MTO: the second member of a Drosophila dual copper-thionein system

Drosophila MTO metal binding features were analyzed for comparison with MTN, the paralogous Drosophila metallothionein, and to classify MTO as either zinc- or copper-thionein. This was achieved by a combination of in vivo, in vitro and in silico methodologies. All the results unambiguously classified MTO as a second Drosophila copper-thionein, putting Drosophila forward as the only metazoan in which any zinc-thionein has still to be reported. Interestingly, experimental data only showed minor differences in the coordinative behavior of both MTs, but provided a characteristic spectroscopic fingerprint, revealing the possible binding of chloride anions in certain metal-MTO aggregates.     

Drosophila innate immunity and response to fungal infections

The fruit fly Drosophila melanogaster is an important model for the analysis of the interaction between host immune systems and fungal pathogens. Recent experiments have extended our understanding of the Toll-based signalling pathway critical to response to fungal infections, and identified new elements involved in cellular and humoral-based defences. The fly immune system shows remarkable sophistication in its ability to discriminate among pathogens, and the powerful genetics available to researchers studying the adult fly response, and the ability to manipulate cultured phagocytic cell lines with RNAi, are allowing researchers to dissect the molecular details of the process.     

Immune-deficient Drosophila melanogaster: a model for the innate immune response to human fungal pathogens

We explored the host-pathogen interactions of the human opportunistic fungus Candida albicans using Drosophila melanogaster. We established that a Drosophila strain devoid of functional Toll receptor is highly susceptible to the human pathogen C. albicans. Using this sensitive strain, we have been able to show that a set of specific C. albicans mutants of different virulence in mammalian infection models are also impaired in virulence in Drosophila and remarkably display the same rank order of virulence. This immunodeficient insect model also revealed virulence properties undetected in an immunocompetent murine model of infection. The genetic systems available in both host and pathogen will enable the identification of host-specific components and C. albicans genes involved in the host-fungal interplay.     

Origins of the other metazoan body plans: the evolution of larval forms

Bilaterian animal body plan origins are not solely about adult forms. Most animals have larvae with body plans, ontogenies and ecologies distinct from adults. There are two primary hypotheses for larval origins. The first hypothesis suggests that the first animals were small pelagic forms similar to modern larvae, with adult bilaterian body plans evolved subsequently. The second hypothesis suggests that adult bilaterian body plans evolved first and that larval body plans arose by interpolation of features into direct-developing ontogenies. The two hypotheses have different consequences for understanding parsimony in evolution of larvae and of developmental genetic mechanisms. If primitive metazoans were like modern larvae and distinct adult forms evolved independently, there should be little commonality of patterning genes among adult body plans. However, sharing of patterning genes is observed. If larvae arose by co-option of adult bilaterian-expressed genes into independently evolved larval forms, larvae may show morphological convergence, but with distinct patterning genes, and this is observed. Thus, comparative studies of gene expression support independent origins of larval features. Precambrian and Cambrian embryonic fossils are also consistent with direct development of the adult as being primitive, with planktonic larvae arising during the Cambrian. Larvae have continued to co-opt genes and evolve new features, allowing study of developmental evolution.     

涉及临床各科的侵袭性真菌感染

真菌数量大、种类多、分布广。真菌感染因菌种的毒力、感染途径和宿主免疫状态等差异而出现不同的临床表现,临床各科医生都会遇到真菌病患者。真菌病的诊断取决于在病变组织内发现病原真菌成分如菌丝和(或)孢子。从病变组织中分离出真菌是菌种鉴定前提,也是抗真菌治疗的依据。“重视临床、强调菌学”是医学真菌研究的基本思路。真菌学家应该在联系临床与实验室中起关键作用。     

Drosophila Protein interaction Map (DPiM): A paradigm for metazoan protein complex interactions

Proteins perform essential cellular functions as part of protein complexes, often in conjunction with RNA, DNA, metabolites and other small molecules. The genome encodes thousands of proteins but not all of them are expressed in every cell type; and expressed proteins are not active at all times. Such diversity of protein expression and function accounts for the level of biological intricacy seen in nature. Defining protein-protein interactions in protein complexes, and establishing the when, what and where of potential interactions, is therefore crucial to understanding the cellular function of any protein—especially those that have not been well studied by traditional molecular genetic approaches. We generated a large-scale resource of affinity-tagged expression-ready clones and used co-affinity purification combined with tandem mass-spectrometry to identify protein partners of nearly 5,000 Drosophila melanogaster proteins. The resulting protein complex “map” provided a blueprint of metazoan protein complex organization. Here we describe how the map has provided valuable insights into protein function in addition to generating hundreds of testable hypotheses. We also discuss recent technological advancements that will be critical in addressing the next generation of questions arising from the map.     

Mutagenicity of fungal metabolites related to aflatoxin biosynthesis.

Fungal metabolites identified as the intermediates in aflatoxin biosynthetic pathway were screened for their mutagenic activity to Salmonella typhimurium TA98. Norsolorinic acid, averufin, and versiconal acetate were found to possess questionable mutagenic activity, but versicolorin A, and sterigmatocystin were significant mutagens relative to aflatoxin B1. The mutagenic activity appears to be related to the bisfuran and not the anthraquinone moiety of the molecule, even though the latter is a key structure of such potent carcinogenic mycotoxin as luteoskyrin.     

Origin recognition complex binding to a metazoan replication origin

The initiation of DNA replication in eukaryotic cells at the onset of S phase requires the origin recognition complex (ORC) [1]. This six-subunit complex, first isolated in Saccharomyces cerevisiae [2], is evolutionarily conserved [1]. ORC participates in the formation of the prereplicative complex [3], which is necessary to establish replication competence. The ORC-DNA interaction is well established for autonomously replicating sequence (ARS) elements in yeast in which the ARS consensus sequence [4] (ACS) constitutes part of the ORC binding site [2, 5]. Little is known about the ORC-DNA interaction in metazoa. For the Drosophila chorion locus, it has been suggested that ORC binding is dispersed [6]. We have analyzed the amplification origin (ori) II/9A of the fly, Sciara coprophila. We identified a distinct 80-base pair (bp) ORC binding site and mapped the replication start site located adjacent to it. The binding of ORC to this 80-bp core region is ATP dependent and is necessary to establish further interaction with an additional 65-bp of DNA. This is the first time that both the ORC binding site and the replication start site have been identified in a metazoan amplification origin. Thus, our findings extend the paradigm from yeast ARS1 to multicellular eukaryotes, implicating ORC as a determinant of the position of replication initiation.     

In silico analyses of Fsf1 sequences, a new group of fungal proteins orthologous to the metazoan sideroblastic anemia-related sideroflexin family

Sideroblastic anemias are pathologies observed in metazoan species characterized by accumulation of iron in the mitochondria (sideroblasts), defective erythropoiesis, and iron overload. Some genes have been associated with sideroblastic anemia, e.g. delta-aminolevulinic acid synthase gene (e-ALAS2). Recently, a new sideroblastic-associated protein family was discovered in metazoans and termed sideroflexin (Sfxn). The metazoan Sfxn family comprises five groups of paralogous proteins, present in mitochondria and whose functions are unknown. Using an in silico approach, we have identified and characterized new sideroflexin sequences from the genomes of different fungal species. An in-depth phylogenetic analysis of these new fungal Sfxn sequences (termed Fsf1p) showed that they form a distinct clade within the metazoan Sfxn family. Hydrophobic cluster analysis and transmembrane topological mapping allowed us to compare conserved regions among Fsf1 and Sfxn proteins. The results indicate that Fsf1 probably belongs to an ancient, mitochondrial group of proteins, necessary to maintain the homeostasis of iron within this organelle.     

ARWEN: a program to detect tRNA genes in metazoan mitochondrial nucleotide sequences

MOTIVATION: Mitochondrial genomes encode their own transfer RNAs (tRNAs). These are often degenerate in sequence and structure compared to tRNAs in their bacterial ancestors. This is one of the reasons why current tRNA gene predictor programs perform poorly identifying mitochondrial tRNA genes. As a consequence there is a need for a new program with the specific aim of predicting these tRNAs. RESULTS: In this study, we present the software ARWEN that identifies tRNA genes in metazoan mitochondrial nucleotide sequences. ARWEN detects close to 100% of previously annotated genes. AVAILABILITY: An online version, software for download and test results are available at www.acgt.se/online.html     

Physicochemical monitoring of wood coating degradation related to fungal disfigurement

Analytical methods for the assessment of coating degradation are numerous. While providing data concerning the physicochemical condition of the sample during weathering, it is worth investigating the relation with fungal disfigurement in laboratory experiments. Coated wooden samples were subjected to artificial ageing for 2000 h while their behaviour was monitored with infrared spectroscopy, UV spectroscopy, differential scanning calorimetry, water uptake determination and contact angle measurements. Data analysis comprised extraction of quantitative values from IR series, UV absorption calculation, straightforward mathematical operations for glass transition determination, water uptake coefficient calculations and drop shape analysis of water droplets. Unweathered and weathered samples were also subjected to fungal attack in a laboratory set-up based on the principles of the EN 152 test procedure. Linking degradation data with biological susceptibility provides a better insight in property related biological damage.     

The origin of metazoan development: a palaeobiological perspective

The rapid diversification of early Metazoa remains one of the most puzzling events in the fossil record. Several models have been proposed to explain a critical aspect of this event: the origin of Metazoan development. These include the origin of the eukaryotic cell, environmental triggers, key innovations or selection among cell lineages. Here, the first three hypotheses are evaulated within a phylogenetic framework using fossil, molecular and developmental evidence. Many elements of metazoan development are widely distributed among unicellular eukaryotes, yet only 3 of the 23 multicellular eukaryotic lineages evolved complex development. Molecular evidence indicates the lineage leading to the eukaryotic cell is nearly as old as the eubacterial and archaebacterial lineages, although the symbiotic events established that the eukaryotic cell probably occurred about 1.5 billion years ago. Yet Metazoa did not appear until 1000 to 600 million years ago (Myr), suggesting the origin of metazoan development must be linked to either an environmental trigger, perhaps an increase in atmospheric oxygen, or key innovations such as the development of collagen. Yet the first model fails to explain the unique appearance of complex development in Metazoa, while the latter fails to explain the simultaneous diversification of several ‘protist’ groups along with the Metazoa. A more complete model of the origin of metazoan development combines environmental triggering of a series of innovations, with successive innovations generating radiations of metazoan clades as lineages breached functional thresholds. The elaboration of new cell classes and the appearance of such developmental innovations as cell sheets may have been of particular importance. Evolutionary biologists often implicitly assume that evolution is a uniformitarian, time-homogeneous process without strong temporal asymmetries in evolutionary mechanisms, rate or context. Yet evolutionary patterns do exhibit such asymmetries, raising the possibility that such innovations as metazoan development impose non-uniformities of evolutionary process.     

How to build a biofilm: a fungal perspective

Biofilms are differentiated masses of microbes that form on surfaces and are surrounded by an extracellular matrix. Fungal biofilms, especially those of the pathogen Candida albicans, are a cause of infections associated with medical devices. Such infections are particularly serious because biofilm cells are relatively resistant to many common antifungal agents. Several in vitro models have been used to elucidate the developmental stages and processes required for C. albicans biofilm formation, and recent studies have begun to define biofilm genetic control. It is clear that cell-substrate and cell-cell interactions, hyphal differentiation and extracellular matrix production are key steps in biofilm development. Drug resistance is acquired early in biofilm formation, and appears to be governed by different mechanisms in early and late biofilms. Quorum sensing might be an important factor in dispersal of biofilm cells. The past two years have seen the emergence of several genomic strategies to uncover global events in biofilm formation and directed studies to understand more specific events, such as hyphal formation, in the biofilm setting.     

Clash of kingdoms or why Drosophila larvae positively respond to fungal competitors

BACKGROUND: Competition with filamentous fungi has been demonstrated to be an important cause of mortality for the vast group of insects that depend on ephemeral resources (e.g. fruit, dung, carrion). Recent data suggest that the well-known aggregation of Drosophila larvae across decaying fruit yields a competitive advantage over mould, by which the larvae achieve a higher survival probability in larger groups compared with smaller ones. Feeding and locomotor behaviour of larger larval groups is assumed to cause disruption of fungal hyphae, leading to suppression of fungal growth, which in turn improves the chances of larval survival to the adult stage. Given the relationship between larval density, mould suppression and larval survival, the present study has tested whether fungal-infected food patches elicit communal foraging behaviour on mould-infected sites by which larvae might hamper mould growth more efficiently. RESULTS: Based on laboratory experiments in which Drosophila larvae were offered the choice between fungal-infected and uninfected food patches, larvae significantly aggregated on patches containing young fungal colonies. Grouping behaviour was also visible when larvae were offered only fungal-infected or only uninfected patches; however, larval aggregation was less strong under these conditions than in a heterogeneous environment (infected and uninfected patches). CONCLUSION: Because filamentous fungi can be deadly competitors for insect larvae on ephemeral resources, social attraction of Drosophila larvae to fungal-infected sites leading to suppression of mould growth may reflect an adaptive behavioural response that increases insect larval fitness and can thus be discussed as an anti-competitor behaviour. These observations support the hypothesis that adverse environmental conditions operate in favour of social behaviour. In a search for the underlying mechanisms of communal behaviour in Drosophila, this study highlights the necessity of investigating the role of inter-kingdom competition as a potential driving force in the evolution of spatial behaviour in insects.     

Identification of a Drosophila brain-gut peptide related to the neuropeptide Y family.

A neuropeptide F (NPF) was isolated from the fruit fly, Drosophila mellanogaster, based on a radioimmunoassay for a gut peptide from the corn earworm, Helicoverpa zea. A partial sequence was obtained from the fly peptide, and a genomic sequence coding for NPF was cloned after inverse polymerase chain reaction and shown to exist as a single genomic copy. The encoded, putative prepropeptide can be processed into an amidated NPF with 36 residues that is related to invertebrate NPF's and the neuropeptide Y family of vertebrates. In situ hybridization and immunocytochemistry showed that Drosophila NPF was expressed in the brain and midgut of fly larvae and adults.     

Defining phyla: morphological and molecular clues to metazoan evolution

None of the supraspecific taxonomic categories can be defined objectively. Each taxon should of course be monophyletic, but there is no morphological or molecular character that identifies, for example, the phylum level. This has led some authors to abandon the Linnaean categories, but they appear to be practical "handles" in daily communication. It has been proposed that each phylum exhibits a characteristic Bauplan, but the identification of such "types" have in practice proved difficult or impossible for several phyla. Monophyly of some of the approximately 30 morphology-based phyla has been put in question by molecular studies, but recent reports clearly show that the 18S rRNA molecule, which has been used extensively in phylogenetic analyses, cannot be used alone in identifying phyla (or other higher taxonomic groups). Some higher taxa, for example Chordata, Vertebrata, and Echinodermata, consistently show up as monophyletic in the analyses, whereas molluscan and annelidan subgroups just as consistently are mixed with each other and with a number of other protostomian phyla in varying patterns.