Cathepsin L protease (CPL-1) is essential for yolk processing during embryogenesis in Caenorhabditis elegans

CTSL-2 upon specifically recognizing Vibrio splendidus directly cleaves complement C3 to promote the bacterial phagocytosis and degradation in oyster

Cathepsin L (CTSL) as a cysteine cathepsin protease mediates complement C3 cleavage and pathogen degradation. In the present study, a CTSL homolog was identified from Crassostrea gigas (designated as CgCTSL-2). Its mRNA expression increased significantly in hemocytes after Vibrio splendidus stimulation. The activity of rCgCTSL-2 was induced after incubation with LPS or V. splendidus in Ca2+-dependent manner. rCgCTSL-2 could specifically bound V. splendidus in Ca2+-dependent manner. The co-localization of rCgCTSL-2 and V. splendidus was observed in cell-free hemolymph. Upon binding V. splendidus, CgCTSL-2 interacted with CgC3 in cell-free hemolymph and hemocytes. CgC3 fragments in CgCTSL-2-RNAi oysters and full length CgC3 in rCgCTSL-2-treated oysters were both reduced in cell-free hemolymph, respectively. CgC3 fragments were accumulated in CgCTSL-2-RNAi or rCgCTSL-2-treated oysters. The co-localizations of V. splendidus, CgC3, CgCD18, CgCTSL-2 and lysosomes were observed in hemocytes. These results suggested that CgCTSL-2 upon binding V. splendidus directly interacted with CgC3 to lead to CgC3 cleavage and then CgC3 fragments coated on V. splendidus were mediated by CgCD18 into CTSL-2-lysosome pathway.

Silencing Ditylenchus destructor cathepsin L-like cysteine protease has negative pleiotropic effect on nematode ontogenesis

Ditylenchus destructor is a migratory plant-parasitic nematode that severely harms many agriculturally important crops. The control of this pest is difficult, thus efficient strategies for its management in agricultural production are urgently required. Cathepsin L-like cysteine protease (CPL) is one important protease that has been shown to participate in various physiological and pathological processes. Here we decided to characterize the CPL gene (Dd-cpl-1) from D. destructor. Analysis of Dd-cpl-1 gene showed that Dd-cpl-1 gene contains a signal peptide, an I29 inhibitor domain with ERFNIN and GNFD motifs, and a peptidase C1 domain with four conserved active residues, showing evolutionary conservation with other nematode CPLs. RT-qPCR revealed that Dd-cpl-1 gene displayed high expression in third-stage juveniles (J3s) and female adults. In situ hybridization analysis demonstrated that Dd-cpl-1 was expressed in the digestive system and reproductive organs. Silencing Dd-cpl-1 in 1-cell stage eggs of D. destructor by RNAi resulted in a severely delay in development or even in abortive morphogenesis during embryogenesis. The RNAi-mediated silencing of Dd-cpl-1 in J2s and J3s resulted in a developmental arrest phenotype in J3 stage. In addition, silencing Dd-cpl-1 gene expression in female adults led to a 57.43% decrease in egg production. Finally, Dd-cpl-1 RNAi-treated nematodes showed a significant reduction in host colonization and infection. Overall, our results indicate that Dd-CPL-1 plays multiple roles in D. destructor ontogenesis and could serve as a new potential target for controlling D. destructor.

Cathepsin L regulates oocyte meiosis and preimplantation embryo development

Early embryonic loss, caused by reduced embryo developmental competence, is the major cause of subfertility in humans and animals. This embryo developmental competence is determined during oocyte maturation and the first embryo divisions. Therefore, it is essential to identify the underlying molecules regulating these critical developmental stages. Cathepsin L (CTSL), a lysosomal cysteine protease, is involved in regulating cell cycle progression, proliferation and invasion of different cell types. However, CTSL role in mammalian embryo development is unknown. Using bovine in vitro maturation and culture systems, we show that CTSL is a key regulator for embryo developmental competence. We employed a specific CTSL detection assay in live cells to show that CTSL activity correlates with meiotic progression and early embryo development. Inhibiting CTSL activity during oocyte maturation or early embryo development significantly impaired oocyte and embryo developmental competence as evidenced by lower cleavage, blastocyst and hatched blastocyst rates. Moreover, enhancing CTSL activity, using recombinant CTSL (rCTSL), during oocyte maturation or early embryo development significantly improved oocyte and embryo developmental competence. Importantly, rCTSL supplementation during oocyte maturation and early embryo development significantly improved the developmental competence of heat-shocked oocytes/embryos which are notoriously known for reduced quality. Altogether, these results provide novel evidence that CTSL plays a pivotal role in regulating oocyte meiosis and early embryonic development.

Insight into crustacean cathepsins: Structure-evolutionary relationships and functional roles in physiological processes

Cathepsins belong to a group of proteins that are present in both prokaryotic and eukaryotic organisms and have an extremely high degree of evolutionary conservation. These proteins are functionally active in extracellular environments as soluble enzymatic proteins or attached to plasma membrane receptors. In addition, they occur in cellular secretory vesicles, mitochondria, the cytosol, and within the nuclei of eukaryotic cells. Cathepsins are classified into various groups based on their sequence variations, leading to their structural and functional diversification. The molecular understanding of the physiology of crustaceans has shown that proteases, including cathepsins, are expressed ubiquitously. They also contain one of the central regulatory systems for crustacean reproduction, growth, and immune responses. This review focuses on various aspects of the crustaceans cathepsins and emphasizes their biological roles in different physiological processes such as reproduction, growth, development, and immune responses. We also describe the bioactivity of crustaceans cathepsins. Because of the vital biological roles that cathepsins play as cellular proteases in physiological processes, they have been proposed as potential novel targets for the development of management strategies for the aquaculture industries.

Fusion and expansion of vitellogenin vesicles during Caenorhabditis elegans intestinal senescence

Some of the most conspicuous aging phenotypes of C. elegans are related to post-reproductive production of vitellogenins (Vtg), which form yolk protein (YP) complexes after processing and lipid loading. Vtg/YP levels show huge increases with age, and inhibition of this extends lifespan, but how subcellular and organism-wide distribution of these proteins changes with age has not been systematically explored. Here, this has been done to understand how vitellogenesis promotes aging. The age-associated changes of intestinal vitellogenin vesicles (VVs), pseudocoelomic yolk patches (PYPs), and gonadal yolk organelles (YOs) have been characterized by immuno-electron microscopy. We find that from reproductive adult day 2 (AD 2) to post-reproductive AD 6 and AD 9, intestinal VVs expand from 0.2 to 3-4 μm in diameter or by >3000 times in volume, PYPs increase by >3 times in YP concentration and volume, while YOs in oocytes shrink slightly from 0.5 to 0.4 μm in diameter or by 49% in volume. In AD 6 and AD 9 worms, mislocalized YOs found in the hypodermis, uterine cells, and the somatic gonadal sheath can reach a size of 10 μm across in the former two tissues. This remarkable size increase of VVs and that of mislocalized YOs in post-reproductive worms are accompanied by extensive fusion between these Vtg/YP-containing vesicular structures in somatic cells. In contrast, no fusion is seen between YOs in oocytes. We propose that in addition to the continued production of Vtg, excessive fusion between VVs and mislocalized YOs in the soma worsen the aging pathologies seen in C. elegans.

Characterization of Insulin-like Peptide (ILP) and Its Potential Role in Ovarian Development of the Cuttlefish Sepiella japonica

The insulin-like peptide (ILP) family is well known for regulating reproduction in invertebrates, while its role in mollusks remains largely unknown. In this study, we first isolated and characterized the ILP gene in the cuttlefish Sepiella japonica. The full-length SjILP cDNA obtained was 926 bp and encoded a precursor protein of 161 amino acids. The precursor protein consisted of a signal peptide, a B chain, a C-peptide, and an A chain. It possessed the typical features of ILP proteins, including two cleavage sites (KR) and eight conserved cysteines. To define the function of SjILP, the expression of SjILP in different tissues and ovarian development stages were analyzed using qRT-PCR. SjILP was mainly expressed in the ovary, and its gene expression correlated with ovarian development. Furthermore, silencing SjILP using RNA interference (RNAi) dramatically decreased the expression levels of four ovarian-development-related genes (vitellogenin1, vitellogenin2, cathepsin L1-like, and follistatin). These data suggest the critical role of SjILP in the regulation of ovarian development in S. japonica.

Endomitosis controls tissue-specific gene expression during development

Polyploid cells contain more than 2 copies of the genome and are found in many plant and animal tissues. Different types of polyploidy exist, in which the genome is confined to either 1 nucleus (mononucleation) or 2 or more nuclei (multinucleation). Despite the widespread occurrence of polyploidy, the functional significance of different types of polyploidy is largely unknown. Here, we assess the function of multinucleation in Caenorhabditis elegans intestinal cells through specific inhibition of binucleation without altering genome ploidy. Through single-worm RNA sequencing, we find that binucleation is important for tissue-specific gene expression, most prominently for genes that show a rapid up-regulation at the transition from larval development to adulthood. Regulated genes include vitellogenins, which encode yolk proteins that facilitate nutrient transport to the germline. We find that reduced expression of vitellogenins in mononucleated intestinal cells leads to progeny with developmental delays and reduced fitness. Together, our results show that binucleation facilitates rapid up-regulation of intestine-specific gene expression during development, independently of genome ploidy, underscoring the importance of spatial genome organization for polyploid cell function.

Why do some cells contain more than one nucleus? By comparing mononucleated and multinucleated polyploid cells in C. elegans, this study shows that having multiple nuclei is important for optimal transcriptional upregulation of developmentally controlled genes.

Potential Molecular Mimicry Proteins Responsive to α-pinene in Bursaphelenchus xylophilus

: Bursaphelenchus xylophilus is a nematode species that has damaged pine trees worldwide, but its pathogenesis has not been fully characterized. α-pinene helps protect host species during the early B. xylophilus infection and colonization stages. In this study, we identified potential molecular mimicry proteins based on a comparative transcriptomic analysis of B. xylophilus. The expression levels of three genes encoding secreted B. xylophilus proteins were influenced by α-pinene. We cloned one gene encoding a thaumatin-like protein, Bx-tlp-2 (accession number MK000287), and another gene encoding a cysteine proteinase inhibitor, Bx-cpi (accession number MK000288). Additionally, α-pinene appeared to induce Bx-tlp-1 expression, but had the opposite effect on Bx-cpi expression. An analysis of the expression of the potential molecular mimicry proteins in B. xylophilus infecting pine trees revealed that the α-pinene content was consistent with the expression levels of Bx-tlp-1 (Bx-cpi) and Pm-tlp (Pm-cpi) over time. Thus, these genes likely have important roles contributing to the infection of pine species by B. xylophilus. The results of this study may be relevant for future investigations of the functions of Bx-tlp-1, Bx-tlp-2 and Bx-cpi, which may provide a point to explore the relationship between B. xylophilus and host pines.

Peripheral cathepsin L inhibition induces fat loss in C. elegans and mice through promoting central serotonin synthesis

BACKGROUND

Cathepsin L and some other cathepsins have been implicated in the development of obesity in humans and mice. The functional inactivation of the proteases reduces fat accumulation during mammalian adipocyte differentiation. However, beyond degrading extracellular matrix protein fibronectin, the molecular mechanisms by which cathepsins control fat accumulation remain unclear. We now provide evidence from Caenorhabditis elegans and mouse models to suggest a conserved regulatory circuit in which peripheral cathepsin L inhibition lowers fat accumulation through promoting central serotonin synthesis.

RESULTS

We established a C. elegans model of fat accumulation using dietary supplementation with glucose and palmitic acid. We found that nutrient supplementation elevated fat storage in C. elegans, and along with worm fat accumulation, an increase in the expression of cpl-1 was detected using real-time PCR and western blot. The functional inactivation of cpl-1 reduced fat storage in C. elegans through activating serotonin signaling. Further, knockdown of cpl-1 in the intestine and hypodermis promoted serotonin synthesis in worm ADF neurons and induced body fat loss in C. elegans via central serotonin signaling. We found a similar regulatory circuit in high-fat diet-fed mice. Cathepsin L knockout promoted fat loss and central serotonin synthesis. Intraperitoneal injection of the cathepsin L inhibitor CLIK195 similarly reduced body weight gain and white adipose tissue (WAT) adipogenesis, while elevating brain serotonin level and WAT lipolysis and fatty acid β-oxidation. These effects of inhibiting cathepsin L were abolished by intracranial injection of p-chlorophenylalanine, inhibitor of a rate-limiting enzyme for serotonin synthesis.

CONCLUSION

This study reveals a previously undescribed molecular mechanism by which peripheral CPL-1/cathepsin L inhibition induces fat loss in C. elegans and mice through promoting central serotonin signaling.

Molecular and functional characterization of the American cockroach, Periplaneta americana, Rab5: the first exopterygotan low molecular weight ovarian GTPase during oogenesis

The small Rab GTPases are key regulators of membrane vesicle trafficking. Ovaries of Periplaneta americana (Linnaeus) (Blattodea: Blattidae) have small molecular weight GTP/ATP-binding proteins during early and late vitellogenic periods of oogenesis. However, the identification and characterization of the detected proteins have not been yet reported. Herein, we cloned a cDNA encoding Rab5 from the American cockroach, P. americana, ovaries (PamRab5). It comprises 796 bp, encoding a protein of 213 amino acid residues with a predicted molecular weight of 23.5 kDa. PamRab5 exists as a single-copy gene in the P. americana genome, as revealed by Southern blot analysis. An approximate 2.6 kb ovarian mRNA was transcribed especially at high levels in the previtellogenic ovaries, detected by Northern blot analysis. The muscle and head tissues also showed high levels of PamRab5 transcript. PamRab5 protein was localized, via immunofluorescence labeling, to germline-derived cells of the oocytes, very early during oocyte differentiation. Immunoblotting detected a ∼25 kDa signal as a membrane-associated form revealed after application of detergent in the extraction buffer, and 23 kDa as a cytosolic form consistent with the predicted molecular weight from amino acid sequence in different tissues including ovary, muscles and head. The PamRab5 during late vitellogenic periods is required to regulate the endocytotic machinery during oogenesis in this cockroach. This is the first report on Rab5 from a hemimetabolan, and presents an inaugural step in probing the molecular premises of insect oocyte endocytotic trafficking important for oogenesis and embryonic development.

Cysteine proteases during larval migration and development of helminths in their final host

Neglected tropical diseases caused by metazoan parasites are major public health concerns, and therefore, new methods for their control and elimination are needed. Research over the last 25 years has revealed the vital contribution of cysteine proteases to invasion of and migration by (larval) helminth parasites through host tissues, in addition to their roles in embryogenesis, molting, egg hatching, and yolk degradation. Their central function to maintaining parasite survival in the host has made them prime intervention targets for novel drugs and vaccines. This review focuses on those helminth cysteine proteases that have been functionally characterized during the varied early stages of development in the human host and embryogenesis.

Draft genome of the honey bee ectoparasitic mite, Tropilaelaps mercedesae, is shaped by the parasitic life history

The number of managed honey bee colonies has considerably decreased in many developed countries in recent years and ectoparasitic mites are considered as major threats to honey bee colonies and health. However, their general biology remains poorly understood. We sequenced the genome of Tropilaelaps mercedesae, the prevalent ectoparasitic mite infesting honey bees in Asia, and predicted 15 190 protein-coding genes that were well supported by the mite transcriptomes and proteomic data. Although amino acid substitutions have been accelerated within the conserved core genes of two mites, T. mercedesae and Metaseiulus occidentalis, T. mercedesae has undergone the least gene family expansion and contraction between the seven arthropods we tested. The number of sensory system genes has been dramatically reduced, but T. mercedesae contains all gene sets required to detoxify xenobiotics. T. mercedesae is closely associated with a symbiotic bacterium (Rickettsiella grylli-like) and Deformed Wing Virus, the most prevalent honey bee virus. T. mercedesae has a very specialized life history and habitat as the ectoparasitic mite strictly depends on the honey bee inside a stable colony. Thus, comparison of the genome and transcriptome sequences with those of a tick and free-living mites has revealed the specific features of the genome shaped by interaction with the honey bee and colony environment. Genome and transcriptome sequences of T. mercedesae, as well as Varroa destructor (another globally prevalent ectoparasitic mite of honey bee), not only provide insights into the mite biology, but may also help to develop measures to control the most serious pests of the honey bee.

The cathepsin S cysteine proteinase of the burrowing nematode Radopholus similis is essential for the reproduction and invasion

BACKGROUND

The nematode Radopholus similis is an important migratory endoparasite of plants. Cysteine proteinases such as cathepsin S (CPS) play key roles during embryonic development, invasion, and pathogenesis in nematodes and many other animal parasites. This study was designed to investigate the molecular characterization and functions of a cathepsin S protease in R. similis and to find new targets for its control.

RESULTS

Rs-CPS of R. similis, Hg-CPS of Heterodera glycines and Ha-CPS of H. avenae are closely genetically related and share the same branch of the phylogenetic tree. Rs-cps is a multi-copy gene that is expressed in the esophageal glands, ovaries, testes, vas deferens, and eggs of R. similis. Rs-cps mRNA transcripts are expressed at varying levels during all developmental stages of R. similis. Rs-cps expression was highest in females. The neurostimulant octopamine did not significantly enhance the ingestion of the dsRNA soaking solution by R. similis but instead had a detrimental effect on nematode activity. The dsRNA soaking solution diffused into the body of R. similis not only through the esophageal lumen but also through the amphids, excretory duct, vagina, anus and cloacal orifice. We confirmed that RNAi significantly suppressed the expression level of Rs-cps and reproductive capability and pathogenicity of R. similis.

CONCLUSIONS

Our results demonstrate that Rs-cps plays important roles in the reproduction, parasitism and pathogenesis of R. similis and could be used as a new potential target for controlling plant parasitic nematodes.

Genetics of Lipid-Storage Management in Caenorhabditis elegans Embryos

Lipids play a pivotal role in embryogenesis as structural components of cellular membranes, as a source of energy, and as signaling molecules. On the basis of a collection of temperature-sensitive embryonic lethal mutants, a systematic database search, and a subsequent microscopic analysis of >300 interference RNA (RNAi)-treated/mutant worms, we identified a couple of evolutionary conserved genes associated with lipid storage in Caenorhabditis elegans embryos. The genes include cpl-1 (cathepsin L-like cysteine protease), ccz-1 (guanine nucleotide exchange factor subunit), and asm-3 (acid sphingomyelinase), which is closely related to the human Niemann-Pick disease-causing gene SMPD1. The respective mutant embryos accumulate enlarged droplets of neutral lipids (cpl-1) and yolk-containing lipid droplets (ccz-1) or have larger genuine lipid droplets (asm-3). The asm-3 mutant embryos additionally showed an enhanced resistance against C band ultraviolet (UV-C) light. Herein we propose that cpl-1, ccz-1, and asm-3 are genes required for the processing of lipid-containing droplets in C. elegans embryos. Owing to the high levels of conservation, the identified genes are also useful in studies of embryonic lipid storage in other organisms.

Out-of-frame start codons prevent translation of truncated nucleo-cytosolic cathepsin L in vivo

The lysosomal protease cathepsin L has been reported to cleave various functionally important cytosolic or nuclear proteins. To explain nucleo-cytosolic localization of cathepsin L, it has been hypothesized that skipping of the first start codon during translation initiation results in an N-terminally truncated protein lacking the endoplasmic reticulum-import signal. Here we demonstrate that out-of-frame AUGs prevent translation of truncated cathepsin L in cell culture as well as in a new knock-in mouse model. We further evaluate potential roles of nuclear cathepsin L during early embryonic development. Our analysis reveals normal epiblast development of cathepsin L-deficient embryos, but uncovers a pronounced lysosomal storage phenotype in the extra-embryonic tissue of the visceral endoderm. In conclusion, the phenotypes of cathepsin L deficiency can be fully assigned to lack of canonically targeted cathepsin L, while the biogenesis and functionality of nucleo-cytosolic cathepsin L remain elusive.

Potential involvement of Brugia malayi cysteine proteases in the maintenance of the endosymbiotic relationship with Wolbachia

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Bm-cpl-3 and Bm-cpl-6 are involved during development and endosymbiosis.

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In tetracycline-treated worms Bm-cpl-3 and -6 are regulated in a bimodal pattern.

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Reduction in Bm-cpl-3 and -6 levels resulted in hindered microfilarial development.

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Reduction in Bm-cpl-3 and -6 levels resulted in reduced Wolbachia DNA levels.

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These enzymes might be strong drug target candidates.

Brugia malayi, a parasitic nematode that causes lymphatic filariasis, harbors endosymbiotic intracellular bacteria, Wolbachia, that are required for the development and reproduction of the worm. The essential nature of this endosymbiosis led to the development of anti-Wolbachia chemotherapeutic approaches for the treatment of human filarial infections. Our study is aimed at identifying specific proteins that play a critical role in this endosymbiotic relationship leading to the identification of potential targets in the adult worms. Filarial cysteine proteases are known to be involved in molting and embryogenesis, processes shown to also be Wolbachia dependent. Based on the observation that cysteine protease transcripts are differentially regulated in response to tetracycline treatment, we focused on defining their role in symbiosis. We observe a bimodal regulation pattern of transcripts encoding cysteine proteases when in vitro tetracycline treated worms were examined. Using tetracycline-treated infertile female worms and purified embryos we established that the first peak of the bimodal pattern corresponds to embryonic transcripts while the second takes place within the hypodermis of the adult worms. Localization studies of the native proteins corresponding to Bm-cpl-3 and Bm-cpl-6 indicate that they are present in the area surrounding Wolbachia, and, in some cases, the proteins appear localized within the bacteria. Both proteins were also found in the inner bodies of microfilariae. The possible role of these cysteine proteases during development and endosymbiosis was further characterized using RNAi. Reduction in Bm-cpl-3 and Bm-cpl-6 transcript levels was accompanied by hindered microfilarial development and release, and reduced Wolbachia DNA levels, making these enzymes strong drug target candidates.

The lysosomal cathepsin protease CPL-1 plays a leading role in phagosomal degradation of apoptotic cells in Caenorhabditis elegans

In Caenorhabditis elegans, the lysosomal cathepsin protease CPL-1 is indispensable for clearance of apoptotic cells by playing a leading role in destruction of cell corpses in phagolysosomes.

During programmed cell death, the clearance of apoptotic cells is achieved by their phagocytosis and delivery to lysosomes for destruction in engulfing cells. However, the role of lysosomal proteases in cell corpse destruction is not understood. Here we report the identification of the lysosomal cathepsin CPL-1 as an indispensable protease for apoptotic cell removal in Caenorhabditis elegans. We find that loss of cpl-1 function leads to strong accumulation of germ cell corpses, which results from a failure in degradation rather than engulfment. CPL-1 is expressed in a variety of cell types, including engulfment cells, and its mutation does not affect the maturation of cell corpse–containing phagosomes, including phagosomal recruitment of maturation effectors and phagosome acidification. Of importance, we find that phagosomal recruitment and incorporation of CPL-1 occurs before digestion of cell corpses, which depends on factors required for phagolysosome formation. Using RNA interference, we further examine the role of other candidate lysosomal proteases in cell corpse clearance but find that they do not obviously affect this process. Collectively, these findings establish CPL-1 as the leading lysosomal protease required for elimination of apoptotic cells in C. elegans.

Caenorhabditis elegans HOPS and CCZ-1 mediate trafficking to lysosome-related organelles independently of RAB-7 and SAND-1

As early endosomes mature, the SAND-1/CCZ-1 complex acts as a guanine nucleotide exchange factor (GEF) for RAB-7 to promote the activity of its effector, HOPS, which facilitates late endosome-lysosome fusion and the consumption of AP-3-containing vesicles. We show that CCZ-1 and the HOPS complex are essential for the biogenesis of gut granules, cell type-specific, lysosome-related organelles (LROs) that coexist with conventional lysosomes in Caenorhabditis elegans intestinal cells. The HOPS subunit VPS-18 promotes the trafficking of gut granule proteins away from lysosomes and functions downstream of or in parallel to the AP-3 adaptor. CCZ-1 also acts independently of AP-3, and ccz-1 mutants mistraffic gut granule proteins. Our results indicate that SAND-1 does not participate in the formation of gut granules. In the absence of RAB-7 activity, gut granules are generated; however, their size and protein composition are subtly altered. These observations suggest that CCZ-1 acts in partnership with a protein other than SAND-1 as a GEF for an alternate Rab to promote gut granule biogenesis. Point mutations in GLO-1, a Rab32/38-related protein, predicted to increase spontaneous guanine nucleotide exchange, specifically suppress the loss of gut granules by ccz-1 and glo-3 mutants. GLO-3 is known to be required for gut granule formation and has homology to SAND-1/Mon1-related proteins, suggesting that CCZ-1 functions with GLO-3 upstream of the GLO-1 Rab, possibly as a GLO-1 GEF. These results support LRO formation occurring via processes similar to conventional lysosome biogenesis, albeit with key molecular differences.

Comparative transcriptome analysis of obligately asexual and cyclically sexual rotifers reveals genes with putative functions in sexual reproduction, dormancy, and asexual egg production

BACKGROUND

Sexual reproduction is a widely studied biological process because it is critically important to the genetics, evolution, and ecology of eukaryotes. Despite decades of study on this topic, no comprehensive explanation has been accepted that explains the evolutionary forces underlying its prevalence and persistence in nature. Monogonont rotifers offer a useful system for experimental studies relating to the evolution of sexual reproduction due to their rapid reproductive rate and close relationship to the putatively ancient asexual bdelloid rotifers. However, little is known about the molecular underpinnings of sex in any rotifer species.

RESULTS

We generated mRNA-seq libraries for obligate parthenogenetic (OP) and cyclical parthenogenetic (CP) strains of the monogonont rotifer, Brachionus calyciflorus, to identify genes specific to both modes of reproduction. Our differential expression analysis identified receptors with putative roles in signaling pathways responsible for the transition from asexual to sexual reproduction. Differential expression of a specific copy of the duplicated cell cycle regulatory gene CDC20 and specific copies of histone H2A suggest that such duplications may underlie the phenotypic plasticity required for reproductive mode switch in monogononts. We further identified differential expression of genes involved in the formation of resting eggs, a process linked exclusively to sex in this species. Finally, we identified transcripts from the bdelloid rotifer Adineta ricciae that have significant sequence similarity to genes with higher expression in CP strains of B. calyciflorus.

CONCLUSIONS

Our analysis of global gene expression differences between facultatively sexual and exclusively asexual populations of B. calyciflorus provides insights into the molecular nature of sexual reproduction in rotifers. Furthermore, our results offer insight into the evolution of obligate asexuality in bdelloid rotifers and provide indicators important for the use of monogononts as a model system for investigating the evolution of sexual reproduction.

Cathepsin L in the orange-spotted grouper, Epinephelus coioides: molecular cloning and gene expression after a Vibrio anguillarum challenge

The orange-spotted grouper, Epinephelus coioides, is an important fish maricultured in many Asian countries. In the present study, the full-length cDNA of cathepsin L, an immunity related gene of fishes, was isolated from E. coioides using rapid amplification of cDNA ends (RACE). It is 1,443 bp in length, including an open reading frame (ORF) of 1,011 bp. The open reading frame encoded a preproprotein of 336 amino acids (aa), which consisted of a signal peptide of 16 aa, a proregion peptide of 98 aa and a mature peptide of 222 aa. The preproprotein contained an oxyanion hole (Gln), a catalytic triad formed by Cys, His and Asn, and the conserved ERWNIN, GNFD and GCNGG motifs, all characteristic of cathepsin L. Homology analysis revealed that the deduced amino acid sequence of E. coioides cathepsin L shared 80.1-94.8 % identity with those of reported fishes. Tissue-dependent mRNA expression analysis showed that the cathepsin L transcript was expressed in all the examined tissues of the healthy E. coioides, being highest in the liver and moderate in the heart, gonad and intestine. After Vibrio anguillarum stimulation, the mRNA expression of cathepsin L in E. coioides was significantly increased in the skin, fin, gills, liver, blood, spleen, head kidney and intestine, with the highest observed in the spleen (10.6-fold) at 12 h post-injection and the next in blood (7.5-fold) at 8 h post-injection. These results provided initial information for further studies on the physiological and immunological roles of the cathepsin L gene in the orange-spotted grouper.

C. elegans BLOC-1 functions in trafficking to lysosome-related gut granules

The human disease Hermansky-Pudlak syndrome results from defective biogenesis of lysosome-related organelles (LROs) and can be caused by mutations in subunits of the BLOC-1 complex. Here we show that C. elegans glo-2 and snpn-1, despite relatively low levels of amino acid identity, encode Pallidin and Snapin BLOC-1 subunit homologues, respectively. BLOC-1 subunit interactions involving Pallidin and Snapin were conserved for GLO-2 and SNPN-1. Mutations in glo-2 and snpn-1,or RNAi targeting 5 other BLOC-1 subunit homologues in a genetic background sensitized for glo-2 function, led to defects in the biogenesis of lysosome-related gut granules. These results indicate that the BLOC-1 complex is conserved in C. elegans. To address the function of C. elegans BLOC-1, we assessed the intracellular sorting of CDF-2::GFP, LMP-1, and PGP-2 to gut granules. We validated their utility by analyzing their mislocalization in intestinal cells lacking the function of AP-3, which participates in an evolutionarily conserved sorting pathway to LROs. BLOC-1(−) intestinal cells missorted gut granule cargo to the plasma membrane and conventional lysosomes and did not have obviously altered function or morphology of organelles composing the conventional lysosome protein sorting pathway. Double mutant analysis and comparison of AP-3(−) and BLOC-1(−) phenotypes revealed that BLOC-1 has some functions independent of the AP-3 adaptor complex in trafficking to gut granules. We discuss similarities and differences of BLOC-1 activity in the biogenesis of gut granules as compared to mammalian melanosomes, where BLOC-1 has been most extensively studied for its role in sorting to LROs. Our work opens up the opportunity to address the function of this poorly understood complex in cell and organismal physiology using the genetic approaches available in C. elegans.

A pro-cathepsin L mutant is a luminal substrate for endoplasmic-reticulum-associated degradation in C. elegans

Endoplasmic-reticulum associated degradation (ERAD) is a major cellular misfolded protein disposal pathway that is well conserved from yeast to mammals. In yeast, a mutant of carboxypeptidase Y (CPY*) was found to be a luminal ER substrate and has served as a useful marker to help identify modifiers of the ERAD pathway. Due to its ease of genetic manipulation and the ability to conduct a genome wide screen for modifiers of molecular pathways, C. elegans has become one of the preferred metazoans for studying cell biological processes, such as ERAD. However, a marker of ERAD activity comparable to CPY* has not been developed for this model system. We describe a mutant of pro-cathepsin L fused to YFP that no longer targets to the lysosome, but is efficiently eliminated by the ERAD pathway. Using this mutant pro-cathepsin L, we found that components of the mammalian ERAD system that participate in the degradation of ER luminal substrates were conserved in C. elegans. This transgenic line will facilitate high-throughput genetic or pharmacological screens for ERAD modifiers using widefield epifluorescence microscopy.

Effects of doxycycline on gene expression in Wolbachia and Brugia malayi adult female worms in vivo

Background

Most filarial nematodes contain Wolbachia symbionts. The purpose of this study was to examine the effects of doxycycline on gene expression in Wolbachia and adult female Brugia malayi.

Methods

Brugia malayi infected gerbils were treated with doxycycline for 6-weeks. This treatment largely cleared Wolbachia and arrested worm reproduction. RNA recovered from treated and control female worms was labeled by random priming and hybridized to the Version 2- filarial microarray to obtain expression profiles.

Results and discussion

Results showed significant changes in expression for 200 Wolbachia (29% of Wolbachia genes with expression signals in untreated worms) and 546 B. malayi array elements after treatment. These elements correspond to known genes and also to novel genes with unknown biological functions. Most differentially expressed Wolbachia genes were down-regulated after treatment (98.5%). In contrast, doxycycline had a mixed effect on B. malayi gene expression with many more genes being significantly up-regulated after treatment (85% of differentially expressed genes). Genes and processes involved in reproduction (gender-regulated genes, collagen, amino acid metabolism, ribosomal processes, and cytoskeleton) were down-regulated after doxycycline while up-regulated genes and pathways suggest adaptations for survival in response to stress (energy metabolism, electron transport, anti-oxidants, nutrient transport, bacterial signaling pathways, and immune evasion).

Conclusions

Doxycycline reduced Wolbachia and significantly decreased bacterial gene expression. Wolbachia ribosomes are believed to be the primary biological target for doxycycline in filarial worms. B. malayi genes essential for reproduction, growth and development were also down-regulated; these changes are consistent with doxycycline effects on embryo development and reproduction. On the other hand, many B. malayi genes involved in energy production, electron-transport, metabolism, anti-oxidants, and others with unknown functions had increased expression signals after doxycycline treatment. These results suggest that female worms are able to compensate in part for the loss of Wolbachia so that they can survive, albeit without reproductive capacity. This study of doxycycline induced changes in gene expression has provided new clues regarding the symbiotic relationship between Wolbachia and B. malayi.

Long-term survival of hydrated resting eggs from Brachionus plicatilis

Background

Several organisms display dormancy and developmental arrest at embryonic stages. Long-term survival in the dormant form is usually associated with desiccation, orthodox plant seeds and Artemia cysts being well documented examples. Several aquatic invertebrates display dormancy during embryonic development and survive for tens or even hundreds of years in a hydrated form, raising the question of whether survival in the non-desiccated form of embryonic development depends on pathways similar to those occurring in desiccation tolerant forms.

Methodology/Principal Findings

To address this question, Illumina short read sequencing was used to generate transcription profiles from the resting and amictic eggs of an aquatic invertebrate, the rotifer, Brachionus plicatilis. These two types of egg have very different life histories, with the dormant or diapausing resting eggs, the result of the sexual cycle and amictic eggs, the non-dormant products of the asexual cycle. Significant transcriptional differences were found between the two types of egg, with amictic eggs rich in genes involved in the morphological development into a juvenile rotifer. In contrast, representatives of classical “stress” proteins: a small heat shock protein, ferritin and Late Embryogenesis Abundant (LEA) proteins were identified in resting eggs. More importantly however, was the identification of transcripts for messenger ribonucleoprotein particles which stabilise RNA. These inhibit translation and provide a valuable source of useful RNAs which can be rapidly activated on the exit from dormancy. Apoptotic genes were also present. Although apoptosis is inconsistent with maintenance of prolonged dormancy, an altered apoptotic pathway has been proposed for Artemia, and this may be the case with the rotifer.

Conclusions

These data represent the first transcriptional profiling of molecular processes associated with dormancy in a non-desiccated form and indicate important similarities in the molecular pathways activated in resting eggs compared with desiccated dormant forms, specifically plant seeds and Artemia.

Cathepsin B differential expression and enzyme processing and activity during Fundulus heteroclitus embryogenesis

The role of lysosomal proteases such as cathepsin B (Ctsb) and one of the paralogs of cathepsin L (Ctsla) during yolk metabolism in fish oocytes is well established. However, the function of Ctsb during embryogenesis, particularly in marine teleosts, has been poorly documented. In this study, the spatio-temporal expression of Ctsb and Ctsla, their enzymatic activities, and the processing of the Ctsb and its cellular localization, was investigated in developing embryos of the killifish (Fundulus heteroclitus). Both fhctsb and fhctsla transcript levels, as well as cathepsin B- and L-like activities, gradually increased in embryos from the 2-4 cell stage up to 7 days post-fertilization. During the morula to gastrula transition an increase of the active FhCtsb single chain form was followed by a rise in cathepsin B activity, which were apparently regulated by post-transcriptional mechanisms. During neurulation, a 8-fold increase in cathepsin B activity was accompanied by a more moderate increase in cathepsin L activity, which was 6-fold enhanced by 7 dpf. These increased catalytic activities were well-correlated to changes in the electrophoretic pattern of yolk proteins and a strong expression of fhctsb and its protein product in the yolk syncytial layer. The increase of cathepsin B activity was further correlated with an increment of the relative amount of the FhCtsb single and double chain forms, both active forms of FhCtsb. These results suggest that FhCtsb may be involved in the mechanisms underlying the onset of gastrulation in F. heteroclitus embryos, and may play complementary roles with FhCtsla during yolk metabolism.

Multivesicular body formation requires OSBP-related proteins and cholesterol

In eukaryotes, different subcellular organelles have distinct cholesterol concentrations, which is thought to be critical for biological functions. Oxysterol-binding protein-related proteins (ORPs) have been assumed to mediate nonvesicular cholesterol trafficking in cells; however, their in vivo functions and therefore the biological significance of cholesterol in each organelle are not fully understood. Here, by generating deletion mutants of ORPs in Caenorhabditis elegans, we show that ORPs are required for the formation and function of multivesicular bodies (MVBs). In an RNAi enhancer screen using obr quadruple mutants (obr-1; -2; -3; -4), we found that MVB-related genes show strong genetic interactions with the obr genes. In obr quadruple mutants, late endosomes/lysosomes are enlarged and membrane protein degradation is retarded, although endocytosed soluble proteins are normally delivered to lysosomes and degraded. We also found that the cholesterol content of late endosomes/lysosomes is reduced in the mutants. In wild-type worms, cholesterol restriction induces the formation of enlarged late endosomes/lysosomes, as observed in obr quadruple mutants, and increases embryonic lethality upon knockdown of MVB-related genes. Finally, we show that knockdown of ORP1L, a mammalian ORP family member, induces the formation of enlarged MVBs in HeLa cells. Our in vivo findings suggest that the proper cholesterol level of late endosomes/lysosomes generated by ORPs is required for normal MVB formation and MVB-mediated membrane protein degradation.

Kinesin-dependent transport results in polarized migration of the nucleus in oocytes and inward movement of yolk granules in meiotic embryos

During female meiosis, meiotic spindles are positioned at the oocyte cortex to allow expulsion of chromosomes into polar bodies. In C. elegans, kinesin-dependent translocation of the entire spindle to the cortex precedes dynein-dependent rotation of one spindle pole toward the cortex. To elucidate the role of kinesin-1 in spindle translocation, we examined the localization of kinesin subunits in meiotic embryos. Surprisingly, kinesin-1 was not associated with the spindle and instead was restricted to the cytoplasm in the middle of the embryo. Yolk granules moved on linear tracks, in a kinesin-dependent manner, away from the cortex, resulting in their concentration in the middle of the embryo where the kinesin was concentrated. These results suggest that cytoplasmic microtubules might be arranged with plus ends extending inward, away from the cortex. This microtubule arrangement would not be consistent with direct transport of the meiotic spindle toward the cortex by kinesin-1. In maturing oocytes, the nucleus underwent kinesin-dependent migration to the future site of spindle attachment at the anterior cortex. Thus the spindle translocation defect observed in kinesin-1 mutants may be a result of failed nuclear migration, which places the spindle too far from the cortex for the spindle translocation mechanism to function.

Functional analysis of the cathepsin-like cysteine protease genes in adult Brugia malayi using RNA interference

Background

Cathepsin-like enzymes have been identified as potential targets for drug or vaccine development in many parasites, as their functions appear to be essential in a variety of important biological processes within the host, such as molting, cuticle remodeling, embryogenesis, feeding and immune evasion. Functional analysis of Caenorhabditis elegans cathepsin L (Ce-cpl-1) and cathepsin Z (Ce-cpz-1) has established that both genes are required for early embryogenesis, with Ce-cpl-1 having a role in regulating in part the processing of yolk proteins. Ce-cpz-1 also has an important role during molting.

Methods and Findings

RNA interference assays have allowed us to verify whether the functions of the orthologous filarial genes in Brugia malayi adult female worms are similar. Treatment of B. malayi adult female worms with Bm-cpl-1, Bm-cpl-5, which belong to group Ia of the filarial cpl gene family, or Bm-cpz-1 dsRNA resulted in decreased numbers of secreted microfilariae in vitro. In addition, analysis of the intrauterine progeny of the Bm-cpl-5 or Bm-cpl Pro dsRNA- and siRNA-treated worms revealed a clear disruption in the process of embryogenesis resulting in structural abnormalities in embryos and a varied differential development of embryonic stages.

Conclusions

Our studies suggest that these filarial cathepsin-like cysteine proteases are likely to be functional orthologs of the C. elegans genes. This functional conservation may thus allow for a more thorough investigation of their distinct functions and their development as potential drug targets.

Filarial nematodes are an important group of human pathogens, causing lymphatic filariasis and onchocerciasis, and infecting around 150 million people throughout the tropics with more than 1.5 billion at risk of infection. Control of filariasis currently relies on mass drug administration (MDA) programs using drugs which principally target the microfilarial life-cycle stage. These control programs are facing major challenges, including the absence of a drug with macrofilaricidal or permanent sterilizing activity, and the possibility of the development of drug-resistance against the drugs available. Cysteine proteases are essential enzymes which play important roles in a wide range of cellular processes, and the cathepsin-like cysteine proteases have been identified as potential targets for drug or vaccine development in many parasites. Here we have studied the function of several of the cathepsin-like enzymes in the filarial nematode, B. malayi, and demonstrate that these cysteine proteases are involved in the development of embryos, show similar functions to their counterparts in C. elegans, and therefore, provide an important target for future drug development targeted to eliminate filariasis.

Cathepsin L is responsible for processing and activation of proheparanase through multiple cleavages of a linker segment

Heparanase is an endo-beta-d-glucuronidase that degrades heparan sulfate in the extracellular matrix and on the cell surface. Human proheparanase is produced as a latent protein of 543 amino acids whose activation involves excision of an internal linker segment (Ser(110)-Gln(157)), yielding the active heterodimer composed of 8- and 50-kDa subunits. Applying cathepsin L knock-out tissues and cultured fibroblasts, as well as cathepsin L gene silencing and overexpression strategies, we demonstrate, for the first time, that removal of the linker peptide and conversion of proheparanase into its active 8 + 50-kDa form is brought about predominantly by cathepsin L. Excision of a 10-amino acid peptide located at the C terminus of the linker segment between two functional cathepsin L cleavage sites (Y156Q and Y146Q) was critical for activation of proheparanase. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry demonstrates that the entire linker segment is susceptible to multiple endocleavages by cathepsin L, generating small peptides. Mass spectrometry demonstrated further that an active 8-kDa subunit can be generated by several alternative adjacent endocleavages, yielding the precise 8-kDa subunit and/or slightly elongated forms. Altogether, the mode of action presented here demonstrates that processing and activation of proheparanase can be brought about solely by cathepsin L. The critical involvement of cathepsin L in proheparanase processing and activation offers new strategies for inhibiting the prometastatic, proangiogenic, and proinflammatory activities of heparanase.

A differential proteomic approach reveals an evolutionary conserved regulation of Nme proteins by Fe65 in C. elegans and mouse

The function of the APP-Fe65 complex is still not definitively understood. To address this point we studied the phenotype of Fe65 (feh-1) ablation, which results in severe developmental defects in C. elegans, including embryonic and larval arrests. To shed light on the complex phenotype of embryonic arrest, we undertook a systematic approach, aiming at the definition of the altered proteomic profile of feh-1 null worms. We defined a panel of 27 regulated proteins, 16 of which actually participating to embryonic development processes in the nematode. Protein spots corresponding to the products of the F25H2.5 gene, the nematode orthologue of mammalian Nm23/Nme gene family members, were consistently up-regulated in feh-1 -/- embryos. We observed similar up-regulation of Nme1 and Nme2 genes, both at the transcript and the protein levels, in the brain of Fe65 knock-out mice, thus highlighting the occurrence of evolutionary conserved mechanisms of Nme expression in nematodes and mammals.

Emerging functions of placental cathepsins

A series of tandem duplications of an ancestral cathepsin L gene has given rise to a family of eight placenta-specific cathepsins in mice. These genes are differentially regulated both spatially and temporally and thus each can perform unique placental functions. Analysis of the function and expression of these genes is yielding new insights into gene regulation and proteolytic processes in placenta, and may dissect critical placental roles of the single human functional ortholog, cathepsin L.

Cathepsin L and cystatin B gene expression discriminates immune coelomic cells in the leech Theromyzon tessulatum

Previous studies evidenced that cystatin B-like gene is specifically expressed and induced in large circulating coelomic cells following bacterial challenge in the leech Theromyzon tessulatum. In order to understand the role of that cysteine proteinase inhibitor during immune response, we investigated the existence of members of cathepsin family. We cloned a cathepsin L-like gene and studied its tissue distribution. Immunohistochemical studies using anti-cathepsin L and anti-cystatin B antibodies and ultrastructural results demonstrated the presence of three distinct coelomic cell populations: (1) the chloragocytes, which were initially defined as large coelomocytes, (2) the granular amoebocytes and (3) small coelomic cells. Among those cells, while chloragocytes contain cystatin B and cathepsin L, granular amoebocytes contain only cathepsin L and the third cell population contains neither cathepsin nor inhibitor. Finally, results evidenced that cathepsin L immunopositive granular amoebocytes are chemoattracted to the site of injury and phagocyte bacteria.

Development of a specific inhibitor for the placental protease, cathepsin P

Gene duplications in rodents have given rise to a family of proteases that are expressed exclusively in placenta. To define the biological role of these enzymes specific inhibitors are needed to differentiate their activities from other more ubiquitously expressed proteases, such as cathepsins B and L. Libraries of peptidyl inhibitors based upon a 4-cyclohexanone pharmacophore were screened for inhibition of cathepsins P, L, and B. The tightest binding dipeptidyl inhibitor for cathepsin P contained Tyr in P(2) and Trp in P(2)('), consistent with the specificity of this enzyme for hydrophobic amino acids at these sites in synthetic substrates. An inhibitor containing Trp in both P(2) and P(2)(') provided better discrimination between cathepsin P and cathepsins B and L. Extension of the inhibitors to include P(3), and P(3)(') amino acids identified an inhibitor with Trp in P(2), P(2)('), and P(3), and Phe in P(3)(') that bound to cathepsin P with a K(i) of 32 nM. This specificity for inhibitors with hydrophobic aromatic amino acids in these four positions is unique among the lysosomal cysteine proteases. This inhibitor bound to cathepsin P an order of magnitude tighter than to mouse and human cathepsin L and two orders of magnitude tighter than to human cathepsin B. Cbz-Trp-Trp-4-cyclohexanone-Trp-Phe-OMe can discriminate cathepsin P from cathepsins B and L and consequently can be used to specifically inhibit and identify cathepsin P in cellular systems.

Expression and purification of an active cysteine protease of Haemonchus contortus using Caenorhabditis elegans

Many proteolytic enzymes of parasitic nematodes have been identified as possible targets of control. Testing these as vaccine or drug targets is often difficult due to the problems of expressing proteases in a correctly folded, active form in standard expression systems. In an effort to overcome these difficulties we have tested Caenorhabditis elegans as an expression system for a Haemonchus contortus cathepsin L cysteine protease, Hc-CPL-1. Recombinant Hc-CPL-1 with a polyhistidine tag added to the C-terminal was expressed in an active and glycosylated form in C. elegans. Optimal expression was obtained expressing Hc-cpl-1 under control of the promoter of the homologous C. elegans cpl-1 gene. The recombinant protein was purified from liquid cultures by nickel chelation chromatography in sufficient amounts for vaccination studies to be carried out. This study provides proof of principle that active, post-translationally modified parasitic nematode proteases can be expressed in C. elegans and this approach can be extended for expression of known protective antigens.

Brugia pahangi: in vivo tissue migration of early L3 alters gene expression

Events occurring during early filarial nematode migrations are central to parasite establishment but rarely studied. Brugia pahangi larvae injected intradermal (ID) into the hind limb of the gerbil (Meriones unguiculatus) can be recovered from the popliteal lymph node (POP) at 3 days post-infection (DPI). They have been designated migrating larvae (IDL3). Alternatively, L3 recovered at 3DPI from the peritoneal cavity (IPL3) do not migrate. Subtracted cDNA libraries using IDL3 and IPL3 revealed distinct gene profiles between IDL3 and IPL3. Troponin-c was significantly upregulated in IDL3, while Cathepsin L was significantly increased in IPL3. Differences in mRNA levels were also observed with these and other genes between IDL3, IPL3 and L3 isolated from mosquitoes (VL3). These data suggest that migratory activity, exposure to potentially different host environments and/or host location may be important external factors in influencing larval gene expression.

Classes and crossreactivity of proteinases in the excretory–secretory products of Caenorhabditis elegans

Proteinases released during the in vitro maintenance of asynchronous cultures of the free-living nematode Caenorhabditis elegans were characterized on the basis of subunit composition, fluorogenic substrate specificity, inhibitor sensitivity and pH optima. Cysteine proteinases are present in the excretory–secretory products (ESP) as indicated by the hydrolysis of cathepsin fluorogenic substrates and confirmed by immunoblotting. Serine proteinases were predominant as indicated by substrate gel analysis and inhibitor studies. The presence of metallo-proteinases was also indicated by inhibitor studies. The optimal pH value for cysteine proteinases was 5.5, while serine proteinases were optimal at pH 8.0. As a control, cultures of Escherichia coli, the diet of C. elegans, were extracted separately and gave no evidence of overlap with C. elegans ESP. Cross reactivity between the ESP of C. elegans and antibodies raised against the ESP of the equine parasite Strongylus vulgaris indicated antigenic relatedness of a proteic epitope. This is the first study to characterize the ESP of C. elegans and to display its relatedness with that of S. vulgaris.

Phylogenetic relationships and gene expression pattern of three different cathepsin L (Ctsl) isoforms in zebrafish: Ctsla is the putative yolk processing enzyme

Certain cysteine proteases, such as cathepsin L (Ctsl), have been involved in yolk processing mechanisms in oocytes and embryos of lower vertebrates. In zebrafish (Danio rerio), three different ctsl genes, ctsla, ctslb and ctslc, have been found in the genome, but their pattern of expression, as well as information on which the encoded enzymes are potentially involved in yolk absorption during embryogenesis, is unknown. Here, phylogenetic and gene structure analysis revealed that zebrafish ctsla and ctslb genes are similar, showing a highly conserved structure in comparison with human ctsl, while ctslc presents different exon organization together with an earlier evolution. Thus, ctslc appears to be evolved from a common ancestral ctsl-like gene, possibly through an early duplication event, whereas ctsla and ctslb may be originated from a second duplication mechanism. Zebrafish ctsla, ctslb and ctslc also showed different patterns of mRNA expression during embryogenesis and in adult tissues. While Ctsla transcripts were accumulated in embryos throughout development and in the adult ovary, those encoding Ctslb were detected only in embryos around the time of hatching as previously reported, and those for Ctslc appeared only in larvae and in some adult tissues, but not in the ovary. In zebrafish and killifish (Fundulus heteroclitus) embryos, Ctsla mRNA was first detected in blastomers, and later in development it was localized in cells of the yolk syncytial layer, an embryonic structure involved in yolk absorption. These data therefore suggested that Ctsla is most likely the putative protease involved in yolk processing in fish embryos, while Ctslc seems not to be required during early embryogenesis in zebrafish.

Suppression of thecup-5mucolipidosis type IV-related lysosomal dysfunction by the inactivation of an ABC transporter inC. elegans

Mutations in MCOLN1, which encodes the protein mucolipin 1, result in the lysosomal storage disease mucolipidosis Type IV. Studies on human mucolipin 1 and on CUP-5, the Caenorhabditis elegans ortholog of mucolipin 1, have shown that these proteins are required for lysosome biogenesis/function. Loss of CUP-5 results in a defect in lysosomal degradation, leading to embryonic lethality. We have identified a mutation in the ABC transporter MRP-4 that rescues the degradation defect and the corresponding lethality, owing to the absence of CUP-5. MRP-4 localizes to endocytic compartments and its levels are elevated in the absence of CUP-5. These results indicate that the lysosomal degradation defect is exacerbated in some cells because of the accumulation of MRP-4 in lysosomes rather than the loss of CUP-5 per se. We also show that under some conditions, loss of MRP-4 rescues the embryonic lethality caused by the loss of the cathepsin L protease, indicating that the accumulation of ABC transporters may be a more general mechanism whereby an initial lysosomal dysfunction is more severely compromised.

Further characterization of the cathepsin L-associated protein and its gene in two species of the brine shrimp, Artemia

The major cysteine protease in embryos and larvae of the brine shrimp Artemia franciscana is a heterodimer composed of a cathepsin L-like polypeptide of 28.5 kDa and a 31.5 kDa polypeptide called the cathepsin L-associated protein or CLAP. In a previous study, CLAP was shown to be a cell adhesion protein containing two Fas I domains and two GTP/ATP binding sites known as Walker A and B motifs. Here, we have characterized CLAP and its genes to better understand the role of this protein in Artemia development. The polymerase chain reaction was used to investigate the structure of the CLAP gene in two species of Artemia, the New World bisexual diploid A. franciscana and the Old World parthenogenetic tetraploid Artemia parthenogenetica. The protein coding region of the CLAP gene from each species was 99.5% identical for a protein of 332 amino acids, while the 3' non-coding region, representing nearly 45% of the gene, was only 86% identical between the two related species. However, while the CLAP gene is intronless in A. franciscana, in A. parthenogenetica the gene contained a mini-intron of 30 base pairs in the 3' non-coding region. The sequences representing the CLAP gene in A. franciscana and A. parthenogenetica have been entered into the NCBI database as AY757920 and DQ100385, respectively. Northern blot analysis showed that while the cathepsin L gene is expressed constitutively in Artemia franciscana embryos and young larvae, the CLAP gene is not expressed in late embryos and young larvae. In contrast, Western blots indicated that CLAP is present in developing embryos and young larvae, at least to the first larval molt, supporting results obtained previously showing CLAP's resistance to degradation by its dimeric partner, cathepsin L. At the protein level we showed that the GTP/ATP binding sites in CLAP are functional with rate constants of 0.024 and 0.022 for GTP and ATP hydrolase activity, respectively. GTP but not ATP also had a slight stimulatory effect on cathepsin L activity of the heterodimeric protease containing CLAP. Our results support the hypothesis that CLAP plays an important role in targeting and expression regulation of cathepsin L activity during early development of Artemia.

Efficacy and specificity of RNA interference in larval life-stages of Ostertagia ostertagi

RNA interference (RNAi) on parasitic nematodes has been described as successful and useful for the identification of novel drug and vaccine candidates. In this study we have evaluated this technology on the cattle parasite Ostertagia ostertagi. Eight different genes were targeted in L1 and L3 O. ostertagi larvae, by electroporation and soaking in dsRNA respectively. Down-regulation of target transcript levels was evaluated by semi-quantitative reverse transcriptase (RT) PCR. In L3 larvae, variable decreases in mRNA levels were observed for 5 genes, ranging from a complete knock down (tropomyosin, beta-tubulin) to a minor decrease (ATPsynthase, superoxide dismutase, polyprotein allergen). However, repeated experiments indicated that effects were sometimes difficult to reproduce. RNAi for ubiquitin, a transthyretin-like protein and a 17 kDa excretion secretion (ES) protein never resulted in a knock down of the transcript. The mRNA levels of 7 non-target genes showed no difference between larvae soaked in C. elegans control dsRNA versus O. ostertagi tropomyosin dsRNA, supporting that the observed reductions are specific for the target gene. Electroporation of L1 larvae proved to be less effective. Reductions in mRNA levels were only noticed for 2 genes and were not reproducible. In conclusion, the results indicate that the RNAi pathway is probably present in O. ostertagi but that the current RNAi techniques can not be used as a reliable screening method.

The Caenorhabditis elegans CPI-2a cystatin-like inhibitor has an essential regulatory role during oogenesis and fertilization

In the present study, we characterized a sterile cpi-2a(ok1256) deletion mutant in Caenorhabditis elegans and showed that CPI-2a has an essential regulatory role during oogenesis and fertilization. We have also shown that the CPI2a inhibitor and both Ce-CPL-1 and Ce-CPZ-1 enzymes are present in the myoepithelial sheath surrounding germ cells, oocytes, and embryos as well as in the yolk granules within normal oocytes. Staining of mutant worms with anti-yolk protein antibodies has indicted that the proteins are not present in the mature oocytes. Moreover, green fluorescent protein expression was absence or reduced in cpi-2a/yp170:gfp mutant oocytes, although it was expressed in one of the successfully developed embryos. Based on these results, we hypothesize that the sterility in cpi-2a(ok1256) mutant worms is potentially caused by two possible mechanisms: 1) defects in the uptake and/or processing of yolk proteins by the growing oocytes and 2) indirect induction of defects in cell-cell signaling that is critical for promoting germ line development, oocyte maturation, ovulation, and fertilization. A defect in any of these processes would have detrimental effects on the development of normal embryos and consequently normal production of progenies as we observed in cpi-2a mutant worms. This is the first study that demonstrates the expression of cysteine proteases and their endogenous inhibitor in the gonadal sheath cells surrounding germ cells and oocytes, which indirectly have established their potential involvement in proteolytic processing of molecules within the gonadal sheath cells, such as components of the extracellular matrix or the cytoskeletal proteins, which are essential for proper cell-cell signaling activities of the gonadal sheath cells during normal maturation and ovulation processes.

Basis of lethality in C. elegans lacking CUP-5, the Mucolipidosis Type IV orthologue

Mutations in MCOLN1, which encodes the protein h-mucolipin-1, result in the lysosomal storage disease Mucolipidosis Type IV. Studies on CUP-5, the human orthologue of h-mucolipin-1 in Caenorhabditis elegans, have shown that these proteins are required for lysosome biogenesis. We show here that the lethality in cup-5 mutant worms is due to two defects, starvation of embryonic cells and general developmental defects. Starvation leads to apoptosis through a CED-3-mediated pathway. We also show that providing worms with a lipid-soluble metabolite partially rescues the embryonic lethality but has no effect on the developmental defects, the major cause of the lethality. These results indicate that supplementing the metabolic deficiency of Mucolipidosis Type IV patients mat not be sufficient to alleviate the symptoms due to tissue degeneration.

The phosphoinositide kinase PIKfyve/Fab1p regulates terminal lysosome maturation in Caenorhabditis elegans

Membrane dynamics is necessary for cell homeostasis and signal transduction and is in part regulated by phosphoinositides. Pikfyve/Fab1p is a phosphoinositide kinase that phosphorylates phosphatidylinositol 3-monophosphate into phosphatidylinositol-3,5-bisphosphate [PtdIns(3,5)P2] and is implicated in membrane homeostasis in yeast and in mammalian cells. These two phosphoinositides are substrates of myotubularin phosphatases found mutated in neuromuscular diseases. We studied the roles of phosphatidylinositol phosphate kinase 3 (PPK-3), the orthologue of PIKfyve/Fab1p, in a multicellular organism, Caenorhabditis elegans. Complete loss of ppk-3 function induces developmental defects characterized by embryonic lethality, whereas partial loss of function leads to growth retardation. At the cellular level, ppk-3 mutants display a striking enlargement of vacuoles positive for lysosome-associated membrane protein 1 in different tissues. In the intestine, RAB-7-positive late endosomes are also enlarged. Membranes of the enlarged lysosomes originate at least in part from smaller lysosomes, and functional and genetic analyses show that the terminal maturation of lysosomes is defective. Protein degradation is not affected in the hypomorphic ppk-3 mutant and is thus uncoupled from membrane retrieval. We measured the level of PtdIns(3,5)P2 and showed that its production is impaired in this mutant. This work strongly suggests that the main function of PPK-3 is to mediate membrane retrieval from matured lysosomes through regulation of PtdIns(3,5)P2.

Using Caenorhabditis elegans for functional analysis of genes of parasitic nematodes

Information on the functional genomics of Caenorhabditis elegans has increased significantly in the last few years with the development of RNA interference. In parasitic nematodes, RNA interference has shown some success in gene knockdown but optimisation of this technique will be required before it can be adopted as a reliable functional genomics tool. Comparative studies in C. elegans remain an appropriate alternative for studying the function and regulation of some parasite genes and will be extremely useful for fully exploiting the increasing parasite genome sequence data becoming available.