马卵母细胞体外成熟的初步研究

采用抽吸法和切割法两种采卵方法收集马卵母细胞,显示采用切割法的卵母细胞回收率为83%,高于抽吸法的回收率46.5%(P＜0.05),在卵母细胞的成熟上,使用M199和DMEM/F12两种培养液为基础液的成熟体系,紧凑型(Cp)COCs和扩展型(Ex)COCs在以M199为基础液和以DMEM/F12为基础液的培养液中的卵母细胞成熟率分别为41.7%和64.7%、46.7%和66.7%,差异不显著(P＞0.05).两种培养体系中成熟的Cp COCs采用Ionomycin与6-DMAP和CHX联合激活,在以M199和以DMEM/F12为基础液的培养液中成熟的卵母细胞的卵裂率分别为45%和57.1%,差异不明显(P＞0.05).     

Cardiomyocyte-restricted restoration of nitric oxide synthase 3 attenuates left ventricular remodeling after chronic pressure overload

Although nitric oxide synthase (NOS)3 is implicated as an important modulator of left ventricular (LV) remodeling, its role in the cardiac response to chronic pressure overload is controversial. We examined whether selective restoration of NOS3 to the hearts of NOS3-deficient mice would modulate the LV remodeling response to transverse aortic constriction (TAC). LV structure and function were compared at baseline and after TAC in NOS3-deficient (NOS3(-/-)) mice and NOS3(-/-) mice carrying a transgene directing NOS3 expression specifically in cardiomyocytes (NOS3(-/-TG) mice). At baseline, echocardiographic assessment of LV dimensions and function, invasive hemodynamic measurements, LV mass, and myocyte width did not differ between the two genotypes. Four weeks after TAC, echocardiographic and hemodynamic indexes of LV systolic function indicated that contractile performance was better preserved in NOS3(-/-TG) mice than in NOS3(-/-) mice. Echocardiographic LV wall thickness and cardiomyocyte width were greater in NOS3(-/-) mice than in NOS3(-/-TG) mice. TAC-induced cardiac fibrosis did not differ between these genotypes. TAC increased cardiac superoxide generation in NOS3(-/-TG) but not NOS3(-/-) mice. The ratio of NOS3 dimers to monomers did not differ before and after TAC in NOS3(-/-TG) mice. Restoration of NOS3 to the heart of NOS3-deficient mice attenuates LV hypertrophy and dysfunction after TAC, suggesting that NOS3 protects against the adverse LV remodeling induced by prolonged pressure overload.     

Physiological responses of the freshwater N2-fixing cyanobacterium Raphidiopsis raciborskii to Fe and N availabilities

The cyanobacterium Raphidiopsis raciborskii is of environmental and social concern in view of its toxicity, bloom-forming characteristics and increasingly widespread occurrence. However, while availability of macronutrients and micronutrients such as N and Fe are critically important for the growth and metabolism of this organism, the physiological response of toxic and non-toxic strains of R. raciborskii to varying Fe and N availabilities remains unclear. By determining physiological parameters as a function of Fe and N availability, we demonstrate that R. raciborskii growth and N₂-fixing activity are facilitated at higher Fe availability under N₂-limited conditions with faster growth of the CS-506 (cylindrospermopsin-producing) strain compared with that of CS-509 (the non-toxic) strain. Radiolabelled Fe uptake assays indicated that R. raciborskii acclimated under Fe-limited conditions acquires Fe at significantly higher rates than under Fe replete conditions, principally via unchelated Fe(II) generated as a result of photoreduction of complexed Fe(III). While N₂-fixation of both strains occurred during both day and night, the CS-506 strain overall exhibited higher N₂-fixing and Fe uptake rates than the CS-509 strain under N-deficient and Fe-limited conditions. The findings of this study highlight that Fe availability is of significance for the ecological advantage of CS-506 over CS-509 in N-deficient freshwaters.     

Genetic diversity, morphological uniformity and polyketide production in dinoflagellates (Amphidinium, Dinoflagellata)

Dinoflagellates are an intriguing group of eukaryotes, showing many unusual morphological and genetic features. Some groups of dinoflagellates are morphologically highly uniform, despite indications of genetic diversity. The species Amphidinium carterae is abundant and cosmopolitan in marine environments, grows easily in culture, and has therefore been used as a 'model' dinoflagellate in research into dinoflagellate genetics, polyketide production and photosynthesis. We have investigated the diversity of 'cryptic' species of Amphidinium that are morphologically similar to A. carterae, including the very similar species Amphidinium massartii, based on light and electron microscopy, two nuclear gene regions (LSU rDNA and ITS rDNA) and one mitochondrial gene region (cytochrome b). We found that six genetically distinct cryptic species (clades) exist within the species A. massartii and four within A. carterae, and that these clades differ from one another in molecular sequences at levels comparable to other dinoflagellate species, genera or even families. Using primers based on an alignment of alveolate ketosynthase sequences, we isolated partial ketosynthase genes from several Amphidinium species. We compared these genes to known dinoflagellate ketosynthase genes and investigated the evolution and diversity of the strains of Amphidinium that produce them.     

Endolithic Phototrophs in Built and Natural Stone

Lichens, algae and cyanobacteria have been detected growing endolithically in natural rock and in stone buildings in various countries of Australasia, Europe and Latin America. Previously these organisms had mainly been described in natural carbonaceous rocks in aquatic environments, with some reports in siliceous rocks, principally from extremophilic regions. Using various culture and microscopy methods, we have detected endoliths in siliceous stone, both natural and cut, in humid temperate and subtropical climates. Such endolithic growth leads to degradation of the stone structure, not only by mechanical means, but also by metabolites liberated by the cells. Using in vitro culture, transmission, optical and fluorescence microscopy, and confocal laser scanning microscopy, both coccoid and filamentous cyanobacteria and algae, including Cyanidiales, have been identified growing endolithically in the facades of historic buildings built from limestone, sandstone, granite, basalt and soapstone, as well as in some natural rocks. Numerically, the most abundant are small, single-celled, colonial cyanobacteria. These small phototrophs are difficult to detect by standard microscope techniques and some of these species have not been previously reported within stone.     

Bioactive Natural Products from Papua New Guinea Marine Sponges

The discovery of novel natural products for drug development relies heavily upon a rich biodiversity, of which the marine environment is an obvious example. Marine natural product research has spawned several drugs and many other candidates, some of which are the focus of current clinical trials. The sponge megadiversity of Papua New Guinea is a rich but underexplored source of bioactive natural products. Here, we review some of the many natural products derived from PNG sponges with an emphasis on those with interesting biological activity and, therefore, drug potential. Many bioactive natural products discussed here appear to be derived from non‐ribosomal peptide and polyketide biosynthesis pathways, strongly suggesting a microbial origin of these compounds. With this in mind, we also explore the notion of sponge‐symbiont biosynthesis of these bioactive compounds and present examples to support the working hypothesis.     

Identification of a Saxitoxin Biosynthesis Gene with a History of Frequent Horizontal Gene Transfers

The paralytic shellfish poisoning (PSP) toxins, saxitoxin, and its derivatives, are produced by a complex and unique biosynthetic pathway. It involves reactions that are rare in other metabolic pathways, however, distantly related organisms, such as dinoflagellates and cyanobacteria, produce these toxins by an identical pathway. Speculative explanations for the unusual phylogenetic distribution of this metabolic pathway have been proposed, including a polyphyletic origin, the involvement of symbiotic bacteria, and horizontal gene transfer. This study describes for the first time the identity of one gene, sxt1, that is involved in the biosynthesis of saxitoxin in cyanobacteria. It encoded an O-carbamoyltransferase (OCTASE) that was proposed to carbamoylate the hydroxymethyl side chain of saxitoxin precursor. Orthologues of sxt1 were exclusively present in PSP-toxic strains of cyanobacteria and had a high sequence similarity to each other. L. wollei had a naturally mutated sxt1 gene that encoded an inactive enzyme, and was incapable of producing carbamoylated PSP-toxin analogues, supporting the proposed function of Sxt1. Phylogenetic analysis revealed that OCATSE genes were present exclusively in prokaryotic organisms and were characterized by a high rate of horizontal gene transfer. OCTASE has most likely evolved from an ancestral O-sialoglycoprotein endopeptidase from proteobacteria, whereas the most likely phylogenetic origin of sxt1 was an ancestral alpha-proteobacterium. The phylogeny of sxt1 suggested that the entire set of genes required for saxitoxin biosynthesis may spread by horizontal gene transfer.     

Characterization of the Gene Cluster Responsible for Cylindrospermopsin Biosynthesis

Toxic cyanobacterial blooms cause economic losses and pose significant public health threats on a global scale. Characterization of the gene cluster for the biosynthesis of the cyanobacterial toxin cylindrospermopsin (cyr) in Cylindrospermopsis raciborskii AWT205 is described, and the complete biosynthetic pathway is proposed. The cyr gene cluster spans 43 kb and is comprised of 15 open reading frames containing genes required for the biosynthesis, regulation, and export of the toxin. Biosynthesis is initiated via an amidinotransfer onto glycine followed by five polyketide extensions and subsequent reductions, and rings are formed via Michael additions in a stepwise manner. The uracil ring is formed by a novel pyrimidine biosynthesis mechanism and tailoring reactions, including sulfation and hydroxylation that complete biosynthesis. These findings enable the design of toxic strain-specific probes and allow the future study of the regulation and biological role of cylindrospermopsin.     

黑素皮质素受体-4的研究进展

黑素皮质素受体 4 (MC4R)是人类中枢神经系统中参与调节肥胖症发生的重要因素 ,可调节动物的体重和采食量。自MC4R基因克隆以来 ,学者们对MC4R的结构 ,生理功能 ,调控 ,作用机制及其基因突变与体重的关系等方面进行了大量的研究。     

用酵母双杂交系统筛选影响apo-AI和SR-BI相互作用的苦豆子活性成分

本文通过将苦豆子总提取物及其分离得到的10个组分加入含有AH109菌株(携带大鼠apo-AI及其受体SR-BI全基因)的培养基中,利用报告基因半乳糖苷酶活力有无变化来寻找能够促进大鼠载脂蛋白apo-AI及其受体SR-BI相互作用的激动剂.经测试,我们观察到苦豆子总提取物(K-1),在上述系统中能显著增强这两种蛋白的相互作用.继续用硅胶柱层析方法从k-1中分出10个组分后,利用酵母双杂交系统再次筛选,发现有五个组分能增强两种蛋白的相互作用,(与空白对照组相比其中有两个组分有极显著差异)另外三个组分显著地抑制上述两种蛋白的相互作用,剩下的两个组分则没有差异.该实验还提示该酵母双杂交系统可能成为一种跟踪具有调脂功能的先导化合物的有效方法.