In epithelial collective migration, leader and follower cells migrate while maintaining cell–cell adhesion and tissue polarity. We have identified a conserved protein and interactors required for maintaining cell adhesion during a simple collective migration in the developing C. elegans male gonad. LINKIN is a previously uncharacterized, transmembrane protein conserved throughout Metazoa. We identified seven atypical FG–GAP domains in the extracellular domain, which potentially folds into a β-propeller structure resembling the α-integrin ligand-binding domain. C. elegans LNKN-1 localizes to the plasma membrane of all gonadal cells, with apical and lateral bias. We identified the LINKIN interactors RUVBL1, RUVBL2, and α-tubulin by using SILAC mass spectrometry on human HEK 293T cells and testing candidates for lnkn-1-like function in C. elegans male gonad. We propose that LINKIN promotes adhesion between neighboring cells through its extracellular domain and regulates microtubule dynamics through RUVBL proteins at its intracellular domain.
In animals, cells can move from one place to another to shape tissues, heal wounds, or defend against invading microbes. A cell may move alone or it may be attached to others and move as part of a group. One member of the group leads this ‘collective migration’, but it is not known how the cells are able to stick to each other and move together.
Collective migration takes place in the male gonad—the organ that makes sperm cells—in larvae of the nematode worm C. elegans. As the gonad matures, a group of cells form a simple chain that can move together. Kato et al. found that a protein called LINKIN must be present for this to happen.
LINKIN is found in the membrane that surrounds animal cells. One section of the protein—called the β-propeller—sits on the outside surface of the membrane. The structure of the β-propeller is similar to a section of another protein—called α-integrin—that also allows cells to attach, suggesting LINKIN may work in a similar way.
LINKIN is found in many animals, so Kato et al. searched for proteins that can interact with it in human cells. This search revealed three proteins that can interact with LINKIN and are required for the cells to move together. Two of the proteins control elements of the internal scaffolding of the cell: this scaffolding, which is known as the cytoskeleton, is involved in moving the cells.
The experiments suggest that LINKIN coordinates the process of binding together with the changes in the cytoskeleton that are needed to allow the cells to move as one. The next challenge is to understand how LINKIN changes the internal program of the cells to achieve this.
human cells; cell migration; organogenesis; cell polarity; protein–protein interactions; C. elegans
Invasive mole cricket species in the genus Scapteriscus have become significant agricultural pests and are continuing to expand their range in North America. Though largely subterranean, adults of some species such as S. borellii are capable of long dispersive flights and phonotaxis to male calling songs to find suitable habitats and mates. Mole crickets in the genus Scapteriscus are known to be attracted to and can be caught by audio lure traps that broadcast synthesized or recorded calling songs. We report improvements in the design and production of electronic controllers for the automation of semi-permanent mole cricket trap lures as well as highly portable audio trap collection designs. Using these improved audio lure traps we collected the first reported individuals of the pest mole cricket S. borellii in California. We describe several characteristic features of the calling song of the California population including that the pulse rate is a function of soil temperature, similar to Florida populations of S. borellii. Further, we show that other calling song characteristics (carrier frequency, intensity, and pulse rate) are significantly different between the populations.
Scapteriscus borellii; mole cricket; cricket trap; calling song
Sleep is characterized by behavioral quiescence, homeostasis, increased arousal threshold, and rapid reversibility. Understanding how these properties are encoded by a neuronal circuit has been difficult, and no single molecular or neuronal pathway has been shown to be responsible for the regulation of sleep. Taking advantage of the well-mapped neuronal connections of Caenorhabditis elegans and the sleep-like states in this animal, we demonstrate the changed properties of both sensory neurons and downstream interneurons that mediate sleep and arousal. The ASH sensory neuron displays reduced sensitivity to stimuli in the sleep-like state, and the activity of the corresponding interneurons in ASH’s motor circuit becomes asynchronous. Restoration of interneuron synchrony is sufficient for arousal. The multilevel circuit depression revealed provides an elegant strategy to promote a robust decrease in arousal while allowing for rapid reversibility of the sleep state.
Sleep; Neural Circuit; ChR2; GCaMP; Cameleon; Avoidance
Trichuris (whipworm) infects 1 billion people worldwide, and causes a disease (trichuriasis) that results in major socioeconomic losses in both humans and pigs. Trichuriasis relates to an inflammation of the large intestine manifested in bloody diarrhoea, and chronic disease can cause malnourishment and stunting in children. Paradoxically, Trichuris of pigs has shown substantial promise as a treatment for human autoimmune disorders, including inflammatory bowel disease (IBD) and multiple sclerosis (MS). Here, we report ~80 megabase (Mb) draft assemblies of the genomes of adult male and female T. suis, and explore stage-, sex- and tissue-specific transcription of messenger and small non-coding RNAs.
Tubulin protomers undergo an extensive array of post-translational modifications to tailor microtubules to specific tasks. One such modification, the acetylation of lysine-40 of α-tubulin, located in the lumen of microtubules, is associated with stable, long-living microtubule structures. MEC-17 was recently identified as the acetyltransferase that mediates this event. We have determined the crystal structure of the catalytic core of human MEC-17 in complex with its cofactor acetyl-CoA at 1.7 Å resolution. The structure reveals that the MEC-17 core adopts a canonical Gcn5-related N-acetyltransferase (GNAT) fold that is decorated with extensive surface loops. An enzymatic analysis of 33 MEC-17 surface mutants identifies hot-spot residues for catalysis and substrate recognition. A large, evolutionarily conserved hydrophobic surface patch is identified that is critical for enzymatic activity, suggesting that specificity is achieved by interactions with the α-tubulin substrate that extend outside of the modified surface loop. An analysis of MEC-17 mutants in C. elegans shows that enzymatic activity is dispensable for touch sensitivity.
X-ray crystallography; Tubulin acetyltransferase; Substrate recognition; C. elegans; Mechanosensation
The deep sea is Earth's largest habitat but little is known about the nature of deep-sea parasitism. In contrast to a few characterized cases of bacterial and protistan parasites, the existence and biological significance of deep-sea parasitic fungi is yet to be understood. Here we report the discovery of a fungus-related parasitic microsporidium, Nematocenator marisprofundi n. gen. n. sp. that infects benthic nematodes at methane seeps on the Pacific Ocean floor. This infection is species-specific and has been temporally and spatially stable over 2 years of sampling, indicating an ecologically consistent host-parasite interaction. A high distribution of spores in the reproductive tracts of infected males and females and their absence from host nematodes' intestines suggests a sexual transmission strategy in contrast to the fecal-oral transmission of most microsporidia. N. marisprofundi targets the host's body wall muscles causing cell lysis, and in severe infection even muscle filament degradation. Phylogenetic analyses placed N. marisprofundi in a novel and basal clade not closely related to any described microsporidia clade, suggesting either that microsporidia-nematode parasitism occurred early in microsporidia evolution or that host specialization occurred late in an ancient deep-sea microsporidian lineage. Our findings reveal that methane seeps support complex ecosystems involving interkingdom interactions between bacteria, nematodes, and parasitic fungi and that microsporidia parasitism exists also in the deep-sea biosphere.
deep-sea methane seeps; nematodes hosts; deep-sea microsporidia parasitism; muscle decomposition; basal fungi in the deep sea
The hookworm Necator americanus is the predominant soil-transmitted human parasite. Adult worms feed on blood in the small intestine, causing iron deficiency anaemia, malnutrition, growth and development stunting in children, and severe morbidity and mortality during pregnancy in women. Characterization of the first hookworm genome sequence (244 Mb, 19,151 genes) identified genes orchestrating the hookworm's invasion of the human host, genes involved in blood feeding and development, and genes encoding proteins that represent new potential drug targets against hookworms. N. americanus has undergone a considerable and unique expansion of immunomodulator proteins, some of which we highlight as potential novel treatments against inflammatory diseases. We also utilize a protein microarray to demonstrate a post-genomic application of the hookworm genome sequence. This genome provides an invaluable resource to boost ongoing efforts towards fundamental and applied post-genomic research, including the development of new methods to control hookworm and human immunological diseases.
nematodes; hookworm; necatoriasis; blood-feeding; SCP/TAPS protein; immunoregulation; anti-inflammation; genome; RNA-Seq; protein microarray
Nematodes have many different reproductive strategies along with their divergent life histories; the ability of hermaphrodite to self- and cross-fertilize is useful for genetic manipulation. Here, we demonstrate the hermaphroditism of the fungal feeding nematode Bursaphelenchus okinawaensis, which was formerly described as a parthenogenetic nematode, and we show its other unique sexual characteristics. To determine that it is hermaphroditic, we performed the following experiments: observation of the pronuclear and chromosome behavior during oogenesis and early embryogenesis; observation of spermatogenesis during the fourth larval stage; investigation of sperm utilization; and investigation of phenotypic segregation after cross-mating using a chemically induced visible mutant. We then investigated the mating preferences and spermatid size difference between males and hermaphrodites. B. okinawaensis males successfully mated only with sperm-depleted old hermaphrodites, and the spermatid sizes of males were almost the same as those of hermaphrodites. Moreover, the sex ratio of cross-fertilized progeny was highly skewed toward hermaphrodites. B. okinawaensis is phylogenetically distant from established model nematodes such as C. elegans and is more closely related to some economically relevant parasitic nematodes. This newly discovered hermaphroditic nematode has great potential for evolutionary and parasitological research.
hermaphroditism; nematode; early embryogenesis; genetics; satellite model
Gene function curation via Gene Ontology (GO) annotation is a common task among Model Organism Database groups. Owing to its manual nature, this task is considered one of the bottlenecks in literature curation. There have been many previous attempts at automatic identification of GO terms and supporting information from full text. However, few systems have delivered an accuracy that is comparable with humans. One recognized challenge in developing such systems is the lack of marked sentence-level evidence text that provides the basis for making GO annotations. We aim to create a corpus that includes the GO evidence text along with the three core elements of GO annotations: (i) a gene or gene product, (ii) a GO term and (iii) a GO evidence code. To ensure our results are consistent with real-life GO data, we recruited eight professional GO curators and asked them to follow their routine GO annotation protocols. Our annotators marked up more than 5000 text passages in 200 articles for 1356 distinct GO terms. For evidence sentence selection, the inter-annotator agreement (IAA) results are 9.3% (strict) and 42.7% (relaxed) in F1-measures. For GO term selection, the IAAs are 47% (strict) and 62.9% (hierarchical). Our corpus analysis further shows that abstracts contain ∼10% of relevant evidence sentences and 30% distinct GO terms, while the Results/Experiment section has nearly 60% relevant sentences and >70% GO terms. Further, of those evidence sentences found in abstracts, less than one-third contain enough experimental detail to fulfill the three core criteria of a GO annotation. This result demonstrates the need of using full-text articles for text mining GO annotations. Through its use at the BioCreative IV GO (BC4GO) task, we expect our corpus to become a valuable resource for the BioNLP research community.
The recognition of molecular patterns associated with specific pathogens or food sources is fundamental to ecology and plays a major role in the evolution of predator-prey relationships . Recent studies showed that nematodes produce an evolutionarily highly conserved family of small molecules, the ascarosides, which serve essential functions in regulating nematode development and behavior [2-4]. Here we show that nematophagous fungi, natural predators of soil-dwelling nematodes , can detect and respond to ascarosides. Nematophagous fungi use specialized trapping devices to catch and consume nematodes, and previous studies demonstrated that most fungal species do not produce traps constitutively but rather initiate trap-formation in response to their prey . We found that ascarosides, which are constitutively secreted by many species of soil-dwelling nematodes, represent a conserved molecular pattern used by nematophagous fungi to detect prey and trigger trap formation. Ascaroside-induced morphogenesis is conserved in several closely related species of nematophagous fungi and occurs only under nutrient-deprived condition. Our results demonstrate that microbial predators eavesdrop on chemical communication among their metazoan prey to regulate morphogenesis, providing a striking example of predator-prey co-evolution. We anticipate that these findings will have broader implications for understanding other inter-kingdom interactions involving nematodes, which are found in almost any ecological niche on Earth.
The nematode Caenorhabditis elegans is an important model organism in genetic research and drug screening because of its relative simplicity, ease of maintenance, amenability to simple genetic manipulation, and relevance to human biology. However, their small size and mobility make nematodes difficult to physically manipulate, particularly with spatial and temporal precision. We have developed a microfluidic device to overcome these challenges and enable fast behavior-based chemical screening in C. elegans. The key components of this easy-to-use device allow rapid loading and housing of C. elegans in a chamber array for chemical screening. A simple two-step loading process enables simultaneous loading of a large number of animals within a few minutes without using any expensive/active off-chip components. In addition, chemicals can be precisely delivered to the worms and exchanged with high temporal precision. To demonstrate this feature and the ability to measure time dependent responses to chemicals, we characterize the transient response of worms exposed to different concentrations of anesthetics. We then use the device to study the effect of chemical signals from hermaphrodite worms on male behavior. The ability of the device to maintain a large number of free moving animals in one field of view over a long period of time permits us to demonstrate an increase in the incidence of a specific behavior in males subjected to worm-conditioned medium. Because our device allows monitoring of a large number of worms with single-animal resolution, we envision that this platform will greatly expedite chemical screening in C. elegans.
WormBase (www.wormbase.org) has been serving the scientific community for over 11 years as the central repository for genomic and genetic information for the soil nematode Caenorhabditis elegans. The resource has evolved from its beginnings as a database housing the genomic sequence and genetic and physical maps of a single species, and now represents the breadth and diversity of nematode research, currently serving genome sequence and annotation for around 20 nematodes. In this article, we focus on WormBase’s role of genome sequence annotation, describing how we annotate and integrate data from a growing collection of nematode species and strains. We also review our approaches to sequence curation, and discuss the impact on annotation quality of large functional genomics projects such as modENCODE.
Caenorhabditis elegans; annotation; community resource; genome; model organism database; nematode; parasitic nematode; sequence curation
Since its release in 2000, WormBase (http://www.wormbase.org) has grown from a small resource focusing on a single species and serving a dedicated research community, to one now spanning 15 species essential to the broader biomedical and agricultural research fields. To enhance the rate of curation, we have automated the identification of key data in the scientific literature and use similar methodology for data extraction. To ease access to the data, we are collaborating with journals to link entities in research publications to their report pages at WormBase. To facilitate discovery, we have added new views of the data, integrated large-scale datasets and expanded descriptions of models for human disease. Finally, we have introduced a dramatic overhaul of the WormBase website for public beta testing. Designed to balance complexity and usability, the new site is species-agnostic, highly customizable, and interactive. Casual users and developers alike will be able to leverage the public RESTful application programming interface (API) to generate custom data mining solutions and extensions to the site. We report on the growth of our database and on our work in keeping pace with the growing demand for data, efforts to anticipate the requirements of users and new collaborations with the larger science community.
The lungworm, Dictyocaulus viviparus, causes parasitic bronchitis in cattle, and is responsible for substantial economic losses in temperate regions of the world. Here, we undertake the first large-scale exploration of available transcriptomic data for this lungworm, examine differences in transcription between different stages/both genders and identify and prioritize essential molecules linked to fundamental metabolic pathways, which could represent novel drug targets. Approximately 3 million expressed sequence tags (ESTs), generated by 454 sequencing from third-stage larvae (L3) as well as adult females and males of D. viviparus, were assembled and annotated. The assembly of these sequences yielded ~61,000 contigs, of which relatively large proportions encoded collagens (4.3%), ubiquitins (2.1%) and serine/threonine protein kinases (1.9%). Subtractive analysis in silico identified 6,928 nucleotide sequences as being uniquely transcribed in L3, and 5,203 and 7,889 transcripts as being exclusive to the adult female and male, respectively. Most peptides predicted from the conceptual translations were nucleoplasmins (L3), serine/threonine protein kinases (female) and major sperm proteins (male). Additional analyses allowed the prediction of three drug target candidates, whose Caenorhabditis elegans homologues were linked to a lethal RNA interference phenotype. This detailed exploration, combined with future transcriptomic sequencing of all developmental stages of D. viviparus, will facilitate future investigations of the molecular biology of this parasitic nematode as well as genomic sequencing. These advances will underpin the discovery of new drug and/or vaccine targets, focused on biotechnological outcomes.
Dictyocaulus viviparous; Bovine lungworm; Next-generation sequencing; Bioinformatics; Transcriptome; Ancylostoma-secreted proteins; Drug target prediction
WormBase (http://www.wormbase.org/) is a highly curated resource dedicated to supporting research using the model organism Caenorhabditis elegans. With an electronic history predating the World Wide Web, WormBase contains information ranging from the sequence and phenotype of individual alleles to genome-wide studies generated using next-generation sequencing technologies. In recent years, we have expanded the contents to include data on additional nematodes of agricultural and medical significance, bringing the knowledge of C. elegans to bear on these systems and providing support for underserved research communities. Manual curation of the primary literature remains a central focus of the WormBase project, providing users with reliable, up-to-date and highly cross-linked information. In this update, we describe efforts to organize the original atomized and highly contextualized curated data into integrated syntheses of discrete biological topics. Next, we discuss our experiences coping with the vast increase in available genome sequences made possible through next-generation sequencing platforms. Finally, we describe some of the features and tools of the new WormBase Web site that help users better find and explore data of interest.
The barber's pole worm, Haemonchus contortus, is one of the most economically important parasites of small ruminants worldwide. Although this parasite can be controlled using anthelmintic drugs, resistance against most drugs in common use has become a widespread problem. We provide a draft of the genome and the transcriptomes of all key developmental stages of H. contortus to support biological and biotechnological research areas of this and related parasites.
The draft genome of H. contortus is 320 Mb in size and encodes 23,610 protein-coding genes. On a fundamental level, we elucidate transcriptional alterations taking place throughout the life cycle, characterize the parasite's gene silencing machinery, and explore molecules involved in development, reproduction, host-parasite interactions, immunity, and disease. The secretome of H. contortus is particularly rich in peptidases linked to blood-feeding activity and interactions with host tissues, and a diverse array of molecules is involved in complex immune responses. On an applied level, we predict drug targets and identify vaccine molecules.
The draft genome and developmental transcriptome of H. contortus provide a major resource to the scientific community for a wide range of genomic, genetic, proteomic, metabolomic, evolutionary, biological, ecological, and epidemiological investigations, and a solid foundation for biotechnological outcomes, including new anthelmintics, vaccines and diagnostic tests. This first draft genome of any strongylid nematode paves the way for a rapid acceleration in our understanding of a wide range of socioeconomically important parasites of one of the largest nematode orders.
In the model organism Caenorhabditis elegans, a class of small molecule signals called ascarosides regulate development, mating and social behaviors. Ascaroside production has been studied in the predominant sex, the hermaphrodite, but not in males, which account for less than 1% of wild-type worms grown under typical laboratory conditions. Using HPLC-MS-based targeted metabolomics, we show that males also produce ascarosides and that their ascaroside profile differs markedly from that of hermaphrodites. Whereas hermaphrodite ascaroside profiles are dominated by ascr#3, containing an α,β-unsaturated fatty acid, males predominantly produce the corresponding dihydro-derivative ascr#10. This small structural modification profoundly affects signaling properties: hermaphrodites are retained by attomole-amounts of male-produced ascr#10, whereas hermaphrodite-produced ascr#3 repels hermaphrodites and attracts males. Male production of ascr#10 is population density-dependent, indicating sensory regulation of ascaroside biosynthesis. Analysis of gene expression data supports a model in which sex-specific regulation of peroxisomal β-oxidation produces functionally different ascaroside profiles.
Nematodes are ubiquitous organisms that have a significant global impact on ecosystems, economies, agriculture, and human health. The applied importance of nematodes and the experimental tractability of many species have promoted their use as models in various research areas, including developmental biology, evolutionary biology, ecology, and animal-bacterium interactions. Nematodes are particularly well suited for investigating host associations with bacteria because all nematodes have interacted with bacteria during their evolutionary history and engage in a diversity of association types. Interactions between nematodes and bacteria can be positive (mutualistic) or negative (pathogenic/parasitic) and may be transient or stably maintained (symbiotic). Furthermore, since many mechanistic aspects of nematode-bacterium interactions are conserved their study can provide broader insights into other types of associations, including those relevant to human diseases. Recently, genome-scale studies have been applied to diverse nematode-bacterial interactions, and have helped reveal mechanisms of communication and exchange between the associated partners. In addition to providing specific information about the system under investigation, these studies also have helped inform our understanding of genome evolution, mutualism, and innate immunity. In this review we will discuss the importance and diversity of nematodes, 'omics' studies in nematode-bacterial systems, and the wider implications of the findings.
Steinernema; Heterorhabditis; Laxus; Brugia; Caenorhabditis elegans; Xenorhabdus; Photorhabdus; Wolbachia
Here we report a low-cost and simple wide field-of-view (FOV) on-chip fluorescence-imaging platform, termed fluorescence Talbot microscopy (FTM), which utilizes the Talbot self-imaging effect to enable efficient fluorescence imaging over a large and directly scalable FOV. The FTM prototype has a resolution of 1.2 μm and an FOV of 3.9 mm × 3.5 mm. We demonstrate the imaging capability of FTM on fluorescently labeled breast cancer cells (SK-BR-3) and human embryonic kidney 293 (HEK) cells expressing green fluorescent protein.
Heterorhabditis bacteriophora are entomopathogenic nematodes that have evolved a mutualism with Photorhabdus luminescens bacteria to function as highly virulent insect pathogens. The nematode provides a safe harbor for intestinal symbionts in soil and delivers the symbiotic bacteria into the insect blood. The symbiont provides virulence and toxins, metabolites essential for nematode reproduction, and antibiotic preservation of the insect cadaver. Approximately half of the 21,250 putative protein coding genes identified in the 77 Mbp high quality draft H. bacteriophora genome sequence were novel proteins of unknown function lacking homologs in Caenorhabditis elegans or any other sequenced organisms. Similarly, 317 of the 603 predicted secreted proteins are novel with unknown function in addition to 19 putative peptidases, 9 peptidase inhibitors and 7 C-type lectins that may function in interactions with insect hosts or bacterial symbionts. The 134 proteins contained mariner transposase domains, of which there are none in C. elegans, suggesting an invasion and expansion of mariner transposons in H. bacteriophora. Fewer Kyoto Encyclopedia of Genes and Genomes Orthologies in almost all metabolic categories were detected in the genome compared with 9 other sequenced nematode genomes, which may reflect dependence on the symbiont or insect host for these functions. The H. bacteriophora genome sequence will greatly facilitate genetics, genomics and evolutionary studies to gain fundamental knowledge of nematode parasitism and mutualism. It also elevates the utility of H. bacteriophora as a bridge species between vertebrate parasitic nematodes and the C. elegans model.
Nematodes compose an abundant and diverse invertebrate phylum with members inhabiting nearly every ecological niche. Panagrellus redivivus (the “microworm”) is a free-living nematode frequently used to understand the evolution of developmental and behavioral processes given its phylogenetic distance to Caenorhabditis elegans. Here we report the de novo sequencing of the genome, transcriptome, and small RNAs of P. redivivus. Using a combination of automated gene finders and RNA-seq data, we predict 24,249 genes and 32,676 transcripts. Small RNA analysis revealed 248 microRNA (miRNA) hairpins, of which 63 had orthologs in other species. Fourteen miRNA clusters containing 42 miRNA precursors were found. The RNA interference, dauer development, and programmed cell death pathways are largely conserved. Analysis of protein family domain abundance revealed that P. redivivus has experienced a striking expansion of BTB domain-containing proteins and an unprecedented expansion of the cullin scaffold family of proteins involved in multi-subunit ubiquitin ligases, suggesting proteolytic plasticity and/or tighter regulation of protein turnover. The eukaryotic release factor protein family has also been dramatically expanded and suggests an ongoing evolutionary arms race with viruses and transposons. The P. redivivus genome provides a resource to advance our understanding of nematode evolution and biology and to further elucidate the genomic architecture leading to free-living lineages, taking advantage of the many fascinating features of this worm revealed by comparative studies.
Panagrellus redivivus; microRNA; BTB domain; F-box; eRF1; cullin
Dishevelled (Dsh or Dvl) is an important signaling protein, playing a key role in Wnt signaling and relaying cellular information for several developmental pathways. Dsh is highly conserved among metazoans and has expanded into a multigene family in most bilaterian lineages, including vertebrates, planarians, and nematodes. These orthologs, where explored, are known to have considerable overlap in function, but evidence for functional specialization continues to mount. We performed a comparative analysis of Dsh across animals to explore protein architecture and identify conserved and divergent features that could provide insight into functional specialization with an emphasis on invertebrates, especially nematodes. We find evidence of dynamic evolution of Dsh, particularly among nematodes, with taxa varying in ortholog number from one to three. We identify a new domain specific to some nematode lineages and find an unexpected nuclear localization signal conserved in many Dsh orthologs. Our findings raise questions of protein evolution in general and provide clues as to how animals have dealt with the complex intricacies of having a protein, such as Dsh, act as a central messenger hub connected to many different and vitally important pathways. We discuss our findings in the context of functional specialization and bring many testable hypotheses to light.
dishevelled; protein evolution; Nematoda; Wnt; C. elegans
The identity of each neuron is determined by the expression of a distinct group of genes comprising its terminal gene battery. The regulatory sequences that control the expression of such terminal gene batteries in individual neurons is largely unknown. The existence of a complete genome sequence for C. elegans and draft genomes of other nematodes let us use comparative genomics to identify regulatory sequences directing expression in the DVA interneuron.
Using phylogenetic comparisons of multiple Caenorhabditis species, we identified conserved non-coding sequences in 3 of 10 genes (fax-1, nmr-1, and twk-16) that direct expression of reporter transgenes in DVA and other neurons. The conserved region and flanking sequences in an 85-bp intronic region of the twk-16 gene directs highly restricted expression in DVA. Mutagenesis of this 85 bp region shows that it has at least four regions. The central 53 bp region contains a 29 bp region that represses expression and a 24 bp region that drives broad neuronal expression. Two short flanking regions restrict expression of the twk-16 gene to DVA. A shared GA-rich motif was identified in three of these genes but had opposite effects on expression when mutated in the nmr-1 and twk-16 DVA regulatory elements.
We identified by multi-species conservation regulatory regions within three genes that direct expression in the DVA neuron. We identified four contiguous regions of sequence of the twk-16 gene enhancer with positive and negative effects on expression, which combined to restrict expression to the DVA neuron. For this neuron a single binding site may thus not achieve sufficient specificity for cell specific expression. One of the positive elements, an 8-bp sequence required for expression was identified in silico by sequence comparisons of seven nematode species, demonstrating the potential resolution of expanded multi-species phylogenetic comparisons.
In the model organism Caenorhabditis elegans, a family of endogenous small molecules, the ascarosides, function as key regulators of developmental timing and behavior that act upstream of conserved signaling pathways. The ascarosides are based on the dideoxysugar ascarylose, which is linked to fatty acid-like side chains of varying lengths derived from peroxisomal β-oxidation. Despite their importance for many aspects of C. elegans biology, knowledge of ascaroside structures, biosynthesis, and homeostasis remains incomplete. We used an MS/MS-based screen to profile ascarosides in C. elegans wild type and mutant metabolomes, which revealed a much greater structural diversity of ascaroside derivatives than previously reported. Comparison of the metabolomes from wild type and a series of peroxisomal β-oxidation mutants showed that the enoyl CoA-hydratase MAOC-1 serves an important role in ascaroside biosynthesis and clarified the functions of two other enzymes, ACOX-1 and DHS-28. We show that following peroxisomal β-oxidation the ascarosides are selectively derivatized with moieties of varied biogenetic origin and that such modifications can dramatically affect biological activity, producing signaling molecules active at low femtomolar concentrations. Based on these results the ascarosides appear as a modular library of small molecule signals, integrating building blocks from three major metabolic pathways; carbohydrate metabolism, peroxisomal β-oxidation of fatty acids, and amino acid catabolism. Our screen further demonstrates that ascaroside biosynthesis is directly affected by nutritional status and that excretion of the final products is highly selective.
Caenorhabditis elegans is the only animal for which a detailed neural connectivity diagram has been constructed. However, synaptic polarities in this diagram, and thus, circuit functions are largely unknown. Here, we deciphered the likely polarities of seven pre-motor neurons implicated in the control of worm's locomotion, using a combination of experimental and computational tools. We performed single and multiple laser ablations in the locomotor interneuron circuit and recorded times the worms spent in forward and backward locomotion. We constructed a theoretical model of the locomotor circuit and searched its all possible synaptic polarity combinations and sensory input patterns in order to find the best match to the timing data. The optimal solution is when either all or most of the interneurons are inhibitory and forward interneurons receive the strongest input, which suggests that inhibition governs the dynamics of the locomotor interneuron circuit. From the five pre-motor interneurons, only AVB and AVD are equally likely to be excitatory, i.e., they have probably similar number of inhibitory and excitatory connections to distant targets. The method used here has a general character and thus can be also applied to other neural systems consisting of small functional networks.
C. elegans; locomotory interneurons; synaptic polarity; locomotion; neural circuit modeling; optimization; laser ablations