Somatic stem cell niche tropism in Wolbachia

Wolbachia are intracellular bacteria found in the reproductive tissue of all major groups of arthropods. They are transmitted vertically from the female hosts to their offspring, in a pattern analogous to mitochondria inheritance. But Wolbachia phylogeny does not parallel that of the host, indicating that horizontal infectious transmission must also occur. Insect parasitoids are considered the most likely vectors, but the mechanism for horizontal transfer is largely unknown. Here we show that newly introduced Wolbachia cross several tissues and infect the germline of the adult Drosophila melanogaster female. Through investigation of bacterial migration patterns during the course of infection, we found that Wolbachia reach the germline through the somatic stem cell niche in the D. melanogaster germarium. In addition, our data suggest that Wolbachia are highly abundant in the somatic stem cell niche of long-term infected hosts, implying that this location may also contribute to efficient vertical transmission. This is, to our knowledge, the first report of an intracellular parasite displaying tropism for a stem cell niche.     

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     

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。     

灰飞虱共生菌Wolbachia引起的细胞质不亲和性

对我国６个地区和日本３个地区灰飞虱的Ｗｏｌｂａｈｉａ感染率，用ＰＣＲ技术进行了检测，结果表明中国的辽宁、北京、上海和云南的灰飞虱的Ｗｏｌｂａｃｈｉａ感染率均接近１００％；四川为５９．６％；而宁夏为０。各地区灰飞虱间的交配实验证明了在Ｗｏｌｂａｃｈｉａ引起的细胞质不亲和现象的存在，Ｗｏｌｂａｃｈｉａ１６ＳｒＤＮＡ的部分测序分析表明，上海、云南和日本出云的灰飞虱发的同为Ｗｏｌｂａｃｈｉａ ｐｉｐｉｅｎ     

Schistosoma mansoni shares a protective oligosaccharide epitope with freshwater and marine snails

The expression of similar antigenic determinants by trematode parasites and their intermediate (invertebrate) or definitive (vertebrate) hosts has been previously reported. Studies of experimental and human infection by the parasite Schistosoma mansoni have revealed the strong immunogenicity of a surface antigen with a relative molecular mass (Mr) 38,000 (38K). Here we provide evidence that the important protective epitope of the 38K molecule is expressed by the uninfected intermediate host of S. mansoni, Biomphalaria glabrata and is synthesized both by the mollusc and by the parasite throughout its life cycle, thus confirming our original hypothesis. Deglycosylation experiments indicate that the protective epitope is an oligosaccharide and in B. glabrata, is associated with a 90K component. Analysis of soluble extracts from different freshwater mollusc species shows that the same protective epitope is found in schistosome as well as in non-schistosome hosts. Moreover, it was also found on the haemocyanin of the keyhole limpet (Megathura crenulata), a carrier protein widely used in immunological studies.     

Population dynamics of Schistosoma mansoni in mice repeatedly exposed to infection

Studies of host resistance to parasite infection are usually based on experimental designs involving a primary infection and subsequent challenge exposure, resistance being recorded as the percentage reduction in parasite establishment in challenged hosts when compared with that in uninfected animals. Few studies have focused on the dynamic nature of helminth establishment and mortality (and their presumed dependency on the rate of current exposure and past experiences of infection) in hosts repeatedly exposed to low levels of infection. Here, we report the results of population studies on the dynamics of resistance to Schistosoma mansoni infection (a helminth parasite) in mice repeatedly exposed to cercarial invasion. Parasite burdens created by different levels and durations of exposure to infection reflect a dynamic interplay between rates of helminth establishment and mortality. Depending on the intensity of exposure, changes in worm load with duration of host infection vary from monotonic growth to a stable average parasite burden to convex curves in which the average load attains a maximum value before decaying in old animals. These trends are similar to observed patterns of S. mansoni infection in human communities.     

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.     

Acute mutation of retinoblastoma gene function is sufficient for cell cycle re-entry

Cancer cells arise from normal cells through the acquisition of a series of mutations in oncogenes and tumour suppressor genes. Mouse models of human cancer often rely on germline alterations that activate or inactivate genes of interest. One limitation of this approach is that germline mutations might have effects other than somatic mutations, owing to developmental compensation. To model sporadic cancers associated with inactivation of the retinoblastoma (RB) tumour suppressor gene in humans, we have produced a conditional allele of the mouse Rb gene. We show here that acute loss of Rb in primary quiescent cells is sufficient for cell cycle entry and has phenotypic consequences different from germline loss of Rb function. This difference is explained in part by functional compensation by the Rb-related gene p107. We also show that acute loss of Rb in senescent cells leads to reversal of the cellular senescence programme. Thus, the use of conditional knockout strategies might refine our understanding of gene function and help to model human cancer more accurately.     

Genome-wide expression dynamics of a marine virus and host reveal features of co-evolution

Interactions between bacterial hosts and their viruses (phages) lead to reciprocal genome evolution through a dynamic co-evolutionary process. Phage-mediated transfer of host genes--often located in genome islands--has had a major impact on microbial evolution. Furthermore, phage genomes have clearly been shaped by the acquisition of genes from their hosts. Here we investigate whole-genome expression of a host and phage, the marine cyanobacterium Prochlorococcus MED4 and the T7-like cyanophage P-SSP7, during lytic infection, to gain insight into these co-evolutionary processes. Although most of the phage genome was linearly transcribed over the course of infection, four phage-encoded bacterial metabolism genes formed part of the same expression cluster, even though they are physically separated on the genome. These genes--encoding photosystem II D1 (psbA), high-light inducible protein (hli), transaldolase (talC) and ribonucleotide reductase (nrd)--are transcribed together with phage DNA replication genes and seem to make up a functional unit involved in energy and deoxynucleotide production for phage replication in resource-poor oceans. Also unique to this system was the upregulation of numerous genes in the host during infection. These may be host stress response genes and/or genes induced by the phage. Many of these host genes are located in genome islands and have homologues in cyanophage genomes. We hypothesize that phage have evolved to use upregulated host genes, leading to their stable incorporation into phage genomes and their subsequent transfer back to hosts in genome islands. Thus activation of host genes during infection may be directing the co-evolution of gene content in both host and phage genomes.     

A haemoglobin switching activity modulates hereditary persistence of fetal haemoglobin

During human development there is a switch from fetal to adult haemoglobin formation, reflecting the differential expression of fetal (G gamma and A gamma) and adult (beta and delta) globin genes. Mutations that inhibit this switch produce variants of the syndrome of hereditary persistence of fetal haemoglobin (HPFH). Adult heterozygotes for these mutants produce 15-30% fetal haemoglobin (HbF) in their red cells. The general assumption is that the mutations result in a permanent switching on of gamma-globin genes. Here, however, we show that fetal globin expression can be turned off in cultures of HPFH cells by an uncharacterized factor in fetal sheep serum. This is the first demonstration that mutations affecting the developmental expression of globin genes can be modulated by exogenous factors. The findings raise the possibility that the phenotype of HPFH is not simply the direct result of mutations in or around globin genes but the consequence of the mutations on the interaction of globin genes with trans-acting regulatory factors.     

Infection of Wolbachia may improve the olfactory response of Drosophila

The endosymbiotic bacterium Wolbachia infects various insects and is primarily known for its ability to manipulate host reproduction.Recent investigations reveal that Wolbachia also affects the activity of somatic cells.We here demonstrated by trap method and T-maze that Wolbachia infection had signifi-cant impact on the olfactory response of Drosophila simulans.Wolbachia-infected flies took shorter time to enter the food trap and were more sensitive to odorant in T-maze than those uninfected controls.The t...     

Genomic island variability facilitates Prochlorococcus-virus coexistence

Prochlorococcus cyanobacteria are extremely abundant in the oceans, as are the viruses that infect them. How hosts and viruses coexist in nature remains unclear, although the presence of both susceptible and resistant cells may allow this coexistence. Combined whole-genome sequencing and PCR screening technology now enables us to investigate the effect of resistance on genome evolution and the genomic mechanisms behind the long-term coexistence of Prochlorococcus and their viruses. Here we present a genome analysis of 77 substrains selected for resistance to ten viruses, revealing mutations primarily in non-conserved, horizontally transferred genes that localize to a single hypervariable genomic island. Mutations affected viral attachment to the cell surface and imposed a fitness cost to the host, manifested by significantly lower growth rates or a previously unknown mechanism of more rapid infection by other viruses. The mutant genes are generally uncommon in nature yet some carry polymorphisms matching those found experimentally. These data are empirical evidence indicating that viral-attachment genes are preferentially located in genomic islands and that viruses are a selective pressure enhancing the diversity of both island genes and island gene content. This diversity emerges as a genomic mechanism that reduces the effective host population size for infection by a given virus, thus facilitating long-term coexistence between viruses and their hosts in nature.     

Molecular Identification of a Wolbachia endosymbiont in Trichogramma dendrolimi

Wolbachia is a common and widespread group of bacteria found in arthropods. These bacteria have evolved various mechanisms for manipulating reproduction of their host. The presence of Wolbachia in a lab strain of the arrhenotokous species Trichogramma dendrolimi was observed by the amplification and sequencing of part of the wsp gene. Aligning the resulting sequences with already published ones, the phylogenetic relationships between Wolbachia found in Trichogramma dendrolimi and in other Trichogramma wasps was established, and the phylogenetic relationships of Wolbachia in Trichogramma were not congruent with their hosts Trichogramma. Some factors contributing to this uncongruence are discussed here.     

Transmission of cutaneous leishmaniasis by sand flies is enhanced by regurgitation of fPPG

Sand flies are the exclusive vectors of the protozoan parasite Leishmania, but the mechanism of transmission by fly bite has not been determined nor incorporated into experimental models of infection. In sand flies with mature Leishmania infections the anterior midgut is blocked by a gel of parasite origin, the promastigote secretory gel. Here we analyse the inocula from Leishmania mexicana-infected Lutzomyia longipalpis sand flies. Analysis revealed the size of the infectious dose, the underlying mechanism of parasite delivery by regurgitation, and the novel contribution made to infection by filamentous proteophosphoglycan (fPPG), a component of promastigote secretory gel found to accompany the parasites during transmission. Collectively these results have important implications for understanding the relationship between the parasite and its vector, the pathology of cutaneous leishmaniasis in humans and also the development of effective vaccines and drugs. These findings emphasize that to fully understand transmission of vector-borne diseases the interaction between the parasite, its vector and the mammalian host must be considered together.     

刚刺颚口线虫流行病学调查及其幼虫对灵长类的易感性

本文报告了刚刺颚口线虫 Gnathostoma hispidum 第一、二中间宿主和转续宿主共 38种。首次证明狲猴 Macaca mulatta可充当本虫的第二中间宿主和转续宿主。用刚刺颚?线虫晚第三期幼虫经皮肤穿刺感染小白鼠和家猫均获得阳性。5种哺乳动物和4种鸟类(其中家禽2种)用同上幼虫人工感染亦获成功。流行学调查和动物实验表明本虫和棘颚口线虫G.spinigerum 的生物学和流行学特性十分相似,同样能感染人体,是人兽共患的重要寄生虫。     

Malaria. Cooperative silencing elements in var genes

Each Plasmodium falciparum malaria parasite carries about 50 var genes from a diverse family that encode variable adhesion proteins on the infected red blood cells of the host, but individual parasites single out just one var gene for expression and silence all the others. Here we show that this silencing is established during the DNA-synthesis phase (S phase) of the cell cycle and that it depends on the cooperative interaction between two elements in separate control regions of each var gene (the 5'-flanking region and the intron). This finding should help to clarify the mechanisms by which parasites coordinate the silencing and activation of var genes that are responsible for antigenic variation in malaria.