌巴西诺卡菌(Nocardia brasiliensis) IFM 0406中发现的具有显著免疫抑制作用(IC50=0.057μg/mL)的二萜糖苷类化合物。BraA发挥免疫抑制活性的作用机制与现有临床常用的免疫抑制剂不同,BraA通过抑制氨基酸转运体L系统的转运进而影响T-淋巴细胞对氨基酸的摄入而发挥免疫抑制作用。相比目前已知的免疫抑制剂环孢菌素A、子囊霉素和他克莫司等,BraA在小鼠混合淋巴细胞反应中显示低毒、高效的优势。因此,BraA作为新型的免疫抑制剂,极具开发潜力,已成为全球免疫抑制剂发现新领域。但其结构复杂、合成困难,原菌种产率低且具有致病性,BraA及其类似物的获得已成为此类新型免疫抑制剂研究的瓶颈。本文综述了BraA的分子特征、药理活性、作用机制、目前获得的BraA类似物和衍生化方面的研究进展,以期为BraA及其类似物的高效生产提供参考。     

Antiproliferative Potential of Olneya tesota PF2 Lectin in Human Acute Monocytic Leukemia Cells

Acute monocytic leukemia is a type of myeloid leukemia that develops in monocytes. The current clinical therapies for leukemia are unsatisfactory due to their side effects and nonspecificity toward target cells. Some lectins display antitumor activity and may specifically recognize cancer cells by binding to carbohydrate structures on their surface. Therefore, this study evaluated the response of the human monocytic leukemia cell lines THP-1 to the Olneya tesota PF2 lectin. The induction of apoptosis and reactive oxygen species production in PF2-treated cells was evaluated by flow cytometry, and the lectin-THP-1 cell interaction and mitochondrial membrane potential were evaluated by confocal fluorescence microscopy. PF2 genotoxicity was evaluated by DNA fragmentation analysis via gel electrophoresis. The results showed that PF2 binds to THP-1 cells, triggers apoptosis and DNA degradation, changes the mitochondrial membrane potential, and increases reactive oxygen species levels in PF2-treated THP-1 cells. These results suggest the potential use of PF2 for developing alternative anticancer treatments with enhanced specificity.     

A robust approach to estimate relative phytoplankton cell abundances from metagenomes

Phytoplankton account for >45% of global primary production, and have an enormous impact on aquatic food webs and on the entire Earth System. Their members are found among prokaryotes (cyanobacteria) and multiple eukaryotic lineages containing chloroplasts. Genetic surveys of phytoplankton communities generally consist of PCR amplification of bacterial (16S), nuclear (18S) and/or chloroplastic (16S) rRNA marker genes from DNA extracted from environmental samples. However, our appreciation of phytoplankton abundance or biomass is limited by PCR-amplification biases, rRNA gene copy number variations across taxa, and the fact that rRNA genes do not provide insights into metabolic traits such as photosynthesis. Here, we targeted the photosynthetic gene psbO from metagenomes to circumvent these limitations: the method is PCR-free, and the gene is universally and exclusively present in photosynthetic prokaryotes and eukaryotes, mainly in one copy per genome. We applied and validated this new strategy with the size-fractionated marine samples collected by Tara Oceans, and showed improved correlations with flow cytometry and microscopy than when based on rRNA genes. Furthermore, we revealed unexpected features of the ecology of these ecosystems, such as the high abundance of picocyanobacterial aggregates and symbionts in the ocean, and the decrease in relative abundance of phototrophs towards the larger size classes of marine dinoflagellates. To facilitate the incorporation of psbO in molecular-based surveys, we compiled a curated database of >18,000 unique sequences. Overall, psbO appears to be a promising new gene marker for molecular-based evaluations of entire phytoplankton communities.     

A chromosome-level genome assembly enables the identification of the follicule stimulating hormone receptor as the master sex-determining gene in the flatfish Solea senegalensis

Sex determination (SD) shows huge variation among fish and a high evolutionary rate, as illustrated by the Pleuronectiformes (flatfishes). This order is characterized by its adaptation to demersal life, compact genomes and diversity of SD mechanisms. Here, we assembled the Solea senegalensis genome, a flatfish of great commercial value, into 82 contigs (614 Mb) combining long- and short-read sequencing, which were next scaffolded using a highly dense genetic map (28,838 markers, 21 linkage groups), representing 98.9% of the assembly. Further, we established the correspondence between the assembly and the 21 chromosomes by using BAC-FISH. Whole genome resequencing of six males and six females enabled the identification of 41 single nucleotide polymorphism variants in the follicle stimulating hormone receptor (fshr) consistent with an XX/XY SD system. The observed sex association was validated in a broader independent sample, providing a novel molecular sexing tool. The fshr gene displayed differential expression between male and female gonads from 86 days post-fertilization, when the gonad is still an undifferentiated primordium, concomitant with the activation of amh and cyp19a1a, testis and ovary marker genes, respectively, in males and females. The Y-linked fshr allele, which included 24 nonsynonymous variants and showed a highly divergent 3D protein structure, was overexpressed in males compared to the X-linked allele at all stages of gonadal differentiation. We hypothesize a mechanism hampering the action of the follicle stimulating hormone driving the undifferentiated gonad toward testis.     

Female control of sperm ejection and retention in the cornsilk fly Euxesta eluta (Diptera: Ulidiidae)

Promiscuous mating systems provide the opportunity for females to bias fertilization toward particular males. However, distinguishing between male sperm competition and active female sperm choice is difficult for species with internal fertilization. Nevertheless, species that store and use sperm of different males in different storing structures and species where females are able to expel all or part of the ejaculates after copulation may be able to bias fertilization. We report a series of experiments aimed at providing evidence of female sperm choice in Euxesta eluta (Hendel), a species of ulidiid fly that expels and consumes ejaculates after copulation. We found no evidence of greater reproductive success for females mated singly, multiply with the same male, or mated multiply with different males. Female E. eluta possesses two spherical spermathecae and a bursa copulatrix for sperm storage, with a ventral receptacle. There was no significant difference in storing more sperm in spermathecae 24 h after copulation than immediately after copulation. Females mated with protein-fed males had greater reproductive success than similar females mated to protein-deprived males. Protein-fed females prevented to consume the ejaculate, retained more sperm when mated to protein-fed males than when mated to protein-deprived males. Our results suggest that female E. eluta can exert control of sperm retention of higher quality males through ejaculate ejection.     

Changes in the structure of ovary tissues and in the ultrastructure of mesocarp cells during ovary senescence or fruit development induced by plant growth substances in Pisum sativum

Structural changes of tissues in unpollinated ovaries of Pisum sativum L. cv. Alaska after treatment with different plant growth substances (gibberellic acid, 2,4-dichlorophenoxyacetic acid, and 6-benzyladenine) or decapitation of the plant were studied. All the treatments resulted in the prevention of cellular disorganization associated with ovary senescence. They effected the enlargement of mesocarp cells and the differentiation of endocarp cells in very similar patterns, suggesting a similar induction of the structural processes involved in fruit development. Ultrastructural changes in mesocarp cells after treatment with gibberellic acid showed that rapid enlargement of mesocarp cells was sustained mainly by a reorganization of the membrane systems directed to the sysnthesis of primary cell wall. Early changes in the subcellular components in mesocarp cells were observed as the first symptoms in ovary senescence.     

INTRACELLULAR AND EXTRACELLULAR AMINO ACID POOLS OF THE MARINE DIATOM PHAEODACTYLUM TRICORNUTUM (BACILLARIOPHYCEAE) GROWN ON UNENRICHED SEAWATER IN HIGH-CELL-DENSITY DIALYSIS CULTURE1

The consumption of inorganic macronutrients (NO₃^?+ NO₂^?, NH₄⁺, and PO₄^?3) and the composition of intra- and extracellular dissolved free amino acid pools (IDFAA and EDFAA, respectively) were determined in continuous-reservoir batch dialysis cultures of the marine diatom Phaeodactylum tricornutum Bohlin maintained on unenriched natural seawater as a growth medium. Nutrient diffusion (Nd), which equals the nutrient uptake of the culture, increased with the cell density and the age of the culture. A concentration of 6.77 × 10⁷ cells · mL^?1 was obtained in stationary phase, which coincided with the NO₃^?+ NO₂^? diffusion limit (Nd_max) of the dialysis apparatus. The Nd_max for NH₄⁺ occurred much earlier, at the end of exponential growth, whereas Nd_max for PO₄^?3 was not attained during the growth cycle of the culture, even in early stationary phase. A significant depletion (77%) of the IDFAA pool during exponential phase was followed by a reestablishment–to approximately 60% of the initial level–of internal pools during linear and stationary growth phases. This recovery occurred during the illuminated portion of the photoperiod (12:12 h LD) and involved principally the amino acids GLN, GLU, β-GLU, and ASN. The recovery of GLN and ASN levels was particularly significant, because the intracellular concentrations of these amino acids were higher at the end of the growth cycle than before. The EDFAA pool was generally dominated by the amino acids SER and GLY+THR; however, during active growth, ORN and LYS often constituted an important fraction. The EDFAA concentration increased until linear growth phase was reached, during which a higher concentration of total free amino acids was attained in darkness than under illumination. The EDFAA component diminished afterward, and in stationary phase this fraction returned to concentrations equivalent to those observed at the beginning of the growth cycle. The variations in EDFAA concentrations were expressed by a pronounced decrease in the cellular excretion of amino acids with increasing cell density. These cellular responses of Phaeodactylum tricornutum in dense culture, specifically the regulation of amino acid excretion and intracellular pool size, may affect the N-conversion coefficient (Y_N). Consequently, by prolonging the linear phase of growth and reducing the concentration of autoinhibitory metabolites by diffusion, a markedly enhanced final cell density can be achieved in cultures grown on natural unenriched seawater.     

Plant preference in relation to life history traits in the zoophytophagous predator Dicyphus hesperus

Dicyphus hesperus Knight (Heteroptera: Miridae) is an omnivorous predator used to control pests of greenhouse vegetables. Plant preferences and life history traits were studied using nine plant species: Lycopersicon esculentum Mill. (Solanaceae), Capsicum annuum L. (Solanaceae), Verbascum thapsus L. (Scrophulariaceae), Nepeta cataria L. (Lamiaceae), Stachys albotomentosa (Lamiaceae), Nicotiana tabacum L. (Solanaceae), Vicia sativa L. (Fabaceae), Zea mays L. (Gramineae), and Chrysanthemum coronarium L. (Asteraceae). Plants were selected from among potential target crops, natural hosts, plants used for mass rearing, and plants on which D. hesperus has not been reported. Plant preference was measured by multi‐choice host plant selection and oviposition assays. Development and reproduction were measured on each of the plant species on both a plant diet alone and on a plant diet supplemented with Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) eggs. Dicyphus hesperus females and nymphs expressed a preference for some plants over others. Plant preference ranged from low preference plants, such as Z. mays, V. sativa, C. coronarium, and C. annuum, to high preference plants such as V. thapsus, N. tabacum, and S. albotomentosa. When E. kuehniella eggs were supplied, there were few differences in the development time and fecundity of D. hesperus among plants, with the exception of corn and broad bean, where fecundity was lower. On a plant diet alone, nymphs were able to complete their development on V. thapsus, C. annuum, and N. cataria. However, mortality and development time were much lower on V. thapsus than on C. annuum and N. cataria. On most of the plant species D. hesperus did not lay any eggs when fed on a plant diet alone. On V. thapsus, females laid a few eggs and lived longer than when fed on prey. Dicyphus hesperus females tended to prefer host plants on which nymph survival without prey was greatest.     

Properties of a Large Complex with NADH Dehydrogenase Activity from Barley Thylakoids

When assays for NAD(P)H-ferricyanide oxidoreductases were performed,activities specific for NADH (0.23 unit (mg protein)^–1)and NADPH (0.68 unit (mg protein)^–1) were detected inchloroplasts isolated from leaves of barley (Hordeum vulgareL.). Activities of chloroplast NADH- and NADPH-ferricyanideoxidoreductase were 5-fold and 25-fold higher, respectively,than the maximum activity that could be attributed to mitochondrialcontamination. Moreover, most of the chloroplast NADH-ferricyanideoxidoreductase (60 to 80%) was solubilized by deoxycholate (DOC)from thylakoids as a single, high-molecular-mass complex thatwas distinguishable from the mitochondrial complex by its lowerelectrophoretic mobility in 3% polyacrylamide, as revealed byreduction of nitro blue tetrazolium (NBT) in the presence ofNADH or NADPH on gels after electrophoresis. The stroma yieldeda single band of a dehydrogenase (66 kDa) that used NADH asits electron donor. Several NADPH-dependent activities weredetected after electrophoresis of the stromal fraction. Moreover,chloroplast-specific activities could be distinguished frommitochondrial activities on the basis of the specificity ofthe donor and the acceptor of electrons, the dependence of theactivities on pH, and the sensitivity to various inhibitors.K_m values for NADH (26 µM) and NADPH (75 µM) werein the same range as those of mitochondrial activities. Mostof the NADPH-dependent activity probably corresponds to thechloroplast ferredoxin-NADP⁺ oxidoreductase. The possibilityis discussed that thylakoid NADH dehydrogenase(s) might be theproduct of chloroplast ndh genes and that this activity is involvedin chlororespiration. (Received April 25, 1994; Accepted December 5, 1994)