Vacuolar-type H+-ATPase E subunit is required for embryogenesis and yolk transfer in Caenorhabditis elegans

Yolk-deprived Caenorhabditis elegans secure brood size at the expense of competitive fitness

Oviparous animals support reproduction via the incorporation of yolk as a nutrient source into the eggs. In Caenorhabditis elegans, however, yolk proteins seem dispensable for fecundity, despite constituting the vast majority of the embryonic protein pool and acting as carriers for nutrient-rich lipids. Here, we used yolk protein-deprived C. elegans mutants to gain insight into the traits that may yet be influenced by yolk rationing. We show that massive yolk provisioning confers a temporal advantage during embryogenesis, while also increasing early juvenile body size and promoting competitive fitness. Opposite to species that reduce egg production under yolk deprivation, our results indicate that C. elegans relies on yolk as a fail-safe to secure offspring survival, rather than to maintain offspring numbers.

An RNAi screen for genes that affect nuclear morphology in Caenorhabditis elegans reveals the involvement of unexpected processes

Aberration in nuclear morphology is one of the hallmarks of cellular transformation. However, the processes that, when mis-regulated, result aberrant nuclear morphology are poorly understood. In this study, we carried out a systematic, high-throughput RNAi screen for genes that affect nuclear morphology in Caenorhabditis elegans embryos. The screen employed over 1700 RNAi constructs against genes required for embryonic viability. Nuclei of early embryos are typically spherical, and their NPCs are evenly distributed. The screen was performed on early embryos expressing a fluorescently tagged component of the nuclear pore complex (NPC), allowing visualization of nuclear shape as well as the distribution of NPCs around the nuclear envelope. Our screen uncovered 182 genes whose downregulation resulted in one or more abnormal nuclear phenotypes, including multiple nuclei, micronuclei, abnormal nuclear shape, anaphase bridges, and abnormal NPC distribution. Many of these genes fall into common functional groups, including some that were not previously known to affect nuclear morphology, such as genes involved in mitochondrial function, the vacuolar ATPase, and the CCT chaperonin complex. The results of this screen add to our growing knowledge of processes that affect nuclear morphology and that may be altered in cancer cells that exhibit abnormal nuclear shape.

High ω3-polyunsaturated fatty acids in fat-1 mice prevent streptozotocin-induced Purkinje cell degeneration through BDNF-mediated autophagy

Loss of Purkinje cells has been implicated in the development of diabetic neuropathy, and this degeneration is characterized by impairment of autophagic processes. We evaluated whether fat-1 transgenic mice, a well-established animal model that endogenously synthesizes ω3 polyunsaturated fatty acids (ω3-PUFA), are protected from Purkinje cell degeneration in streptozotocin (STZ)-treated model with fat-1 mice. STZ-treated fat-1 mice did not develop hyperglycemia, motor deficits, or Purkinje cell loss. The expression of LC3 I, II, Beclin-1 and p62 were increased in the cerebellum of STZ-treated wild-type mice, and these expressions were more increased in STZ-treated fat-1 mice, but not of p62. Moreover, cerebellar Rab7, Cathepsin D, and ATP6E were increased in STZ-treated fat-1 mice. There was also increased BDNF expression in Purkinje cells without any changes in TrkB, and phosphorylation of Akt and CREB in the cerebellums of fat-1 mice. Collectively, these findings indicate that STZ-treated fat-1 mice were protected from Purkinje cell loss and exhibited increased BDNF signaling, enhancing autophagic flux activity in cerebellar Purkinje neurons. These processes may underlie Purkinje cell survival and may be potential therapeutic targets for treatment of motor deficits related to diabetic neuropathy.

Proteomics analysis in Caenorhabditis elegans to elucidate the response induced by tyrosol, an olive phenol that stimulates longevity and stress resistance

Tyrosol (TYR, 2-(4-hydroxyphenyl)ethanol), one of the main phenols in olive oil and olive fruit, significantly strengthens resistance to thermal and oxidative stress in the nematode Caenorhabditis elegans and extends its lifespan. To elucidate the cellular functions regulated by TYR, we have used a proteomic procedure based on 2DE coupled with MS with the aim to identify the proteins differentially expressed in nematodes grown in a medium containing 250 μM TYR. After the comparison of the protein profiles from 250 μM TYR and from control, 28 protein spots were found to be altered in abundance (≥twofold). Analysis by MALDI-TOF/TOF and PMF allowed the unambiguous identification of 17 spots, corresponding to 13 different proteins. These proteins were as follows: vitellogenin-5, vitellogenin-2, bifunctional glyoxylate cycle protein, acyl CoA dehydrogenase-3, alcohol dehydrogenase 1, adenosylhomocysteinase, elongation factor 2, GTP-binding nuclear protein ran-1, HSP-4, protein ENPL-1 isoform b, vacuolar H ATPase 12, vacuolar H ATPase 13, GST 4. Western-blot analysis of yolk protein 170, ras-related nuclear protein, elongation factor 2, and vacuolar H ATPase H subunit supported the proteome evidence.

VHA-19 is essential in Caenorhabditis elegans oocytes for embryogenesis and is involved in trafficking in oocytes

There is an urgent need to develop new drugs against parasitic nematodes, which are a significant burden on human health and agriculture. Information about the function of essential nematode-specific genes provides insight to key nematode-specific processes that could be targeted with drugs. We have characterized the function of a novel, nematode-specific Caenorhabditis elegans protein, VHA-19, and show that VHA-19 is essential in the germline and, specifically, the oocytes, for the completion of embryogenesis. VHA-19 is also involved in trafficking the oocyte receptor RME-2 to the oocyte plasma membrane and is essential for osmoregulation in the embryo, probably because VHA-19 is required for proper eggshell formation via exocytosis of cortical granules or other essential components of the eggshell. VHA-19 may also have a role in cytokinesis, either directly or as an indirect effect of its role in osmoregulation. Critically, VHA-19 is expressed in the excretory cell in both larvae and adults, suggesting that it may have a role in osmoregulation in C. elegans more generally, probably in trafficking or secretion pathways. This is the first time a role for VHA-19 has been described.

Inactivation of conserved C. elegans genes engages pathogen- and xenobiotic-associated defenses

The nematode C. elegans is attracted to nutritious bacteria and is repelled by pathogens and toxins. Here we show that RNAi and toxin-mediated disruption of core cellular activities, including translation, respiration, and protein turnover, stimulate behavioral avoidance of normally attractive bacteria. RNAi of these and other essential processes induces expression of detoxification and innate immune effectors, even in the absence of toxins or pathogens. Disruption of core processes in non-neuronal tissues was sufficient to stimulate aversion behavior, revealing a neuroendocrine axis of control that additionally required serotonergic and Jnk kinase signaling pathways. We propose that surveillance pathways overseeing core cellular activities allow animals to detect invading pathogens that deploy toxins and virulence factors to undermine vital host functions. Variation in cellular surveillance and endocrine pathways controlling behavior, detoxification, and immunity selected by past toxin or microbial interactions could underlie aberrant responses to foods, medicines, and microbes.

Minireview: the role of the vacuolar ATPase in nematodes

The vacuolar ATPase enzyme complex (V-ATPase) pumps protons across membranes, energised by hydrolysis of ATP. It is involved in many physiological processes and has been implicated in many different diseases. While the broader functions of V-ATPases have been reviewed extensively, the role of this complex in nematodes specifically has not. Here, the essential role of the V-ATPase in nematode nutrition, osmoregulation, synthesis of the cuticle, neurobiology and reproduction is discussed. Based on the requirement of V-ATPase activity, or components of the V-ATPase, for these processes, the potential of the V-ATPase as a drug target for nematode parasites, which cause a significant burden to human health and agriculture, is also discussed. The V-ATPase has all the characteristics of a suitable drug target against nematodes, however the challenge will be to develop a high-throughput assay with which to test potential inhibitors.

A high-resolution C. elegans essential gene network based on phenotypic profiling of a complex tissue

High-content screening for gene profiling has generally been limited to single cells. Here, we explore an alternative approach-profiling gene function by analyzing effects of gene knockdowns on the architecture of a complex tissue in a multicellular organism. We profile 554 essential C. elegans genes by imaging gonad architecture and scoring 94 phenotypic features. To generate a reference for evaluating methods for network construction, genes were manually partitioned into 102 phenotypic classes, predicting functions for uncharacterized genes across diverse cellular processes. Using this classification as a benchmark, we developed a robust computational method for constructing gene networks from high-content profiles based on a network context-dependent measure that ranks the significance of links between genes. Our analysis reveals that multi-parametric profiling in a complex tissue yields functional maps with a resolution similar to genetic interaction-based profiling in unicellular eukaryotes-pinpointing subunits of macromolecular complexes and components functioning in common cellular processes.

Vacuolar (H+)-ATPases in Caenorhabditis elegans: what can we learn about giant H+ pumps from tiny worms?

Vacuolar (H(+))-ATPases, also called V-ATPases, are ATP-driven proton pumps that are highly phylogenetically conserved. Early biochemical and cell biological studies have revealed many details of the molecular mechanism of proton pumping and of the structure of the multi-subunit membrane complex, including the stoichiometry of subunit composition. In addition, yeast and mouse genetics have broadened our understanding of the physiological consequences of defective vacuolar acidification and its related disease etiologies. Recently, phenotypic investigation of V-ATPase mutants in Caenorhabditis elegans has revealed unexpected new roles of V-ATPases in both cellular function and early development. In this review, we discuss the functions of the V-ATPases discovered in C. elegans.

The Caenorhabditis elegans Ste20 kinase, GCK-3, is essential for postembryonic developmental timing and regulates meiotic chromosome segregation

Ste20 kinases constitute a large family of serine/threonine kinases with a plethora of biological functions. Members of the GCK-VI subfamily have been identified as important regulators of osmohomeostasis across species functioning upstream of ion channels. Although the expression of the two highly similar mammalian GCK-VI kinases is eminent in a wide variety of tissues, which includes also the testis, their potential roles in development remain elusive. Caenorhabditis elegans contains a single ancestral ortholog termed GCK-3. Here, we report a comprehensive analysis of gck-3 function and demonstrate its requirement for several developmental processes independent of ion homeostasis, i.e., larval progression, vulva, and germ line formation. Consistent with a wide range of gck-3 function we find that endogenous GCK-3 is expressed ubiquitously. The serine/threonine kinase activity of GCK-3, but not its presumed C-terminal substrate interaction domain, is essential for gck-3 gene function. Although expressed in female germ cells, we find GCK-3 progressively accumulating during spermatogenesis where it promotes the first meiotic cell division and facilitates faithful chromosome segregation. In particular, we find that different levels of gck-3 activity appear to be important for various aspects of germ line development. Taken together, our findings suggest that members of the GCK-VI kinase subfamily may act as key regulators of many developmental processes and that this newly described role in meiotic progression might be conserved and an important part of sexual reproduction.

Primary metabolism of chickpea is the initial target of wound inducing early sensed Fusarium oxysporum f. sp. ciceri race I

BACKGROUND

Biotrophic interaction between host and pathogen induces generation of reactive oxygen species that leads to programmed cell death of the host tissue specifically encompassing the site of infection conferring resistance to the host. However, in the present study, biotrophic relationship between Fusarium oxysporum and chickpea provided some novel insights into the classical concepts of defense signaling and disease perception where ROS (reactive oxygen species) generation followed by hypersensitive responses determined the magnitude of susceptibility or resistant potentiality of the host.

METHODOLOGY/PRINCIPAL FINDINGS

Microscopic observations detected wound mediated in planta pathogenic establishment and its gradual progression within the host vascular tissue. cDNA-AFLP showed differential expression of many defense responsive elements. Real time expression profiling also validated the early recognition of the wound inducing pathogen by the host. The interplay between fungus and host activated changes in primary metabolism, which generated defense signals in the form of sugar molecules for combating pathogenic encounter.

CONCLUSIONS/SIGNIFICANCE

The present study showed the limitations of hypersensitive response mediated resistance, especially when foreign encounters involved the food production as well as the translocation machinery of the host. It was also predicted from the obtained results that hypersensitivity and active species generation failed to impart host defense in compatible interaction between chickpea and Fusarium. On the contrary, the defense related gene(s) played a critical role in conferring natural resistance to the resistant host. Thus, this study suggests that natural selection is the decisive factor for selecting and segregating out the suitable type of defense mechanism to be undertaken by the host without disturbing its normal metabolism, which could deviate from the known classical defense mechanisms.

The Caenorhabditis elegans HNF4alpha Homolog, NHR-31, mediates excretory tube growth and function through coordinate regulation of the vacuolar ATPase

Nuclear receptors of the Hepatocyte Nuclear Factor-4 (HNF4) subtype have been linked to a host of developmental and metabolic functions in animals ranging from worms to humans; however, the full spectrum of physiological activities carried out by this nuclear receptor subfamily is far from established. We have found that the Caenorhabditis elegans nuclear receptor NHR-31, a homolog of mammalian HNF4 receptors, is required for controlling the growth and function of the nematode excretory cell, a multi-branched tubular cell that acts as the C. elegans renal system. Larval specific RNAi knockdown of nhr-31 led to significant structural abnormalities along the length of the excretory cell canal, including numerous regions of uncontrolled growth at sites near to and distant from the cell nucleus. nhr-31 RNAi animals were sensitive to acute challenge with ionic stress, implying that the osmoregulatory function of the excretory cell was also compromised. Gene expression profiling revealed a surprisingly specific role for nhr-31 in the control of multiple genes that encode subunits of the vacuolar ATPase (vATPase). RNAi of these vATPase genes resulted in excretory cell defects similar to those observed in nhr-31 RNAi animals, demonstrating that the influence of nhr-31 on excretory cell growth is mediated, at least in part, through coordinate regulation of the vATPase. Sequence analysis revealed a stunning enrichment of HNF4α type binding sites in the promoters of both C. elegans and mouse vATPase genes, arguing that coordinate regulation of the vATPase by HNF4 receptors is likely to be conserved in mammals. Our study establishes a new pathway for regulation of excretory cell growth and reveals a novel role for HNF4-type nuclear receptors in the development and function of a renal system.

The function of many important biological structures requires the construction of very complex cellular shapes. For example, mammalian kidneys or related renal systems in other animals rely on the formation of elongated tubes that maximize surface area to facilitate the exchange of ions between the body and excreted fluid. Defects in kidney development or function may lead to kidney failure or polycystic kidney disease. Mechanisms involved in orchestrating the formation and function of the elaborate tube structures in renal systems are still poorly characterized. Here, we show a novel transcription factor involved in the growth and elongation of an excretory tube in C. elegans. This factor helps manage tube development by regulating genes involved in ion transport and membrane fusion, likely helping to balance the growth of the inner and outer portions of the excretory tube as this structure elongates. This transcription factor shares significant homology with a mammalian protein that participates in hormone signaling and is present in the kidney tubules, suggesting that elongation and growth of tube structures may rely on a new kind of hormonal communication that occurs between distant parts of the cell; this signaling mechanism may be important for appropriate kidney development in humans.

Genes required for osmoregulation and apical secretion in Caenorhabditis elegans

Few studies have investigated whether or not there is an interdependence between osmoregulation and vesicular trafficking. We previously showed that in Caenorhabditis elegans che-14 mutations affect osmoregulation, cuticle secretion, and sensory organ development. We report the identification of seven lethal mutations displaying che-14-like phenotypes, which define four new genes, rdy-1-rdy-4 (rod-like larval lethality and dye-filling defective). rdy-1, rdy-2, and rdy-4 mutations affect excretory canal function and cuticle formation. Moreover, rdy-1 and rdy-2 mutations reduce the amount of matrix material normally secreted by sheath cells in the amphid channel. In contrast, rdy-3 mutants have short cystic excretory canals, suggesting that it acts in a different process. rdy-1 encodes the vacuolar H+-ATPase a-subunit VHA-5, whereas rdy-2 encodes a new tetraspan protein. We suggest that RDY-1/VHA-5 acts upstream of RDY-2 and CHE-14 in some tissues, since it is required for their delivery to the epidermal, but not the amphid sheath, apical plasma membrane. Hence, the RDY-1/VHA-5 trafficking function appears essential in some cells and its proton pump function essential in others. Finally, we show that RDY-1/VHA-5 distribution changes prior to molting in parallel with that of actin microfilaments and propose a model for molting whereby actin provides a spatial cue for secretion.

The V0-ATPase mediates apical secretion of exosomes containing Hedgehog-related proteins in Caenorhabditis elegans

Polarized intracellular trafficking in epithelia is critical in development, immunity, and physiology to deliver morphogens, defensins, or ion pumps to the appropriate membrane domain. The mechanisms that control apical trafficking remain poorly defined. Using Caenorhabditis elegans, we characterize a novel apical secretion pathway involving multivesicularbodies and the release of exosomes at the apical plasma membrane. By means of two different genetic approaches, we show that the membrane-bound V0 sector of the vacuolar H⁺-ATPase (V-ATPase) acts in this pathway, independent of its contribution to the V-ATPase proton pump activity. Specifically, we identified mutations in the V0 “a” subunit VHA-5 that affect either the V0-specific function or the V0+V1 function of the V-ATPase. These mutations allowed us to establish that the V0 sector mediates secretion of Hedgehog-related proteins. Our data raise the possibility that the V0 sector mediates exosome and morphogen release in mammals.

VHA-8, the E subunit of V-ATPase, is essential for pH homeostasis and larval development in C. elegans

Vacuolar H+-ATPase (V-ATPase) is an ATP-dependent proton pump, which transports protons across the membrane. It is a multi-protein complex which is composed of at least 13 subunits. The Caenorhabditis elegans vha-8 encodes the E subunit of V-ATPase which is expressed in the hypodermis, intestine and H-shaped excretory cells. VHA-8 is necessary for proper intestinal function likely through its role in cellular acidification of intestinal cells. The null mutants of vha-8 show a larval lethal phenotype indicating that vha-8 is an essential gene for larval development in C. elegans. Interestingly, characteristics of necrotic cell death were observed in the hypodermis and intestine of the arrested larvae suggesting that pH homeostasis via the E subunit of V-ATPase is required for the cell survival in C. elegans.

Repression of cell-cell fusion by components of the C. elegans vacuolar ATPase complex

Cell-cell fusion initiates fertilization, sculpts tissues during animal development, reprograms stem cells to new differentiated states, and may be a key step in cancer progression. While cell fusion is tightly regulated, the mechanisms that limit fusion to appropriate partners are unknown. Here, we report that the fus-1 gene is essential to repress fusion of epidermal cells in C. elegans: in severe fus-1 mutants, all epidermal cells, except the lateral seam cells, inappropriately fuse into a single large syncytium. This hyperfusion requires EFF-1, an integral membrane protein essential for fusion of epidermal cells into discrete syncytia. FUS-1 is localized to the apical plasma membrane in all epidermal cells potentiated to undergo fusion, whereas it is virtually undetectable in nonfusing seam cells. fus-1 encodes the e subunit of the vacuolar H(+)-ATPase (V-ATPase), and loss of other V-ATPase subunits also causes widespread hyperfusion. These findings raise the possibility of manipulating cell fusion by altering V-ATPase activity.

Characterization of Schizosaccharomyces pombe mutants defective in vacuolar acidification and protein sorting

The vacuolar H+-ATPases (V-ATPases) are ATP-dependent proton pumps responsible for acidification of intracellular compartments in eukaryotic cells. To investigate the functional roles of the V-ATPase in Schizosaccharomyces pombe, the gene vma1 encoding subunit A or vma3 encoding subunit c was disrupted. Both deletion mutants lost the capacity for vacuolar acidification in vivo, and showed sensitivity to neutral pH or high concentrations of divalent cations including Ca2+. The delivery of FM4-64 to the vacuolar membrane and accumulation of Lucifer Yellow CH were strongly inhibited in the vma1 and vma3 mutants. Moreover, deletion of the S. pombe vma1+ or vma3+ gene resulted in pleiotropic phenotypes consistent with lack of vacuolar acidification, including the missorting of vacuolar carboxypeptidase Y, abnormal vacuole morphology, and mating defects. These findings suggest that V-ATPase is essential for endocytosis, ion and pH homeostasis, and for intracellular targeting of vacuolar proteins and vacuolar biogenesis in S. pombe.