A host parasite interaction rescues Drosophila oogenesis defects

The cytoplasmically inherited bacterium Wolbachia pipientis is a widespread parasite of arthropods that manipulates the reproductive biology of its hosts, often to their detriment, in order to foster its own transmission through egg cytoplasm. Here we report that infection by Wolbachia restores fertility to Drosophila melanogaster mutant females prevented from making eggs by protein-coding lesions in Sex-lethal (Sxl), the master regulator of sex determination. Suppression of sterility by Wolbachia discriminates markedly among similar germline-specific Sxl alleles, and is not observed for mutations in other genes that produce similar 'tumorous ovary' phenotypes, including one that blocks Sxl germline expression. This allele and gene specificity indicates that suppression probably results from a specific interaction with Sxl protein, rather than from a bypass of the normal germline requirement for this developmental regulator or from an effect on Sxl expression. The Sxl-Wolbachia interaction provides a rare opportunity to explore host-parasite relationships at the molecular level in a model insect. Furthermore, demonstration that a parasite infection can counteract the deleterious effects of mutations in host genes illustrates how hosts might become dependent on parasites.     

Cloning and characterization of a gene encoding phage-related tail protein (PrTP) of endosymbiont Wolbachia

Wolbachia is an obligatory, maternally inherited intracellular bacterium, known to infect a wide range of arthropods. It has been implicated in causing cytoplasmic incompatibility (CI), parthenogenesis, the feminization of genetic males and male-killing in different hosts. However, the molecular mechanisms by which this fastidious bacterium causes these reproductive abnormalities have not yet been determined. In this study, we report on the cloning and characterization of the gene encoding phage-related tail protein (PrTP) from Wolbachia in Drosophila melanogaster CantonS (wMelCS) and from Wolbachia in Drosophila melanogaster yw67c23 (wMel) by representational difference analysis (RDA) and ligation-mediated PCR (LM-PCR). The functionality of a bipartite nuclear localization signal sequence (NLS) of the gene was also successfully tested in Drosophila S2 cells. PrTP expression in various strains of Wolbachia was investigated. Our results suggest that PrTP may not induce CI directly. However, the existence of prtp provided direct evidence of phage-mediated horizontal gene transfer (HGT) that might play an important role in a variety of reproductive abnormalities of Wolbachia.     

Somatic control over the germline stem cell lineage during Drosophila spermatogenesis

Stem cells divide both to produce new stem cells and to generate daughter cells that can differentiate. The underlying mechanisms are not well understood, but conceptually are of two kinds. Intrinsic mechanisms may control the unequal partitioning of determinants leading to asymmetric cell divisions that yield one stem cell and one differentiated daughter cell. Alternatively, extrinsic mechanisms, involving stromal cell signals, could cause daughter cells that remain in their proper niche to stay stem cells, whereas daughter cells that leave this niche differentiate. Here we use Drosophila spermatogenesis as a model stem cell system to show that there are excess stem cells and gonialblasts in testes that are deficient for Raf activity. In addition, the germline stem cell population remains active for a longer fraction of lifespan than in wild type. Finally, raf is required in somatic cells that surround germ cells. We conclude that a cell-extrinsic mechanism regulates germline stem cell behaviour.     

Infectious parthenogenesis

Parthenogenesis-inducing Wolbachia bacteria are reproductive parasites that cause infected female wasps to produce daughters without mating. This manipulation of the host's reproduction enhances the transmission of Wolbachia to future generations because the bacteria are passed on vertically only from mothers to daughters. Males are dead ends for cytoplasmically inherited bacteria: they do not pass them on to their offspring. Vertical transmission of Wolbachia has been previously considered to be the main mode of transmission. Here we report frequent horizontal transmission from infected to uninfected wasp larvae sharing a common food source. The transferred Wolbachia are then vertically transmitted to the new host's offspring. This natural and unexpectedly frequent horizontal transfer of parthenogensis-inducing Wolbachia intraspecifically has important implications for the co-evolution of Wolbachia and their host.     

Wolbachia在灰飞虱体内的分布

灰飞虱（Laodelphax striatellus)能传播水稻条纹叶枯病,是我国主要的水稻害虫,有些灰飞虱体内含有细胞内共生菌－Wolbachia。Wolbachia是一种细胞质遗传的细胞内共生菌,这类细菌改变了宿主的生殖行为,引起细胞质不相容（CI）,雌性化及孤雌生殖等现象,导致带有Wolbachia的宿主具有生殖优势。采用PCR和Western杂交的方法分析Wolbachia的灰飞虱体内不同组织的分布状况,发现灰飞虱体内Wolbachia除存在于生殖组织外,还广泛分布在头、胸、腹、唾液腺、消化道等非生殖组织中。这种广泛的分布状态说明Wolbachia是在昆虫体内引入、表达与传播外源基因的良好媒介。     

Somatic support cells restrict germline stem cell self-renewal and promote differentiation

Stem cells maintain populations of highly differentiated, short-lived cell-types, including blood, skin and sperm, throughout adult life. Understanding the mechanisms that regulate stem cell behaviour is crucial for realizing their potential in regenerative medicine. A fundamental characteristic of stem cells is their capacity for asymmetric division: daughter cells either retain stem cell identity or initiate differentiation. However, stem cells are also capable of symmetric division where both daughters remain stem cells, indicating that mechanisms must exist to balance self-renewal capacity with differentiation. Here we present evidence that support cells surrounding the stem cells restrict self-renewal and control stem cell number by ensuring asymmetric division. Loss of function of the Drosophila Epidermal growth factor receptor in somatic cells disrupted the balance of self-renewal versus differentiation in the male germline, increasing the number of germline stem cells. We propose that activation of this receptor specifies normal behaviour of somatic support cells; in turn, the somatic cells play a guardian role, providing information that prevents self-renewal of stem cell identity by the germ cell they enclose.     

灰飞虱Wolbachia群体生物学的遗传特性研究

Ｗｏｌｂａｃｈｉａ是存在于多种昆虫生殖器官的一类共生菌,它可能在宿 主群体中引起细菌质不亲和性而给宿 主带来生殖优势。对灰飞虱体内的Ｗｏｌｂａｃｈｉａｆｊｔｆｄｇｐｗ,ｖ ｇｍ ｐｇｃｆｍｗ ｑｎｎｋｕｄｙｊｒ ｄｏ ｎｕｉ     

A conserved RNA-binding protein controls germline stem cells in Caenorhabditis elegans

Germline stem cells are defined by their unique ability to generate more of themselves as well as differentiated gametes. The molecular mechanisms controlling the decision between self-renewal and differentiation are central unsolved problems in developmental biology with potentially broad medical implications. In Caenorhabditis elegans, germline stem cells are controlled by the somatic distal tip cell. FBF-1 and FBF-2, two nearly identical proteins, which together are called FBF ('fem-3 mRNA binding factor'), were originally discovered as regulators of germline sex determination. Here we report that FBF also controls germline stem cells: in an fbf-1 fbf-2 double mutant, germline proliferation is initially normal, but stem cells are not maintained. We suggest that FBF controls germline stem cells, at least in part, by repressing gld-1, which itself promotes commitment to the meiotic cell cycle. FBF belongs to the PUF family ('Pumilio and FBF') of RNA-binding proteins. Pumilio controls germline stem cells in Drosophila females, and, in lower eukaryotes, PUF proteins promote continued mitoses. We suggest that regulation by PUF proteins may be an ancient and widespread mechanism for control of stem cells.     

Successful establishment of Wolbachia in Aedes populations to suppress dengue transmission

Genetic manipulations of insect populations for pest control have been advocated for some time, but there are few cases where manipulated individuals have been released in the field and no cases where they have successfully invaded target populations. Population transformation using the intracellular bacterium Wolbachia is particularly attractive because this maternally-inherited agent provides a powerful mechanism to invade natural populations through cytoplasmic incompatibility. When Wolbachia are introduced into mosquitoes, they interfere with pathogen transmission and influence key life history traits such as lifespan. Here we describe how the wMel Wolbachia infection, introduced into the dengue vector Aedes aegypti from Drosophila melanogaster, successfully invaded two natural A. aegypti populations in Australia, reaching near-fixation in a few months following releases of wMel-infected A. aegypti adults. Models with plausible parameter values indicate that Wolbachia-infected mosquitoes suffered relatively small fitness costs, leading to an unstable equilibrium frequency <30% that must be exceeded for invasion. These findings demonstrate that Wolbachia-based strategies can be deployed as a practical approach to dengue suppression with potential for area-wide implementation.     

Stem cell division is regulated by the microRNA pathway

One of the key characteristics of stem cells is their capacity to divide for long periods of time in an environment where most of the cells are quiescent. Therefore, a critical question in stem cell biology is how stem cells escape cell division stop signals. Here, we report the necessity of the microRNA (miRNA) pathway for proper control of germline stem cell (GSC) division in Drosophila melanogaster. Analysis of GSCs mutant for dicer-1 (dcr-1), the double-stranded RNaseIII essential for miRNA biogenesis, revealed a marked reduction in the rate of germline cyst production. These dcr-1 mutant GSCs exhibit normal identity but are defective in cell cycle control. On the basis of cell cycle markers and genetic interactions, we conclude that dcr-1 mutant GSCs are delayed in the G1 to S transition, which is dependent on the cyclin-dependent kinase inhibitor Dacapo, suggesting that miRNAs are required for stem cells to bypass the normal G1/S checkpoint. Hence, the miRNA pathway might be part of a mechanism that makes stem cells insensitive to environmental signals that normally stop the cell cycle at the G1/S transition.     

Comparative pluripotency analysis of mouse embryonic stem cells derived from wild-type and infertile hermaphrodite somatic cell nuclear transfer blastocysts

Therapeutic cloning, whereby embryonic stem cells （ESCs） are derived from patient-specific cloned blastocysts via somatic cell nuclear transfer （SCNT）, holds great promise for treating many human diseases using regenerative medicine. Teratoma formation and germline transmission have been used to confirm the pluripotency of mouse stem cells, but human embryonic stem cells （hESCs） have not been proven to be fully pluripotent owing to the ethical impossibility of testing for germ line transmis- sion, which would be the strongest evidence for full pluripotency. Therefore, formation of differentiated cells from the three somatic germ layers within a teratoma is taken as the best indicator of pluripotency in hESC lines. The possibility that these lines lack full multi- or pluripotency has not yet been evaluated. In this study, we established 16 mouse ESC lines, including 3 genetically defective nuclear transfer- ESC （ntESC） lines derived from SCNT blastocysts of infertile hermaphrodite F1 mice and 13 ntESC lines derived from SCNT blastocysts of normal F1 mice. We found that the defective ntESCs expressed all in vitro markers of pluripotency and could form teratomas that included derivatives from all three germ layers, but could not be transmitted via the germ line, in contrast with normal ntESCs. Our results in- dicate that teratoma formation assays with hESCs might be an insufficient standard to assess full pluripotency, although they do define multipotency to some degree. More rigorous standards are required to assess the safety of hESCs for therapeutic cloning.     

Apparent absence of transposable elements related to the P elements of D. melanogaster in other species of Drosophila

P elements are transposable elements found in P strain, but usually not in M strain, Drosophila melanogaster, and are responsible for the hybrid dysgenesis that occurs when male D. melanogaster of the P strain mate with females of the M strain (ref. 1 and references therein). Several P elements, which vary in length and genetic effects, have now been cloned. To investigate the evolutionary origin of P elements, we have used a cloned copy of a D. melanogaster P element to look for related sequences in the genomes of six other Drosophila species. We report here that, unlike many other transposable elements found in D. melanogaster, which seem also to be present in other Drosophila species, we have found no sequences closely enough related to P elements to be detected by DNA hybridization in any other Drosophila species. This result supports the hypothesis that P elements have recently invaded D. melanogaster by horizontal transmission.     

植物根尖干细胞微环境的遗传调控

干细胞微环境是平衡干细胞自我更新、多向分化和压力响应的微环境.近年来,通过大量的突变体筛选和现代的影像技术,植物根尖干细胞微环境特化和维持的调控机制取得了很大进展.该文着重概述转录因子网络、激素信号转导、染色质因子和基因组组织因子在调控根尖干细胞微环境中的作用.     

束花石斛和黄花石斛的光合特性研究

研究了大花组的束花石斛和黄花石斛的光合生理,结果表明,2种石斛叶片的解剖结构为异面叶,气孔仅分布在下表面,具气孔盖,叶脉维管束鞘不含叶绿体,无花环型结构,具C3植物特征.2种石斛的光补偿点(LCP)和光饱和点(LSP)分别为5～10μmol/(m2.s)和850～900μmol/(m2.s),最大光合速率(Pn)约为6μmol/(m2.s);CO2补偿点和饱和点分别为80～90μmol/mol和800μmol/mol;光合作用的最适温度在26～30℃.Pn日变化为双峰型曲线,首峰出现在11:00左右,最大光合速率在5～6μmol/(m2.s),次峰出现在15:00左右,夜间不吸收CO2.PEPCase活性低,RuBPCase和GO酶活性较高.以上结果表明,束花石斛和黄花石斛光合作用碳同化途径属C3植物类型,具有半阴生植物的特点.     

Pluripotency of spermatogonial stem cells from adult mouse testis

Embryonic germ cells as well as germline stem cells from neonatal mouse testis are pluripotent and have differentiation potential similar to embryonic stem cells, suggesting that the germline lineage may retain the ability to generate pluripotent cells. However, until now there has been no evidence for the pluripotency and plasticity of adult spermatogonial stem cells (SSCs), which are responsible for maintaining spermatogenesis throughout life in the male. Here we show the isolation of SSCs from adult mouse testis using genetic selection, with a success rate of 27%. These isolated SSCs respond to culture conditions and acquire embryonic stem cell properties. We name these cells multipotent adult germline stem cells (maGSCs). They are able to spontaneously differentiate into derivatives of the three embryonic germ layers in vitro and generate teratomas in immunodeficient mice. When injected into an early blastocyst, SSCs contribute to the development of various organs and show germline transmission. Thus, the capacity to form multipotent cells persists in adult mouse testis. Establishment of human maGSCs from testicular biopsies may allow individual cell-based therapy without the ethical and immunological problems associated with human embryonic stem cells. Furthermore, these cells may provide new opportunities to study genetic diseases in various cell lineages.     

Generation of pluripotent stem cells from adult human testis

Human primordial germ cells and mouse neonatal and adult germline stem cells are pluripotent and show similar properties to embryonic stem cells. Here we report the successful establishment of human adult germline stem cells derived from spermatogonial cells of adult human testis. Cellular and molecular characterization of these cells revealed many similarities to human embryonic stem cells, and the germline stem cells produced teratomas after transplantation into immunodeficient mice. The human adult germline stem cells differentiated into various types of somatic cells of all three germ layers when grown under conditions used to induce the differentiation of human embryonic stem cells. We conclude that the generation of human adult germline stem cells from testicular biopsies may provide simple and non-controversial access to individual cell-based therapy without the ethical and immunological problems associated with human embryonic stem cells.     

Centrosome misorientation reduces stem cell division during ageing

Asymmetric division of adult stem cells generates one self-renewing stem cell and one differentiating cell, thereby maintaining tissue homeostasis. A decline in stem cell function has been proposed to contribute to tissue ageing, although the underlying mechanism is poorly understood. Here we show that changes in the stem cell orientation with respect to the niche during ageing contribute to the decline in spermatogenesis in the male germ line of Drosophila. Throughout the cell cycle, centrosomes in germline stem cells (GSCs) are oriented within their niche and this ensures asymmetric division. We found that GSCs containing misoriented centrosomes accumulate with age and that these GSCs are arrested or delayed in the cell cycle. The cell cycle arrest is transient, and GSCs appear to re-enter the cell cycle on correction of centrosome orientation. On the basis of these findings, we propose that cell cycle arrest associated with centrosome misorientation functions as a mechanism to ensure asymmetric stem cell division, and that the inability of stem cells to maintain correct orientation during ageing contributes to the decline in spermatogenesis. We also show that some of the misoriented GSCs probably originate from dedifferentiation of spermatogonia.