Isolation and Characterization of High-Temperature-Induced Dauer Formation Mutants in Caenorhabditis elegans

Neuronal IL-17 controls Caenorhabditis elegans developmental diapause through CEP-1/p53

During metazoan development, how cell division and metabolic programs are coordinated with nutrient availability remains unclear. Here, we show that nutrient availability signaled by the neuronal cytokine, ILC-17.1, switches Caenorhabditis elegans development between reproductive growth and dormancy by controlling the activity of the tumor suppressor p53 ortholog, CEP-1. Specifically, upon food availability, ILC-17.1 signaling by amphid neurons promotes glucose utilization and suppresses CEP-1/p53 to allow growth. In the absence of ILC-17.1, CEP-1/p53 is activated, up-regulates cell-cycle inhibitors, decreases phosphofructokinase and cytochrome C expression, and causes larvae to arrest as stress-resistant, quiescent dauers. We propose a model whereby ILC-17.1 signaling links nutrient availability and energy metabolism to cell cycle progression through CEP-1/p53. These studies describe ancestral functions of IL-17 s and the p53 family of proteins and are relevant to our understanding of neuroimmune mechanisms in cancer. They also reveal a DNA damage-independent function of CEP-1/p53 in invertebrate development and support the existence of a previously undescribed C. elegans dauer pathway.

The ACE inhibitor captopril inhibits ACN-1 to control dauer formation and aging

The renin-angiotensin-aldosterone system (RAAS) plays a well-characterized role regulating blood pressure in mammals. Pharmacological and genetic manipulation of the RAAS has been shown to extend lifespan in Caenorhabditis elegans, Drosophila and rodents, but its mechanism is not well defined. Here, we investigate the angiotensin-converting enzyme (ACE) inhibitor drug captopril, which extends lifespan in worms and mice. To investigate the mechanism, we performed a forward genetic screen for captopril-hypersensitive mutants. We identified a missense mutation that causes a partial loss of function of the daf-2 receptor tyrosine kinase gene, a powerful regulator of aging. The homologous mutation in the human insulin receptor causes Donohue syndrome, establishing these mutant worms as an invertebrate model of this disease. Captopril functions in C. elegans by inhibiting ACN-1, the worm homolog of ACE. Reducing the activity of acn-1 via captopril or RNA interference promoted dauer larvae formation, suggesting that acn-1 is a daf gene. Captopril-mediated lifespan extension was abrogated by daf-16(lf) and daf-12(lf) mutations. Our results indicate that captopril and acn-1 influence lifespan by modulating dauer formation pathways. We speculate that this represents a conserved mechanism of lifespan control.

Identification of the functional domain of the dense core vesicle biogenesis factor HID-1

Large dense core vesicles (LDCVs) mediate the regulated release of neuropeptides and peptide hormones. HID-1 is a trans-Golgi network (TGN) localized peripheral membrane protein contributing to LDCV formation. There is no information about HID-1 structure or domain architecture, and thus it remains unknown how HID-1 binds to the TGN and performs its function. We report that the N-terminus of HID-1 mediates membrane binding through a myristoyl group with a polybasic amino acid patch but lacks specificity for the TGN. In addition, we show that the C-terminus serves as the functional domain. Indeed, this isolated domain, when tethered to the TGN, can rescue the neuroendocrine secretion and sorting defects observed in HID-1 KO cells. Finally, we report that a point mutation within that domain, identified in patients with endocrine and neurological deficits, leads to loss of function.

The ACE-inhibitor drug captopril inhibits ACN-1 to control dauer formation and aging

The renin-angiotensin-aldosterone system (RAAS) plays a well-characterized role regulating blood pressure in mammals. Pharmacological and genetic manipulation of the RAAS has been shown to extend lifespan in C. elegans , Drosophila , and rodents, but its mechanism is not well defined. Here we investigate the angiotensin-converting enzyme (ACE) inhibitor drug captopril, which extends lifespan in worms and mice. To investigate the mechanism, we performed a forward genetic screen for captopril hypersensitive mutants. We identified a missense mutation that causes a partial loss-of-function of the daf-2 receptor tyrosine kinase gene, a powerful regulator of aging. The homologous mutation in the human insulin receptor causes Donohue syndrome, establishing these mutant worms as an invertebrate model of this disease. Captopril functions in C. elegans by inhibiting ACN-1, the worm homolog of ACE. Reducing the activity of acn-1 via captopril or RNAi promoted dauer larvae formation, suggesting acn-1 is a daf gene. Captopril-mediated lifespan extension xwas abrogated by daf-16(lf) and daf-12(lf) mutations. Our results indicate that captopril and acn-1 control aging by modulating dauer formation pathways. We speculate that this represents a conserved mechanism of lifespan control.

Summary Statement

Captopril and acn-1 control aging. By demonstrating they regulate dauer formation and interact with daf genes, including a new DAF-2(A261V) mutant corresponding to a human disease variant, we clarified the mechanism.

Global Profiling of Genes Expressed in the Silk Glands of Philippine-Reared Mulberry Silkworms (Bombyx mori)

RNA sequencing was used to assemble transcriptome data for Philippine-reared silkworm and compare gene expression profiles of strains reared in high- and low-temperature environments. RNA was isolated from the silk glands of fifth instar larvae and mRNA-enriched libraries were sequenced using Illumina NextSeq 500. Transcriptome reads were assembled using reference-based and de novo assemblers, and assemblies were evaluated using different metrics for transcriptome quality, including the read mapping rate, E90N50, RSEM-eval, and the presence of single-copy orthologs. All transcriptome assemblies were able to reconstruct >40,000 transcripts. Differential expression analysis found 476 differentially expressed genes (DEGs; 222 upregulated, 254 downregulated) in strains reared in different temperatures. Among the top DEGs were myrosinase, heat shock proteins, serine protease inhibitors, dehydrogenases, and regulators of the juvenile hormone. Validation of some of the top DEGs using qPCR supported the findings of the in silico analysis. GO term enrichment analysis reveals an overrepresentation of GO terms related to nucleotide metabolism and biosynthesis, lipid and carbohydrate metabolic processes, regulation of transcription, nucleotide binding, protein binding, metal binding, catalytic activity, oxidoreductase activity, and hydrolase activity. The data provided here will serve as a resource for improving local strains and increasing silk production of Philippine-reared B. mori strains.

HSF-1: Guardian of the Proteome Through Integration of Longevity Signals to the Proteostatic Network

Discoveries made in the nematode Caenorhabditis elegans revealed that aging is under genetic control. Since these transformative initial studies, C. elegans has become a premier model system for aging research. Critically, the genes, pathways, and processes that have fundamental roles in organismal aging are deeply conserved throughout evolution. This conservation has led to a wealth of knowledge regarding both the processes that influence aging and the identification of molecular and cellular hallmarks that play a causative role in the physiological decline of organisms. One key feature of age-associated decline is the failure of mechanisms that maintain proper function of the proteome (proteostasis). Here we highlight components of the proteostatic network that act to maintain the proteome and how this network integrates into major longevity signaling pathways. We focus in depth on the heat shock transcription factor 1 (HSF1), the central regulator of gene expression for proteins that maintain the cytosolic and nuclear proteomes, and a key effector of longevity signals.

Insulin signaling and osmotic stress response regulate arousal and developmental progression of C. elegans at hatching

The progression of animal development from embryonic to juvenile life depends on the coordination of organism-wide responses with environmental conditions. We found that two transcription factors that function in interneuron differentiation in Caenorhabditis elegans, fax-1, and unc-42, are required for arousal and progression from embryogenesis to larval life by potentiating insulin signaling. The combination of mutations in either transcription factor and a mutation in daf-2 insulin receptor results in a novel perihatching arrest phenotype; embryos are fully developed but inactive, often remaining trapped within the eggshell, and fail to initiate pharyngeal pumping. This pathway is opposed by an osmotic sensory response pathway that promotes developmental arrest and a sleep state at the end of embryogenesis in response to elevated salt concentration. The quiescent state induced by loss of insulin signaling or by osmotic stress can be reversed by mutations in genes that are required for sleep. Therefore, countervailing signals regulate late embryonic arousal and developmental progression to larval life, mechanistically linking the two responses. Our findings demonstrate a role for insulin signaling in an arousal circuit, consistent with evidence that insulin-related regulation may function in control of sleep states in many animals. The opposing quiescent arrest state may serve as an adaptive response to the osmotic threat from high salinity environments.

Hormonal Regulation of Diapause and Development in Nematodes, Insects, and Fishes

Diapause is a state of developmental arrest adopted in response to or in anticipation of environmental conditions that are unfavorable for growth. In many cases, diapause is facultative, such that animals may undergo either a diapause or a non-diapause developmental trajectory, depending on environmental cues. Diapause is characterized by enhanced stress resistance, reduced metabolism, and increased longevity. The ability to postpone reproduction until suitable conditions are found is important to the survival of many animals, and both vertebrate and invertebrate species can undergo diapause. The decision to enter diapause occurs at the level of the whole animal, and thus hormonal signaling pathways are common regulators of the diapause decision. Unlike other types of developmental arrest, diapause is programmed, such that the diapause developmental trajectory includes a pre-diapause preparatory phase, diapause itself, recovery from diapause, and post-diapause development. Therefore, developmental pathways are profoundly affected by diapause. Here, I review two conserved hormonal pathways, insulin/IGF signaling (IIS) and nuclear hormone receptor signaling (NHR), and their role in regulating diapause across three animal phyla. Specifically, the species reviewed are Austrofundulus limnaeus and Nothobranchius furzeri annual killifishes, Caenorhabditis elegans nematodes, and insect species including Drosophila melanogaster, Culex pipiens, and Bombyx mori. In addition, the developmental changes that occur as a result of diapause are discussed, with a focus on how IIS and NHR pathways interact with core developmental pathways in C. elegans larvae that undergo diapause.

Mutations in HID1 Cause Syndromic Infantile Encephalopathy and Hypopituitarism

OBJECTIVE

Precursors of peptide hormones undergo posttranslational modifications within the trans-Golgi network (TGN). Dysfunction of proteins involved at different steps of this process cause several complex syndromes affecting the central nervous system (CNS). We aimed to clarify the genetic cause in a group of patients characterized by hypopituitarism in combination with brain atrophy, thin corpus callosum, severe developmental delay, visual impairment, and epilepsy.

METHODS

Whole exome sequencing was performed in seven individuals of six unrelated families with these features. Postmortem histopathological and HID1 expression analysis of brain tissue and pituitary gland were conducted in one patient. Functional consequences of the homozygous HID1 variant p.R433W were investigated by Seahorse XF Assay in fibroblasts of two patients.

RESULTS

Bi-allelic variants in the gene HID1 domain-containing protein 1 (HID1) were identified in all patients. Postmortem examination confirmed cerebral atrophy with enlarged lateral ventricles. Markedly reduced expression of pituitary hormones was found in pituitary gland tissue. Colocalization of HID1 protein with the TGN was not altered in fibroblasts of patients compared to controls, while the extracellular acidification rate upon stimulation with potassium chloride was significantly reduced in patient fibroblasts compared to controls.

INTERPRETATION

Our findings indicate that mutations in HID1 cause an early infantile encephalopathy with hypopituitarism as the leading presentation, and expand the list of syndromic CNS diseases caused by interference of TGN function. ANN NEUROL 2021;90:149-164.

Fast genetic mapping using insertion-deletion polymorphisms in Caenorhabditis elegans

Genetic mapping is used in forward genetics to narrow the list of candidate mutations and genes corresponding to the mutant phenotype of interest. Even with modern advances in biology such as efficient identification of candidate mutations by whole-genome sequencing, mapping remains critical in pinpointing the responsible mutation. Here we describe a simple, fast, and affordable mapping toolkit that is particularly suitable for mapping in Caenorhabditis elegans. This mapping method uses insertion-deletion polymorphisms or indels that could be easily detected instead of single nucleotide polymorphisms in commonly used Hawaiian CB4856 mapping strain. The materials and methods were optimized so that mapping could be performed using tiny amount of genetic material without growing many large populations of mutants for DNA purification. We performed mapping of previously known and unknown mutations to show strengths and weaknesses of this method and to present examples of completed mapping. For situations where Hawaiian CB4856 is unsuitable, we provide an annotated list of indels as a basis for fast and easy mapping using other wild isolates. Finally, we provide rationale for using this mapping method over other alternatives as a part of a comprehensive strategy also involving whole-genome sequencing and other methods.

Background mutation in strain RB2126 affects the locomotion behavior of flp-1 mutants

The FLP-1 neuropeptide is involved in locomotion, mechanosensation, and reproduction. Strain RB2126 is reported to contain the flp-1(ok2811) mutation, a prospective null allele. Here we report that strain RB2126, in addition to flp-1(ok2811), also contains two additional background mutations. One of the mutations gives the animals a constitutive dauer phenotype (Daf-c), and complementation testing confirms that it is in the Daf-c gene daf-11. The second mutation is isolated based on the fact that it partially suppresses the elevated body curvature of flp-1(ok2811) mutants, but it remains uncloned. The updated genotype of RB2126 strain is flp-1(ok2811); daf-11(yak155); yak156.

A Natural Mutational Event Uncovers a Life History Trade-Off via Hormonal Pleiotropy

Environmental signals often control central life history decisions, including the choice between reproduction and somatic maintenance. Such adaptive developmental plasticity occurs in the nematode Caenorhabditis elegans, where environmental cues govern whether larvae will develop directly into reproducing adults or arrest their development to become stress-resistant dauer larvae. Here, we identified a natural variant underlying enhanced sensitivity to dauer-inducing cues in C. elegans: a 92-bp deletion in the cis-regulatory region of the gene eak-3. This deletion reduces synthesis or activity of the steroid hormone dafachronic acid (DA), thereby increasing environmental sensitivity for dauer induction. Consistent with known pleiotropic roles of DA, this eak-3 variant significantly slows down reproductive growth. We experimentally show that, although the eak-3 deletion can provide a fitness advantage through facilitated dauer production in stressful environments, this allele becomes rapidly outcompeted in favorable environments. The identified eak-3 variant therefore reveals a trade-off in how hormonal responses influence both the pace of developmental timing and the way in which environmental sensitivity controls adaptive plasticity. Together, our results show how a single mutational event altering hormonal signaling can lead to the emergence of a complex life history trade-off.

Profiling microRNAs through development of the parasitic nematode Haemonchus identifies nematode-specific miRNAs that suppress larval development

Parasitic nematodes transition between dramatically different free-living and parasitic stages, with correctly timed development and migration crucial to successful completion of their lifecycle. However little is known of the mechanisms controlling these transitions. microRNAs (miRNAs) negatively regulate gene expression post-transcriptionally and regulate development of diverse organisms. Here we used microarrays to determine the expression profile of miRNAs through development and in gut tissue of the pathogenic nematode Haemonchus contortus. Two miRNAs, mir-228 and mir-235, were enriched in infective L3 larvae, an arrested stage analogous to Caenorhabditis elegans dauer larvae. We hypothesized that these miRNAs may suppress development and maintain arrest. Consistent with this, inhibitors of these miRNAs promoted H. contortus development from L3 to L4 stage, while genetic deletion of C. elegans homologous miRNAs reduced dauer arrest. Epistasis studies with C. elegans daf-2 mutants showed that mir-228 and mir-235 synergise with FOXO transcription factor DAF-16 in the insulin signaling pathway. Target prediction suggests that these miRNAs suppress metabolic and transcription factor activity required for development. Our results provide novel insight into the expression and functions of specific miRNAs in regulating nematode development and identify miRNAs and their target genes as potential therapeutic targets to limit parasite survival within the host.

A functional study of all 40 Caenorhabditis elegans insulin-like peptides

The human genome encodes 10 insulin-like genes, whereas the Caenorhabditis elegans genome remarkably encodes 40 insulin-like genes. Knockout strategies to determine the roles of all the insulin/insulin-like peptide ligands (INS) in C. elegans has been challenging due to functional redundancy. Here, we individually overexpressed each of the 40 ins genes pan-neuronally, and monitored multiple phenotypes including: L1 arrest life span, neuroblast divisions under L1 arrest, dauer formation, and fat accumulation, as readouts to characterize the functions of each INS in vivo Of the 40 INS peptides, we found functions for 35 INS peptides and functionally categorized each as agonists, antagonists, or of pleiotropic function. In particular, we found that 9 of 16 agonistic INS peptides shortened L1 arrest life span and promoted neuroblast divisions during L1 arrest. Our study revealed that a subset of β-class INS peptides that contain a distinct F peptide sequence are agonists. Our work is the first to categorize the structures of INS peptides and relate these structures to the functions of all 40 INS peptides in vivo Our findings will promote the study of insulin function on development, metabolism, and aging-related diseases.

Regulation of Age-related Decline by Transcription Factors and Their Crosstalk with the Epigenome

Aging is a complex phenomenon, where damage accumulation, increasing deregulation of biological pathways, and loss of cellular homeostasis lead to the decline of organismal functions over time. Interestingly, aging is not entirely a stochastic process and progressing at a constant rate, but it is subject to extensive regulation, in the hands of an elaborate and highly interconnected signaling network. This network can integrate a variety of aging-regulatory stimuli, i.e. fertility, nutrient availability, or diverse stresses, and relay them via signaling cascades into gene regulatory events - mostly of genes that confer stress resistance and thus help protect from damage accumulation and homeostasis loss. Transcription factors have long been perceived as the pivotal nodes in this network. Yet, it is well known that the epigenome substantially influences eukaryotic gene regulation, too. A growing body of work has recently underscored the importance of the epigenome also during aging, where it not only undergoes drastic age-dependent changes but also actively influences the aging process. In this review, we introduce the major signaling pathways that regulate age-related decline and discuss the synergy between transcriptional regulation and the epigenetic landscape.

The dense-core vesicle maturation protein CCCP-1 binds RAB-2 and membranes through its C-terminal domain

Dense-core vesicles (DCVs) are secretory organelles that store and release modulatory neurotransmitters from neurons and endocrine cells. Recently, the conserved coiled-coil protein CCCP-1 was identified as a component of the DCV biogenesis pathway in the nematode Caenorhabditis elegans. CCCP-1 binds the small GTPase RAB-2 and colocalizes with it at the trans-Golgi. Here, we report a structure-function analysis of CCCP-1 to identify domains of the protein important for its localization, binding to RAB-2, and function in DCV biogenesis. We find that the CCCP-1 C-terminal domain (CC3) has multiple activities. CC3 is necessary and sufficient for CCCP-1 localization and for binding to RAB-2, and is required for the function of CCCP-1 in DCV biogenesis. In addition, CCCP-1 binds membranes directly through its CC3 domain, indicating that CC3 may comprise a previously uncharacterized lipid-binding motif. We conclude that CCCP-1 is a coiled-coil protein that binds an activated Rab and localizes to the Golgi via its C-terminus, properties similar to members of the golgin family of proteins. CCCP-1 also shares biophysical features with golgins; it has an elongated shape and forms oligomers.

Phenotypic plasticity and remodeling in the stress-induced Caenorhabditis elegans dauer

Organisms are often capable of modifying their development to better suit their environment. Under adverse conditions, the nematode Caenorhabditis elegans develops into a stress-resistant alternative larval stage called dauer. The dauer stage is the primary survival stage for C. elegans in nature. Large-scale tissue remodeling during dauer conveys resistance to harsh environments. The environmental and genetic regulation of the decision to enter dauer has been extensively studied. However, less is known about the mechanisms regulating tissue remodeling. Changes to the cuticle and suppression of feeding in dauers lead to an increased resistance to external stressors. Meanwhile reproductive development arrests during dauer while preserving the ability to reproduce once favorable environmental conditions return. Dramatic remodeling of neurons, glia, and muscles during dauer likely facilitate dauer-specific behaviors. Dauer-specific pulsation of the excretory duct likely mediates a response to osmotic stress. The power of C. elegans genetics has uncovered some of the molecular pathways regulating dauer tissue remodeling. In addition to genes that regulate single remodeling events, several mutants result in pleiotropic defects in dauer remodeling. This review details the individual aspects of morphological changes that occur during dauer formation and discusses molecular mechanisms regulating these processes. The dauer stage provides us with an excellent model for understanding phenotypic plasticity and remodeling from the individual cell to an entire animal. WIREs Dev Biol 2017, 6:e278. doi: 10.1002/wdev.278 For further resources related to this article, please visit the WIREs website.

Describing the Diapause-Preparatory Proteome of the Beetle Colaphellus bowringi and Identifying Candidates Affecting Lipid Accumulation Using Isobaric Tags for Mass Spectrometry-Based Proteome Quantification (iTRAQ)

Prior to entering diapause, insects must prepare themselves physiologically to withstand the stresses of arresting their development for a lengthy period. While studies describing the biochemical and cellular milieu of the maintenance phase of diapause are accumulating, few studies have taken an “omics” approach to describing molecular events during the diapause preparatory phase. We used isobaric tags and mass spectrometry (iTRAQ) to quantitatively compare the expression profiles of proteins identified during the onset of diapause preparation phase in the heads of adult female cabbage beetles, Colaphellus bowringi. A total of 3,175 proteins were identified, 297 of which were differentially expressed between diapause-destined and non-diapause-destined female adults and could therefore be involved in diapause preparation in this species. Comparison of identified proteins with protein function databases shows that many of these differentially expressed proteins enhanced in diapause destined beetles are involved in energy production and conversion, carbohydrate metabolism and transport, and lipid metabolism. Further hand annotation of differentially abundant peptides nominates several associated with stress hardiness, including HSPs and antioxidants, as well as neural development. In contrast, non-diapause destined beetles show substantial increases in cuticle proteins, suggesting additional post-emergence growth. Using RNA interference to silence a fatty acid-binding protein (FABP) that was highly abundant in the head of diapause-destined females prevented the accumulation of lipids in the fat body, a common product of diapause preparation in this species and others. Surprisingly, RNAi against the FABP also affected the transcript abundance of several heat shock proteins. These results suggest that the identified differentially expressed proteins that play vital roles in lipid metabolism may also contribute somehow to enhanced hardiness to environmental stress that is characteristic of diapause.

Neuronal function of the mRNA decapping complex determines survival of Caenorhabditis elegans at high temperature through temporal regulation of heterochronic gene expression

In response to adverse environmental cues, Caenorhabditis elegans larvae can temporarily arrest development at the second moult and form dauers, a diapause stage that allows for long-term survival. This process is largely regulated by certain evolutionarily conserved signal transduction pathways, but it is also affected by miRNA-mediated post-transcriptional control of gene expression. The 5'-3' mRNA decay mechanism contributes to miRNA-mediated silencing of target mRNAs in many organisms but how it affects developmental decisions during normal or stress conditions is largely unknown. Here, we show that loss of the mRNA decapping complex activity acting in the 5'-3' mRNA decay pathway inhibits dauer formation at the stressful high temperature of 27.5°C, and instead promotes early developmental arrest. Our genetic data suggest that this arrest phenotype correlates with dysregulation of heterochronic gene expression and an aberrant stabilization of lin-14 mRNA at early larval stages. Restoration of neuronal dcap-1 activity was sufficient to rescue growth phenotypes of dcap-1 mutants at both high and normal temperatures, implying the involvement of common developmental timing mechanisms. Our work unveils the crucial role of 5'-3' mRNA degradation in proper regulation of heterochronic gene expression programmes, which proved to be essential for survival under stressful conditions.

A histone H4 lysine 20 methyltransferase couples environmental cues to sensory neuron control of developmental plasticity

Animals change developmental fates in response to external cues. In the nematode Caenorhabditis elegans, unfavorable environmental conditions induce a state of diapause known as dauer by inhibiting the conserved DAF-2 insulin-like signaling (ILS) pathway through incompletely understood mechanisms. We have previously established a role for the C. elegans dosage compensation protein DPY-21 in the control of dauer arrest and DAF-2 ILS. Here, we show that the histone H4 lysine 20 methyltransferase SET-4, which also influences dosage compensation, promotes dauer arrest in part by repressing the X-linked ins-9 gene, which encodes a new agonist insulin-like peptide (ILP) expressed specifically in the paired ASI sensory neurons that are required for dauer bypass. ins-9 repression in dauer-constitutive mutants requires DPY-21, SET-4 and the FoxO transcription factor DAF-16, which is the main target of DAF-2 ILS. By contrast, autosomal genes encoding major agonist ILPs that promote reproductive development are not repressed by DPY-21, SET-4 or DAF-16/FoxO. Our results implicate SET-4 as a sensory rheostat that reinforces developmental fates in response to environmental cues by modulating autocrine and paracrine DAF-2 ILS.

Caenorhabditis elegans DAF-2 as a Model for Human Insulin Receptoropathies

Human exome sequencing has dramatically increased the rate of identification of disease-associated polymorphisms. However, examining the functional consequences of those variants has created an analytic bottleneck. Insulin-like signaling in Caenorhabditis elegans has long provided a model to assess consequences of human insulin signaling mutations, but this has not been evaluated in the context of current genetic tools. We have exploited strains derived from the Million Mutation Project (MMP) and gene editing to explore further the evolutionary relationships and conservation between the human and C. elegans insulin receptors. Of 40 MMP alleles analyzed in the C. elegans insulin-like receptor gene DAF-2, 35 exhibited insulin-like signaling indistinguishable from wild-type animals, indicating tolerated mutations. Five MMP alleles proved to be novel dauer-enhancing mutations, including one new allele in the previously uncharacterized C-terminus of DAF-2. CRISPR-Cas9 genome editing was used to confirm the phenotypic consequence of six of these DAF-2 mutations and to replicate an allelic series of known human disease mutations in a highly conserved tyrosine kinase active site residue, demonstrating the utility of C. elegans for directly modeling human disease. Our results illustrate the challenges associated with prediction of the phenotypic consequences of amino acid substitutions, the value of assaying mutant isoform function in vivo, and how recently developed tools and resources afford the opportunity to expand our understanding even of highly conserved regulatory modules such as insulin signaling. This approach may prove generally useful for modeling phenotypic consequences of candidate human pathogenic mutations in conserved signaling and developmental pathways.

Thermotolerant genes essential for survival at a critical high temperature in thermotolerant ethanologenic Zymomonas mobilis TISTR 548

BACKGROUND

High-temperature fermentation (HTF) technology is expected to reduce the cost of bioconversion of biomass to fuels or chemicals. For stable HTF, the development of a thermotolerant microbe is indispensable. Elucidation of the molecular mechanism of thermotolerance would enable the thermal stability of microbes to be improved.

RESULTS

Thermotolerant genes that are essential for survival at a critical high temperature (CHT) were identified via transposon mutagenesis in ethanologenic, thermotolerant Zymomonas mobilis TISTR 548. Surprisingly, no genes for general heat shock proteins except for degP were included. Cells with transposon insertion in these genes showed a defect in growth at around 39 °C but grew normally at 30 °C. Of those, more than 60% were found to be sensitive to ethanol at 30 °C, indicating that the mechanism of thermotolerance partially overlaps with that of ethanol tolerance in the organism. Products of these genes were classified into nine categories of metabolism, membrane stabilization, transporter, DNA repair, tRNA modification, protein quality control, translation control, cell division, and transcriptional regulation.

CONCLUSIONS

The thermotolerant genes of Escherichia coli and Acetobacter tropicalis that had been identified can be functionally classified into 9 categories according to the classification of those of Z. mobilis, and the ratio of thermotolerant genes to total genomic genes in Z. mobilis is nearly the same as that in E. coli, though the ratio in A. tropicalis is relatively low. There are 7 conserved thermotolerant genes that are shared by these three or two microbes. These findings suggest that Z. mobilis possesses molecular mechanisms for its survival at a CHT that are similar to those in E. coli and A. tropicalis. The mechanisms may mainly contribute to membrane stabilization, protection and repair of damage of macromolecules and maintenance of cellular metabolism at a CHT. Notably, the contribution of heat shock proteins to such survival seems to be very low.

HID-1 is required for homotypic fusion of immature secretory granules during maturation

Secretory granules, also known as dense core vesicles, are generated at the trans-Golgi network and undergo several maturation steps, including homotypic fusion of immature secretory granules (ISGs) and processing of prehormones to yield active peptides. The molecular mechanisms governing secretory granule maturation are largely unknown. Here, we investigate a highly conserved protein named HID-1 in a mouse model. A conditional knockout of HID-1 in pancreatic β cells leads to glucose intolerance and a remarkable increase in the serum proinsulin/insulin ratio caused by defective proinsulin processing. Large volume three-dimensional electron microscopy and immunofluorescence imaging reveal that ISGs are much more abundant in the absence of HID-1. We further demonstrate that HID-1 deficiency prevented secretory granule maturation by blocking homotypic fusion of immature secretory granules. Our data identify a novel player during the early maturation of immature secretory granules.

A peroxiredoxin, PRDX-2, is required for insulin secretion and insulin/IIS-dependent regulation of stress resistance and longevity

Peroxiredoxins (Prx) are abundant thiol peroxidases with a conserved anti-ageing role. In contrast to most animals, the nematode worm, Caenorhabditis elegans, encodes a single cytosolic 2-Cys Prx, PRDX-2, rendering it an excellent model for examining how peroxiredoxins affect animal physiology and ageing. Our previous work revealed that, although PRDX-2 protects against the toxicity of peroxides, enigmatically, prdx-2-mutant animals are hyper-resistant to other forms of oxidative stress. Here, we have investigated the basis for this increased resistance. Mammalian FOXO and Nrf2 transcription factors directly promote the expression of a range of detoxification enzymes. We show that the FOXO orthologue, DAF-16, and the Nrf2 orthologue, SKN-1, are required for the increased stress resistance of prdx-2-mutant worms. Our data suggest that PRDX-2 is required for normal levels of insulin secretion and hence the inhibition of DAF-16 and SKN-1 by insulin/IGF-1-like signalling (IIS) under nutrient-rich conditions. Intriguingly, loss of PRDX-2 increases DAF-16 and SKN-1 activities sufficiently to increase arsenite resistance without initiating other IIS-inhibited processes. Together, these data suggest that loss of peroxiredoxin function may increase stress resistance by reducing insulin secretion, but that further changes in insulin signalling are required for the reprogramming of development and fat metabolism. In addition, we reveal that the temperature-dependent prolongevity function of PRDX-2 is required for the extended lifespan associated with several pathways, including further reductions in IIS.

Loss of C. elegans GON-1, an ADAMTS9 Homolog, Decreases Secretion Resulting in Altered Lifespan and Dauer Formation

ADAMTS9 is a metalloprotease that cleaves components of the extracellular matrix and is also implicated in transport from the endoplasmic reticulum (ER) to the Golgi. It has been reported that an ADAMTS9 gene variant is associated with type 2 diabetes. The underlying pathology of type 2 diabetes is insulin resistance and beta-cell dysfunction. However, the molecular mechanisms underlying ADAMTS9 function in beta cells and peripheral tissues are unknown. We show that loss of C. elegans GON-1, an ADAMTS9 homolog, alters lifespan and dauer formation. GON-1 loss impairs secretion of proteins such as insulin orthologs and TGF-beta, and additionally impacts insulin/IGF-1 signaling in peripheral tissues. The function of the GON domain, but not the protease domain, is essential for normal lifespan and dauer formation in these scenarios. We conclude that the GON domain is critical for ADAMTS9/GON-1 function across species, which should help the understanding of type 2 diabetes in humans.

Autonomous and nonautonomous regulation of Wnt-mediated neuronal polarity by the C. elegans Ror kinase CAM-1

Wnts are a conserved family of secreted glycoproteins that regulate various developmental processes in metazoans. Three of the five Caenorhabditis elegans Wnts, CWN-1, CWN-2 and EGL-20, and the sole Wnt receptor of the Ror kinase family, CAM-1, are known to regulate the anterior polarization of the mechanosensory neuron ALM. Here we show that CAM-1 and the Frizzled receptor MOM-5 act in parallel pathways to control ALM polarity. We also show that CAM-1 has two functions in this process: an autonomous signaling function that promotes anterior polarization and a nonautonomous Wnt-antagonistic function that inhibits anterior polarization. These antagonistic activities can account for the weak ALM phenotypes displayed by cam-1 mutants. Our observations suggest that CAM-1 could function as a Wnt receptor in many developmental processes, but the analysis of cam-1 mutants may fail to reveal CAM-1's role as a receptor in these processes because of its Wnt-antagonistic activity. In this model, loss of CAM-1 results in increased levels of Wnts that act through other Wnt receptors, masking CAM-1's autonomous role as a Wnt receptor.

Pharyngeal pumping inhibition and avoidance by acute exposure to high CO2 levels are both regulated by the BAG neurons via different molecular pathways

Carbon dioxide (CO2) is a key molecule in many biological processes. Studies in humans, mice, D. melanogaster, C. elegans, unicellular organisms and plants have shed light on the molecular pathways activated by elevated levels of CO2. However, the mechanisms that organisms use to sense and respond to high CO2 levels remain largely unknown. Previous work has shown that C. elegans quickly avoid elevated CO2 levels using mechanisms that involve the BAG, ASE and AFD neurons via cGMP- and calcium- signaling pathways. Here, we discuss our recent finding that exposure of C. elegans to high CO2 levels leads to a very rapid cessation in the contraction of the pharynx muscles. Surprisingly, none of the tested CO2 avoidance mutants affected the rapid pumping inhibition response to elevated CO2 levels. A forward genetic screen identified that the hid-1-mediated pathway of dense core vesicle maturation regulates the pumping inhibition, probably through affecting neuropeptide secretion. Genetic studies and laser ablation experiments showed that the CO2 response of the pharyngeal muscle pumping is regulated by the BAG neurons, the same neurons that mediate CO2 avoidance.

Identification and characterization of novel factors that act in the nonsense-mediated mRNA decay pathway in nematodes, flies and mammals

Nonsense-mediated mRNA decay (NMD) is a surveillance mechanism that degrades mRNAs harboring premature termination codons (PTCs). We have conducted a genome-wide RNAi screen in Caenorhabditis elegans that resulted in the identification of five novel NMD genes that are conserved throughout evolution. Two of their human homologs, GNL2 (ngp-1) and SEC13 (npp-20), are also required for NMD in human cells. We also show that the C. elegans gene noah-2, which is present in Drosophila melanogaster but absent in humans, is an NMD factor in fruit flies. Altogether, these data identify novel NMD factors that are conserved throughout evolution, highlighting the complexity of the NMD pathway and suggesting that yet uncovered novel factors may act to regulate this process.

The response to high CO2 levels requires the neuropeptide secretion component HID-1 to promote pumping inhibition

Carbon dioxide (CO2) is a key molecule in many biological processes; however, mechanisms by which organisms sense and respond to high CO2 levels remain largely unknown. Here we report that acute CO2 exposure leads to a rapid cessation in the contraction of the pharynx muscles in Caenorhabditis elegans. To uncover the molecular mechanisms underlying this response, we performed a forward genetic screen and found that hid-1, a key component in neuropeptide signaling, regulates this inhibition in muscle contraction. Surprisingly, we found that this hid-1-mediated pathway is independent of any previously known pathways controlling CO2 avoidance and oxygen sensing. In addition, animals with mutations in unc-31 and egl-21 (neuropeptide secretion and maturation components) show impaired inhibition of muscle contraction following acute exposure to high CO2 levels, in further support of our findings. Interestingly, the observed response in the pharynx muscle requires the BAG neurons, which also mediate CO2 avoidance. This novel hid-1-mediated pathway sheds new light on the physiological effects of high CO2 levels on animals at the organism-wide level.

Unexpected role for dosage compensation in the control of dauer arrest, insulin-like signaling, and FoxO transcription factor activity in Caenorhabditis elegans

During embryogenesis, an essential process known as dosage compensation is initiated to equalize gene expression from sex chromosomes. Although much is known about how dosage compensation is established, the consequences of modulating the stability of dosage compensation postembryonically are not known. Here we define a role for the Caenorhabditis elegans dosage compensation complex (DCC) in the regulation of DAF-2 insulin-like signaling. In a screen for dauer regulatory genes that control the activity of the FoxO transcription factor DAF-16, we isolated three mutant alleles of dpy-21, which encodes a conserved DCC component. Knockdown of multiple DCC components in hermaphrodite and male animals indicates that the dauer suppression phenotype of dpy-21 mutants is due to a defect in dosage compensation per se. In dpy-21 mutants, expression of several X-linked genes that promote dauer bypass is elevated, including four genes encoding components of the DAF-2 insulin-like pathway that antagonize DAF-16/FoxO activity. Accordingly, dpy-21 mutation reduced the expression of DAF-16/FoxO target genes by promoting the exclusion of DAF-16/FoxO from nuclei. Thus, dosage compensation enhances dauer arrest by repressing X-linked genes that promote reproductive development through the inhibition of DAF-16/FoxO nuclear translocation. This work is the first to establish a specific postembryonic function for dosage compensation in any organism. The influence of dosage compensation on dauer arrest, a larval developmental fate governed by the integration of multiple environmental inputs and signaling outputs, suggests that the dosage compensation machinery may respond to external cues by modulating signaling pathways through chromosome-wide regulation of gene expression.

APOL1 null alleles from a rural village in India do not correlate with glomerulosclerosis

BACKGROUND

Among African-Americans, genome wide association revealed a strong correlation between the G1 and G2 alleles of APOL1 (apolipoproteinL1, also called trypanolytic factor) and kidney diseases including focal and segmental glomerulosclerosis, HIV-associated nephropathy and hypertensive nephrosclerosis. In the prevailing hypothesis, heterozygous APOL1 G1 and G2 alleles increase resistance against Trypanosoma that cause African sleeping sickness, resulting in positive selection of these alleles, but when homozygous the G1 and G2 alleles predispose to glomerulosclerosis. While efforts are underway to screen patients for G1 and G2 alleles and to better understand "APOL1 glomerulopathy," no data prove that these APOL1 sequence variants cause glomerulosclerosis. G1 and G2 correlate best with glomerulosclerosis as recessive alleles, which suggests a loss of function mutation for which proof of causality is commonly tested with homozygous null alleles. This test cannot be performed in rodents as the APOL gene cluster evolved only in primates. However, there is a homozygous APOL1 null human being who lives in a village in rural India. This individual and his family offer a unique opportunity to test causality between APOL1 null alleles and glomerulosclerosis.

METHODS AND FINDINGS

We obtained clinical data, blood and urine from this APOL1 null patient and 50 related villagers. Based on measurements of blood pressure, BUN, creatinine, albuminuria, genotyping and immunoblotting, this APOL1 null individual does not have glomerulosclerosis, nor do his relatives who carry APOL1 null alleles.

CONCLUSIONS

This small study cannot provide definitive conclusions but the absence of glomerulosclerosis in this unique population is consistent with the possibility that African-American glomerulosclerosis is caused, not by loss of APOL1 function, but by other mechanisms including a subtle gain of function or by the "genetic hitchhiking" of deleterious mutations in a gene linked to APOL1 G1 and G2.

A quantitative model of normal Caenorhabditis elegans embryogenesis and its disruption after stress

The invariant lineage of Caenorhabditis elegans has powerful potential for quantifying developmental variability in normal and stressed embryos. Previous studies of division timing by automated lineage tracing suggested that variability in cell cycle timing is low in younger embryos, but manual lineage tracing of specific lineages suggested that variability may increase for later divisions. We developed improved automated lineage tracing methods that allowroutine lineage tracing through the last round of embryonic cell divisions and we applied these methods to trace the lineage of 18 wild-type embryos. Cell cycle lengths, division axes and cell positions are remarkably consistent among these embryos at all stages, with only slight increase in variability later in development. The resulting quantitative 4-dimensional model of embryogenesis provides a powerful reference dataset to identify defects in mutants or in embryos that have experienced environmental perturbations. We also traced the lineages of embryos imaged at higher temperatures to quantify the decay in developmental robustness under temperature stress. Developmental variability increases modestly at 25°C compared with 22°C and dramatically at 26°C, and we identify homeotic transformations in a subset of embryos grown at 26°C. The deep lineage tracing methods provide a powerful tool for analysis of normal development, gene expression and mutants and we provide a graphical user interface to allow other researchers to explore the average behavior of arbitrary cells in a reference embryo.

p21-activated kinase interacts with Wnt signaling to regulate tissue polarity and gene expression

Wnt signaling is mediated by three classes of receptors, Frizzled, Ryk, and Ror. In Caenorhabditis elegans, Wnt signaling regulates the anterior/posterior polarity of the P7.p vulval lineage, and mutations in lin-17/Frizzled cause loss or reversal of P7.p lineage polarity. We found that pak-1/Pak (p21-activated kinase), along with putative activators of Pak, nck-1/Nck, and ced-10/Rac, regulates P7.p polarity. Mutations in these genes suppress the polarity defect of lin-17 mutants. Furthermore, mutations in pak-1, nck-1, and ced-10 cause constitutive dauer formation at 27 °C, a phenotype also observed in egl-20/Wnt and cam-1/Ror mutants. In HEK293T cells, Pak1 can antagonize canonical Wnt signaling. Moreover, overexpression of Ror2 leads to phosphorylation of Pak1. Together, these results indicate that Pak interacts with Wnt signaling to regulate tissue polarity and gene expression.

Gαo and Gαq regulate the expression of daf-7, a TGFβ-like gene, in Caenorhabditis elegans

Caenorhabditis elegans enter an alternate developmental stage called dauer in unfavorable conditions such as starvation, overcrowding, or high temperature. Several evolutionarily conserved signaling pathways control dauer formation. DAF-7/TGFβ and serotonin, important ligands in these signaling pathways, affect not only dauer formation, but also the expression of one another. The heterotrimeric G proteins GOA-1 (Gα_o) and EGL-30 (Gα_q) mediate serotonin signaling as well as serotonin biosynthesis in C. elegans. It is not known whether GOA-1 or EGL-30 also affect dauer formation and/or daf-7 expression, which are both modulated in part by serotonin. The purpose of this study is to better understand the relationship between proteins important for neuronal signaling and developmental plasticity in both C. elegans and humans. Using promoter-GFP transgenic worms, it was determined that both goa-1 and egl-30 regulate daf-7 expression during larval development. In addition, the normal daf-7 response to high temperature or starvation was altered in goa-1 and egl-30 mutants. Despite the effect of goa-1 and egl-30 mutations on daf-7 expression in various environmental conditions, there was no effect of the mutations on dauer formation. This paper provides evidence that while goa-1 and egl-30 are important for normal daf-7 expression, mutations in these genes are not sufficient to disrupt dauer formation.

HID-1 is a novel player in the regulation of neuropeptide sorting

Peptide hormones and neuropeptides are packaged and stored in a specialized intracellular organelle called the dense core vesicle. It remains elusive how peptide cargoes are correctly sorted. In the present study, we show that a highly conserved Golgi-localized protein named HID-1 acts to prevent mis-sorting of peptide cargoes to lysosomes for degradation via a PtdIns3P-dependent trafficking pathway. Epistasis analysis suggests that rab-2 is epistatic to hid-1.

HID-1 is a peripheral membrane protein primarily associated with the medial- and trans- Golgi apparatus

Caenorhabditis elegans hid-1 gene was first identified in a screen for mutants with a high-temperature-induced dauer formation (Hid) phenotype. Despite the fact that the hid-1 gene encodes a novel protein (HID-1) which is highly conserved from Caenorhabditis elegans to mammals, the domain structure, subcellular localization, and exact function of HID-1 remain unknown. Previous studies and various bioinformatic softwares predicted that HID-1 contained many transmembrane domains but no known functional domain. In this study, we revealed that mammalian HID-1 localized to the medial- and trans- Golgi apparatus as well as the cytosol, and the localization was sensitive to brefeldin A treatment. Next, we demonstrated that HID-1 was a peripheral membrane protein and dynamically shuttled between the Golgi apparatus and the cytosol. Finally, we verified that a conserved N-terminal myristoylation site was required for HID-1 binding to the Golgi apparatus. We propose that HID-1 is probably involved in the intracellular trafficking within the Golgi region.

RNAi screen of DAF-16/FOXO target genes in C. elegans links pathogenesis and dauer formation

The DAF-16/FOXO transcription factor is the major downstream output of the insulin/IGF1R signaling pathway controlling C. elegans dauer larva development and aging. To identify novel downstream genes affecting dauer formation, we used RNAi to screen candidate genes previously identified to be regulated by DAF-16. We used a sensitized genetic background [eri-1(mg366); sdf-9(m708)], which enhances both RNAi efficiency and constitutive dauer formation (Daf-c). Among 513 RNAi clones screened, 21 displayed a synthetic Daf-c (SynDaf) phenotype with sdf-9. One of these genes, srh-100, was previously identified to be SynDaf, but twenty have not previously been associated with dauer formation. Two of the latter genes, lys-1 and cpr-1, are known to participate in innate immunity and six more are predicted to do so, suggesting that the immune response may contribute to the dauer decision. Indeed, we show that two of these genes, lys-1 and clc-1, are required for normal resistance to Staphylococcus aureus. clc-1 is predicted to function in epithelial cohesion. Dauer formation exhibited by daf-8(m85), sdf-9(m708), and the wild-type N2 (at 27°C) were all enhanced by exposure to pathogenic bacteria, while not enhanced in a daf-22(m130) background. We conclude that knockdown of the genes required for proper pathogen resistance increases pathogenic infection, leading to increased dauer formation in our screen. We propose that dauer larva formation is a behavioral response to pathogens mediated by increased dauer pheromone production.

HID-1, a new component of the peptidergic signaling pathway

hid-1 was originally identified as a Caenorhabditis elegans gene encoding a novel conserved protein that regulates the decision to enter into the enduring dauer larval stage. We isolated a novel allele of hid-1 in a forward genetic screen for mutants mislocalizing RBF-1 rabphilin, a RAB-27 effector. Here we demonstrate that HID-1 functions in the nervous system to regulate neuromuscular signaling and in the intestine to regulate the defecation motor program. We further show that a conserved N-terminal myristoylated motif of both invertebrate and vertebrate HID-1 is essential for its association with intracellular membranes in nematodes and PC12 cells. C. elegans neuronal HID-1 resides on intracellular membranes in neuronal cell somas; however, the kinesin UNC-104 also transports HID-1 to synaptic regions. HID-1 accumulates in the axons of unc-13 and unc-31 mutants, suggesting it is associated with neurosecretory vesicles. Consistent with this, genetic studies place HID-1 in a peptidergic signaling pathway. Finally, a hid-1 null mutation reduces the levels of endogenous neuropeptides and alters the secretion of fluorescent-tagged cargos derived from neuronal and intestinal dense core vesicles (DCVs). Taken together, our findings indicate that HID-1 is a novel component of a DCV-based neurosecretory pathway and that it regulates one or more aspects of the biogenesis, maturation, or trafficking of DCVs.

Localization of a guanylyl cyclase to chemosensory cilia requires the novel ciliary MYND domain protein DAF-25

In harsh conditions, Caenorhabditis elegans arrests development to enter a non-aging, resistant diapause state called the dauer larva. Olfactory sensation modulates the TGF-β and insulin signaling pathways to control this developmental decision. Four mutant alleles of daf-25 (abnormal DAuer Formation) were isolated from screens for mutants exhibiting constitutive dauer formation and found to be defective in olfaction. The daf-25 dauer phenotype is suppressed by daf-10/IFT122 mutations (which disrupt ciliogenesis), but not by daf-6/PTCHD3 mutations (which prevent environmental exposure of sensory cilia), implying that DAF-25 functions in the cilia themselves. daf-25 encodes the C. elegans ortholog of mammalian Ankmy2, a MYND domain protein of unknown function. Disruption of DAF-25, which localizes to sensory cilia, produces no apparent cilia structure anomalies, as determined by light and electron microscopy. Hinting at its potential function, the dauer phenotype, epistatic order, and expression profile of daf-25 are similar to daf-11, which encodes a cilium-localized guanylyl cyclase. Indeed, we demonstrate that DAF-25 is required for proper DAF-11 ciliary localization. Furthermore, the functional interaction is evolutionarily conserved, as mouse Ankmy2 interacts with guanylyl cyclase GC1 from ciliary photoreceptors. The interaction may be specific because daf-25 mutants have normally-localized OSM-9/TRPV4, TAX-4/CNGA1, CHE-2/IFT80, CHE-11/IFT140, CHE-13/IFT57, BBS-8, OSM-5/IFT88, and XBX-1/D2LIC in the cilia. Intraflagellar transport (IFT) (required to build cilia) is not defective in daf-25 mutants, although the ciliary localization of DAF-25 itself is influenced in che-11 mutants, which are defective in retrograde IFT. In summary, we have discovered a novel ciliary protein that plays an important role in cGMP signaling by localizing a guanylyl cyclase to the sensory organelle.

The C. elegans developmental timing protein LIN-42 regulates diapause in response to environmental cues

Environmental conditions can have a major impact on developmental progression in animals. For example, when C. elegans larvae encounter harsh conditions they can reversibly halt the passage of developmental time by forming a long-lived dauer larva at the end of the second larval stage. Here, we show that the period homolog lin-42, known to control developmental time, also acts as a component of a switch that mediates dauer entry. Loss of lin-42 function renders animals hypersensitive to dauer formation under stressful conditions, whereas misexpression of lin-42 in the pre-dauer stage inhibits dauer formation, indicating that lin-42 acts as a negative regulator of this life history decision. These phenotypes place LIN-42 in opposition to the ligand-free form of the nuclear receptor DAF-12, which indirectly senses environmental conditions and helps to integrate external cues into developmental decisions. Mutations that impair DAF-12 ligand binding are exquisitely sensitive to the absence of lin-42, whereas overexpression of LIN-42 can suppress the dauer constitutive phenotype of a ligand-insensitive daf-12 mutant, suggesting that LIN-42 and DAF-12 are intimate partners in controlling the decision to become a dauer larva. The functional outputs of Period family proteins and nuclear receptors also converge in other organisms, suggesting that the relationship between lin-42 and daf-12 represents an ancient genetic framework for responding to environmental stimuli.

Genetics of extracellular matrix remodeling during organ growth using the Caenorhabditis elegans pharynx model

The organs of animal embryos are typically covered with an extracellular matrix (ECM) that must be carefully remodeled as these organs enlarge during post-embryonic growth; otherwise, their shape and functions may be compromised. We previously described the twisting of the Caenorhabditis elegans pharynx (here called the Twp phenotype) as a quantitative mutant phenotype that worsens as that organ enlarges during growth. Mutations previously known to cause pharyngeal twist affect membrane proteins with large extracellular domains (DIG-1 and SAX-7), as well as a C. elegans septin (UNC-61). Here we show that two novel alleles of the C. elegans papilin gene, mig-6(et4) and mig-6(sa580), can also cause the Twp phenotype. We also show that overexpression of the ADAMTS protease gene mig-17 can suppress the pharyngeal twist in mig-6 mutants and identify several alleles of other ECM-related genes that can cause or influence the Twp phenotype, including alleles of fibulin (fbl-1), perlecan (unc-52), collagens (cle-1, dpy-7), laminins (lam-1, lam-3), one ADAM protease (sup-17), and one ADAMTS protease (adt-1). The Twp phenotype in C. elegans is easily monitored using light microscopy, is quantitative via measurements of the torsion angle, and reveals that ECM components, metalloproteinases, and ECM attachment molecules are important for this organ to retain its correct shape during post-embryonic growth. The Twp phenotype is therefore a promising experimental system to study ECM remodeling and diseases.

Changes in gene expression in the permissive larval host lightbrown apple moth (Epiphyas postvittana, Tortricidae) in response to EppoNPV (Baculoviridae) infection

Host cell and virus gene expression were measured five days after per os inoculation of 3rd instar lightbrown apple moth (LBAM) larvae with the Epiphyas postvittana nucleopolyhedrovirus (EppoNPV). Microarray analysis identified 84 insect genes that were up-regulated and 18 genes that were down-regulated in virus-infected larvae compared with uninfected larvae. From the 134 viral open reading frames represented on the microarray, 81 genes showed strong expression. Of the 38 functionally identifiable regulated insect genes, 23 coded for proteins that have roles in one of five processes; regulation of transcription and translation, induction of apoptosis, and maintenance of both juvenility and actin cytoskeletal integrity. Of the 34 functionally identifiable viral genes that were most strongly expressed, 12 had functions associated with these five processes, as did a further seven viral genes which were expressed at slightly lower levels. A survey of the LBAM-expressed sequence tag library identified further genes involved in these processes. In total, 135 insect genes and 38 viral genes were analysed by quantitative polymerase chain reaction. Twenty-one insect genes were strongly up-regulated and 31 genes strongly down-regulated. All 38 viral genes examined were highly expressed. These data suggest that induction of apoptosis and regulation of juvenility are the major 'battlegrounds' between virus and insect, with the majority of changes observed representing viral control of insect gene expression. Transcription and translational effects seem to be exerted largely through modulation of mRNA and protein degradation. Examples of attempts by the insect to repel the infection via changes in gene expression within these same processes were, however, also noted. The data also showed the extent to which viral transcription dominated in the infected insects at five days post inoculation.

A potent dauer pheromone component in Caenorhabditis elegans that acts synergistically with other components

In the model organism Caenorhabditis elegans, the dauer pheromone is the primary cue for entry into the developmentally arrested, dauer larval stage. The dauer is specialized for survival under harsh environmental conditions and is considered "nonaging" because larvae that exit dauer have a normal life span. C. elegans constitutively secretes the dauer pheromone into its environment, enabling it to sense its population density. Several components of the dauer pheromone have been identified as derivatives of the dideoxy sugar ascarylose, but additional unidentified components of the dauer pheromone contribute to its activity. Here, we show that an ascaroside with a 3-hydroxypropionate side chain is a highly potent component of the dauer pheromone that acts synergistically with previously identified components. Furthermore, we show that the active dauer pheromone components that are produced by C. elegans vary depending on cultivation conditions. Identifying the active components of the dauer pheromone, the conditions under which they are produced, and their mechanisms of action will greatly extend our understanding of how chemosensory cues from the environment can influence such fundamental processes as development, metabolism, and aging in nematodes and in higher organisms.

C. elegans dauer formation and the molecular basis of plasticity

Because life is often unpredictable, dynamic, and complex, all animals have evolved remarkable abilities to cope with changes in their external environment and internal physiology. This regulatory plasticity leads to shifts in behavior and metabolism, as well as to changes in development, growth, and reproduction, which is thought to improve the chances of survival and reproductive success. In favorable environments, the nematode Caenorhabditis elegans develops rapidly to reproductive maturity, but in adverse environments, animals arrest at the dauer diapause, a long-lived stress resistant stage. A molecular and genetic analysis of dauer formation has revealed key insights into how sensory and dietary cues are coupled to conserved endocrine pathways, including insulin/IGF, TGF-beta, serotonergic, and steroid hormone signal transduction, which govern the choice between reproduction and survival. These and other pathways reveal a molecular basis for metazoan plasticity in response to extrinsic and intrinsic signals.

Notch signalling is required for both dauer maintenance and recovery in C. elegans

The Notch signalling pathway is conserved among higher metazoans and is used repeatedly throughout development to specify distinct cell fates among populations of equipotent cells. Mounting evidence suggests that Notch signalling may also be crucial in neuronal function in postmitotic, differentiated neurons. Here, we demonstrate a novel role for the canonical Notch signalling pathway in postmitotic neurons during a specialised ;diapause-like' post-embryonic developmental stage in C. elegans called dauer. Our data suggest that cell signalling downstream of the developmental decision to enter dauer leads to the activation of Notch-responding genes in postmitotic neurons. Consistent with this, we demonstrate that glp-1, one of the two C. elegans Notch receptors, and its ligand lag-2 are expressed in neurons during the dauer stage, and both genes are required to maintain this stage in a daf-7/TGFbeta dauer constitutive background. Our genetic data also suggest that a second Notch receptor, lin-12, functions upstream of, or in parallel with, insulin-like signalling components in response to replete growth conditions to promote dauer recovery. Based on our findings, cues associated with the onset of dauer ultimately trigger a glp-1-dependent Notch signalling cascade in neurons to maintain this developmental state. Then, as growth conditions improve, activation of the LIN-12 Notch receptor cooperates with the insulin-like signalling pathway to signal recovery from the dauer stage.

The C. elegans ROR receptor tyrosine kinase, CAM-1, non-autonomously inhibits the Wnt pathway

Inhibitors of Wnt signaling promote normal development and prevent cancer by restraining when and where the Wnt pathway is activated. ROR proteins, a class of Wnt-binding receptor tyrosine kinases, inhibit Wnt signaling by an unknown mechanism. To clarify how RORs inhibit the Wnt pathway, we examined the relationship between Wnts and the sole C. elegans ROR homolog, cam-1, during C. elegans vulval development, a Wnt-regulated process. We found that loss and overexpression of cam-1 causes reciprocal defects in Wnt-mediated cell-fate specification. Our molecular and genetic analyses revealed that the CAM-1 extracellular domain (ECD) is sufficient to non-autonomously antagonize multiple Wnts, suggesting that the CAM-1/ROR ECD sequesters Wnts. A sequestration model is supported by our findings that the CAM-1 ECD binds to several Wnts in vitro. These results demonstrate how ROR proteins help to refine the spatial pattern of Wnt activity in a complex multicellular environment.

Thermal variation reveals natural variation between isolates of Caenorhabditis elegans

The free-living nematode Caenorhabditis elegans is distributed globally and found in many varied habitats. However, in comparison to our understanding of the genetics of the species, little is known about natural variation and many major life history traits appear to show only limited differences between isolates. Here we show that temperature affects the lifetime fecundity and the reproductive timing of C. elegans and that there is a genotype by environment interaction, with isolates varying in how lifetime fecundity changes with temperature. We show that the lower lifetime fecundity observed at higher temperatures is primarily due to a reduction in the number of functional sperm. Further, isolates vary in their lifetime fecundity because of inter-isolate differences in this effect of temperature on the number of functional sperm.

Public and private mechanisms of life extension in Caenorhabditis elegans

Model organisms have been widely used to study the ageing phenomenon in order to learn about human ageing. Although the phylogenetic diversity between vertebrates and some of the most commonly used model systems could hardly be greater, several mechanisms of life extension are public (common characteristic in divergent species) and likely share a common ancestry. Dietary restriction, reduced IGF-signaling and, seemingly, reduced ROS-induced damage are the best known mechanisms for extending longevity in a variety of organisms. In this review, we summarize the knowledge of ageing in the nematode Caenorhabditis elegans and compare the mechanisms of life extension with knowledge from other model organisms.

Mechanisms and evolution of environmental responses in Caenorhabditis elegans

We review mechanistic and evolutionary aspects of interactions between the model organism Caenorhabditis elegans and its environment. In particular, we focus on environmental effects affecting developmental mechanisms. We describe natural and laboratory environments of C. elegans and provide an overview of the different environmental responses of this organism. We then show how two developmental processes respond to changes in the environment. First, we discuss the development of alternative juvenile stages, the dauer and non-dauer larva. This example illustrates how development responds to variation in the environment to generate complex phenotypic variation. Second, we discuss the development of the C. elegans vulva. This example illustrates how development responds to variation in the environment while generating an invariant final phenotype.