Sperm isolation and biochemical analysis of the major sperm protein from Caenorhabditis elegans

RNAi-dependent expression of sperm genes in ADL chemosensory neurons is required for olfactory responses in Caenorhabditis elegans

Environmental conditions experienced early in the life of an animal can result in gene expression changes later in its life history. We have previously shown that C. elegans animals that experienced the developmentally arrested and stress resistant dauer stage (postdauers) retain a cellular memory of early-life stress that manifests during adulthood as genome-wide changes in gene expression, chromatin states, and altered life history traits. One consequence of developmental reprogramming in C. elegans postdauer adults is the downregulation of osm-9 TRPV channel gene expression in the ADL chemosensory neurons resulting in reduced avoidance to a pheromone component, ascr#3. This altered response to ascr#3 requires the principal effector of the somatic nuclear RNAi pathway, the Argonaute (AGO) NRDE-3. To investigate the role of the somatic nuclear RNAi pathway in regulating the developmental reprogramming of ADL due to early-life stress, we profiled the mRNA transcriptome of control and postdauer ADL in wild-type and nrde-3 mutant adults. We found 711 differentially expressed (DE) genes between control and postdauer ADL neurons, 90% of which are dependent upon NRDE-3. Additionally, we identified a conserved sequence that is enriched in the upstream regulatory sequences of the NRDE-3-dependent differentially expressed genes. Surprisingly, 214 of the ADL DE genes are considered "germline-expressed", including 21 genes encoding the Major Sperm Proteins and two genes encoding the sperm-specific PP1 phosphatases, GSP-3 and GSP-4. Loss of function mutations in gsp-3 resulted in both aberrant avoidance and attraction behaviors. We also show that an AGO pseudogene, Y49F6A.1 (wago-11), is expressed in ADL and is required for ascr#3 avoidance. Overall, our results suggest that small RNAs and reproductive genes program the ADL mRNA transcriptome during their developmental history and highlight a nexus between neuronal and reproductive networks in calibrating animal neuroplasticity.

Loss of mammalian glutaminase orthologs impairs sperm function in Caenorhabditis elegans

The decline in sperm function is a major cause of human male infertility. Glutaminase, a mitochondrial enzyme that catalyzes the hydrolysis of glutamine to generate glutamate, takes part in many diverse biological processes such as neurotransmission, metabolism, and cellular senescence. Here we report the role of glutaminase in regulating sperm function. By generating a triple mutant that harbors a loss-of-function allele for each of all three mammalian glutaminase orthologs, we found that glutaminase gene activity is required for optimal Caenorhabditis elegans sperm function. Tissue-specific gene manipulations showed that germline glutaminase activity plays an important role. Moreover, transcriptional profiling and antioxidant treatment suggested that glutaminase promotes sperm function by maintaining cellular redox homeostasis. As maintaining a low level of ROS is crucial to human sperm function, it is very likely that glutaminase plays a similar role in humans and therefore can be a potential target for treating human male infertility.

Membrane-associated cytoplasmic granules carrying the Argonaute protein WAGO-3 enable paternal epigenetic inheritance in Caenorhabditis elegans

Epigenetic inheritance describes the transmission of gene regulatory information across generations without altering DNA sequences, enabling offspring to adapt to environmental conditions. Small RNAs have been implicated in this, through both the oocyte and the sperm. However, as much of the cellular content is extruded during spermatogenesis, it is unclear whether cytoplasmic small RNAs can contribute to epigenetic inheritance through sperm. Here we identify a sperm-specific germ granule, termed the paternal epigenetic inheritance (PEI) granule, that mediates paternal epigenetic inheritance by retaining the cytoplasmic Argonaute protein WAGO-3 during spermatogenesis in Caenorhabditis elegans. We identify the PEI granule proteins PEI-1 and PEI-2, which have distinct functions in this process: granule formation, Argonaute selectivity and subcellular localization. We show that PEI granule segregation is coupled to the transport of sperm-specific secretory vesicles through PEI-2 in an S-palmitoylation-dependent manner. PEI-like proteins are found in humans, suggesting that the identified mechanism may be conserved.

The intrinsically disordered protein SPE-18 promotes localized assembly of MSP in Caenorhabditis elegans spermatocytes

Many specialized cells use unconventional strategies of cytoskeletal control. Nematode spermatocytes discard their actin and tubulin following meiosis, and instead employ the regulated assembly/disassembly of the Major Sperm Protein (MSP) to drive sperm motility. However, prior to the meiotic divisions, MSP is sequestered through its assembly into paracrystalline structures called fibrous bodies (FBs). The accessory proteins that direct this sequestration process have remained mysterious. This study reveals SPE-18 as an intrinsically disordered protein that is essential for MSP assembly within FBs. In spe-18 mutant spermatocytes, MSP forms disorganized cortical fibers, and the cells arrest in meiosis without forming haploid sperm. In wild-type spermatocytes, SPE-18 localizes to pre-FB complexes and functions with the kinase SPE-6 to localize MSP assembly. Changing patterns of SPE-18 localization uncover previously unappreciated complexities in FB maturation. Later, within newly individualized spermatids, SPE-18 is rapidly lost, yet SPE-18 loss alone is insufficient for MSP disassembly. Our findings reveal an alternative strategy for sequestering cytoskeletal elements, not as monomers but in localized, bundled polymers. Additionally, these studies provide an important example of disordered proteins promoting ordered cellular structures.

Loss of flavin adenine dinucleotide (FAD) impairs sperm function and male reproductive advantage in C. elegans

Exposure to environmental stress is clinically established to influence male reproductive health, but the impact of normal cellular metabolism on sperm quality is less well-defined. Here we show that impaired mitochondrial proline catabolism, reduces energy-storing flavin adenine dinucleotide (FAD) levels, alters mitochondrial dynamics toward fusion, and leads to age-related loss of sperm quality (size and activity), which diminishes competitive fitness of the animal. Loss of the 1-pyrroline-5-carboxylate dehydrogenase enzyme alh-6 that catalyzes the second step in mitochondrial proline catabolism leads to premature male reproductive senescence. Reducing the expression of the proline catabolism enzyme alh-6 or FAD biosynthesis pathway genes in the germline is sufficient to recapitulate the sperm-related phenotypes observed in alh-6 loss-of-function mutants. These sperm-specific defects are suppressed by feeding diets that restore FAD levels. Our results define a cell autonomous role for mitochondrial proline catabolism and FAD homeostasis on sperm function and specify strategies to pharmacologically reverse these defects.

Major sperm protein BxMSP10 is required for reproduction and egg hatching in Bursaphelenchus xylophilus

The pine wood nematode Bursaphelenchus xylophilus is a disastrous pathogen of pine forests in East Asia and Europe. Despite its decimating effect on pine forests, efficient and environmentally friendly methods available to control the pine wood nematode (PWN) are limited. The most abundant protein in nematode sperm, major sperm proteins (MSPs) have only been discovered in nematodes. In this study, phylogenetic analysis showed that BxMSP10 was highly conserved in the nematode and had a closer phylogenetic relationship with free-living nematodes than with plant-parasitic nematode species. BxMSP10 was specifically expressed in the seminal vesicle of male adults. dsRNA of BxMSP10 significantly decreased reproduction, egg hatching and population maintenance in B. xylophilus. These results indicated that BxMSP10 was a potential candidate for application in the control of B. xylophilus.

Proteomic and evolutionary analyses of sperm activation identify uncharacterized genes in Caenorhabditis nematodes

BACKGROUND

Nematode sperm have unique and highly diverged morphology and molecular biology. In particular, nematode sperm contain subcellular vesicles known as membranous organelles that are necessary for male fertility, yet play a still unknown role in overall sperm function. Here we take a novel proteomic approach to characterize the functional protein complement of membranous organelles in two Caenorhabditis species: C. elegans and C. remanei.

RESULTS

We identify distinct protein compositions between membranous organelles and the activated sperm body. Two particularly interesting and undescribed gene families-the Nematode-Specific Peptide family, group D and the here designated Nematode-Specific Peptide family, group F-localize to the membranous organelle. Both multigene families are nematode-specific and exhibit patterns of conserved evolution specific to the Caenorhabditis clade. These data suggest gene family dynamics may be a more prevalent mode of evolution than sequence divergence within sperm. Using a CRISPR-based knock-out of the NSPF gene family, we find no evidence of a male fertility effect of these genes, despite their high protein abundance within the membranous organelles.

CONCLUSIONS

Our study identifies key components of this unique subcellular sperm component and establishes a path toward revealing their underlying role in reproduction.

Rapid Gene Family Evolution of a Nematode Sperm Protein Despite Sequence Hyper-conservation

Reproductive proteins are often observed to be the most rapidly evolving elements within eukaryotic genomes. The major sperm protein (MSP) is unique to the phylum Nematoda and is required for proper sperm locomotion and fertilization. Here, we annotate the MSP gene family and analyze their molecular evolution in 10 representative species across Nematoda. We show that MSPs are hyper-conserved across the phylum, having maintained an amino acid sequence identity of 83.5–97.7% for over 500 million years. This extremely slow rate of evolution makes MSPs some of the most highly conserved genes yet identified. However, at the gene family level, we show hyper-variability in both gene copy number and genomic position within species, suggesting rapid, lineage-specific gene family evolution. Additionally, we find evidence that extensive gene conversion contributes to the maintenance of sequence identity within chromosome-level clusters of MSP genes. Thus, while not conforming to the standard expectation for the evolution of reproductive proteins, our analysis of the molecular evolution of the MSP gene family is nonetheless consistent with the widely repeatable observation that reproductive proteins evolve rapidly, in this case in terms of the genomic properties of gene structure, copy number, and genomic organization. This unusual evolutionary pattern is likely generated by strong pleiotropic constraints acting on these genes at the sequence level, balanced against expansion at the level of the whole gene family.

From phenologs to silent suppressors: Identifying potential therapeutic targets for human disease

Orthologous phenotypes, or phenologs, are seemingly unrelated phenotypes generated by mutations in a conserved set of genes. Phenologs have been widely observed and accepted by those who study model organisms, and allow one to study a set of genes in a model organism to learn more about the function of those genes in other organisms, including humans. At the cellular and molecular level, these conserved genes likely function in a very similar mode, but are doing so in different tissues or cell types and can result in different phenotypic effects. For example, the RAS-RAF-MEK-MAPK pathway in animals is a highly conserved signaling pathway that animals adopted for numerous biological processes, such as vulval induction in Caenorhabditis elegans and cell proliferation in mammalian cells; but this same gene set has been co-opted to function in a variety of cellular contexts. In this review, I give a few examples of how suppressor screens in model organisms (with a emphasis on C. elegans) can identify new genes that function in a conserved pathway in many other organisms. I also demonstrate how the identification of such genes can lead to important insights into mammalian biology. From such screens, an occasional silent suppressor that does not cause a phenotype on its own is found; such suppressors thus make for good candidates as therapeutic targets.

The C. elegans VAPB homolog VPR-1 is a permissive signal for gonad development

VAMP/synaptobrevin-associated proteins (VAPs) contain an N-terminal major sperm protein domain (MSPd) that is associated with amyotrophic lateral sclerosis. VAPs have an intracellular housekeeping function, as well as an extracellular signaling function mediated by the secreted MSPd. Here we show that the C. elegans VAP homolog VPR-1 is essential for gonad development. vpr-1 null mutants are maternal effect sterile due to arrested gonadogenesis following embryo hatching. Somatic gonadal precursor cells and germ cells fail to proliferate fully and complete their respective differentiation programs. Maternal or zygotic vpr-1 expression is sufficient to induce gonadogenesis and fertility. Genetic mosaic and cell type-specific expression studies indicate that vpr-1 activity is important in the nervous system, germ line and intestine. VPR-1 acts in parallel to Notch signaling, a key regulator of germline stem cell proliferation and differentiation. Neuronal vpr-1 expression is sufficient for gonadogenesis induction during a limited time period shortly after hatching. These results support the model that the secreted VPR-1 MSPd acts at least in part on gonadal sheath cell precursors in L1 to early L2 stage hermaphrodites to permit gonadogenesis.

Highlighted Article:vpr-1 null mutants are sterile upon hatching, a defect rescued by the expression of MSPd from almost any tissue except for the somatic gonad itself. See also the companion paper by Schultz et al.

Mitigating Motor Neuronal Loss in C. elegans Model of ALS8

ALS8 is a late-onset familial autosomal dominant form of Amyotrophic Lateral Sclerosis (ALS) caused by a point mutation (P56S) in the VAPB gene (VAMP associated protein isoform B). Here, we generated two C. elegans models of the disease: a transgenic model where human VAPB wild-type (WT) or P56S mutant was expressed in a subset of motor neurons, and a second model that targeted inducible knockdown of the worm’s orthologue, vpr-1. Overexpression of human VAPB in DA neurons caused a backward locomotion defect, axonal misguidance, and premature neuronal death. Knockdown of vpr-1 recapitulated the reduction in VAPB expression associated with sporadic cases of human ALS. It also caused backward locomotion defects as well as an uncoordinated phenotype, and age-dependent, progressive motor neuronal death. Furthermore, inhibiting phosphatidylinositol-4 (PtdIns 4)-kinase activity with PIK-93 reduced the incidence of DA motor neuron loss and improved backward locomotion. This supports the loss of VAPB function in ALS8 pathogenesis and suggests that reducing intracellular PtdIns4P might be an effective therapeutic strategy in delaying progressive loss of motor neurons.

Lungworm seroprevalence in free-ranging harbour seals and molecular characterisation of marine mammal MSP

Harbour seals (Phoca vitulina) are frequently infected with the lungworms Otostrongylus circumlitus and Parafilaroides gymnurus. The infection is often accompanied by secondary bacterial infections and can cause severe bronchopneumonia and even death in affected animals. Hitherto, the detection of lungworm infections was based on post mortem investigations from animals collected within stranding networks and a valid detection method for live free-ranging harbour seals was not available. Recently, an ELISA was developed for detecting lungworm antibodies in harbour seal serum, using major sperm protein (MSP) of the bovine lungworm, Dictyocaulus viviparus as recombinant diagnostic antigen. To determine lungworm seroprevalence in free-ranging harbour seals, serum was taken from four different seal age groups (n = 313) resulting in an overall prevalence of 17.9% (18.9% of males, 16.7% of females). 0.7% of harbour seals up to six weeks of age were seropositive, as were 89% of seals between six weeks and six months, 53.6% between six and 18 months and 24.2% of seals over 18 months of age. In the 18 months and over age group, seropositive animals showed statistically significant reductions in body weight (P = 0.003) and length (P < 0.001). Sera from lungworm infected harbour seals in rehabilitation (n = 6) revealed that duration of antibody persistence may be similar to that of lungworm infected cattle, but further studies are needed to confirm this. Phylogenetic analyses of MSP sequences of different marine and terrestrial mammal parasitic nematodes revealed that lungworm MSP of the genus Dictyocaulus (superfamily Trichostrongyloidea) is more closely related to metastrongylid marine mammal lungworms than to trichostrongylid nematodes of terrestrial hosts.

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First study on lungworm seroprevalence in live free-ranging harbour seals.

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Total seroprevalence was 17.9%, but age-dependent differences were observed.

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Six weeks to six months old seals showed highest prevalences (89% positives).

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Seropositive adult seals showed significantly reduced body weight and length.

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Phylogenetic tree construction using MSP of marine and terrestrial mammal parasites.

A recombinant antigen-based enzyme-linked immunosorbent assay (ELISA) for lungworm detection in seals

BACKGROUND

Pinnipeds are frequently infected by the lungworms Otostrongylus circumlitus and Parafilaroides gymnurus (Metastrongyloidea). Infections are frequently associated with secondary bacterial bronchopneumonia and are often lethal. To date, a reliable lungworm diagnosis in individual seals is only possible during necropsy as examination of faeces collected from resting places does not allow assignment to individuals. Therefore, a diagnostic tool for lungworm detection in living seals is desirable for monitoring health of seals in the wild and in captivity. Previously, an ELISA based on recombinant bovine lungworm major sperm protein (MSP) as diagnostic antigen was developed for lungworm diagnosis in cattle. In the present study, this test was adapted for detection of antibodies against lungworms in harbour (Phoca vitulina) and grey seals (Halichoerus grypus). Furthermore, sera of northern elephant seals (Mirounga angustirostris) were tested to evaluate whether the harbour/grey seal ELISA is suitable for this seal species as well.

METHODS

For ELISA evaluation, lungworm-positive and -negative sera of harbour and grey seals were analysed using horseradish peroxidase (HRP)-conjugated Protein A as secondary antibody. Optical density was measured and a receiver operating characteristic (ROC) analysis was performed to determine a cut-off value. Potential cross-reactions were examined by testing serum of seals positive for gastrointestinal and heart nematodes, but negative for lungworm infections. In addition, sera of northern elephant seals were analysed.

RESULTS

Harbour and grey seal serum samples showed significant differences in optical density (OD) between serum of infected and uninfected animals resulting in a cut-off value of 0.422 OD with a specificity of 100% (95% CI: 87.23-100%) and a sensitivity of 97.83% (95% CI: 88.47-99.94%). Cross-reactions with heart or gastrointestinal nematodes were not observed. Analysis of northern elephant seal samples resulted in detection of antibodies in animals positive for lungworm larvae at faecal examination.

CONCLUSIONS

The ELISA presented is a valuable method for detection of lungworm infections in live harbour and grey seals, providing a monitoring tool to reveal epidemiological dynamics of lungworm infections during health surveillance in free-ranging seals. Furthermore, ELISA results may aid institutions with harbour and grey seals under human care on decisions regarding anthelminthic treatment of individual animals.

The regulation of spermatogenesis and sperm function in nematodes

In the nematode C. elegans, both males and self-fertile hermaphrodites produce sperm. As a result, researchers have been able to use a broad range of genetic and genomic techniques to dissect all aspects of sperm development and function. Their results show that the early stages of spermatogenesis are controlled by transcriptional and translational processes, but later stages are dominated by protein kinases and phosphatases. Once spermatids are produced, they participate in many interactions with other cells - signals from the somatic gonad determine when sperm activate and begin to crawl, signals from the female reproductive tissues guide the sperm, and signals from sperm stimulate oocytes to mature and be ovulated. The sperm also show strong competitive interactions with other sperm and oocytes. Some of the molecules that mediate these processes have conserved functions in animal sperm, others are conserved proteins that have been adapted for new roles in nematode sperm, and some are novel proteins that provide insights into evolutionary change. The advent of new techniques should keep this system on the cutting edge of research in cellular and reproductive biology.

Eph receptor signaling in C. elegans

Eph receptor protein-tyrosine kinases are among the oldest known animal receptors and have greatly expanded in number during vertebrate evolution. Their complex transduction mechanisms are capable of bidirectional and bimodal (multi-response) signaling. Eph receptors are expressed in almost every cell type in the human body, yet their roles in development, physiology, and disease are incompletely understood. Studies in C. elegans have helped identify biological functions of these receptors, as well as transduction mechanisms. Here we review advances in our understanding of Eph receptor signaling made using the C. elegans model system.

Macro-level modeling of the response of C. elegans reproduction to chronic heat stress

A major goal of systems biology is to understand how organism-level behavior arises from a myriad of molecular interactions. Often this involves complex sets of rules describing interactions among a large number of components. As an alternative, we have developed a simple, macro-level model to describe how chronic temperature stress affects reproduction in C. elegans. Our approach uses fundamental engineering principles, together with a limited set of experimentally derived facts, and provides quantitatively accurate predictions of performance under a range of physiologically relevant conditions. We generated detailed time-resolved experimental data to evaluate the ability of our model to describe the dynamics of C. elegans reproduction. We find considerable heterogeneity in responses of individual animals to heat stress, which can be understood as modulation of a few processes and may represent a strategy for coping with the ever-changing environment. Our experimental results and model provide quantitative insight into the breakdown of a robust biological system under stress and suggest, surprisingly, that the behavior of complex biological systems may be determined by a small number of key components.

The physiological acquisition of amoeboid motility in nematode sperm: is the tail the only thing the sperm lost?

Nematode spermatozoa are highly specialized amoeboid cells that must acquire motility through the extension of a single pseudopod. Despite morphological and molecular differences with flagellated spermatozoa (including a non-actin-based cytoskeleton), nematode sperm must also respond to cues present in the female reproductive tract that render them motile, thereby allowing them to locate and fertilize the egg. The factors that trigger pseudopod extension in vivo are unknown, although current models suggest the activation through proteases acting on the sperm surface resulting in a myriad of biochemical, physiological, and morphological changes. Compelling evidence shows that pseudopod extension is under the regulation of physiological events also observed in other eukaryotic cells (including flagellated sperm) that involve membrane rearrangements in response to extracellular cues that initiate various signal transduction pathways. An integrative approach to the study of nonflagellated spermatozoa will shed light on the identification of unique and conserved processes during fertilization among different taxa.

Spermatogenesis-defective (spe) mutants of the nematode Caenorhabditis elegans provide clues to solve the puzzle of male germline functions during reproduction

In most species, each sex produces gametes, usually either sperm or oocytes, from its germline during gametogenesis. The sperm and oocyte subsequently fuse together during fertilization to create the next generation. This review focuses on spermatogenesis and the roles of sperm during fertilization in the nematode Caenorhabditis elegans, where suitable mutants are readily obtained. So far, 186 mutants defective in the C. elegans male germline functions have been isolated, and many of these mutations are alleles for one of the approximately 60 spermatogenesis-defective (spe) genes. Many cloned spe genes are expressed specifically in the male germline, where they play roles during spermatogenesis (spermatid production), spermiogenesis (spermatid activation into spermatozoa), and/or fertilization. Moreover, several spe genes are orthologs of mammalian genes, suggesting that the reproductive processes of the C. elegans and the mammalian male germlines might share common pathways at the molecular level.

Sperm and oocyte communication mechanisms controlling C. elegans fertility

During sexual reproduction in many species, sperm and oocyte secrete diffusible signaling molecules to help orchestrate the biological symphony of fertilization. In the Caenorhabditis elegans gonad, bidirectional signaling between sperm and oocyte is important for guiding sperm to the fertilization site and inducing oocyte maturation. The molecular mechanisms that regulate sperm guidance and oocyte maturation are being delineated. Unexpectedly, these mechanisms are providing insight into human diseases, such as amyotrophic lateral sclerosis, spinal muscular atrophy, and cancer. Here we review sperm and oocyte communication in C. elegans and discuss relationships to human disorders.

Conservation of MAP kinase activity and MSP genes in parthenogenetic nematodes

Background

MAP (mitogen-activated protein) kinase activation is a prerequisite for oocyte maturation, ovulation and fertilisation in many animals. In the hermaphroditic nematode Caenorhabditis elegans, an MSP (major sperm protein) dependent pathway is utilised for MAP kinase activation and successive oocyte maturation with extracellular MSP released from sperm acting as activator. How oocyte-to-embryo transition is triggered in parthenogenetic nematode species that lack sperm, is not known.

Results

We investigated two key elements of oocyte-to-embryo transition, MSP expression and MAP kinase signaling, in two parthenogenetic nematodes and their close hermaphroditic relatives. While activated MAP kinase is present in all analysed nematodes irrespective of the reproductive mode, MSP expression differs. In contrast to hermaphroditic or bisexual species, we do not find MSP expression at the protein level in parthenogenetic nematodes. However, genomic sequence analysis indicates that functional MSP genes are present in several parthenogenetic species.

Conclusions

We present three alternative interpretations to explain our findings. (1) MSP has lost its function as a trigger of MAP kinase activation and is not expressed in parthenogenetic nematodes. Activation of the MAP kinase pathway is achieved by another, unknown mechanism. Functional MSP genes are required for occasionally emerging males found in some parthenogenetic species. (2) Because of long-term disadvantages, parthenogenesis is of recent origin. MSP genes remained intact during this short intervall although they are useless. As in the first scenario, an unknown mechanism is responsible for MAP kinase activation. (3) The molecular machinery regulating oocyte-to-embryo transition in parthenogenetic nematodes is conserved with respect to C. elegans, thus requiring intact MSP genes. However, MSP expression has been shifted to non-sperm cells and is reduced below the detection limits, but is still sufficient to trigger MAP kinase activation and embryogenesis.

MSP hormonal control of the oocyte MAP kinase cascade and reactive oxygen species signaling

The MSP domain is a conserved immunoglobulin-like structure that is important for C. elegans reproduction and human motor neuron survival. C. elegans MSPs are the most abundant proteins in sperm, where they function as intracellular cytoskeletal proteins and secreted hormones. Secreted MSPs bind to multiple receptors on oocyte and ovarian sheath cell surfaces to induce oocyte maturation and sheath contraction. MSP binding stimulates oocyte MPK-1 ERK MAP Kinase (MAPK) phosphorylation, but the function and mechanism are not well understood. Here we show that the Shp class protein-tyrosine phosphatase PTP-2 acts in oocytes downstream of sheath/oocyte gap junctions to promote MSP-induced MPK-1 phosphorylation. PTP-2 functions in the oocyte cytoplasm, not at the cell surface to inhibit multiple RasGAPs, resulting in sustained Ras activation. We also provide evidence that MSP promotes production of reactive oxygen species (ROS), which act as second messengers to augment MPK-1 phosphorylation. The Cu/Zn superoxide dismutase SOD-1, an enzyme that catalyzes ROS breakdown in the cytoplasm, inhibits MPK-1 phosphorylation downstream of or in parallel to ptp-2. Our results support the model that MSP triggers PTP-2/Ras activation and ROS production to stimulate MPK-1 activity essential for oocyte maturation. We propose that secreted MSP domains and Cu/Zn superoxide dismutases function antagonistically to control ROS and MAPK signaling.

A Caenorhabditis elegans RNA-directed RNA polymerase in sperm development and endogenous RNA interference

Short interfering RNAs (siRNAs) are a class of regulatory effectors that enforce gene silencing through formation of RNA duplexes. Although progress has been made in identifying the capabilities of siRNAs in silencing foreign RNA and transposable elements, siRNA functions in endogenous gene regulation have remained mysterious. In certain organisms, siRNA biosynthesis involves novel enzymes that act as RNA-directed RNA polymerases (RdRPs). Here we analyze the function of a Caenorhabditis elegans RdRP, RRF-3, during spermatogenesis. We found that loss of RRF-3 function resulted in pleiotropic defects in sperm development and that sperm defects led to embryonic lethality. Notably, sperm nuclei in mutants of either rrf-3 or another component of the siRNA pathway, eri-1, were frequently surrounded by ectopic microtubule structures, with spindle abnormalities in a subset of the resulting embryos. Through high-throughput small RNA sequencing, we identified a population of cellular mRNAs from spermatogenic cells that appear to serve as templates for antisense siRNA synthesis. This set of genes includes the majority of genes known to have enriched expression during spermatogenesis, as well as many genes not previously known to be expressed during spermatogenesis. In a subset of these genes, we found that RRF-3 was required for effective siRNA accumulation. These and other data suggest a working model in which a major role of the RRF-3/ERI pathway is to generate siRNAs that set patterns of gene expression through feedback repression of a set of critical targets during spermatogenesis.

Molecular characterization and real-time PCR transcriptional analysis of Dictyocaulus viviparus major sperm proteins

Major sperm proteins (MSPs) represent a protein family occurring in nematodes only. Identification of the 3' and 5' untranslated region (UTR) completed the so far partial msp complementary DNA sequences of the bovine lungworm Dictyocaulus viviparus. The full-length transcript contains sequence tracts consistent with the Kozak and polyadenylation consensus sequence. On genomic level, three full-length sequences differing in three nucleotides were determined containing a 65-bp phase zero intron. Conceptual translation inferred two MSP isoforms due to one substitution within the 126-amino acid polypeptide. Bioinformatic analysis predicted that bovine lungworm MSP folds into an immunoglobulin-like seven-stranded beta sandwich as known for Caenorhabditis elegans and Ascaris suum. Furthermore, bovine lungworm MSP is confidentially predicted to be N-terminal-acetylated and secreted via a non-classical pathway. Quantitative real-time polymerase chain reaction analysis using ten developmental lungworm stages showed that msp is transcribed mainly in adult male parasites and in some degree in hypobiotic L5. However, marginal msp transcription was detectable in all of the investigated developmental lungworm stages.

Large P body-like RNPs form in C. elegans oocytes in response to arrested ovulation, heat shock, osmotic stress, and anoxia and are regulated by the major sperm protein pathway

As Caenorhabditis elegans hermaphrodites age, sperm become depleted, ovulation arrests, and oocytes accumulate in the gonad arm. Large ribonucleoprotein (RNP) foci form in these arrested oocytes that contain RNA-binding proteins and translationally masked maternal mRNAs. Within 65 min of mating, the RNP foci dissociate and fertilization proceeds. The majority of arrested oocytes with foci result in viable embryos upon fertilization, suggesting that foci are not deleterious to oocyte function. We have determined that foci formation is not strictly a function of aging, and the somatic, ceh-18, branch of the major sperm protein pathway regulates the formation and dissociation of oocyte foci. Our hypothesis for the function of oocyte RNP foci is similar to the RNA-related functions of processing bodies (P bodies) and stress granules; here, we show three orthologs of P body proteins, DCP-2, CAR-1 and CGH-1, and two markers of stress granules, poly (A) binding protein (PABP) and TIA-1, appear to be present in the oocyte RNP foci. Our results are the first in vivo demonstration linking components of P bodies and stress granules in the germ line of a metazoan. Furthermore, our data demonstrate that formation of oocyte RNP foci is inducible in non-arrested oocytes by heat shock, osmotic stress, or anoxia, similar to the induction of stress granules in mammalian cells and P bodies in yeast. These data suggest commonalities between oocytes undergoing delayed fertilization and cells that are stressed environmentally, as to how they modulate mRNAs and regulate translation.

spe-10 encodes a DHHC-CRD zinc-finger membrane protein required for endoplasmic reticulum/Golgi membrane morphogenesis during Caenorhabditis elegans spermatogenesis

C. elegans spermatogenesis employs lysosome-related fibrous body-membranous organelles (FB-MOs) for transport of many cellular components. Previous work showed that spe-10 mutants contain FB-MOs that prematurely disassemble, resulting in defective transport of FB components into developing spermatids. Consequently, spe-10 spermatids are smaller than wild type and contain defective FB-MO derivatives. In this article, we show that spe-10 encodes a four-pass integral membrane protein that has a DHHC-CRD zinc-finger motif. The DHHC-CRD motif is found in a large, diverse family of proteins that have been implicated in palmitoyl transfer during protein lipidation. Seven spe-10 mutants were analyzed, including missense, nonsense, and deletion mutants. An antiserum to SPE-10 showed significant colocalization with a known marker for the FB-MOs during wild-type spermatogenesis. In contrast, the spe-10(ok1149) deletion mutant lacked detectable SPE-10 staining; this mutant lacks a spe-10 promoter and most coding sequence. The spe-10(eb64) missense mutation, which changes a conserved residue within the DHHC-CRD domain in all homologues, behaves as a null mutant. These results suggest that wild-type SPE-10 is required for the MO to properly deliver the FB to the C. elegans spermatid and the DHHC-CRD domain is essential for this function.

C. elegans sperm bud vesicles to deliver a meiotic maturation signal to distant oocytes

The major sperm protein (MSP) is the central cytoskeletal element required for actin-independent motility of nematode spermatozoa. MSP has a dual role in Caenorhabditis elegans reproduction, functioning as a hormone for both oocyte meiotic maturation and ovarian muscle contraction. The identification of the signaling function of MSP raised the question, how do spermatozoa, which are devoid of ribosomes, ER and Golgi, release a cytoplasmic protein lacking a signal sequence? Here, we provide evidence that MSP export occurs by the budding of novel vesicles that have both inner and outer membranes with MSP sandwiched in between. MSP vesicles are apparently labile structures that generate long-range MSP gradients for signaling at the oocyte cell surface. Both spermatozoa and non-motile spermatids bud MSP vesicles, but their stability and signaling properties differ. Budding protrusions from the cell body contain MSP, but not the MSD proteins, which counteract MSP filament assembly. We propose that MSP generates the protrusive force for its own vesicular export.

Cell Polarity and the Cytoskeleton in theCaenorhabditis ElegansZygote

The anterior-posterior axis of the Caenorhabditis elegans zygote forms shortly after fertilization when the sperm pronucleus and its associated centrosomal asters provide a cue that establishes the anterior-posterior (AP) body axis. In response to this cue, the microfilament cytoskeleton polarizes the distribution of a group of widely conserved, cortically localized regulators called the PAR proteins, which are required for the first mitotic division to be asymmetric. These asymmetries include a posterior displacement of the first mitotic spindle and the differential segregation of cell-fate determinants to the anterior and posterior daughters produced by the first cleavage of the zygote. Here we review recent advances in our understanding of the mechanisms that polarize the one-cell zygote to generate an AP axis of asymmetry.

An Eph receptor sperm-sensing control mechanism for oocyte meiotic maturation in Caenorhabditis elegans

During sexual reproduction in most animals, oocytes arrest in meiotic prophase and resume meiosis (meiotic maturation) in response to sperm or somatic cell signals. Despite progress in delineating mitogen-activated protein kinase (MAPK) and CDK/cyclin activation pathways involved in meiotic maturation, it is less clear how these pathways are regulated at the cell surface. The Caenorhabditis elegans major sperm protein (MSP) signals oocytes, which are arrested in meiotic prophase, to resume meiosis and ovulate. We used DNA microarray data and an in situ binding assay to identify the VAB-1 Eph receptor protein-tyrosine kinase as an MSP receptor. We show that VAB-1 and a somatic gonadal sheath cell-dependent pathway, defined by the CEH-18 POU-class homeoprotein, negatively regulate meiotic maturation and MAPK activation. MSP antagonizes these inhibitory signaling circuits, in part by binding VAB-1 on oocytes and sheath cells. Our results define a sperm-sensing control mechanism that inhibits oocyte maturation, MAPK activation, and ovulation when sperm are unavailable for fertilization. MSP-domain proteins are found in diverse animal taxa, where they may regulate contact-dependent Eph receptor signaling pathways.

A sperm cytoskeletal protein that signals oocyte meiotic maturation and ovulation

Caenorhabditis elegans oocytes, like those of most animals, arrest during meiotic prophase. Sperm promote the resumption of meiosis (maturation) and contraction of smooth muscle-like gonadal sheath cells, which are required for ovulation. We show that the major sperm cytoskeletal protein (MSP) is a bipartite signal for oocyte maturation and sheath contraction. MSP also functions in sperm locomotion, playing a role analogous to actin. Thus, during evolution, MSP has acquired extracellular signaling and intracellular cytoskeletal functions for reproduction. Proteins with MSP-like domains are found in plants, fungi, and other animals, suggesting that related signaling functions may exist in other phyla.

How the assembly dynamics of the nematode major sperm protein generate amoeboid cell motility

Nematode sperm are amoeboid cells that use a major sperm protein (MSP) cytoskeleton in place of a conventional actin cytoskeleton to power their amoeboid motility. In these simple, specialized cells cytoskeletal dynamics is tightly coupled to locomotion. Studies have capitalized on this feature to explore the key structural properties of MSP and to reconstitute motility both in vivo and in vitro. This review discusses how the mechanistic properties shared by the MSP machinery and actin-based motility systems lead to a "push-pull" mechanism for amoeboid cell motility in which cytoskeletal assembly and disassembly at opposite ends of the lamellipodium are associated with independent forces for protrusion of the leading edge and retraction of the cell body.

Genome-wide analysis of developmental and sex-regulated gene expression profiles in Caenorhabditis elegans

We have constructed DNA microarrays containing 17,871 genes, representing about 94% of the 18,967 genes currently annotated in the Caenorhabditis elegans genome. These DNA microarrays can be used as a tool to define a nearly complete molecular profile of gene expression levels associated with different developmental stages, growth conditions, or worm strains. Here, we used these full-genome DNA microarrays to show the relative levels of gene expression for nearly every gene during development, from eggs through adulthood. These expression data can help reveal when a gene may act during development. We also compared gene expression in males to that of hermaphrodites and found a total of 2,171 sex-regulated genes (P < 0.05). The sex-regulated genes provide a global view of the differences between the sexes at a molecular level and identify many genes likely to be involved in sex-specific differentiation and behavior.

Genome-wide analysis of developmental and sex-regulated gene expression profiles in Caenorhabditis elegans

We have constructed DNA microarrays containing 17,871 genes, representing about 94% of the 18,967 genes currently annotated in the Caenorhabditis elegans genome. These DNA microarrays can be used as a tool to define a nearly complete molecular profile of gene expression levels associated with different developmental stages, growth conditions, or worm strains. Here, we used these full-genome DNA microarrays to show the relative levels of gene expression for nearly every gene during development, from eggs through adulthood. These expression data can help reveal when a gene may act during development. We also compared gene expression in males to that of hermaphrodites and found a total of 2,171 sex-regulated genes (P < 0.05). The sex-regulated genes provide a global view of the differences between the sexes at a molecular level and identify many genes likely to be involved in sex-specific differentiation and behavior.

On the control of oocyte meiotic maturation and ovulation in Caenorhabditis elegans

Prior to fertilization, oocytes undergo meiotic maturation (cell cycle progression) and ovulation (expulsion from the ovary). To begin the study of these processes in Caenorhabditis elegans, we have defined a time line of germline and somatic events by video microscopy. As the oocyte matures, its nuclear envelope breaks down and its cell cortex rearranges. Immediately thereafter, the oocyte is ovulated by increasing contraction of the myoepithelial gonadal sheath and relaxation of the distal spermatheca. By systematically altering the germ cell contents of the hermaphrodite using mutant strains, we have uncovered evidence of four cell-cell interactions that regulate maturation and ovulation. (1) Both spermatids and spermatozoa induce oocyte maturation. In animals with a feminized germline, maturation is inhibited and oocytes arrest in diakinesis. The introduction of sperm by mating restores maturation. (2) Sperm also directly promote sheath contraction. In animals with a feminized or tumorous germline, contractions are infrequent, whereas in animals with a masculinized germline or with sperm introduced by mating, contractions are frequent. (3 and 4) The maturing oocyte both induces spermathecal dilation and modulates sheath contractions at ovulation; dilation of the distal spermatheca and sharp increases in sheath contraction rates are only observed in the presence of a maturing oocyte.

The presenilin protein family member SPE-4 localizes to an ER/Golgi derived organelle and is required for proper cytoplasmic partitioning during Caenorhabditis elegans spermatogenesis

During Caenorhabditis elegans spermatogenesis, asymmetric partitioning of cellular components principally occurs via ER/Golgi-derived organelles, named fibrous body-membranous organelles. In C. elegans spe-4 mutants, morphogenesis of fibrous body-membranous organelle complexes is defective and spermatogenesis arrests at an unusual cellular stage with four haploid nuclei within a common cytoplasm. The spe-4 encoded integral membrane protein is a diverged member of the presenilin family implicated in early onset Alzheimer's disease. Specific antisera were used to show that SPE-4 resides within the fibrous body-membranous organelles membranes during wild-type spermatogenesis. Several spe-4 recessive mutants were examined for SPE-4 immunoreactivity and a deletion mutant lacks detectable SPE-4 while either of two missense mutants synthesize and localize immunoreactive SPE-4 within their fibrous body-membranous organelles. One of these missense mutations is located within a motif that is common to all presenilins. spe-4 mutants were also examined for other partitioning defects and tubulin was found to accumulate in unusual deposits close to the plasma membrane. These results suggest that wild-type SPE-4 is required for proper localization of macromolecules that are subject to asymmetric partitioning during spermatogenesis.

Sperm precedence in a hermaphroditic nematode (Caenorhabditis elegans) is due to competitive superiority of male sperm

When male and hermaphrodite Caenorhabditis elegans mate, the male's sperm outcompete the hermaphrodite's own sperm and fertilize a majority of the offspring. Here, we investigate the mechanism of male sperm precedence. We rule out the possibility that male sperm are stronger and more competitive because they are activated later than hermaphrodite sperm. We also find that a previously known gender difference in sperm activation does not influence sperm competition. Male sperm, rinsed free of seminal fluid, retained the capacity to take precedence after artificial insemination. Therefore, we conclude that male sperm themselves are competitively superior to hermaphrodite sperm. This trait maximizes outcrossing after mating and may increase both genetic diversity and heterozygosity of offspring whose parents, due to self-fertilization, may be highly homozygous.

Caenorhabditis elegans cyclin A- and B-type genes: a cyclin A multigene family, an ancestral cyclin B3 and differential germline expression

We have cloned cDNAs for Caenorhabditis elegans cyclins A1, B and B3. While cyclins A1 and B are most closely related to either A- or B-type cyclins of other species, cyclin B3 is less related to these cyclins. However, this cyclin is most similar to the recently identified chicken cyclin B3. Our identification of a Caenorhabditis homolog demonstrates that cyclin B3 has been conserved in evolution. Cyclin A1 is a member of an A-type multigene family; however the cyclin A1 cDNA only recognizes a single band on northern blots. A single-sized RNA is also observed for the cyclin B3 cDNA. In contrast, three different transcripts are observed for the cyclin B cDNA. Based on our analyses using RNAs from germline-defective mutants and from populations enriched for males, one cyclin B transcript is specific to the paternal germline. The two other cyclin B transcripts, as well as the cyclin A1 and cyclin B3 transcripts, are most abundant in the maternal germline and are only present at low levels in other tissues. Moreover, the 3′ untranslated regions of each Caenorhabditis cyclin cDNA possess several copies of potential translational control elements shown in Xenopus and Drosophila maternal cyclin mRNAs to function during oogenesis and early embryogenesis.

Comparative fine structure of sperm of Heterodera schachtii and Punctodera chalcoensis, with phylogenetic implications for Heteroderinae (Nemata: Heteroderidae)

The fine structure of sperm of Heterodera schachtii and Punctodera chalcoensis demonstrates a high degree of interspecific morphological and developmental diversity, particularly in comparison with previously examined Heteroderinae that develop cysts, including Globodera tabacum, as well as out-groups that lack cysts, including species of Verutus, Meloidodera, and Ekphymatodera. Sperm of P. chalcoensis are much smaller and have fewer filopodia than those of species of Heterodera and Globodera. However, the distribution of filopodia on only part of the body, the smooth surface of the filopodia, and the presence of cortical microtubules are traits shared by the three genera with cysts. Unique features shared by P. chalcoensis and Globodera species include the short persistence of fibrous bodies after spermiogenesis and the lack of sperm polarization in the female genital tract. These traits are absent in Heterodera species. Conversely, chromatin remains unchanged with respect to condensation during sperm development in P. chalcoensis and species of Heterodera but not in Globodera. Patterns of evolution of sperm may be useful for testing hypotheses of the phylogeny of Heteroderinae, but the diversity is so great that character coding will be required for a large number of representative species.