scabrous modifies epithelial cell adhesion and extends the range of lateral signalling during development of the spaced bristle pattern in Drosophila.

The role of scabrous (sca) in the evenly spaced bristle pattern of Drosophila is explored. Loss-of-function of sca results in development of an excess of bristles. Segregation of alternately spaced bristle precursors and epidermal cells from a group of equipotential cells relies on lateral inhibition mediated by Notch and Delta (Dl). In this process, presumptive bristle precursors inhibit the neural fate of neighbouring cells, causing them to adopt the epidermal fate. We show that Dl, a membrane-bound ligand for Notch, can inhibit adjacent cells, in direct contact with the precursor, in the absence of Sca. In contrast, inhibition of cells not adjacent to the precursor requires, in addition, Sca, a secreted molecule with a fibrinogen-related domain. Over-expression of Sca in a wild-type background, leads to increased spacing between bristles, suggesting that the range of signalling has been increased. scabrous acts nonautonomously, and we present evidence that, during bristle precursor segregation, Sca is required to maintain the normal adhesive properties of epithelial cells. The possible effects of such changes on the range of signalling are discussed. We also show that the sensory organ precursors extend numerous fine cytoplasmic extensions bearing Dl molecules, and speculate on a possible role for these structures during signalling.     

On the roles of Notch, Delta, kuzbanian, and inscuteable during the development of Drosophila embryonic neuroblast lineages

The generation of cellular diversity in the nervous system involves the mechanism of asymmetric cell division. Besides an array of molecules, including the Par protein cassette, a heterotrimeric G protein signalling complex, Inscuteable plays a major role in controlling asymmetric cell division, which ultimately leads to differential activation of the Notch signalling pathway and correct specification of the two daughter cells. In this context, Notch is required to be active in one sibling and inactive in the other. Here, we investigated the requirement of genes previously known to play key roles in sibling cell fate specification such as members of the Notch signalling pathway, e.g., Notch (N), Delta (Dl), and kuzbanian (kuz) and a crucial regulator of asymmetric cell division, inscuteable (insc) throughout lineage progression of 4 neuroblasts (NB1-1, MP2, NB4-2, and NB7-1). Notch-mediated cell fate specification defects were cell-autonomous and were observed in all neuroblast lineages even in cells born from late ganglion mother cells (GMC) within the lineages. We also show that Dl functions non-autonomously during NB lineage progression and clonal cells do not require Dl from within the clone. This suggests that within a NB lineage Dl is dispensable for sibling cell fate specification. Furthermore, we provide evidence that kuz is involved in sibling cell fate specification in the central nervous system. It is cell-autonomously required in the same postmitotic cells which also depend on Notch function. This indicates that KUZ is required to facilitate a functional Notch signal in the Notch-dependent cell for correct cell fate specification. Finally, we show that three neuroblast lineages (NB1-1, NB4-2, and NB7-1) require insc function for sibling cell fate specification in cells born from early GMCs whereas insc is not required in cells born from later GMCs of the same lineages. Thus, there is differential requirement for insc for cell fate specification depending on the stage of lineage progression of NBs.     

A late role for a subset of neurogenic genes to limit sensory precursor recruitments in Drosophila embryos

Summary In Drosophila, mutations in a class of genes, the neurogenic genes, produce an excess of neurons. This neural hyperplasia has been attributed to the formation of more than the normal number of neuronal precursor cells at the expense of epidermal cells. In order to find out whether the neurogenic genes only act at this intial step of neurogenesis, we studied the replication pattern of the sensory organ precursor cells by monitoring BrdU incorporation in embryos mutant for Notch (N), Delta (Dl), mastermind (mam), almondex (amx), neuralized (neu), big brain (bib) and the Enhancer of split-Complex (E(spl)-C). Using temperature sensitive alleles of two of the neurogenic genes, DI and N, we also induced an acute increase of replicating sensory precursors by shifting briefly to the restricted temperature. We have found that the loss of function of all the seven neurogenic loci that were tested causes an increase in replicating sensory precursor cells, consistent with the model that these neurogenic genes normally participate in the process of restricting the number of neuronal precursors. Whereas the temporal pattern of replication appeared normal in mutants of five of the seven neurogenic loci, in N and mam embryos replicating PNS cells are present beyond the time when they normally undergo replication. Experiments with colchicine suggest that many of these late replicating cells may be newly emerging precursors and probably not additional cell divisions of already recruited precursors. Thus, different neurogenic genes may be required over different periods of time for the specification of sensory precursor cells. Correspondence to: R. Bodmer     

Arrangement of bristles as a function of bristle number on a leg segment inDrosophila melanogaster

Summary The arrangement of bristles on a leg segment of the fruitflyDrosophila melanogaster was studied in various mutants that have abnormal numbers of bristles on this segment. Eighteen mutations at six different genetic loci were analyzed, plus five double or triple mutant combinations. Recessive mutations at theachaete-scute locus were found to affect distinct groups of bristles:achaete mutations remove mechanosensory bristles, whereasscute mutations remove mainly chemosensory bristles. Mechanosensory bristles remain uniformly spaced along the longitudinal axis unless their number decreases below a certain threshold, suggesting that spacing is controlled by cell interactions that cannot function when bristle cells are too far apart. Above a certain threshold, bristle spacing and alignment both become irregular, perhaps due to excessive force from these same interactions. Chemosensory bristles occupy definite positions that are virtually unaffected by removal of individual bristles from the array. Extra chemosensory bristles develop only near the six normal sites. At two of the six sites the multiple bristles tend to exhibit uniform longitudinal spacing — a property confined to mechanosensory bristles in wild-type flies. To explain the various mutant phenotypes the following scheme is proposed, with different mutations directly or indirectly affecting each step: (1) spots and stripes are demarcated within the pattern area, (2) one bristle cell normally arises within each spot, multiple bristle cells within each stripe, (3) incipient bristle cells inhibit neighboring cells from becoming bristle cells, and (4) the bristle cells within each stripe become aligned to form rows and then repel one another to generate uniform spacing.     

新疆14种青兰属植物叶表皮微形态结构研究

应用光学显微镜和扫描电镜,对新疆14种青兰属(DracocephalumL.)植物叶片的微形态特征进行观察,结果表明:该属植物只有宽齿青兰(Dracocephalum paulsenii Briq.)叶的下表皮细胞为多边形,其余种植物叶的上、下表皮均为不规则形;垂周壁式样有深波状、波状、浅波状、平直-弓形;气孔器均为横列型;气孔形状有椭圆形、长椭圆形、宽椭圆形、近圆形;表皮毛的类型为小刺毛、短柔毛、长柔毛、头状腺毛和盾状腺毛。在不同种间甚至是同种植物叶的上、下表皮上,气孔器的大小、气孔密度、气孔指数、气孔外拱盖内缘、表皮毛、角质层纹饰等的微形态特征都存在很大的差异,可为探讨本属种间的分类、亲缘关系和演化趋势提供理论依据。     

肿瘤中neu基因的过量表达及其抑制

neu基因编码一种和表皮生长因子受体同源的磷酸蛋白,具有酪氨酸激酶的活性.近年来在多种人类肿瘤中发现neu基因的扩增和(或)过量表达.一些蛋白质因子或化学药物可以在转录水平阻遏neu基因的过量表达或者降低其产物p185^neu的酪氨酸激酶活性,抑制具有neu基因过量表达的癌细胞的转移和增殖.     

Sensitive periods for abnormal patterning on a leg segment inDrosophila melanogaster

Summary The development of a leg segment of the fruitflyDrosophila melanogaster was analyzed in order to determine whether the orderliness of the segment's bristle pattern originates via waves of cellular interactions, such as those that organize the retina. Fly development was perturbed at specific times by either teratogenic agents (gamma rays, heat shock, or the drug mitomycin C) or temperature-sensitive mutations (l(1)63, l(1) Notch^ts1, orl(1) shibire ^ts1 ), and the resulting abnormalities (e.g., missing or extra structures) were mapped within the pattern area. If bristles develop in a linear sequence across the pattern, then they should show sensitivity to perturbations in the same order, and wavefronts of cuticular defects should result. Contrary to this prediction, the maps reveal no evidence for any directional waves of sensitivity. Nevertheless, other clues were uncovered as to the nature and timing of patterning events. Chemosensory bristles show earlier sensitivities than mechanosensory bristles, and longer bristles precede shorter ones. The types and sequence of cuticular abnormalities imply the following stages of bristle pattern development: (1) scattered inception of bristle mother cells, each surrounded by an inhibitory field, (2) alignment of the mother cells into rows, (3) differential mitoses, (4) assignment of cuticular fates to the mitotic progeny, (5) polytenization of the bristle cells, (6) fine-tuning adjustments in bristle spacing, and (7) signalling from bristle cells to adjacent epidermal cells, inducing them to form bracts.     

Identification and characterization of the mammalian association and actin-nucleating domains in the Rickettsia conorii autotransporter protein, Sca2

Establishment of infection by spotted fever group rickettsial species is dependent on the ability of these bacteria to adhere to and invade the host endothelium. Recent studies have attributed these processes to a handful of rickettsial surface proteins from the surface cell antigen (sca) family of autotransporters. A rickettsial autotransporter from Rickettsia conorii, Sca2, has been shown to be sufficient to mediate both adherence and invasion of human endothelial cells and to participate in intracellular actin‐based motility. Here we identify a region of Sca2 capable of interacting with the mammalian cell surface and show that this function of Sca2 is independent and separable from its actin nucleation activity. Furthermore, pre‐incubation of mammalian cells with the Sca2 mammalian association region prior to R. conorii infection can competitively inhibit rickettsial invasion, suggesting that Sca2 plays an important role in the initial interaction with mammalian cells. Together, our results demonstrate that the Sca2 autotransporter protein in R. conorii contains distinct functional domains that likely are involved in mediating cellular interactions at the plasma membrane and the host cytosol.     

中国瓜馥木属植物叶片结构的解剖观察

采用叶片表皮离析法、扫描电镜和石蜡制片法,研究了中国分布的番荔枝科瓜馥木属19种植物叶片的形态结构。结果表明:瓜馥木属叶片形态和结构具有较多的相似性,如叶片表皮均具有2-多个细胞的单列丝状毛,表皮细胞内具有一个晶簇,气孔器均为平列型,只分布在叶片的远轴面,远轴面的表皮细胞平周壁形成一个乳突,叶片主脉的维管组织除具有正常的维管组织外,还具有一个小的副维管束等,这些特征有助于区分番荔枝科植物的属间关系,支持瓜馥木属是一个很自然的类群。但叶片表皮毛的形态及分布,表皮细胞的形状、叶肉中栅栏组织和海绵组织的结构、远轴面的乳突大小以及叶主脉维管组织的细微结构则具有种间差异。尤其有助于区分小萼瓜馥木和黑风藤、广西瓜馥木和独山瓜馥木、上思瓜馥木和东方瓜馥木等形态相似、难以区分的植物种类。该研究结果为该属的系统研究和种间正确区分提供了重要资料。     

凤仙花近缘种间核型分析与叶表皮微形态研究

为探究凤仙花近缘种植物的细胞学和微形态学方面的亲缘关系,该文选取荔波凤仙花(Impatiens liboensis)及近缘种赤水凤仙花(I.chishuiensis)和管茎凤仙花(I.tubulosa)的根尖和叶表皮为实验材料,采用体细胞染色体常规压片法和叶表皮光学显微镜观察法对凤仙花近缘种植物进行染色体及叶表皮特征研...     

The FUSCA genes of Arabidopsis: negative regulators of light responses

More than 200 fusca mutants of Arabidopsis have been isolated and characterised, defining 14 complementation groups. Mutations in at least nine FUSCA genes cause light-dependent phenotypic changes in the absence of light: high levels of anthocyanin accumulation in both the embryo and the seedling, inhibition of hypocotyl elongation, apical hook opening, and unfolding of cotyledons. In double mutants, the fusca phenotype is epistatic to the hy phytochromedeficiency phenotype, indicating that the FUSCA genes act downstream of phytochrome. By contrast, the accumulation of anthocyanin is suppressed by mutations in TT and TTG genes, which affect the biosynthesis of anthocyanin, placing the FUSCA genes upstream of those genes. Regardless of the presence or absence of anthocyanin, fusca mutations limit cell expansion and cause seedling lethality. In somatic sectors, mutant fus1 cells are viable; expressing tissue-specific phenotypes: reduced cell expansion and accumulation of anthocyanin in subepidermal tissue, formation of ectopic trichomes but no reduced cell expansion in epidermal tissue. Our results suggest a model of FUSCA gene action in light-induced signal transduction.     

Cooperative functions of Hes/Hey genes in auditory hair cell and supporting cell development

Notch-mediated lateral inhibition has been reported to regulate auditory hair cell and supporting cell development from common precursors. While the Notch effector genes Hes1, Hes5 and Hey1 are expressed in the developing cochlea, inactivation of either of them causes only mild abnormality, suggesting their functional redundancy. To explore the roles of Hes/Hey genes in cochlear development, we examined compound heterozygous or homozygous mutant mice that lacked Hes1, Hes5 and Hey1 alleles. We found that a reduction in Hes/Hey gene dosage led to graded increase of hair cell formation. However, if at least one allele of Hes1, Hes5 or Hey1 was intact, excessive hair cells were accompanied by overproduction of supporting cells, suggesting that the hair cell increase does not occur at the expense of supporting cells, and that each Hes/Hey gene functions to induce supporting cells. By contrast, when all alleles of Hes1, Hes5 and Hey1 were inactivated, the number of hair cells increased more drastically, whereas that of supporting cells was unchanged compared with control, suggesting that supporting cell formation was balanced by their overproduction and fate conversion into hair cells. The increase of the cell numbers seemed to occur after the prosensory domain formation in the mutants because the proliferation state and the size of the prosensory domain were not affected. Thus, Hes1, Hes5 and Hey1 cooperatively inhibit hair cell formation, and one allele of Hes1, Hes5 or Hey1 is sufficient for supporting cell production probably by lateral inhibition in the sensory epithelium. Strikingly, Hes/Hey mutations lead to disorganized cell alignment and polarity and to hearing loss despite hair cell overproduction. These results suggest that Hes/Hey gene dosage is essential not only for generation of appropriate numbers of hair cells and supporting cells by controlling cell proliferation and lateral inhibition but also for the hearing ability by regulating the cell alignment and polarity.     

喀斯特地区莎叶兰的解剖构造及其环境适应性

以广西西北部雅长兰科植物保护区的莎叶兰( Cymbidium cyperifolium)为对象,采用石蜡切片法对莎叶兰叶片和根的解剖构造及其对喀斯特环境的适应性进行了研究。结果表明：(1)莎叶兰叶片的上表皮覆盖有较厚的角质层,气孔均分布于下表皮,且凸出表皮细胞之上;各表皮性状在叶片不同部位存在显著差异,叶片下部的气孔密度、气孔指数和气孔长度最大,表皮细胞密度以叶片上部的最大;叶片属于等面叶,叶肉无栅栏组织和海绵组织的分化;叶脉为明显的平行脉,且粗细交互分布;(2)莎叶兰根的横切面包括根被、皮层、中柱3部分,其中根被细胞排列紧密,为生活细胞;皮层由薄壁细胞组成;根部维管束属于辐射维管束,14原型。菌根粗壮,稀根毛,共生真菌主要分布于根被及皮层中,菌丝体通过根被薄壁细胞间隙及内、外皮层的通道细胞进行侵染。(3)莎叶兰叶片和根的结构不仅有湿生植物特征,如叶片相对较薄、气孔少且凸出表皮细胞、冠/根比值大等;还有旱生植物的特征,如叶片角质层较厚、机械组织发达、细胞结构紧密、具含晶细胞,肉质根具根被,内、外皮层细胞壁明显增厚等。这些结构是莎叶兰对当地缺水、干湿季明显、分布于林下多石砾土壤的生长环境的一种高度适应性表现。     

The sporulation capable (sca) mutation of Saccharomyces cerevisiae is an allele of the SIR2 gene

Summary We have used the special properties of the spo13-1 mutation in order to study the regulation of yeast meiosis by the mating type loci. We have found that both the rme1-1 mutation and the sca mutation allow haploid meiosis in spo13-1 strains. Therefore, haploid meiosis is regulated in the same manner as diploid meiosis. Unlike rme1-1, the sca mutation allows meiosis through derepression of the silent mating type cassettes; sca strains can sporulate only because they express both MAT a and MAT information. We have found further that sca is an allele of SIR2, one of the genes involved in repression of the silent cassettes. Therefore, the RME1 gene is the only known candidate for a master negative regulator through which the MAT locus controls meiosis.     

The choice of cell fate in the epidermis of Drosophila

In Drosophila, neural precursors are formed in a spaced pattern separated by intervening epidermal cells. Segregation of neural and epidermal lineages relies on cellular interactions. Failure of this cell communication, as in the mutants Notch (N), Delta, and shaggy, results in most or all of the cells becoming neural. Cells mutant for N and shaggy, but not Delta, autonomously adopt the neural fate when adjacent to wild-type cells in mosaics. Furthermore, wild-type cells adopt the epidermal fate if adjacent cells express a lower level of N activity than themselves, but produce neural precursors if adjacent cells express a higher level of N activity. This shows that there is competition between the cells and that the N protein is required for the mechanism whereby the cells choose between alternative fates. It also suggests that N acts as a receptor for an inhibitory signal emanating from the neural precursors.     

中国看麦娘属植物叶表皮微形态研究

看麦娘属是禾本科早熟禾亚科的重要类群,中国分布有8种。该研究采用光学显微镜和电子扫描电镜,对中国看麦娘属7种植物的叶下表皮(含叶鞘下表皮)微形态特征进行观察并探讨其分类学意义。结果表明：(1)看麦娘属叶鞘下表皮长细胞的形状呈长筒状或短筒状,深波状弯曲的细胞壁,脉间短细胞密布,单生或对生,形状多为新月形或椭圆形,脉区硅细胞为椭圆形,平行形或低圆屋顶形的气孔器,看麦娘属叶鞘下表皮特征高度一致,分类价值不大。(2)看麦娘属植物叶下表皮和叶鞘下表皮的显微结构存在很大不同,看麦娘属植物叶下表皮长细胞多为长筒状或短筒状或长菱形,平周壁平直或不明显弯曲,脉间区短细胞分布或无,脉区刺毛密布,脉间区有或无刺细胞的分布,平行形的气孔器,脉区分布的硅细胞多为长方形边缘呈波状弯曲。看麦娘属植物叶下表皮的不同主要体现在脉间区长细胞的形状及平周壁的弯曲与否,脉间区短细胞出现或无,脉间区刺细胞的分布数量以及气孔器的列数。7种植物的叶表皮微形态的分类检索表据此列出。依据叶表皮微形态划分的组与根据外部特征划分的组并不完全一致。但是,由于该文仅研究了7种,叶表皮微形态对于看麦娘属的分类意义还需要更深入的研究。     

抱茎独行菜MUM4基因的克隆及分析

抱茎独行菜(Lepidium perfoliatum L.)为十字花科具典型粘液繁殖体植物,为探究该植物中种皮粘液质基因（MUCILAGE-MODIFIED4,MUM4,该基因在拟南芥中编码NDP-L-鼠李糖合成酶)的功能,通过生物信息学分析设计引物克隆得到抱茎独行菜MUM4基因,命名为LpMUM4。同源比对分析结果表明,LpMUM4与拟南芥AtMUM4基因具有很高的一致性。qRT-PCR结果表明,该基因在抱茎独行菜各组织中均有表达,在角果和根中的表达量最高,且其表达量随角果的发育表现出渐强的趋势。免疫组织化学定位分析表明,LpMUM4基因于角果发育的早期阶段在内珠被和外珠被都有表达,而在外珠被的表皮和亚表皮中表达量更高,至角果发育的最后阶段,其表达集中于表皮和亚表皮层,这可能与抱茎独行菜的外珠被发育成种皮及粘液质的生成有关。将LpMUM4基因转化拟南芥,该基因的过表达对位于粘液质合成途径中的上游基因AtTTG1具有显著的抑制作用。表型比对观察显示,转基因拟南芥与其野生型植株形态无显著差异,这可能是因为抱茎独行菜种皮的发育和粘液质的形成是一个多基因调控的复杂过程,某一基因的过表达或许不会引起明显的表型变化。     

Cleavage of di- and tripeptides by Prevotella ruminicola

The final step in the conversion of protein to amino acids by the common Gram-negative rumen bacterium, Prevotella (formerly Bacteroides) ruminicola , is the cleavage of di- and tripeptides. Dipeptidase and tripeptidase activities were predominantly cytoplasmic, and toluene treatment increased the rate of Ala₂ and Ala₃ hydrolysis by whole cells, suggesting that transport limited the rate of hydrolysis of extracellular di- and tripeptides. The hydrolysis of Ala₂ and Ala₃ by whole cells was not affected by protonophores, ionophores or dicyclohexylcarbodiimide, but Ala₂ hydrolysis by EDTA-treated cells was inhibited by the Ca²⁺/H⁺ ionophore, tetronasin. Ala₃ hydrolysis was not affected by protonophores or ionophores in EDTA-treated cells. The dipeptidase of strain M384 was inhibited > 99% by 1,10-phenanthroline and 39% by EDTA but not other protease inhibitors, consistent with the enzyme being a metalloprotease. Tripeptidase was insensitive to protease inhibitors, except for a 33% inhibition by EDTA. Cleavage of tripeptides occurred at the bond adjacent to the N-terminal amino acid. Distinct di-, tri- and oligopeptidase peaks were obtained by anion-exchange liquid chromatography of disrupted cells. Banding patterns on native PAGE using activity staining also indicated that P. ruminicola M384 had separate single dipeptidase and tripeptidase enzymes which hydrolysed a range of peptides. The dipeptidase of strain M384 was different from other strains of P. ruminicola: strains GA33 and B₁4 had activities which ran at the same R_f; strain GA33 had another band of lower activity; strain 23 had two bands different from those of the other strains. The tripeptidases ran at the same R_f for the different strains. Dipeptidase activity of all strains was inhibited by 1,10-phenanthroline on gels. Gel permeation chromatography indicated that the M_r of the dipeptidases from strains M384 and B₁4 were 115 000 and 114 500 respectively, and 112 500 and 121 500 for the corresponding tripeptidases. Thus the metabolism of small peptides by P. ruminicola involves separate permeases and intracellular peptidases for di- and tripeptides.     

发酵乳杆菌CSC-19胞外粗多糖提取物抑制单核细胞增生李斯特菌生物被膜形成能力的研究

【目的】筛选能有效抑制单核细胞增生李斯特菌(Listeria monocytogenes,LM)形成生物被膜的乳酸菌,分析其活性成分并进行功能表征。【方法】采用结晶紫染色法筛选抑制LM形成生物被膜的不同乳酸菌提取物;通过酸中和、蛋白酶处理及热处理,推测抑制生物被膜活性物质以胞外多糖(extracellular crude polysaccharide,ECP)为主;乙醇沉淀法提取目标乳酸菌分离株胞外粗多糖,分析其抑制生物被膜形成活性和对LM生长的影响;运用激光共聚焦扫描显微镜(laser confocal scanning microscopy,LCSM)和扫描电子显微镜(scanning electron microscopy,SEM)观察胞外粗多糖对生物被膜细胞形态和结构的影响。【结果】发酵乳杆菌CSC-19发酵上清液对1516-2LM生物被膜的抑制率为81.7%;经热和蛋白酶处理后,发酵上清抑制生物被膜形成的活性未发生显著变化(P>0.05),表明发酵上清液中抑制生物被膜形成的物质可能为胞外多糖;在不抑制LM生长的条件下所提取的胞外粗多糖抑制生物被膜形成能力具有浓度依赖性。激光共聚焦扫描显微镜和扫描电子显微镜结果显示,胞外粗多糖显著抑制了生物被膜的形成能力,生物被膜三维、有组织的蜂窝状结构被破坏,仅有少量的粘附细胞分散于细胞爬片表面。【结论】发酵乳杆菌CSC-19胞外粗多糖能有效抑制LM生物被膜的形成,有望应用于高效防控该菌污染食品。