Molecular biological mechanisms of speciation

Growing recognition that much of the evolutionary history of eukaryotic genomes reflects the operation of turnover processes involving repetitive DNA sequences has led to the recent formulation of models describing speciation as a consequence of such turnover. These models are of three general kinds: those attributing hybrid infertility to the process of transposition, those attributing hybrid infertility to mispairing between chromosomes of divergent repetitive DNA composition, and those assuming that change in repetitive DNA's can reset coordinated gene regulation. These models are discussed with respect to the kinds of evidence needed for their corroboration and to their significance for questions related to macroevolutionary punctuated equilibria and genetic revolutions.     

Molecular mechanisms of axon guidance

Axons are guided along specific pathways by attractive and repulsive cues in the extracellular environment. Genetic and biochemical studies have led to the identification of highly conserved families of guidance molecules, including netrins, Slits, semaphorins, and ephrins. Guidance cues steer axons by regulating cytoskeletal dynamics in the growth cone through signaling pathways that are still only poorly understood. Elaborate regulatory mechanisms ensure that a given cue elicits the right response from the right axons at the right time but is otherwise ignored. With such regulatory mechanisms in place, a relatively small number of guidance factors can be used to generate intricate patterns of neuronal wiring.     

Molecular mechanisms of the biological clock in cultured fibroblasts

In mammals, the central circadian pacemaker resides in the hypothalamic suprachiasmatic nucleus (SCN), but circadian oscillators also exist in peripheral tissues. Here, using wild-type and cryptochrome (mCry)-deficient cell lines derived from mCry mutant mice, we show that the peripheral oscillator in cultured fibroblasts is identical to the oscillator in the SCN in (i) temporal expression profiles of all known clock genes, (ii) the phase of the various mRNA rhythms (i.e., antiphase oscillation of Bmal1 and mPer genes), (iii) the delay between maximum mRNA levels and appearance of nuclear mPER1 and mPER2 protein, (iv) the inability to produce oscillations in the absence of functional mCry genes, and (v) the control of period length by mCRY proteins.     

Molecular and cellular mechanisms of leukocyte chemotaxis

The application of modern scientific methods to the study of leukocyte function has begun to reveal the molecular and cytostructural bases of the chemotactic responses of these cells. Leukocyte chemotaxis is initiated by the binding of chemoattractants to distinct plasma membrane receptors; this finding alters transmembrane potential and activates ionic fluxes. The subsequent sequence of metabolic processes leads to a rearrangement of cytoskeletal elements that is manifested by orientation and migration of the cells toward the source of the chemotactic gradient.     

一类带功能性捕食者-食饵系统解的渐近性

研究了一类带功能性的具有周期系数的捕食者-食饵系统,系统捕食者和食饵2个物种在有界区域Ω内的相互作用．应用周期上、下解方法讨论系统的解的长时间渐近行为,得到相应的正解在拟解之间．     

Molecular mechanisms and forces involved in the adhesion and fusion of amphiphilic bilayers

The surface forces apparatus technique was used for measuring the adhesion, deformation, and fusion of bilayers supported on mica surfaces in aqueous solutions. The most important force leading to the direct fusion of bilayers is the hydrophobic interaction, although the occurrence of fusion is not simply related to the force law between bilayers. Bilayers do not need to "overcome" some repulsive force barrier, such as hydration, before they can fuse. Instead, once bilayer surfaces come within about 1 nanometer of each other, local deformations and molecular rearrangements allow them to "bypass" these forces.     

基于转录组测序解析南瓜子叶黄化的分子机理

为研究南瓜叶色黄化突变的机制，挖掘黄化相关关键基因，试验以南瓜自然黄化突变体为试材，通过高通量RNA测序(RNA-seq)对苗期子叶进行转录组分析。结果表明：从检测的26 445个表达基因中鉴定出12 687个差异表达基因(DEGs),包括6 444个上调基因，6 243个下调基因；其中2 321个DEGs是转录因子编码基因。选取14个与光合色素密切相关的DEGs进行实时荧光定量PCR(qRT-PCR)分析，发现它们的基因表达水平与转录组测序结果一致。经KEGG富集分析，发现卟啉和叶绿素(Chl)生物合成、光系统Ⅰ、光系统Ⅱ、光合作用-天线蛋白、电子传递和F型ATP酶相关基因的表达显著下调。谷氨酰-tRNA还原酶、镁离子螯合酶、叶绿素a加氧酶基因异常表达，血红素代谢相关基因表达上调抑制了Chl合成；β-胡萝卜素3-羟基酶促进了类胡萝卜素生成；另外，光合作用过程受阻也反馈抑制Chl合成，Chl合成受阻和类胡萝卜素合成受促导致南瓜叶色黄化。研究结果为南瓜黄化突变的分子机制提供了新的见解，为关键基因功能分析和南瓜育种奠定了基础。     

蒙古扁桃菌根苗对干旱胁迫的分子响应机制

【目的】探明菌根对蒙古扁桃(Prunus mongolica)抗旱能力影响的分子机制。【方法】对生长45 d的菌根化蒙古扁桃与非菌根化蒙古扁桃进行非干旱胁迫和干旱胁迫处理,非干旱胁迫蒙古扁桃在处理期间每天补充水分;干旱胁迫处理蒙古扁桃从培育45 d开始停止浇水,模拟自然干旱胁迫,持续时间15 d。试验结束后,每个处理选12株进行叶长、叶宽、叶片脱落数及生物量的测定和统计;另选12株采用高通量测序方法进行转录组测序,并对其差异表达转录本进行GO和KEGG富集分析。【结果】干旱胁迫条件下,菌根化苗木底部的一些叶片会脱落,而非菌根化苗木叶片几乎不脱落;同时,菌根化苗木的地下生物量显著高于非菌根化苗木。通过高通量测序发现,4个处理文库共获得43 641个转录本;在P0.001时,菌根化蒙古扁桃干旱胁迫(MD)与非干旱胁迫(MCK)处理相比,存在820个差异表达转录本;干旱胁迫条件下,菌根化苗木(MD)与非菌根化苗木(ND)相比,存在3 751个差异表达转录本;非干旱胁迫条件下,菌根化苗木(MCK)与非菌根化苗木(NCK)相比,存在2 315个差异表达转录本。GO富集分析发现,MD与ND处理文库间的细胞组分、分子功能和生化过程3类主要功能分类的差异表达转录本,较MD与MCK处理文库间均增加;MCK与NCK处理文库间差异转录本的分类结果同MD与ND处理文库间基本相同,只是在分子功能分类中多出通道调节活性这一功能。经KEGG富集分析发现,天线蛋白、类胡萝卜素生物合成途径、激素信号传导途径、N代谢途径、过氧化物酶体、植物昼夜节律和MAPK信号途径等与干旱胁迫存在密切联系。实时荧光定量PCR表明转录组测序数据可靠。【结论】菌根化处理可以提高蒙古扁桃的抗旱能力。     

体细胞Caspase-3信号通路及DNA甲基化调控卵泡闭锁的分子机制

为了揭示caspase-3等细胞凋亡相关基因及DNA甲基化水平在小鼠卵泡闭锁中的作用,小鼠经注射10 IU hCG后,在0、12、24、48、72和96 h解剖取出卵巢,用HE染色、DNA电泳、免疫组化、RT-PCR技术、甲基化酶切等试验方法,研究在卵泡发育及闭锁过程中caspase-3等凋亡相关基因的表达及DNA甲基化水平的变化.结果表明:bax、caspase-3的表达量在48 h以前持续减少,在48 h达到最低值,在72 h显著增多(P<0.05),且在卵腔液中大量表达;甲基化水平在48 h以前持续减少,在48 h达到最低值,在72 h显著增多(P<0.05);卵泡凋亡程度在48 h之前也持续减少,在72 h显著增多(P<0.05).bcl-2的表达量在48 h之前持续增加,在72 h显著减少(P<0.05).提示:卵泡的发育和闭锁可能受体细胞Caspase信号通路调控,并通过卵腔液发挥作用决定其存亡;另外,甲基化水平的改变可能与卵泡的闭锁直接相关.     

尿素-SDS—PAGE测定小分子多肽相对分子质量方法的建立

试验旨在建立一种简易快速测定小分子多肽相对分子质量的SDS—PAGE电泳方法。通过改进分离胶交联度为6％,丙烯酰胺总浓度为15％,并加入6％的尿素,对所测得的多肽相对分子质量进行线性回归分析。结果表明,得到的标准曲线线性相关系数R2达到0．9938,测得条带的相对分子质量分别为9．2129kD,建立的方法操作简单、耗时短,且小分子多肽成像清晰,是一种具有很高实用价值的测定方法。     

生物炭添加下枯草芽孢杆菌应对镉胁迫的分子机制

为了探究生物炭添加前后枯草芽孢杆菌应对镉胁迫的分子机制，本研究基于转录组测序，对比分析了枯草芽孢杆菌在4种体系（正常体系、镉胁迫体系、生物炭体系、生物炭-镉胁迫体系）中的基因表达差异。结果表明：在镉胁迫压力下，枯草芽孢杆菌共产生1 932个差异表达基因，其中上调基因967个，下调基因965个。枯草芽孢杆菌的代谢活性受到明显抑制，但是其鞭毛组装和细菌趋化性通路明显增强，离子转运和阳离子跨膜转运蛋白功能条目的基因表达也呈现上调，说明枯草芽孢杆菌通过上调细胞运动及离子转运相关基因的表达来规避镉毒性压力。相比于镉胁迫体系，在生物炭-镉胁迫体系中，细菌共产生1 541个差异表达基因，其中上调基因691个，下调基因850个。生物炭的存在增强了枯草芽孢杆菌生物过程、细胞组分和分子功能基因的表达，枯草芽孢杆菌物质和能源代谢相关通路的基因表达均呈现上调，并且细菌体内镉抗性基因czcD、cadA和膜功能相关差异基因的表达也以上调为主，说明生物炭可以缓解镉胁迫对枯草芽孢杆菌的毒性效应，并可刺激枯草芽孢杆菌的金属抗性能力。     

Molecular mechanisms controlling seed set in cereal crop species under stress and non-stress conditions

Maximizing seed yield is the ultimate breeding goal in important cereal crop species. Seed set is a key developmental stage in the process of seed formation, which determines grain number, seed mass, and realized yield potential, and can be severely affected by abiotic and biotic stresses. However, seed set can also be substantially reduced by genetic factors even under optimal fertilization conditions. The underlying molecular genetic mechanisms are still obscure. In this review, we elucidate the process of seed set of cereal crop species in detail, including development of floral structures, formation of viable gametes, double fertilization, seed development, and abortion. We discuss how genetic and non-genetic factors affect seed set in different development stages. Finally, we will propose novel strategies to study genetic mechanisms controlling seed set and exploit genetic resources to improve seed set in cereal crop species.     

抑制杨木APMP纸浆返黄技术的研究(Ⅰ)——助剂处理对黑杨APMP纸浆返黄的抑制作用

为减少APMP纸浆的返黄 ,该文主要研究了使用紫外光吸收剂、自由基清除剂等助剂处理黑杨APMP纸浆后 ,对其干 湿热和光返黄的抑制作用效果 .抗坏血酸可促进纸浆干 湿热返黄 ,在较大用量下 ,抗坏血酸及次亚磷酸钠对纸浆具有一定的光稳定作用 ;聚乙二醇对纸浆的光稳定效果较差 .对比研究几种紫外光吸收剂抑制纸浆光诱导返黄作用效果 ,ZW 1和ZW 2优于其它紫外光吸收剂 ,ZW 1在较低用量时对纸浆就有着较好的光稳定效果 ;较大用量下 ,ZW 2处理的纸浆抗长时间光老化能力略优于ZW 1.综合比较 ,所用助剂单独处理抑制黑杨APMP纸浆光诱导返黄能力大小排序为 :ZW 1>ZW 2 >抗坏血酸 >次亚磷酸钠 >ZW 3 >ZW 4>聚乙二醇     

环保型饲料添加剂研究进展

抗生素作为抗菌促生长剂添加到饲粮中,具有显著的防病、促生长作用.随着科学的发展和认识的深入,抗生素在饲料中长期使用的弊端也逐渐被人们所认识.     

浅析农业多功能性与农业结构调整

分析了国内外现代农业的发展趋势,阐述了农业多功能性在农业结构调整中的应用,并提出了基于农业多功能性的农业结构调整建议。     

浅析食品添加剂在饮料中的应用

阐述饮料里有代表性的食品添加剂、及其在果蔬汁饮料、碳酸饮料、蛋白饮料中运用和危害,然后对食品添加剂发展趋向进行了展望。     

Optimization of the compositions of meat products with food additives

Data are given on optimizing multicomponent compositions of meat products with the use of modern method of processing experimental data based on adapted artificial intelligence methodology.     

Molecular evidence for the early evolution of photosynthesis

The origin and evolution of photosynthesis have long remained enigmatic due to a lack of sequence information of photosynthesis genes across the entire photosynthetic domain. To probe early evolutionary history of photosynthesis, we obtained new sequence information of a number of photosynthesis genes from the green sulfur bacterium Chlorobium tepidum and the green nonsulfur bacterium Chloroflexus aurantiacus. A total of 31 open reading frames that encode enzymes involved in bacteriochlorophyll/porphyrin biosynthesis, carotenoid biosynthesis, and photosynthetic electron transfer were identified in about 100 kilobase pairs of genomic sequence. Phylogenetic analyses of multiple magnesium-tetrapyrrole biosynthesis genes using a combination of distance, maximum parsimony, and maximum likelihood methods indicate that heliobacteria are closest to the last common ancestor of all oxygenic photosynthetic lineages and that green sulfur bacteria and green nonsulfur bacteria are each other's closest relatives. Parsimony and distance analyses further identify purple bacteria as the earliest emerging photosynthetic lineage. These results challenge previous conclusions based on 16S ribosomal RNA and Hsp60/Hsp70 analyses that green nonsulfur bacteria or heliobacteria are the earliest phototrophs. The overall consensus of our phylogenetic analysis, that bacteriochlorophyll biosynthesis evolved before chlorophyll biosynthesis, also argues against the long-held Granick hypothesis.     

Molecular determinants for the tissue specificity of SERMs

Selective estrogen receptor modulators (SERMs) mimic estrogen action in certain tissues while opposing it in others. The therapeutic effectiveness of SERMs such as tamoxifen and raloxifene in breast cancer depends on their antiestrogenic activity. In the uterus, however, tamoxifen is estrogenic. Here, we show that both tamoxifen and raloxifene induce the recruitment of corepressors to target gene promoters in mammary cells. In endometrial cells, tamoxifen, but not raloxifene, acts like estrogen by stimulating the recruitment of coactivators to a subset of genes. The estrogen-like activity of tamoxifen in the uterus requires a high level of steroid receptor coactivator 1 (SRC-1) expression. Thus cell type- and promoter-specific differences in coregulator recruitment determine the cellular response to SERMs.