The chitin synthase genes chs-1 and chs-2 are essential for C. elegans development and responsible for chitin deposition in the eggshell and pharynx, respectively

Root-knot nematodes induce pattern-triggered immunity in Arabidopsis thaliana roots

Root-knot nematodes (RKNs; Meloidogyne spp.) are plant parasites with a broad host range causing great losses worldwide. To parasitize their hosts, RKNs establish feeding sites in roots known as giant cells. The majority of work studying plant-RKN interactions in susceptible hosts addresses establishment of the giant cells and there is limited information on the early defense responses. Here we characterized early defense or pattern-triggered immunity (PTI) against RKNs in Arabidopsis thaliana. To address PTI, we evaluated known canonical PTI signaling mutants with RKNs and investigated the expression of PTI marker genes after RKN infection using both quantitative PCR and β-glucuronidase reporter transgenic lines. We showed that PTI-compromised plants have enhanced susceptibility to RKNs, including the bak1-5 mutant. BAK1 is a common partner of distinct receptors of microbe- and damage-associated molecular patterns. Furthermore, our data indicated that nematode recognition leading to PTI responses involves camalexin and glucosinolate biosynthesis. While the RKN-induced glucosinolate biosynthetic pathway was BAK1-dependent, the camalexin biosynthetic pathway was only partially dependent on BAK1. Combined, our results indicate the presence of BAK1-dependent and -independent PTI against RKNs in A. thaliana, suggesting the existence of diverse nematode recognition mechanisms.

In Vivo Interaction Proteomics in Caenorhabditis elegans Embryos Provides New Insights into P Granule Dynamics

Studying protein interactions in whole organisms is fundamental to understanding development. Here, we combine in vivo expressed GFP-tagged proteins with quantitative proteomics to identify protein-protein interactions of selected key proteins involved in early C. elegans embryogenesis. Co-affinity purification of interaction partners for eight bait proteins resulted in a pilot in vivo interaction map of proteins with a focus on early development. Our network reflects known biology and is highly enriched in functionally relevant interactions. To demonstrate the utility of the map, we looked for new regulators of P granule dynamics and found that GEI-12, a novel binding partner of the DYRK family kinase MBK-2, is a key regulator of P granule formation and germline maintenance. Our data corroborate a recently proposed model in which the phosphorylation state of GEI-12 controls P granule dynamics. In addition, we find that GEI-12 also induces granule formation in mammalian cells, suggesting a common regulatory mechanism in worms and humans. Our results show that in vivo interaction proteomics provides unique insights into animal development.

Automated parasite faecal egg counting using fluorescence labelling, smartphone image capture and computational image analysis

Intestinal parasites are a concern in veterinary medicine worldwide and for human health in the developing world. Infections are identified by microscopic visualisation of parasite eggs in faeces, which is time-consuming, requires technical expertise and is impractical for use on-site. For these reasons, recommendations for parasite surveillance are not widely adopted and parasite control is based on administration of rote prophylactic treatments with anthelmintic drugs. This approach is known to promote anthelmintic resistance, so there is a pronounced need for a convenient egg counting assay to promote good clinical practice. Using a fluorescent chitin-binding protein, we show that this structural carbohydrate is present and accessible in shells of ova of strongyle, ascarid, trichurid and coccidian parasites. Furthermore, we show that a cellular smartphone can be used as an inexpensive device to image fluorescent eggs and, by harnessing the computational power of the phone, to perform image analysis to count the eggs. Strongyle egg counts generated by the smartphone system had a significant linear correlation with manual McMaster counts (R(2)=0.98), but with a significantly lower coefficient of variation (P=0.0177). Furthermore, the system was capable of differentiating equine strongyle and ascarid eggs similar to the McMaster method, but with significantly lower coefficients of variation (P<0.0001). This demonstrates the feasibility of a simple, automated on-site test to detect and/or enumerate parasite eggs in mammalian faeces without the need for a laboratory microscope, and highlights the potential of smartphones as relatively sophisticated, inexpensive and portable medical diagnostic devices.

Genomic Analyses of Sperm Fate Regulator Targets Reveal a Common Set of Oogenic mRNAs in Caenorhabditis elegans

Germ cell specification as sperm or oocyte is an ancient cell fate decision, but its molecular regulation is poorly understood. In Caenorhabditis elegans, the FOG-1 and FOG-3 proteins behave genetically as terminal regulators of sperm fate specification. Both are homologous to well-established RNA regulators, suggesting that FOG-1 and FOG-3 specify the sperm fate post-transcriptionally. We predicted that FOG-1 and FOG-3, as terminal regulators of the sperm fate, might regulate a battery of gamete-specific differentiation genes. Here we test that prediction by exploring on a genomic scale the messenger RNAs (mRNAs) associated with FOG-1 and FOG-3. Immunoprecipitation of the proteins and their associated mRNAs from spermatogenic germlines identifies 81 FOG-1 and 722 FOG-3 putative targets. Importantly, almost all FOG-1 targets are also FOG-3 targets, and these common targets are strongly biased for oogenic mRNAs. The discovery of common target mRNAs suggested that FOG-1 and FOG-3 work together. Consistent with that idea, we find that FOG-1 and FOG-3 proteins co-immunoprecipitate from both intact nematodes and mammalian tissue culture cells and that they colocalize in germ cells. Taking our results together, we propose a model in which FOG-1 and FOG-3 work in a complex to repress oogenic transcripts and thereby promote the sperm fate.

Group 2 innate lymphoid cells utilize the IRF4-IL-9 module to coordinate epithelial cell maintenance of lung homeostasis

Group 2 innate lymphoid cells (ILC2s) have an important role in acute allergic lung inflammation. Given their distribution and function, lung ILC2s are hypothesized to coordinate epithelial responses to the external environment; however, how barrier surveillance is linked to ILC2 activation remains unclear. Here, we demonstrate that alveolar type II cells are the main source of interleukin (IL)-33 and thymic stromal lymphopoietin (TSLP) generated in response to chitin or migratory helminths. IL-33 and TSLP synergistically induce an interferon regulatory factor 4 (IRF4)-IL-9 program in ILC2s, and autocrine IL-9 promotes rapid IL-5 and IL-13 production required for optimal epithelial responses in the conducting airways. Thus, ILC2s link alveolar function to regulation of airway flow, revealing a key interaction between resident lymphoid and structural cells that might underlie similar organizational hierarchies in other organs.

Reproductive Aging Drives Protein Accumulation in the Uterus and Limits Lifespan in C. elegans

Aging in Caenorhabditis elegans is characterized by widespread physiological and molecular changes, but the mechanisms that determine the rate at which these changes occur are not well understood. In this study, we identify a novel link between reproductive aging and somatic aging in C. elegans. By measuring global age-related changes in the proteome, we identify a previously uncharacterized group of secreted proteins in the adult uterus that dramatically increase in abundance with age. This accumulation is blunted in animals with an extended reproductive period and accelerated in sterile animals lacking a germline. Uterine proteins are not removed in old post-reproductive animals or in young vulvaless worms, indicating that egg-laying is necessary for their rapid removal in wild-type young animals. Together, these results suggest that age-induced infertility contributes to extracellular protein accumulation in the uterus with age. Finally, we show that knocking down multiple age-increased proteins simultaneously extends lifespan. These results provide a mechanistic example of how the cessation of reproduction contributes to detrimental changes in the soma, and demonstrate how the timing of reproductive decline can influence the rate of aging.

To understand the process of aging at the molecular level in C. elegans, we measured changes in protein abundance with age, determined whether these age-related protein changes lead to dysfunction in old animals, and have elucidated one of the upstream pathways responsible for these aging changes. We found that egg-laying in young worms permits removal of a novel class of proteins present in the uterus. When the reproductive period ends, the removal of uterine proteins stops, causing them to accumulate to toxic levels. This shows that the timing of reproductive decline influences the rate of somatic aging. The concept that the reproductive period has a direct role in specifying the rate of aging of the soma likely applies to other species as well.

Tissue-specific transcriptomics and proteomics of a filarial nematode and its Wolbachia endosymbiont

Background

Filarial nematodes cause debilitating human diseases. While treatable, recent evidence suggests drug resistance is developing, necessitating the development of novel targets and new treatment options. Although transcriptomic and proteomic studies around the nematode life cycle have greatly enhanced our knowledge, whole organism approaches have not provided spatial resolution of gene expression, which can be gained by examining individual tissues. Generally, due to their small size, tissue dissection of human-infecting filarial nematodes remains extremely challenging. However, canine heartworm disease is caused by a closely related and much larger filarial nematode, Dirofilaria immitis. As with many other filarial nematodes, D. immitis contains Wolbachia, an obligate bacterial endosymbiont present in the hypodermis and developing oocytes within the uterus. Here, we describe the first concurrent tissue-specific transcriptomic and proteomic profiling of a filarial nematode (D. immitis) and its Wolbachia (wDi) in order to better understand tissue functions and identify tissue-specific antigens that may be used for the development of new diagnostic and therapeutic tools.

Methods

Adult D. immitis worms were dissected into female body wall (FBW), female uterus (FU), female intestine (FI), female head (FH), male body wall (MBW), male testis (MT), male intestine (MI), male head (MH) and 10.1186/s12864-015-2083-2 male spicule (MS) and used to prepare transcriptomic and proteomic libraries.

Results

Transcriptomic and proteomic analysis of several D. immitis tissues identified many biological functions enriched within certain tissues. Hierarchical clustering of the D. immitis tissue transcriptomes, along with the recently published whole-worm adult male and female D. immitis transcriptomes, revealed that the whole-worm transcriptome is typically dominated by transcripts originating from reproductive tissue. The uterus appeared to have the most variable transcriptome, possibly due to age. Although many functions are shared between the reproductive tissues, the most significant differences in gene expression were observed between the uterus and testis. Interestingly, wDi gene expression in the male and female body wall is fairly similar, yet slightly different to that of Wolbachia gene expression in the uterus. Proteomic methods verified 32 % of the predicted D. immitis proteome, including over 700 hypothetical proteins of D. immitis. Of note, hypothetical proteins were among some of the most abundant Wolbachia proteins identified, which may fulfill some important yet still uncharacterized biological function.

Conclusions

The spatial resolution gained from this parallel transcriptomic and proteomic analysis adds to our understanding of filarial biology and serves as a resource with which to develop future therapeutic strategies against filarial nematodes and their Wolbachia endosymbionts.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-2083-2) contains supplementary material, which is available to authorized users.

Large-scale identification of wheat genes resistant to cereal cyst nematode Heterodera avenae using comparative transcriptomic analysis

Background

Cereal cyst nematode Heterodera avenae, an important soil-borne pathogen in wheat, causes numerous annual yield losses worldwide, and use of resistant cultivars is the best strategy for control. However, target genes are not readily available for breeding resistant cultivars. Therefore, comparative transcriptomic analyses were performed to identify more applicable resistance genes for cultivar breeding.

Methods

The developing nematodes within roots were stained with acid fuchsin solution. Transcriptome assemblies and redundancy filteration were obtained by Trinity, TGI Clustering Tool and BLASTN, respectively. Gene Ontology annotation was yielded by Blast2GO program, and metabolic pathways of transcripts were analyzed by Path_finder. The ROS levels were determined by luminol-chemiluminescence assay. The transcriptional gene expression profiles were obtained by quantitative RT-PCR.

Results

The RNA-sequencing was performed using an incompatible wheat cultivar VP1620 and a compatible control cultivar WEN19 infected with H. avenae at 24 h, 3 d and 8 d. Infection assays showed that VP1620 failed to block penetration of H. avenae but disturbed the transition of developmental stages, leading to a significant reduction in cyst formation. Two types of expression profiles were established to predict candidate resistance genes after developing a novel strategy to generate clean RNA-seq data by removing the transcripts of H. avenae within the raw data before assembly. Using the uncoordinated expression profiles with transcript abundance as a standard, 424 candidate resistance genes were identified, including 302 overlapping genes and 122 VP1620-specific genes. Genes with similar expression patterns were further classified according to the scales of changed transcript abundances, and 182 genes were rescued as supplementary candidate resistance genes. Functional characterizations revealed that diverse defense-related pathways were responsible for wheat resistance against H. avenae. Moreover, phospholipase was involved in many defense-related pathways and localized in the connection position. Furthermore, strong bursts of reactive oxygen species (ROS) within VP1620 roots infected with H. avenae were induced at 24 h and 3 d, and eight ROS-producing genes were significantly upregulated, including three class III peroxidase and five lipoxygenase genes.

Conclusions

Large-scale identification of wheat resistance genes were processed by comparative transcriptomic analysis. Functional characterization showed that phospholipases associated with ROS production played vital roles in early defense responses to H. avenae via involvement in diverse defense-related pathways as a hub switch. This study is the first to investigate the early defense responses of wheat against H. avenae, not only provides applicable candidate resistance genes for breeding novel wheat cultivars, but also enables a better understanding of the defense mechanisms of wheat against H. avenae.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-2037-8) contains supplementary material, which is available to authorized users.

ChtVis-Tomato, a genetic reporter for in vivo visualization of chitin deposition in Drosophila

Chitin is a polymer of N-acetylglucosamine that is abundant and widely found in the biological world. It is an important constituent of the cuticular exoskeleton that plays a key role in the insect life cycle. To date, the study of chitin deposition during cuticle formation has been limited by the lack of a method to detect it in living organisms. To overcome this limitation, we have developed ChtVis-Tomato, an in vivo reporter for chitin in Drosophila. ChtVis-Tomato encodes a fusion protein that contains an apical secretion signal, a chitin-binding domain (CBD), a fluorescent protein and a cleavage site to release it from the plasma membrane. The chitin reporter allowed us to study chitin deposition in time lapse experiments and by using it we have identified unexpected deposits of chitin fibers in Drosophila pupae. ChtVis-Tomato should facilitate future studies on chitin in Drosophila and other insects.

Chitin, a key factor in immune regulation: lesson from infection with fungi and chitin bearing parasites

The probability of infection with fungi, as well as parasitic nematodes or arthropods may increase in overcrowded population of animals and human. The widespread overuse of drugs and immunosuppressants for veterinary or medical treatment create an opportunity for many pathogenic species. The aim of the review is to present the common molecular characteristics of such pathogens as fungi and nematodes and other chitin bearing animals, which may both activate and downregulate the immune response of the host. Although these pathogens are evolutionary distinct and distant, they may provoke similar immune mechanisms. The role of chitin in these phenomena will be reviewed, highlighting the immune reactions that may be induced in mammals by this natural polymer.

FBN-1, a fibrillin-related protein, is required for resistance of the epidermis to mechanical deformation during C. elegans embryogenesis

During development, biomechanical forces contour the body and provide shape to internal organs. Using genetic and molecular approaches in combination with a FRET-based tension sensor, we characterized a pulling force exerted by the elongating pharynx (foregut) on the anterior epidermis during C. elegans embryogenesis. Resistance of the epidermis to this force and to actomyosin-based circumferential constricting forces is mediated by FBN-1, a ZP domain protein related to vertebrate fibrillins. fbn-1 was required specifically within the epidermis and FBN-1 was expressed in epidermal cells and secreted to the apical surface as a putative component of the embryonic sheath. Tiling array studies indicated that fbn-1 mRNA processing requires the conserved alternative splicing factor MEC-8/RBPMS. The conserved SYM-3/FAM102A and SYM-4/WDR44 proteins, which are linked to protein trafficking, function as additional components of this network. Our studies demonstrate the importance of the apical extracellular matrix in preventing mechanical deformation of the epidermis during development.

DOI:http://dx.doi.org/10.7554/eLife.06565.001

For an animal embryo to develop, its cells must organize themselves into tissues and organs. For example, skin and the lining of internal organs—such as the lungs and gut—are made from cells called epithelial cells, which are tightly linked to form flat sheets.

In a microscopic worm called Caenorhabditis elegans, the outermost layer of epithelial cells (called the epidermis) forms over the surface of the embryo early on in embryonic development. Shortly afterwards, the embryonic epidermis experiences powerful contractions along the surface of the embryo. The force generated by these contractions converts the embryo from an oval shape to a roughly cylindrical form. These contractions also squeeze the internal tissues and organs, which correspondingly elongate along with the epidermis.

It has been known for decades that such ‘mechanical’ forces are important for the normal development of embryos. However, it remains poorly understood how these forces generate tissues and organs of the proper shape—partly because it is difficult to measure forces in living embryos. It is also not clear how the mechanical properties of specific tissues are controlled.

Now, Kelley, Yochem, Krieg et al. have analyzed the development of C. elegans' embryos and discovered a novel mechanical interplay between the feeding organ (called the pharynx) and the worm's epidermis. The experiments involved studying several mutant worms that perturb epidermal contractions and disrupt the attachment of the pharynx to the epidermis. These studies suggested that the pharynx exerts a strong inward pulling force on the epidermis during development. Using recently developed methods, Kelley, Yochem, Krieg et al. then measured mechanical forces within intact worm embryos and demonstrated that greater forces were experienced in cells that were being pulled by the pharynx.

Kelley, Yochem, Krieg et al. further analyzed how the epidermis normally resists this pulling force from the pharynx and implicated a protein called FBN-1. This worm protein is structurally related to a human protein that is affected in people with a disorder called Marfan Syndrome. Worm embryos without the FBN-1 protein become severely deformed because they are unable to withstand mechanical forces at the epidermis. FBN-1 is normally synthesized and then transported to the outside of the worm embryo by epidermal cells, where it is thought to assemble into a meshwork of long fibers. This provides a strong scaffold that attaches to the epidermis to prevent the epidermis from undergoing excessive deformation while it experiences mechanical forces.

The work of Kelley, Yochem, Krieg et al. provides an opportunity to understand how FBN-1 and other fiber-forming proteins are produced and transported to the cell surface. Moreover, these findings may have implications for human diseases and birth defects that result from an inability of tissues to respond appropriately to mechanical forces.

DOI:http://dx.doi.org/10.7554/eLife.06565.002

Molecular docking and site-directed mutagenesis of a Bacillus thuringiensis chitinase to improve chitinolytic, synergistic lepidopteran-larvicidal and nematicidal activities

Bacterial chitinases are useful in the biocontrol of agriculturally important pests and fungal pathogens. However, the utility of naturally occurring bacterial chitinases is often limited by their low enzyme activity. In this study, we constructed mutants of a Bacillus thuringiensis chitinase with enhanced activity based on homology modeling, molecular docking, and the site-directed mutagenesis of target residues to modify spatial positions, steric hindrances, or hydrophilicity/hydrophobicity. We first identified a gene from B. thuringiensis YBT-9602 that encodes a chitinase (Chi9602) belonging to glycosyl hydrolase family 18 with conserved substrate-binding and substrate-catalytic motifs. We constructed a structural model of a truncated version of Chi9602 (Chi9602_35-459) containing the substrate-binding domain using the homologous 1ITX protein of Bacillus circulans as the template. We performed molecular docking analysis of Chi9602_35-459 using di-N-acetyl-D-glucosamine as the ligand. We then selected 10 residues of interest from the docking area for the site-directed mutagenesis experiments and expression in Escherichia coli. Assays of the chitinolytic activity of the purified chitinases revealed that the three mutants exhibited increased chitinolytic activity. The ChiW50A mutant exhibited a greater than 60 % increase in chitinolytic activity, with similar pH, temperature and metal ion requirements, compared to wild-type Chi9602. Furthermore, ChiW50A exhibited pest-controlling activity and antifungal activity. Remarkable synergistic effects of this mutant with B. thuringiensis spore-crystal preparations against Helicoverpa armigera and Caenorhabditis elegans larvae and obvious activity against several plant-pathogenic fungi were observed.

Deciphering the genetic programme triggering timely and spatially-regulated chitin deposition

Organ and tissue formation requires a finely tuned temporal and spatial regulation of differentiation programmes. This is necessary to balance sufficient plasticity to undergo morphogenesis with the acquisition of the mature traits needed for physiological activity. Here we addressed this issue by analysing the deposition of the chitinous extracellular matrix of Drosophila, an essential element of the cuticle (skin) and respiratory system (tracheae) in this insect. Chitin deposition requires the activity of the chitin synthase Krotzkopf verkehrt (Kkv). Our data demonstrate that this process equally requires the activity of two other genes, namely expansion (exp) and rebuf (reb). We found that Exp and Reb have interchangeable functions, and in their absence no chitin is produced, in spite of the presence of Kkv. Conversely, when Kkv and Exp/Reb are co-expressed in the ectoderm, they promote chitin deposition, even in tissues normally devoid of this polysaccharide. Therefore, our results indicate that both functions are not only required but also sufficient to trigger chitin accumulation. We show that this mechanism is highly regulated in time and space, ensuring chitin accumulation in the correct tissues and developmental stages. Accordingly, we observed that unregulated chitin deposition disturbs morphogenesis, thus highlighting the need for tight regulation of this process. In summary, here we identify the genetic programme that triggers the timely and spatially regulated deposition of chitin and thus provide new insights into the extracellular matrix maturation required for physiological activity.

In this work we studied the maturation of the extracellular matrix during Drosophila embryogenesis. Drosophila deposit a chitin-rich extracellular matrix with key physiological functions, such as the control of organ size and shape, and cuticle formation. Chitin synthesis depends on chitin synthases, and in Drosophila the gene krotzkopf verkehrt (kkv) encodes the main enzyme of this family. Our observations indicate that Kkv alone is not sufficient to induce chitin formation. We have identified another function (which is exerted by the activity of two genes encoding MH2-domain proteins) that are equally required for chitin deposition. The most striking result of our analysis is that the presence of Kkv and the newly identified function is sufficient to trigger chitin deposition in ectodermally-derived tissues, even if they are normally devoid of this polysaccharide. Importantly, we also demonstrate that unregulated chitin deposition (absent, advanced, or ectopic) leads to severe defects in morphogenesis. We show that the temporal and spatial pattern of kkv and the other two genes perfectly recapitulates the deposition of chitin, thereby unveiling a highly co-ordinated mechanism for the acquisition of mature traits.

Early divergence, broad distribution, and high diversity of animal chitin synthases

Even though chitin is one of the most abundant biopolymers in nature, current knowledge on chitin formation is largely based only on data from fungi and insects. This study reveals unanticipated broad taxonomic distribution and extensive diversification of chitin synthases (CSs) in Metazoa, shedding new light on the relevance of chitin in animals and suggesting unforeseen complexity of chitin synthesis in many groups. We uncovered robust orthologs to insect type CSs in several representatives of deuterostomes, which generally are not thought to possess chitin. This suggests a broader distribution and function of chitin in this branch of the animal kingdom. We characterize a new CS type present not only in basal metazoans such as sponges and cnidarians but also in several bilaterian representatives. The most extensive diversification of CSs took place during emergence of lophotrochozoans, the third large group of protostomes next to arthropods and nematodes, resulting in coexistence of up to ten CS paralogs in molluscs. Independent fusion to different kinds of myosin motor domains in fungi and lophotrochozoans points toward high relevance of CS interaction with the cytoskeleton for fine-tuned chitin secretion. Given the fundamental role that chitin plays in the morphology of many animals, the here presented CS diversification reveals many evolutionary complexities. Our findings strongly suggest a very broad and multifarious occurrence of chitin and question an ancestral role as cuticular component. The molecular mechanisms underlying regulation of animal chitin synthesis are most likely far more complex and diverse than existing data from insects suggest.

Communication between oocytes and somatic cells regulates volatile pheromone production in Caenorhabditis elegans

Males of the androdioecious species Caenorhabditis elegans are more likely to attempt to mate with and successfully inseminate C. elegans hermaphrodites that do not concurrently harbor sperm. Although a small number of genes have been implicated in this effect, the mechanism by which it arises remains unknown. In the context of the battle of the sexes, it is also unknown whether this effect is to the benefit of the male, the hermaphrodite, or both. We report that successful contact between mature sperm and oocyte in the C. elegans gonad at the start of fertilization causes the oocyte to release a signal that is transmitted to somatic cells in its mother, with the ultimate effect of reducing her attractiveness to males. Changes in hermaphrodite attractiveness are tied to the production of a volatile pheromone, the first such pheromone described in C. elegans.

Dynamically-expressed prion-like proteins form a cuticle in the pharynx of Caenorhabditis elegans

In molting animals, a cuticular extracellular matrix forms the first barrier to infection and other environmental insults. In the nematode Caenorhabditis elegans there are two types of cuticle: a well-studied collagenous cuticle lines the body, and a poorly-understood chitinous cuticle lines the pharynx. In the posterior end of the pharynx is the grinder, a tooth-like cuticular specialization that crushes food prior to transport to the intestine for digestion. We here show that the grinder increases in size only during the molt. To gain molecular insight into the structure of the grinder and pharyngeal cuticle, we performed a microarray analysis to identify mRNAs increased during the molt. We found strong transcriptional induction during the molt of 12 of 15 previously identified abu genes encoding Prion-like (P) glutamine (Q) and asparagine (N) rich PQN proteins, as well as 15 additional genes encoding closely related PQN proteins. abu/pqn genes, which we name the abu/pqn paralog group (APPG) genes, were expressed in pharyngeal cells and the proteins encoded by two APPG genes we tested localized to the pharyngeal cuticle. Deleting the APPG gene abu-14 caused abnormal pharyngeal cuticular structures and knocking down other APPG genes resulted in abnormal cuticular function. We propose that APPG proteins promote the assembly and function of a unique cuticular structure. The strong developmental regulation of the APPG genes raises the possibility that such genes would be identified in transcriptional profiling experiments in which the animals' developmental stage is not precisely staged.

Two classes of gap junction channels mediate soma-germline interactions essential for germline proliferation and gametogenesis in Caenorhabditis elegans

In all animals examined, somatic cells of the gonad control multiple biological processes essential for germline development. Gap junction channels, composed of connexins in vertebrates and innexins in invertebrates, permit direct intercellular communication between cells and frequently form between somatic gonadal cells and germ cells. Gap junctions comprise hexameric hemichannels in apposing cells that dock to form channels for the exchange of small molecules. Here we report essential roles for two classes of gap junction channels, composed of five innexin proteins, in supporting the proliferation of germline stem cells and gametogenesis in the nematode Caenorhabditis elegans. Transmission electron microscopy of freeze-fracture replicas and fluorescence microscopy show that gap junctions between somatic cells and germ cells are more extensive than previously appreciated and are found throughout the gonad. One class of gap junctions, composed of INX-8 and INX-9 in the soma and INX-14 and INX-21 in the germ line, is required for the proliferation and differentiation of germline stem cells. Genetic epistasis experiments establish a role for these gap junction channels in germline proliferation independent of the glp-1/Notch pathway. A second class of gap junctions, composed of somatic INX-8 and INX-9 and germline INX-14 and INX-22, is required for the negative regulation of oocyte meiotic maturation. Rescue of gap junction channel formation in the stem cell niche rescues germline proliferation and uncovers a later channel requirement for embryonic viability. This analysis reveals gap junctions as a central organizing feature of many soma–germline interactions in C. elegans.

Chitin deposition on the embryonic cuticle of Rhodnius prolixus: the reduction of CHS transcripts by CHS-dsRNA injection in females affects chitin deposition and eclosion of the first instar nymph

In a previous study, we found that the embryonic cuticle of Rhodnius prolixus is a chitin-based structure that helps the first instar nymph to hatch from the chorion. Here, we investigated how the reduction of transcripts induced by CHS dsRNA injection affects R. prolixus embryogenesis and eclosion. Deposition of chitin in the embryonic cuticle begins later at embryogenesis, around day 8, and ends approximately at day 15, when the insects are ready for eclosion. In R. prolixus, chitin deposition follows pari passu with the synthesis of the chitin synthase mRNA, indicating a regulation at the transcriptional level. The reduction of the chitin synthase gene transcripts by the injection of CHS dRNA prevented chitin deposition during embryonic cuticle formation, being lethal to hatching nymphs, which end up dying while stuck in the chorionic border trying to leave the chorion. The successful eclosion rates were reduced by 60% in animals treated with CHS dsRNA when compared to animals injected with a control (dsRNA no related gene or water). We found that the harmful effects on oviposition and eclosion are possibly due to changes in the structure of the embryonic cuticle, as observed by directly comparing the morphology of control and chitin-deficient embryonic cuticles under the transmission electron microscope. The lack of chitin and changes in its morphological characteristics appears to alter the embryonic cuticle physiology and functionality. Additionally, we observed that the effects of CHS dRNA treatment on R. prolixus females lasted up to 3 egg-laying cycles (∼100 days), pointing to R. prolixus as a useful model for developmental studies.

High prevalence of chitotriosidase deficiency in Peruvian Amerindians exposed to chitin-bearing food and enteroparasites

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Catalytic deficiency of chitotriosidase has a very high frequency in Amerindians highly exposed to chitin from enteroparasites and diet.

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Mutation frequencies are similar to those found in East Asian populations, and is probably conserved for a founder effect.

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Such condition precludes the use of CHIT1 as a disease biomarker in South American populations with strong ethnic ancestry.

The human genome encodes a gene for an enzymatically active chitinase (CHIT1) located in a single copy on Chromosome 1, which is highly expressed by activated macrophages and in other cells of the innate immune response. Several dysfunctional mutations are known in CHIT1, including a 24-bp duplication in Exon 10 causing catalytic deficiency. This duplication is a common variant conserved in many human populations, except in West and South Africans. Thus it has been proposed that human migration out of Africa and the consequent reduction of exposure to chitin from environmental factors may have enabled the conservation of dysfunctional mutations in human chitinases. Our data obtained from 85 indigenous Amerindians from Peru, representative of populations characterized by high prevalence of chitin-bearing enteroparasites and intense entomophagy, reveal a very high frequency of the 24-bp duplication (47.06%), and of other single nucleotide polymorphisms which are known to partially affect enzymatic activity (G102S: 42.7% and A442G/V: 25.5%). Our finding is in line with a founder effect, but appears to confute our previous hypothesis of a protective role against parasite infection and sustains the discussion on the redundancy of chitinolytic function.

The olfactory neuron AWC promotes avoidance of normally palatable food following chronic dietary restriction

Changes in metabolic state alter foraging behavior and food preference in animals. Here, I show that normally attractive food becomes repulsive to Caenorhabditis elegans if animals are chronically undernourished as a result of alimentary tract defects. This behavioral plasticity is achieved in two ways: increased food leaving and induction of aversive behavior towards food. A particularly strong food avoider is defective in the chitin synthase that makes the pharyngeal lining. Food avoidance induced by underfeeding is mediated by cGMP signaling in the olfactory neurons AWC and AWB, and the gustatory neurons ASJ and ASK. Food avoidance is enhanced by increased population density and is reduced if the animals are unable to correctly interpret their nutritional state as a result of defects in the AMP kinase or TOR/S6kinase pathways. The TGF-β/DBL-1 pathway suppresses food avoidance and the cellular basis for this is distinct from its role in aversive olfactory learning of harmful food. This study suggests that nutritional state feedback via nutrient sensors, population size and olfactory neurons guides food preference in C. elegans.

Evolutionarily dynamic roles of a PUF RNA-binding protein in the somatic development of Caenorhabditis briggsae

Gene duplication and divergence has emerged as an important aspect of developmental evolution. The genomes of Caenorhabditis nematodes encode an ancient family of PUF RNA-binding proteins. Most have been implicated in germline development, and are often redundant with paralogs of the same sub-family. An exception is Cbr-puf-2 (one of three Caenorhabditis briggsae PUF-2 sub-family paralogs), which is required for development past the second larval stage. Here, we provide a detailed functional characterization of Cbr-puf-2. The larval arrest of Cbr-puf-2 mutant animals is caused by inefficient breakdown of bacterial food, which leads to starvation. Cbr-puf-2 is required for the normal grinding cycle of the muscular terminal bulb during early larval stages, and is transiently expressed in this tissue. In addition, rescue of larval arrest reveals that Cbr-puf-2 also promotes normal vulval development. It is expressed in the anchor cell (which induces vulval fate) and vulval muscles, but not in the vulva precursor cells (VPCs) themselves. This contrasts with the VPC-autonomous repression of vulval development described for the Caenorhabditis elegans homologs fbf-1/2. These different roles for PUF proteins occur even as the vulva and pharynx maintain highly conserved anatomies across Caenorhabditis, indicating pervasive developmental system drift (DSD). Because Cbr-PUF-2 shares RNA-binding specificity with its paralogs and with C. elegans FBF, we suggest that functional novelty of RNA-binding proteins evolves through changes in the site of their expression, perhaps in concert with cis-regulatory evolution in target mRNAs.

Hierarchical assembly of the eggshell and permeability barrier in C. elegans

Assembly of the trilaminar eggshell and development of the permeability barrier after fertilization in C. elegans are distinct in their timing and mechanism.

In metazoans, fertilization triggers the assembly of an extracellular coat that constitutes the interface between the embryo and its environment. In nematodes, this coat is the eggshell, which provides mechanical rigidity, prevents polyspermy, and is impermeable to small molecules. Using immunoelectron microscopy, we found that the Caenorhabditis elegans eggshell was composed of an outer vitelline layer, a middle chitin layer, and an inner layer containing chondroitin proteoglycans. The switch between the chitin and proteoglycan layers was achieved by internalization of chitin synthase coincident with exocytosis of proteoglycan-containing cortical granules. Inner layer assembly did not make the zygote impermeable as previously proposed. Instead, correlative light and electron microscopy demonstrated that the permeability barrier was a distinct envelope that formed in a separate step that required fatty acid synthesis, the sugar-modifying enzyme PERM-1, and the acyl chain transfer enzyme DGTR-1. These findings delineate the hierarchy of eggshell assembly and define key molecular mechanisms at each step.

Species-specific shells: Chitin synthases and cell mechanics in molluscs

The size, morphology and species-specific texture of mollusc shell biominerals is one of the unresolved questions in nature. In search of molecular control principles, chitin has been identified by Weiner and Traub (FEBS Lett. 1980, 111:311–316) as one of the organic compounds with a defined co-organization with mineral phases. Chitin fibers can be aligned with certain mineralogical axes of crystalline calcium carbonate in a species-specific manner. These original observations motivated the functional characterization of chitin forming enzymes in molluscs. The full-length cDNA cloning of mollusc chitin synthases identified unique myosin domains as part of the biological control system. The potential impact of molecular motors and other conserved domains of these complex transmembrane enzymes on the evolution of shell biomineralization is investigated and discussed in this article.

Pharyngeal polysaccharide deacetylases affect development in the nematode C. elegans and deacetylate chitin in vitro

Chitin (β-1,4-linked-N-acetylglucosamine) provides structural integrity to the nematode eggshell and pharyngeal lining. Chitin is synthesized in nematodes, but not in plants and vertebrates, which are often hosts to parasitic roundworms; hence, the chitin metabolism pathway is considered a potential target for selective interventions. Polysaccharide deacetylases (PDAs), including those that convert chitin to chitosan, have been previously demonstrated in protists, fungi and insects. We show that genes encoding PDAs are distributed throughout the phylum Nematoda, with the two paralogs F48E3.8 and C54G7.3 found in C. elegans. We confirm that the genes are somatically expressed and show that RNAi knockdown of these genes retards C. elegans development. Additionally, we show that proteins from the nematode deacetylate chitin in vitro, we quantify the substrate available in vivo as targets of these enzymes, and we show that Eosin Y (which specifically stains chitosan in fungal cells walls) stains the C. elegans pharynx. Our results suggest that one function of PDAs in nematodes may be deacetylation of the chitinous pharyngeal lining.

The Caenorhabditis elegans epidermis as a model skin. II: differentiation and physiological roles

The Caenorhabditis elegans epidermis forms one of the principal barrier epithelia of the animal. Differentiation of the epidermis begins in mid embryogenesis and involves apical-basal polarization of the cytoskeletal and secretory systems as well as cellular junction formation. Secretion of the external cuticle layers is one of the major developmental and physiological specializations of the epidermal epithelium. The four post-embryonic larval stages are separated by periodic moults, in which the epidermis generates a new cuticle with stage-specific characteristics. The differentiated epidermis also plays key roles in endocrine signaling, fat storage, and ionic homeostasis. The epidermis is intimately associated with the development and function of the nervous system, and may have glial-like roles in modulating neuronal function. The epidermis provides passive and active defenses against skin-penetrating pathogens and can repair small wounds. Finally, age-dependent deterioration of the epidermis is a prominent feature of aging and may affect organismal aging and lifespan.

The eggshell in the C. elegans oocyte-to-embryo transition

In egg-laying animals, embryonic development takes place within the highly specialized environment provided by the eggshell and its underlying extracellular matrix. Far from being simply a passive physical support, the eggshell is a key player in many early developmental events. Herein, we review current understanding of eggshell structure, biosynthesis, and function in zygotic development of the nematode, C. elegans. Beginning at sperm contact or entry, eggshell layers are produced sequentially. The earlier outer layers are required for secretion or organization of inner layers, and layers differ in composition and function. Developmental events that depend on the eggshell include polyspermy barrier generation, high fidelity meiotic chromosome segregation, osmotic barrier synthesis, polar body extrusion, anterior-posterior polarization, and organization of membrane and cortical proteins. The C. elegans eggshell is proving to be an excellent, tractable system to study the molecular cues of the extracellular matrix that instruct cell polarity and early development.

Regulation of the C. elegans molt by pqn-47

C. elegans molts at the end of each of its four larval stages but this cycle ceases at the reproductive adult stage. We have identified a regulator of molting, pqn-47. Null mutations in pqn-47 cause a developmental arrest at the first larval molt, showing that this gene activity is required to transit the molt. Mutants with weak alleles of pqn-47 complete the larval molts but fail to exit the molting cycle at the adult stage. These phenotypes suggest that pqn-47 executes key aspects of the molting program including the cessation of molting cycles. The pqn-47 gene encodes a protein that is highly conserved in animal phylogeny but probably misannotated in genome sequences due to much less significant homology to a yeast transcription factor. A PQN-47::GFP fusion gene is expressed in many neurons, vulval precursor cells, the distal tip cell (DTC), intestine, and the lateral hypodermal seam cells but not in the main body hypodermal syncytium (hyp7) that underlies, synthesizes, and releases most of the collagenous cuticle. A functional PQN-47::GFP fusion protein localizes to the cytoplasm rather than the nucleus at all developmental stages, including the periods preceding and during ecdysis when genetic analysis suggests that pqn-47 functions. The cytoplasmic localization of PQN-47::GFP partially overlaps with the endoplasmic reticulum, suggesting that PQN-47 is involved in the extensive secretion of cuticle components or hormones that occurs during molts. The mammalian and insect homologues of pqn-47 may serve similar roles in regulated secretion.

New insights into the mechanism of fertilization in nematodes

Fertilization results from the fusion of male and female gametes in all sexually reproducing organisms. Much of nematode fertility work was focused on Caenorhabditis elegans and Ascaris suum. The C. elegans hermaphrodite produces a limited number of sperm initially and then commits to the exclusive production of oocytes. The postmeiotic differentiation called spermiogenesis converts sessile spermatids into motile spermatozoa. The motility of spermatozoa depends on dynamic assembly and disassembly of a major sperm protein-based cytoskeleton uniquely found in nematodes. Both self-derived and male-derived spermatozoa are stored in spermatheca, the site of fertilization in hermaphrodites. The oocyte is arrested in meiotic prophase I until a sperm-derived signal relieves the inhibition allowing the meiotic maturation to occur. Oocyte undergoes meiotic maturation, enters into spermatheca, gets fertilized, completes meiosis, and exits into uterus as a zygote. This review focuses on our current understanding of the events around fertilization in nematodes.

EGG molecules couple the oocyte-to-embryo transition with cell cycle progression

The oocyte-to-embryo transition is a precisely coordinated process in which an oocyte becomes fertilized and transitions to an embryonic program of events. The molecules involved in this process have not been well studied. Recently, a group of interacting molecules in C. elegans have been described as coordinating the oocyte-to-embryo transition with the advancement of the cell cycle. Genes egg-3, egg-4, and egg-5 represent a small class of regulatory molecules known as protein-tyrosine phosphase-like proteins, which can bind phosphorylated substrates and act as scaffolding molecules or inhibitors. These genes are responsible for coupling the movements and activities of regulatory kinase mbk-2 with advancement of the cell cycle during the oocyte-to-embryo transition.

Fertilization and the oocyte-to-embryo transition in C. elegans

Fertilization is a complex process comprised of numerous steps. During fertilization, two highly specialized and differentiated cells (sperm and egg) fuse and subsequently trigger the development of an embryo from a quiescent, arrested oocyte. Molecular interactions between the sperm and egg are necessary for regulating the developmental potential of an oocyte, and precise coordination and regulation of gene expression and protein function are critical for proper embryonic development. The nematode Caenorhabditis elegans has emerged as a valuable model system for identifying genes involved in fertilization and the oocyte-to-embryo transition as well as for understanding the molecular mechanisms that govern these processes. In this review, we will address current knowledge of the molecular underpinnings of gamete interactions during fertilization and the oocyte-to-embryo transition in C. elegans. We will also compare our knowledge of these processes in C. elegans to what is known about similar processes in mammalian, specifically mouse, model systems.

The C. elegans hyaluronidase: a developmentally significant enzyme with chondroitin-degrading activity at both acidic and neutral pH

Mammalian hyaluronidases degrade hyaluronan and some structurally related glycosaminoglycans. We generated a deletion mutant in the Caenorhabditis elegans orthologue of mammalian hyaluronidase, hya-1. Mutant animals are viable and grossly normal, but exhibit defects in vulval morphogenesis and egg-laying and showed increased staining with alcian blue, consistent with an accumulation of glycosaminoglycan. A hya-1::GFP reporter was expressed in a restricted pattern in somatic tissues of the animal with strongest expression in the intestine, the PLM sensory neurons and the vulva. Total protein extracts from wild-type animals exhibited chondroitin-degrading but not hyaluronan-degrading activity. Chondroitinase activities were observed at both neutral and acidic pH conditions while both neutral and acidic activities were absent in extracts from hya-1 mutant strains. We also evaluated the function of oga-1, which encodes the C. elegans orthologue of MGEA-5, a protein with hyaluronan-degrading activity in vitro. oga-1 is expressed in muscles, vulval cells and the scavenger-like coelomocytes. An oga-1 mutant strain exhibited egg-laying and vulval defects similar to those of hya-1; chondroitinase activity was unaffected in this mutant.

Repositioning of an existing drug for the neglected tropical disease Onchocerciasis

Onchocerciasis, or river blindness, is a neglected tropical disease caused by the filarial nematode Onchocerca volvulus that affects more than 37 million people, mainly in third world countries. Currently, the only approved drug available for mass treatment is ivermectin, however, drug resistance is beginning to emerge, thus, new therapeutic targets and agents are desperately needed to treat and cure this devastating disease. Chitin metabolism plays a central role in invertebrate biology due to the critical structural function of chitin for the organism. Taken together with its absence in mammals, targeting chitin is an appealing therapeutic avenue. Importantly, the chitinase OvCHT1 from O. volvulus was recently discovered, however, its exact role in the worm's metabolism remains unknown. A screening effort against OvCHT1 was conducted using the Johns Hopkins Clinical Compound Library that contains over 1,500 existing drugs. Closantel, a veterinary anthelmintic with known proton ionophore activities, was identified as a potent and specific inhibitor of filarial chitinases, an activity not previously reported for this compound. Notably, closantel was found also to completely inhibit molting of O. volvulus infective L3 stage larvae. Closantel appears to target two important biochemical processes essential to filarial parasites. To begin to unravel closantel's effects, a retro-fragment-based study was used to define structural elements critical for closantel's chitinase inhibitor function. As resources towards the development of new agents that target neglected tropical diseases are scant, the finding of an existing drug with impact against O. volvulus provides promise in the hunt for new therapies against river blindness.

Common trends in mutualism revealed by model associations between invertebrates and bacteria

Mutually beneficial interactions between microorganisms and animals are a conserved and ubiquitous feature of biotic systems. In many instances animals, including humans, are dependent on their microbial associates for nutrition, defense, or development. To maintain these vital relationships, animals have evolved processes that ensure faithful transmission of specific microbial symbionts between generations. Elucidating mechanisms of transmission and symbiont specificity has been aided by the study of experimentally tractable invertebrate animals with diverse and highly evolved associations with microorganisms. Here, we review several invertebrate model systems that contribute to our current understanding of symbiont transmission, recognition, and specificity. Although the details of transmission and symbiont selection vary among associations, comparisons of diverse mutualistic associations are revealing a number of common themes, including restriction of symbiont diversity during transmission and glycan-lectin interactions during partner selection and recruitment.

The role of basophils in helminth infection

Protective immunity against gastrointestinal and tissue dwelling helminths is coordinated by interaction of different effector cells of the innate and adaptive immune system. Helminths induce a strong type 2 immune response which is characterized by high levels of IgE and increased numbers of Th2 cells, eosinophils, mast cells and basophils. Basophils are rapidly mobilized after helminth infection and can be efficiently recruited into lymphoid and peripheral tissues where they execute their effector functions. Recent work demonstrated that basophils contribute to initiation and execution of type 2 immunity. This review discusses the potential role of basophils for protective immunity against helminths.

Chitin stimulates expression of acidic mammalian chitinase and eotaxin-3 by human sinonasal epithelial cells in vitro

BACKGROUND

Sinonasal epithelial cells participate in host defense by initiating innate immune mechanisms against potential pathogens. Antimicrobial innate mechanisms have been shown to involve Th1-like inflammatory responses. Although epithelial cells can also be induced by Th2 cytokines to express proeosinophilic mediators, no environmental agents have been identified that promote this effect.

METHODS

Human sinonasal epithelial cells from patients with chronic rhinosinusitis with nasal polyps (CRSwNPs) and controls were harvested and grown in primary culture. Cell cultures were exposed to a range of concentrations of chitin for 24 hours, and mRNA for acidic mammalian chitinase (AMCase), eotaxin-3, and thymic stromal-derived lymphopoietin (TSLP) were assessed. Other cultures were exposed to interleukin 4 (IL- 4) alone and in combination with dust-mite antigen (DMA) for 36 hours. Extracted mRNA and cell culture supernatant were analyzed for expression of AMCase and eotaxin-3.

RESULTS

Chitin induced a dose-dependent expression of AMCase and eotaxin-3 mRNA but not TSLP. Patients with recalcitrant CRSwNPs showed lower baseline expression of AMCase when compared with treatment-responsive CRSwNP and less induction of AMCase expression by chitin. DMA did not directly induce expression of AMCase or eotaxin-3. Expression of eotaxin-3 was stimulated by IL-4 and further enhanced with the addition of DMA. Levels of AMCase were not significantly affected by either IL-4 or DMA exposure. In some cases, the combination of IL-4 and DMA was able to induce AMCase expression in cell cultures not producing AMCase at baseline.

CONCLUSION

The abundant biopolymer chitin appears to be recognized by a yet uncharacterized receptor on sinonasal epithelial cells. Chitin stimulates production of AMCase and eotaxin-3, two pro-Th2 effector proteins. This finding suggests the existence of a novel innate immune pathway for local defense against chitin-containing organisms in the sinonasal tract. Dysregulation of this function could precipitate or exacerbate Th2 inflammation, potentially acting as an underlying factor in recalcitrant CRSwNP.

Two cytochrome P450s in Caenorhabditis elegans are essential for the organization of eggshell, correct execution of meiosis and the polarization of embryo

The role of lipids in the process of embryonic development of Caenorhabditis elegans is still poorly understood. Cytochrome P450s, a class of lipid-modifying enzymes, are good candidates to be involved in the production or degradation of lipids essential for development. We investigated two highly similar cytochrome P450s in C. elegans, cyp-31A2 and cyp-31A3, that are homologs of the gene responsible for Bietti crystalline corneoretinal dystrophy in humans. Depletion of both cytochromes either by RNAi or using a double deletion mutant, led to the failure of establishing the correct polarity of the embryo and to complete the extrusion of the polar bodies during meiosis. In addition, the egg became osmotic sensitive and permeable to dyes. The phenotype of cyp-31A2 or cyp-31A3 is very similar to a class of mutants that have polarization and osmotic defects (POD), thus the genes were renamed to pod-7 and pod-8, respectively. Electron microscopic analysis demonstrated that the activity of pod-7/pod-8 is crucial for the proper assembly of the eggshell and, in particular, for the production of its lipid-rich layer. Using a complementation with lipid extracts, we show that POD-7/POD-8 function together with a NADPH cytochrome P450 reductase, coded by emb-8, and are involved in the production of lipid(s) required for eggshell formation.

Embryonic desiccation resistance in Aedes aegypti: presumptive role of the chitinized serosal cuticle

Background

One of the major problems concerning dengue transmission is that embryos of its main vector, the mosquito Aedes aegypti, resist desiccation, surviving several months under dry conditions. The serosal cuticle (SC) contributes to mosquito egg desiccation resistance, but the kinetics of SC secretion during embryogenesis is unknown. It has been argued that mosquito SC contains chitin as one of its components, however conclusive evidence is still missing.

Results

We observed an abrupt acquisition of desiccation resistance during Ae. aegypti embryogenesis associated with serosal cuticle secretion, occurring at complete germ band extension, between 11 and 13 hours after egglaying. After SC formation embryos are viable on dry for at least several days. The presence of chitin as one of the SC constituents was confirmed through Calcofluor and WGA labeling and chitin quantitation. The Ae. aegypti Chitin Synthase A gene (AaCHS1) possesses two alternatively spliced variants, AaCHS1a and AaCHS1b, differentially expressed during Ae. aegypti embryonic development. It was verified that at the moment of serosal cuticle formation, AaCHS1a is the sole variant specifically expressed.

Conclusion

In addition to the peritrophic matrix and exoskeleton, these findings confirm chitin is also present in the mosquito serosal cuticle. They also point to the role of the chitinized SC in the desiccation resistance of Ae. aegypti eggs. AaCHS1a expression would be responsible for SC chitin synthesis. With this embryological approach we expect to shed new light regarding this important physiological process related to the Ae. aegypti life cycle.

Structure of the pharynx in the adult nematode Anguillicoloides crassus (Nematoda: Rhabditida)

The structure of the pharynx of the adult female nematode Anguillicoloides crassus (Spirurina) has been studied for the first time using light and transmission electron microscopy. The cylindrical pharynx consists of a short anterior muscular corpus and an enlarged posterior glandular and muscular postcorpus. The main cellular components of the pharynx of A. crassus include the muscle cells, the marginal cells, the nerve cells, and 1 dorsal and 2 subventral glands. New observations for nematodes include: (1) the non-contractile regions of pharyngeal musculature in the corpus have specific appearance; (2) the ventrosublateral longitudinal nerve in the pharynx has an enlarged, enucleated anterior part, with a pronounced palmate projections; and (3) abundant lysosomelike membranous bodies consisting of myelinlike figures of varied size present in marginal cells and pharyngointestinal valve. The 2 subventral glands and, apparently, the single dorsal gland, have their openings at the same level, i.e., at the border between the corpus and postcorpus. The pharyngeal-intestinal valve joins the pharynx to the intestine. Knowledge of the ultrastructure of these complex characters may be useful in understanding of functional features, and for comparative morphology as well as evolutionary considerations within the Chromadorea.

EGG-3 regulates cell-surface and cortex rearrangements during egg activation in Caenorhabditis elegans

Fertilization triggers egg activation and converts the egg into a developing embryo. The events of this egg-to-embryo transition typically include the resumption of meiosis, the reorganization of the cortical actin cytoskeleton, and the remodeling of the oocyte surface. The factors that regulate sperm-dependent egg-activation events are not well understood. Caenorhabditis elegans EGG-3, a member of the protein tyrosine phosphatase-like (PTPL) family, is essential for regulating cell-surface and cortex rearrangements during egg activation in response to sperm entry. Although fertilization occurred normally in egg-3 mutants, the polarized dispersal of F-actin is altered, a chitin eggshell is not formed, and no polar bodies are produced. EGG-3 is associated with the oocyte plasma membrane in a pattern that is similar to CHS-1 and MBK-2. CHS-1 is required for eggshell deposition, whereas MBK-2 is required for the degradation of maternal proteins during the egg-to-embryo transition. The localization of CHS-1 and EGG-3 are interdependent and both genes were required for the proper localization of MBK-2 in oocytes. Therefore, EGG-3 plays a central role in egg activation by influencing polarized F-actin dynamics and the localization or activity of molecules that are directly involved in executing the egg-to-embryo transition.

Mining predicted essential genes of Brugia malayi for nematode drug targets

We report results from the first genome-wide application of a rational drug target selection methodology to a metazoan pathogen genome, the completed draft sequence of Brugia malayi, a parasitic nematode responsible for human lymphatic filariasis. More than 1.5 billion people worldwide are at risk of contracting lymphatic filariasis and onchocerciasis, a related filarial disease. Drug treatments for filariasis have not changed significantly in over 20 years, and with the risk of resistance rising, there is an urgent need for the development of new anti-filarial drug therapies. The recent publication of the draft genomic sequence for B. malayi enables a genome-wide search for new drug targets. However, there is no functional genomics data in B. malayi to guide the selection of potential drug targets. To circumvent this problem, we have utilized the free-living model nematode Caenorhabditis elegans as a surrogate for B. malayi. Sequence comparisons between the two genomes allow us to map C. elegans orthologs to B. malayi genes. Using these orthology mappings and by incorporating the extensive genomic and functional genomic data, including genome-wide RNAi screens, that already exist for C. elegans, we identify potentially essential genes in B. malayi. Further incorporation of human host genome sequence data and a custom algorithm for prioritization enables us to collect and rank nearly 600 drug target candidates. Previously identified potential drug targets cluster near the top of our prioritized list, lending credibility to our methodology. Over-represented Gene Ontology terms, predicted InterPro domains, and RNAi phenotypes of C. elegans orthologs associated with the potential target pool are identified. By virtue of the selection procedure, the potential B. malayi drug targets highlight components of key processes in nematode biology such as central metabolism, molting and regulation of gene expression.

The structure of mollusc larval shells formed in the presence of the chitin synthase inhibitor Nikkomycin Z

BACKGROUND

Chitin self-assembly provides a dynamic extracellular biomineralization interface. The insoluble matrix of larval shells of the marine bivalve mollusc Mytilus galloprovincialis consists of chitinous material that is distributed and structured in relation to characteristic shell features. Mollusc shell chitin is synthesized via a complex transmembrane chitin synthase with an intracellular myosin motor domain.

RESULTS

Enzymatic mollusc chitin synthesis was investigated in vivo by using the small-molecule drug NikkomycinZ, a structural analogue to the sugar donor substrate UDP-N-acetyl-D-glucosamine (UDP-GlcNAc). The impact on mollusc shell formation was analyzed by binocular microscopy, polarized light video microscopy in vivo, and scanning electron microscopy data obtained from shell material formed in the presence of NikkomycinZ. The partial inhibition of chitin synthesis in vivo during larval development by NikkomycinZ (5 microM - 10 microM) dramatically alters the structure and thus the functionality of the larval shell at various growth fronts, such as the bivalve hinge and the shell's edges.

CONCLUSION

Provided that NikkomycinZ mainly affects chitin synthesis in molluscs, the presented data suggest that the mollusc chitin synthase fulfils an important enzymatic role in the coordinated formation of larval bivalve shells. It can be speculated that chitin synthesis bears the potential to contribute via signal transduction pathways to the implementation of hierarchical patterns into chitin mineral-composites such as prismatic, nacre, and crossed-lamellar shell types.

Essential role of chitinase in the development of the filarial nematode Acanthocheilonema viteae

Chitinases of pathogens have been proposed as potential targets of vaccines or specific inhibitors. We studied the genomic organization, transcript levels, developmental expression, and biological function of chitinases in the rodent filarial nematode Acanthocheilonema viteae, a model organism for human-pathogenic filarial worms. Characterization of nine genomic clones from an A. viteae phage library and Southern blot experiments revealed the existence of three different chitinase genes, two of which could theoretically yield functional transcripts. The deduced proteins of these genes had the common modular organization of family 18 chitinases. Northern blot experiments and rapid amplification of cDNA ends-PCR with adult worms and larval stages showed that only one gene is expressed, with high variation in transcript levels, as determined by real-time PCR. Chitinase transcript levels were lowest in the late male stage 4 larva (L4) and peaked in the stage 3 larva (L3), which was corroborated by Western blotting. RNA interference (RNAi) experiments showed that treatment of L3 and adult female worms with double-stranded RNA of chitinase inhibited molting of L3 worms and hatching of microfilariae. RNAi also led to the death of 50% of female worms, revealing the essential role of chitinase in the life cycle of filarial nematodes.

Cortical granule exocytosis in C. elegans is regulated by cell cycle components including separase

In many organisms, cortical granules undergo exocytosis following fertilization, releasing cargo proteins that modify the extracellular covering of the zygote. We identified cortical granules in Caenorhabditis elegans and have found that degranulation occurs in a wave that initiates in the vicinity of the meiotic spindle during anaphase I. Previous studies identified genes that confer an embryonic osmotic sensitivity phenotype, thought to result from abnormal eggshell formation. Many of these genes are components of the cell cycle machinery. When we suppressed expression of several of these genes by RNAi, we observed that cortical granule trafficking was disrupted and the eggshell did not form properly. We conclude that osmotic sensitivity phenotypes occur because of defects in trafficking of cortical granules and the subsequent formation of an impermeable eggshell. We identified separase as a key cell cycle component that is required for degranulation. Separase localized to cortically located filamentous structures in prometaphase I upon oocyte maturation. After fertilization, separase disappeared from these structures and appeared on cortical granules by anaphase I. RNAi of sep-1 inhibited degranulation in addition to causing extensive chromosomal segregation failures. Although the temperature-sensitive sep-1(e2406) allele exhibited similar inhibition of degranulation, it had minimal effects on chromosome segregation. These observations lead us to speculate that SEP-1 has two separable yet coordinated functions: to regulate cortical granule exocytosis and to mediate chromosome separation.

Chitotriosidase deficiency is not associated with human hookworm infection in a Papua New Guinean population

Human chitotriosidase (CHIT1) is a chitinolytic enzyme with suggested anti-fungal properties. Previous studies have suggested that chitotriosidase may also protect individuals against filarial nematode infections and malaria. A mutant allele, which renders chitotriosidase unstable and enzymatically inactive, is found at a frequency of >20% in Caucasians and other populations. This allele is found at much lower frequency in parts of West Africa where malarial and intestinal helminth infections are endemic. Here, we investigate whether there is a significant association between chitotriosidase genotype and the intensity of hookworm infection in 693 individuals from five villages in Papua New Guinea. Individuals were genotyped for chitotriosidase using a PCR-based assay. There was no association between CHIT1 genotype and the intensity of hookworm infection as determined by faecal egg counts. The frequency of the mutant allele was 0.251, very similar to that found in non-endemic countries. The extent of geographical variation in allele frequencies across worldwide populations was not high (F(st)=0.11), and does not provide evidence for directional selection at this locus between different geographical areas. We conclude that the CHIT1 genotype does not play a crucial role in protection against hookworm infection. This does not correlate with a previous study that linked the mutant CHIT1 genotype to filariasis susceptibility. The possible reasons for this discrepancy are discussed.

Biosynthesis of truncated N-linked oligosaccharides results from non-orthologous hexosaminidase-mediated mechanisms in nematodes, plants, and insects

In many invertebrates and plants, the N-glycosylation profile is dominated by truncated paucimannosidic N-glycans, i.e. glycans consisting of a simple trimannosylchitobiosyl core often modified by core fucose residues. Even though they lack antennal N-acetylglucosamine residues, the biosynthesis of these glycans requires the sequential action of GlcNAc transferase I, Golgi mannosidase II, and, finally, beta-N-acetylglucosaminidases. In Drosophila, the recently characterized enzyme encoded by the fused lobes (fdl) gene specifically removes the non-reducing N-acetylglucosamine residue from the alpha1,3-antenna of N-glycans. In the present study, we examined the products of five beta-N-acetylhexosaminidase genes from Caenorhabditis elegans (hex-1 to hex-5, corresponding to reading frames T14F9.3, C14C11.3, Y39A1C.4, Y51F10.5, and Y70D2A.2) in addition to three from Arabidopsis thaliana (AtHEX1, AtHEX2, and AtHEX3, corresponding to reading frames At1g65590, At3g55260, and At1g05590). Based on homology, the Caenorhabditis HEX-1 and all three Arabidopsis enzymes are members of the same sub-family as the aforementioned Drosophila fused lobes enzyme but either act as chitotriosidases or non-specifically remove N-acetylglucosamine from both N-glycan antennae. The other four Caenorhabditis enzymes are members of a distinct sub-family; nevertheless, two of these enzymes displayed the same alpha1,3-antennal specificity as the fused lobes enzyme. Furthermore, a deletion of part of the Caenorhabditis hex-2 gene drastically reduces the native N-glycan-specific hexosaminidase activity in mutant worm extracts and results in a shift in the N-glycan profile, which is a demonstration of its in vivo enzymatic relevance. Based on these data, it is hypothesized that the genetic origin of paucimannosidic glycans in nematodes, plants, and insects involves highly divergent members of the same hexosaminidase gene family.

Identification of chitin in the prismatic layer of the shell and a chitin synthase gene from the Japanese pearl oyster, Pinctada fucata

The shell of the Japanese pearl oyster, Pinctada fucata, consists of two layers, the prismatic layer on the outside and the nacreous layer on the inside, both of which comprise calcium carbonate and organic matrices. Previous studies indicate that the nacreous organic matrix of the central layer of the framework surrounding the aragonite tablet is beta-chitin, but it remains unknown whether organic matrices in the prismatic layer contain chitin or not. In the present study, we identified chitin in the prismatic layer of the Japanese pearl oyster, Pinctada fucata, with a combination of Calcofluor White staining with IR and NMR spectral analyses. Furthermore, we cloned a cDNA encoding chitin synthase (PfCHS1) that produces chitin, contributing to the formation of the framework for calcification in the shell.