NCR-1 and NCR-2, theC. eleganshomologs of the human Niemann-Pick type C1 disease protein, function upstream of DAF-9 in the dauer formation pathways

Two NPC1 homologous proteins are involved in asexual reproduction, pathogenicity, and lipid trafficking in Phytophthora sojae

Niemann-Pick type C (NPC) disease is characterized by lysosomal lipid storage disorders and defects in lipid trafficking, primarily due to mutations in the NPC1 protein. Two NPC1 homologous proteins are present in the genome of Phytophthora sojae, named as PsNPC1-1 and PsNPC1-2. Both proteins exhibit high sequence identity, consistent conserved functional domains, similar gene expression patterns, and comparable subcellular localization. Deletion of a single PsNPC1 gene did not result in significant phenotypic changes. However, simultaneous deletion of both PsNPC1 genes led to reduced mycelial growth, decreased sporangial production, impaired pathogenicity, and an inability to release normal zoospores in P. sojae. Furthermore, dysfunction of PsNPC1s did not completely block the absorption and utilization of exogenous sterols by P. sojae. While lipidome analysis revealed that the relative contents of fatty acyls, sphingolipids and saccharolipids were significantly elevated in the double-gene deletion mutant, alongside obvious alterations in glycerophospholipid and glycerolipid metabolism. Additionally, we observed a significant down-regulation of PsCDP-AP protein along with its interactions with both PsNPC1s. Deletion of PsCDP-AP also impaired asexual reproduction and virulence of P. sojae. These findings demonstrate that both PsNPC1 proteins may collaborate with other key regulators to modulate asexual reproduction, pathogenicity and lipid trafficking in P. sojae.

Activated hedgehog and insulin ligands by decreased transcriptional factor DAF-16 mediate transgenerational nanoplastic toxicity in Caenorhabditis elegans

In Caenorhabditis elegans, transcriptional factor DAF-16 in insulin signaling pathway played important role in regulating transgenerational nanoplastic toxicity. Activation of insulin signals mediated transgenerational toxicity of polystyrene nanoparticle (PS-NP) by inhibiting DAF-16. Among identified germline ligands, expression of wrt-3 encoding hedgehog ligand was increased by RNAi of daf-16 in PS-NP exposed C. elegans. In PS-NP exposed C. elegans, expressions of 4 other germline hedgehog ligand genes and 10 hedgehog receptor genes were increased by daf-16 RNAi. Among these candidate genes, expressions of hedgehog ligand genes (grl-15, grl-16, qua-1, and wrt-1) and hedgehog receptor genes (ptr-23, scp-1, ptd-2, and ncr-1) could be increased by PS-NP (1-100 μg/L), and their transgenerational expressions were observed after PS-NP exposure. RNAi of grl-15, grl-16, qua-1, wrt-1, ptr-23, scp-1, ptd-2, and ncr-1 caused resistance to transgenerational PS-NP toxicity. In nematodes exposed to PS-NPs, RNAi of wrt-3, grl-15, grl-16, qua-1, and wrt-1 at parental generation (P0-G) inhibited expressions of ptr-23, scp-1, ptd-2, and ncr-1 in their offspring. Moreover, we observed increased expressions of insulin peptides genes (ins-3, ins-39, and daf-28) in PS-NP exposed daf-16(RNAi) nematodes, suggesting formation of feedback loop. We raise the molecular basis for formation of toxicity on multiple generations after nanoplastic exposure at P0-G.

The small GTPase RAB-18 is involved in regulating development/diapause by recruiting the intestinal cholesterol transporter NCR-1 onto the apical side in Caenorhabditis elegans

RAB family proteins, which are small GTPases, are integral to the process of eukaryotic membrane trafficking. In the nematode, Caenorhabditis elegans, 31 RAB proteins have been identified through genome sequencing. Using an RNAi screen specifically targeting C. elegans rab genes, we identified multiple genes that are involved in the regulation of larval development, in particular, the rab-18 gene. Our molecular genetic studies resulted in several findings. First, RAB-18 predominantly functions in the intestine to regulate larval development by modulating steroid hormone signaling. Second, the C. elegans cholesterol transporter NCR-1 is a target of RAB-18 in the intestine. Third, the membrane trafficking of NCR-1 to the apical side in intestinal cells is particularly influenced by RAB-18. Finally, RAB-18 and NCR-1 possibly co-localize on membrane vesicles. Our study is the first to demonstrate the relationship between a RAB protein and a cholesterol transporter, in which the RAB protein probably drives the transporter to the apical membrane in the intestine to regulate cholesterol uptake. This study provides insight into the molecular mechanisms underlying human disease stemming from a transport defect of cholesterol and its derivative.

Differential roles of lysosomal cholesterol transporters in the development of C. elegans NMJs

Cholesterol homeostasis in neurons is critical for synapse formation and maintenance. Neurons with impaired cholesterol uptake undergo progressive synapse loss and eventual degeneration. To investigate the molecular mechanisms of neuronal cholesterol homeostasis and its role during synapse development, we studied motor neurons of Caenorhabditis elegans because these neurons rely on dietary cholesterol. Combining lipidomic analysis, we discovered that NCR-1, a lysosomal cholesterol transporter, promotes cholesterol absorption and synapse development. Loss of ncr-1 causes smaller synapses, and low cholesterol exacerbates the deficits. Moreover, NCR-1 deficiency hinders the increase in synapses under high cholesterol. Unexpectedly, NCR-2, the NCR-1 homolog, increases the use of cholesterol and sphingomyelins and impedes synapse formation. NCR-2 deficiency causes an increase in synapses regardless of cholesterol concentration. Inhibiting the degradation or synthesis of sphingomyelins can induce or suppress the synaptic phenotypes in ncr-2 mutants. Our findings indicate that neuronal cholesterol homeostasis is differentially controlled by two lysosomal cholesterol transporters and highlight the importance of neuronal cholesterol homeostasis in synapse development.

Transcriptome analysis of East Asian common octopus, Octopus sinensis, paralarvae

BACKGROUND

The genes involved in cephalopod development and their association with hatching and survival during early life stages have been extensively studied. However, few studies have investigated the paralarvae transcriptome of the East Asian common octopus (Octopus sinen sis).

OBJECTIVE

This study aimed to identify the genes related to embryonic development and hatching in O. sinensis using RNA sequencing (RNA-seq) and verify the genes most relevant to different embryonic stages.

METHODS

RNA samples from hatched and 25 days post-hatching (dph) O. sinensis paralarvae were used to construct cDNA libraries. Clean reads from individual samples were aligned to the reference O. sinensis database to identify the differentially expressed genes (DEGs) between the 0- and 25-dph paralarvae libraries. Real-time quantitative polymerase chain reaction (RT-qPCR) was used to supplement the RNA-seq data for embryogenic developmental stages.

RESULTS

A total of 12,597 transcripts were annotated and 5,468 DEGs were identified between the 0- and 25-dph O. sinensis paralarvae, including 2,715 upregulated and 2,753 downregulated transcripts in the 25-dph paralarvae. Several key DEGs were related to transmembrane transport, lipid biosynthesis, monooxygenase activity, lipid transport, neuropeptide signaling, transcription regulation, and protein-cysteine S-palmitoyltransferase activity during the post-hatching development of O. sinensis paralarvae. RT-qPCR analysis further revealed that SLC5A3A, ABCC12, and NPC1 transcripts in 20 and/or 30 days post-fertilization (dpf) embryos were significantly higher (p < 0.05) than those in 10-dpf embryos.

CONCLUSION

Transcriptome profiles provide molecular targets to understand the embryonic development, hatching, and survival of O. sinensis paralarvae, and enhance octopus production.

Mobilization of cholesterol induces the transition from quiescence to growth in Caenorhabditis elegans through steroid hormone and mTOR signaling

Recovery from the quiescent developmental stage called dauer is an essential process in C. elegans and provides an excellent model to understand how metabolic transitions contribute to developmental plasticity. Here we show that cholesterol bound to the small secreted proteins SCL-12 or SCL-13 is sequestered in the gut lumen during the dauer state. Upon recovery from dauer, bound cholesterol undergoes endocytosis into lysosomes of intestinal cells, where SCL-12 and SCL-13 are degraded and cholesterol is released. Free cholesterol activates mTORC1 and is used for the production of dafachronic acids. This leads to promotion of protein synthesis and growth, and a metabolic switch at the transcriptional level. Thus, mobilization of sequestered cholesterol stores is the key event for transition from quiescence to growth, and cholesterol is the major signaling molecule in this process.

The Niemann-Pick type diseases – A synopsis of inborn errors in sphingolipid and cholesterol metabolism

Disturbances of lipid homeostasis in cells provoke human diseases. The elucidation of the underlying mechanisms and the development of efficient therapies represent formidable challenges for biomedical research. Exemplary cases are two rare, autosomal recessive, and ultimately fatal lysosomal diseases historically named "Niemann-Pick" honoring the physicians, whose pioneering observations led to their discovery. Acid sphingomyelinase deficiency (ASMD) and Niemann-Pick type C disease (NPCD) are caused by specific variants of the sphingomyelin phosphodiesterase 1 (SMPD1) and NPC intracellular cholesterol transporter 1 (NPC1) or NPC intracellular cholesterol transporter 2 (NPC2) genes that perturb homeostasis of two key membrane components, sphingomyelin and cholesterol, respectively. Patients with severe forms of these diseases present visceral and neurologic symptoms and succumb to premature death. This synopsis traces the tortuous discovery of the Niemann-Pick diseases, highlights important advances with respect to genetic culprits and cellular mechanisms, and exposes efforts to improve diagnosis and to explore new therapeutic approaches.

Cannabinoids activate the insulin pathway to modulate mobilization of cholesterol in C. elegans

The nematode Caenorhabditis elegans requires exogenous cholesterol to survive and its depletion leads to early developmental arrest. Thus, tight regulation of cholesterol storage and distribution within the organism is critical. Previously, we demonstrated that the endocannabinoid (eCB) 2-arachidonoylglycerol (2-AG) plays a key role in C. elegans since it modulates sterol mobilization. However, the mechanism remains unknown. Here we show that mutations in the ocr-2 and osm-9 genes, coding for transient receptors potential V (TRPV) ion channels, dramatically reduce the effect of 2-AG in cholesterol mobilization. Through genetic analysis in combination with the rescue of larval arrest induced by sterol starvation, we found that the insulin/IGF-1signaling (IIS) pathway and UNC-31/CAPS, a calcium-activated regulator of neural dense-core vesicles release, are essential for 2-AG-mediated stimulation of cholesterol mobilization. These findings indicate that 2-AG-dependent cholesterol trafficking requires the release of insulin peptides and signaling through the DAF-2 insulin receptor. These results suggest that 2-AG acts as an endogenous modulator of TRPV signal transduction to control intracellular sterol trafficking through modulation of the IGF-1 signaling pathway

Image segmentation and separation of spectrally similar dyes in fluorescence microscopy by dynamic mode decomposition of photobleaching kinetics

BACKGROUND

Image segmentation in fluorescence microscopy is often based on spectral separation of fluorescent probes (color-based segmentation) or on significant intensity differences in individual image regions (intensity-based segmentation). These approaches fail, if dye fluorescence shows large spectral overlap with other employed probes or with strong cellular autofluorescence.

RESULTS

Here, a novel model-free approach is presented which determines bleaching characteristics based on dynamic mode decomposition (DMD) and uses the inferred photobleaching kinetics to distinguish different probes or dye molecules from autofluorescence. DMD is a data-driven computational method for detecting and quantifying dynamic events in complex spatiotemporal data. Here, DMD is first used on synthetic image data and thereafter used to determine photobleaching characteristics of a fluorescent sterol probe, dehydroergosterol (DHE), compared to that of cellular autofluorescence in the nematode Caenorhabditis elegans. It is shown that decomposition of those dynamic modes allows for separating probe from autofluorescence without invoking a particular model for the bleaching process. In a second application, DMD of dye-specific photobleaching is used to separate two green-fluorescent dyes, an NBD-tagged sphingolipid and Alexa488-transferrin, thereby assigning them to different cellular compartments.

CONCLUSIONS

Data-based decomposition of dynamic modes can be employed to analyze spatially varying photobleaching of fluorescent probes in cells and tissues for spatial and temporal image segmentation, discrimination of probe from autofluorescence and image denoising. The new method should find wide application in analysis of dynamic fluorescence imaging data.

Both entry to and exit from diapause arrest in Caenorhabditis elegans are regulated by a steroid hormone pathway

Diapause arrest in animals such as Caenorhabditis elegans is tightly regulated so that animals make appropriate developmental decisions amidst environmental challenges. Fully understanding diapause requires mechanistic insight of both entry and exit from the arrested state. Although a steroid hormone pathway regulates the entry decision into C. elegans dauer diapause, its role in the exit decision is less clear. A complication to understanding steroid hormonal regulation of dauer has been the peculiar fact that steroid hormone mutants such as daf-9 form partial dauers under normal growth conditions. Here, we corroborate previous findings that daf-9 mutants remain capable of forming full dauers under unfavorable growth conditions and establish that the daf-9 partial dauer state is likely a partially exited dauer that has initiated but cannot complete the dauer exit process. We show that the steroid hormone pathway is both necessary for and promotes complete dauer exit, and that the spatiotemporal dynamics of steroid hormone regulation during dauer exit resembles that of dauer entry. Overall, dauer entry and dauer exit are distinct developmental decisions that are both controlled by steroid hormone signaling.

Summary: In animals such as Caenorhabditis elegans, a steroid hormone pathway controls both the entry and exit decisions into and out of the developmentally arrested dauer state in response to environmental signaling.

Regulation and functions of membrane lipids: Insights from Caenorhabditis elegans

The Caenorhabditis elegans plasma membrane is composed of glycerophospholipids and sphingolipids with a small cholesterol. The C. elegans obtain the majority of the membrane lipids by modifying fatty acids present in the bacterial diet. The metabolic pathways of membrane lipid biosynthesis are well conserved across the animal kingdom. In C. elegans CDP-DAG and Kennedy pathway produce glycerophospholipids. Meanwhile, the sphingolipids are synthesized through a different pathway. They have evolved remarkably diverse mechanisms to maintain membrane lipid homeostasis. For instance, the lipid bilayer stress operates to accomplish homeostasis during any perturbance in the lipid composition. Meanwhile, the PAQR-2/IGLR-2 complex works with FLD-1 to balance unsaturated to saturated fatty acids to maintain membrane fluidity. The loss of membrane lipid homeostasis is observed in many human genetic and metabolic disorders. Since C. elegans conserved such genes and pathways, it can be used as a model organism.

On the role of dauer in the adaptation of nematodes to a parasitic lifestyle

Nematodes are presumably the most abundant Metazoa on Earth, and can even be found in some of the most hostile environments of our planet. Various types of hypobiosis evolved to adapt their life cycles to such harsh environmental conditions. The five most distal major clades of the phylum Nematoda (Clades 8-12), formerly referred to as the Secernentea, contain many economically relevant parasitic nematodes. In this group, a special type of hypobiosis, dauer, has evolved. The dauer signalling pathway, which culminates in the biosynthesis of dafachronic acid (DA), is intensively studied in the free-living nematode Caenorhabditis elegans, and it has been hypothesized that the dauer stage may have been a prerequisite for the evolution of a wide range of parasitic lifestyles among other nematode species. Biosynthesis of DA is not specific for hypobiosis, but if it results in exit of the hypobiotic state, it is one of the main criteria to define certain behaviour as dauer. Within Clades 9 and 10, the involvement of DA has been validated experimentally, and dauer is therefore generally accepted to occur in those clades. However, for other clades, such as Clade 12, this has hardly been explored. In this review, we provide clarity on the nomenclature associated with hypobiosis and dauer across different nematological subfields. We discuss evidence for dauer-like stages in Clades 8 to 12 and support this with a meta-analysis of available genomic data. Furthermore, we discuss indications for a simplified dauer signalling pathway in parasitic nematodes. Finally, we zoom in on the host cues that induce exit from the hypobiotic stage and introduce two hypotheses on how these signals might feed into the dauer signalling pathway for plant-parasitic nematodes. With this work, we contribute to the deeper understanding of the molecular mechanisms underlying hypobiosis in parasitic nematodes. Based on this, novel strategies for the control of parasitic nematodes can be developed.

Steroid hormone pathways coordinate developmental diapause and olfactory remodeling in Pristionchus pacificus

Developmental and behavioral plasticity allow animals to prioritize alternative genetic programs during fluctuating environments. Behavioral remodeling may be acute in animals that interact with host organisms, since reproductive adults and the developmentally arrested larvae often have different ethological needs for chemical stimuli. To understand the genes that coordinate the development and host-seeking behavior, we used the entomophilic nematode Pristionchus pacificus to characterize dauer-constitutive mutants (Daf-c) that inappropriately enter developmental diapause to become dauer larvae. We found two Daf-c loci with dauer-constitutive and cuticle exsheathment phenotypes that can be rescued by the feeding of Δ7-dafachronic acid, and that are dependent on the conserved canonical steroid hormone receptor Ppa-DAF-12. Specifically at one locus, deletions in the sole hydroxysteroid dehydrogenase (HSD) in P. pacificus resulted in Daf-c phenotypes. Ppa-hsd-2 is expressed in the canal-associated neurons (CANs) and excretory cells whose homologous cells in Caenorhabditis elegans are not known to be involved in the dauer decision. While in wildtype only dauer larvae are attracted to host odors, hsd-2 mutant adults show enhanced attraction to the host beetle pheromone, along with ectopic activation of a marker for putative olfactory neurons, Ppa-odr-3. Surprisingly, this enhanced odor attraction acts independently of the Δ7-DA/DAF-12 module, suggesting that Ppa-HSD-2 may be responsible for several steroid hormone products involved in coordinating the dauer decision and host-seeking behavior in P. pacificus.

On the origins and conceptual frameworks of natural plasticity-Lessons from single-cell models in C. elegans

How flexible are cell identities? This problem has fascinated developmental biologists for several centuries and can be traced back to Abraham Trembley's pioneering manipulations of Hydra to test its regeneration abilities in the 1700s. Since the cell theory in the mid-19th century, developmental biology has been dominated by a single framework in which embryonic cells are committed to specific cell fates, progressively and irreversibly acquiring their differentiated identities. This hierarchical, unidirectional and irreversible view of cell identity has been challenged in the past decades through accumulative evidence that many cell types are more plastic than previously thought, even in intact organisms. The paradigm shift introduced by such plasticity calls into question several other key traditional concepts, such as how to define a differentiated cell or more generally cellular identity, and has brought new concepts, such as distinct cellular states. In this review, we want to contribute to this representation by attempting to clarify the conceptual and theoretical frameworks of cell plasticity and identity. In the context of these new frameworks we describe here an atlas of natural plasticity of cell identity in C. elegans, including our current understanding of the cellular and molecular mechanisms at play. The worm further provides interesting cases at the borderlines of cellular plasticity that highlight the conceptual challenges still ahead. We then discuss a set of future questions and perspectives arising from the studies of natural plasticity in the worm that are shared with other reprogramming and plasticity events across phyla.

Starvation Responses Throughout the Caenorhabditiselegans Life Cycle

Caenorhabditis elegans survives on ephemeral food sources in the wild, and the species has a variety of adaptive responses to starvation. These features of its life history make the worm a powerful model for studying developmental, behavioral, and metabolic starvation responses. Starvation resistance is fundamental to life in the wild, and it is relevant to aging and common diseases such as cancer and diabetes. Worms respond to acute starvation at different times in the life cycle by arresting development and altering gene expression and metabolism. They also anticipate starvation during early larval development, engaging an alternative developmental program resulting in dauer diapause. By arresting development, these responses postpone growth and reproduction until feeding resumes. A common set of signaling pathways mediates systemic regulation of development in each context but with important distinctions. Several aspects of behavior, including feeding, foraging, taxis, egg laying, sleep, and associative learning, are also affected by starvation. A variety of conserved signaling, gene regulatory, and metabolic mechanisms support adaptation to starvation. Early life starvation can have persistent effects on adults and their descendants. With its short generation time, C. elegans is an ideal model for studying maternal provisioning, transgenerational epigenetic inheritance, and developmental origins of adult health and disease in humans. This review provides a comprehensive overview of starvation responses throughout the C. elegans life cycle.

Understanding and Treating Niemann-Pick Type C Disease: Models Matter

Biomedical research aims to understand the molecular mechanisms causing human diseases and to develop curative therapies. So far, these goals have been achieved for a small fraction of diseases, limiting factors being the availability, validity, and use of experimental models. Niemann–Pick type C (NPC) is a prime example for a disease that lacks a curative therapy despite substantial breakthroughs. This rare, fatal, and autosomal-recessive disorder is caused by defects in NPC1 or NPC2. These ubiquitously expressed proteins help cholesterol exit from the endosomal–lysosomal system. The dysfunction of either causes an aberrant accumulation of lipids with patients presenting a large range of disease onset, neurovisceral symptoms, and life span. Here, we note general aspects of experimental models, we describe the line-up used for NPC-related research and therapy development, and we provide an outlook on future topics.

Identification of a Novel Link between the Intermediate Filament Organizer IFO-1 and Cholesterol Metabolism in the Caenorhabditis elegans Intestine

The intestine is an organ essential to organismal nutrient absorption, metabolic control, barrier function and immunoprotection. The Caenorhabditis elegans intestine consists of 20 cells harboring a dense intermediate filament network positioned below the apical plasma membrane that forms a junction-anchored sheath around the intestinal lumen. This evolutionarily conserved arrangement provides mechanical and overall stress-protection, and it serves as an important model for deciphering the role of intestinal architecture in metazoan biology. We recently reported that the loss-of-function mutation of the intestinal intermediate filament organizer IFO-1 perturbs this architecture, leading to reduced body size and reproduction. Here, we demonstrate that the IFO-1 mutation dramatically affects cholesterol metabolism. Mutants showed an increased sensitivity to cholesterol depletion, reduced cholesterol uptake, and cholesterol transfer to the gonads, which is also observed in worms completely lacking an intermediate filament network. Accordingly, we found striking similarities to transcriptome and lipidome profiles of a nuclear hormone receptor (NHR)-8 mutant. NHR-8 is homologous to mammalian LXR (liver X receptor) that serves as a sterol sensor and transcriptional regulator of lipid metabolism. Remarkably, increasing exogenous cholesterol partially rescues the developmental retardation in IFO-1 mutants. Our results uncover a novel link of the intestinal intermediate filament cytoskeleton to cholesterol metabolism that contributes to compromised growth and reproduction.

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.

Elucidating the molecular and developmental biology of parasitic nematodes: Moving to a multiomics paradigm

In the past two decades, significant progress has been made in the sequencing, assembly, annotation and analyses of genomes and transcriptomes of parasitic worms of socioeconomic importance. This progress has somewhat improved our knowledge and understanding of these pathogens at the molecular level. However, compared with the free-living nematode Caenorhabditis elegans, the areas of functional genomics, transcriptomics, proteomics and metabolomics of parasitic nematodes are still in their infancy, and there are major gaps in our knowledge and understanding of the molecular biology of parasitic nematodes. The information on signalling molecules, molecular pathways and microRNAs (miRNAs) that are known to be involved in developmental processes in C. elegans and the availability of some molecular resources (draft genomes, transcriptomes and some proteomes) for selected parasitic nematodes provide a basis to start exploring the developmental biology of parasitic nematodes. Indeed, some studies have identified molecules and pathways that might associate with developmental processes in related, parasitic nematodes, such as Haemonchus contortus (barber's pole worm). However, detailed information is often scant and 'omics resources are limited, preventing a proper integration of 'omic data sets and comprehensive analyses. Moreover, little is known about the functional roles of pheromones, hormones, signalling pathways and post-transcriptional/post-translational regulations in the development of key parasitic nematodes throughout their entire life cycles. Although C. elegans is an excellent model to assist molecular studies of parasitic nematodes, its use is limited when it comes to explorations of processes that are specific to parasitism within host animals. A deep understanding of parasitic nematodes, such as H. contortus, requires substantially enhanced resources and the use of integrative 'omics approaches for analyses. The improved genome and well-established in vitro larval culture system for H. contortus provide unprecedented opportunities for comprehensive studies of the transcriptomes (mRNA and miRNA), proteomes (somatic, excretory/secretory and phosphorylated proteins) and lipidomes (e.g., polar and neutral lipids) of this nematode. Such resources should enable in-depth explorations of its developmental biology at a level, not previously possible. The main aims of this review are (i) to provide a background on the development of nematodes, with a particular emphasis on the molecular aspects involved in the dauer formation and exit in C. elegans; (ii) to critically appraise the current state of knowledge of the developmental biology of parasitic nematodes and identify key knowledge gaps; (iii) to cover salient aspects of H. contortus, with a focus on the recent advances in genomics, transcriptomics, proteomics and lipidomics as well as in vitro culturing systems; (iv) to review recent advances in our knowledge and understanding of the molecular and developmental biology of H. contortus using an integrative multiomics approach, and discuss the implications of this approach for detailed explorations of signalling molecules, molecular processes and pathways likely associated with nematode development, adaptation and parasitism, and for the identification of novel intervention targets against these pathogens. Clearly, the multiomics approach established recently is readily applicable to exploring a wide range of interesting and socioeconomically significant parasitic worms (including also trematodes and cestodes) at the molecular level, and to elucidate host-parasite interactions and disease processes.

Diapause in a tropical oil-collecting bee: molecular basis unveiled by RNA-Seq

BACKGROUND

Diapause is a natural phenomenon characterized by an arrest in development that ensures the survival of organisms under extreme environmental conditions. The process has been well documented in arthropods. However, its molecular basis has been mainly studied in species from temperate zones, leaving a knowledge gap of this phenomenon in tropical species. In the present study, the Neotropical and solitary bee Tetrapedia diversipes was employed as a model for investigating diapause in species from tropical zones. Being a bivoltine insect, Tetrapedia diversipes produce two generations of offspring per year. The first generation, normally born during the wet season, develops faster than individuals from the second generation, born after the dry season. Furthermore, it has been shown that the development of the progeny, of the second generation, is halted at the 5th larval instar, and remains in larval diapause during the dry season. Towards the goal of gaining a better understanding of the diapause phenomenon we compared the global gene expression pattern, in larvae, from both reproductive generations and during diapause. The results demonstrate that there are similarities in the observed gene expression patterns to those already described for temperate climate models, and also identify diapause-related genes that have not been previously reported in the literature.

RESULTS

The RNA-Seq analysis identified 2275 differentially expressed transcripts, of which 1167 were annotated. Of these genes, during diapause, 352 were upregulated and 815 were downregulated. According to their biological functions, these genes were categorized into the following groups: cellular detoxification, cytoskeleton, cuticle, sterol and lipid metabolism, cell cycle, heat shock proteins, immune response, circadian clock, and epigenetic control.

CONCLUSION

Many of the identified genes have already been described as being related to diapause; however, new genes were discovered, for the first time, in this study. Among those, we highlight: Niemann-Pick type C1, NPC2 and Acyl-CoA binding protein homolog (all involved in ecdysteroid synthesis); RhoBTB2 and SASH1 (associated with cell cycle regulation) and Histone acetyltransferase KAT7 (related to epigenetic transcriptional regulation). The results presented here add important findings to the understanding of diapause in tropical species, thus increasing the comprehension of diapause-related molecular mechanisms.

Endocannabinoids in Caenorhabditis elegans are essential for the mobilization of cholesterol from internal reserves

Proper cholesterol transport is crucial for the functionality of cells. In C. elegans, certain cholesterol derivatives called dafachronic acids (DAs) govern the entry into diapause. In their absence, worms form a developmentally arrested dauer larva. Thus, cholesterol transport to appropriate places for DA biosynthesis warrants the reproductive growth. Recently, we discovered a novel class of glycosphingolipids, PEGCs, required for cholesterol mobilization/transport from internal storage pools. Here, we identify other components involved in this process. We found that strains lacking polyunsaturated fatty acids (PUFAs) undergo increased dauer arrest when grown without cholesterol. This correlates with the depletion of the PUFA-derived endocannabinoids 2-arachidonoyl glycerol and anandamide. Feeding of these endocannabinoids inhibits dauer formation caused by PUFAs deficiency or impaired cholesterol trafficking (e.g. in Niemann-Pick C1 or DAF-7/TGF-β mutants). Moreover, in parallel to PEGCs, endocannabinoids abolish the arrest induced by cholesterol depletion. These findings reveal an unsuspected function of endocannabinoids in cholesterol trafficking regulation.

Subcellular Nanorheology Reveals Lysosomal Viscosity as a Reporter for Lysosomal Storage Diseases

We describe a new method to measure viscosity within subcellular organelles of a living cell using nanorheology. We demonstrate proof of concept by measuring viscosity in lysosomes in multiple cell types and disease models. The lysosome is an organelle responsible for the breakdown of complex biomolecules. When different lysosomal proteins are defective, they are unable to break down specific biological substrates, which get stored within the lysosome, causing about 70 fatal diseases called lysosomal storage disorders (LSDs). Although the buildup of storage material is critical to the pathology of these diseases, methods to monitor cargo accumulation in the lysosome are lacking for most LSDs. Using passive particle tracking nanorheology and fluorescence recovery after photobleaching, we report that viscosity in the lysosome increases significantly during cargo accumulation in several LSD models. In a mammalian cell culture model of Niemann Pick C, lysosomal viscosity directly correlates with the levels of accumulated cholesterol. We also observed increased viscosity in diverse LSD models in Caenorhabditis elegans, revealing that lysosomal viscosity is a powerful reporter with which to monitor substrate accumulation in LSDs for new diagnostics or to assay therapeutic efficacy.

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.

Molting in C. elegans

Molting is an essential developmental process for the majority of animal species on Earth. During the molting process, which is a specialized form of extracellular matrix (ECM) remodeling, the old apical ECM, or cuticle, is replaced with a new one. Many of the genes and pathways identified as important for molting in nematodes are highly conserved in vertebrates and include regulators and components of vesicular trafficking, steroid-hormone signaling, developmental timers, and hedgehog-like signaling. In this review, we discuss what is known about molting, with a focus on studies in Caenorhabditis elegans. We also describe the key structural elements of the cuticle that must be released, newly synthesized, or remodeled for proper molting to occur.

Phosphorylated glycosphingolipids essential for cholesterol mobilization in Caenorhabditis elegans

The nematode Caenorhabditis elegans requires exogenous cholesterol to survive and its depletion leads to early developmental arrest. Thus, tight regulation of cholesterol storage and distribution within the organism is indispensable. Here, we present a novel class of C. elegans phosphorylated glycosphingolipids, phosphoethanolamine glucosylceramides (PEGCs), capable of rescuing larval arrest induced by sterol starvation. We describe the total synthesis of a major PEGC species and demonstrate that the PEGC synthetic counterpart suppresses the dauer-constitutive phenotype of Niemann-Pick C1 (NPC1) and DAF-7/TGF-β mutant worms caused by impaired intracellular sterol trafficking. PEGC biosynthesis depends on functional NPC1 and TGF-β, indicating that these proteins control larval development at least partly through PEGC. Furthermore, glucosylceramide deficiency dramatically reduced PEGC amounts. However, the resulting developmental arrest could be rescued by oversaturation of food with cholesterol. Taken together, these data show that PEGC is essential for C. elegans development through its regulation of sterol mobilization.

Assessing cholesterol storage in live cells and C. elegans by stimulated Raman scattering imaging of phenyl-Diyne cholesterol

We report a cholesterol imaging method using rationally synthesized phenyl-diyne cholesterol (PhDY-Chol) and stimulated Raman scattering (SRS) microscope. The phenyl-diyne group is biologically inert and provides a Raman scattering cross section that is 88 times larger than the endogenous C = O stretching mode. SRS microscopy offers an imaging speed that is faster than spontaneous Raman microscopy by three orders of magnitude, and a detection sensitivity of 31 μM PhDY-Chol (~1,800 molecules in the excitation volume). Inside living CHO cells, PhDY-Chol mimics the behavior of cholesterol, including membrane incorporation and esterification. In a cellular model of Niemann-Pick type C disease, PhDY-Chol reflects the lysosomal accumulation of cholesterol, and shows relocation to lipid droplets after HPβCD treatment. In live C. elegans, PhDY-Chol mimics cholesterol uptake by intestinal cells and reflects cholesterol storage. Together, our work demonstrates an enabling platform for study of cholesterol storage and trafficking in living cells and vital organisms.

Enzymes for ecdysteroid biosynthesis: their biological functions in insects and beyond

Steroid hormones are responsible for the coordinated regulation of many aspects of biological processes in multicellular organisms. Since the last century, many studies have identified and characterized steroidogenic enzymes in vertebrates, including mammals. However, much less is known about invertebrate steroidogenic enzymes. In the last 15 years, a number of steroidogenic enzymes and their functions have been characterized in ecdysozoan animals, especially in the fruit fly Drosophila melanogaster. In this review, we summarize the latest knowledge of enzymes crucial for synthesizing ecdysteroids, the principal insect steroid hormones. We also discuss the functional conservation and diversity of ecdysteroidogenic enzymes in other insects and even non-insect species, such as nematodes, vertebrates, and lower eukaryotes.

The NHR-8 nuclear receptor regulates cholesterol and bile acid homeostasis in C. elegans

Hormone-gated nuclear receptors (NRs) are conserved transcriptional regulators of metabolism, reproduction, and homeostasis. Here we show that C. elegans NHR-8 NR, a homolog of vertebrate liver X and vitamin D receptors, regulates nematode cholesterol balance, fatty acid desaturation, apolipoprotein production, and bile acid metabolism. Loss of nhr-8 results in a deficiency in bile acid-like steroids, called the dafachronic acids, which regulate the related DAF-12/NR, thus controlling entry into the long-lived dauer stage through cholesterol availability. Cholesterol supplementation rescues various nhr-8 phenotypes, including developmental arrest, unsaturated fatty acid deficiency, reduced fertility, and shortened life span. Notably, nhr-8 also interacts with daf-16/FOXO to regulate steady-state cholesterol levels and is synthetically lethal in combination with insulin signaling mutants that promote unregulated growth. Our studies provide important insights into nuclear receptor control of cholesterol balance and metabolism and their impact on development, reproduction, and aging in the context of larger endocrine networks.

Genetic dissection of a cell-autonomous neurodegenerative disorder: lessons learned from mouse models of Niemann-Pick disease type C

Understanding neurodegenerative disease progression and its treatment requires the systematic characterization and manipulation of relevant cell types and molecular pathways. The neurodegenerative lysosomal storage disorder Niemann-Pick disease type C (NPC) is highly amenable to genetic approaches that allow exploration of the disease biology at the organismal, cellular and molecular level. Although NPC is a rare disease, genetic analysis of the associated neuropathology promises to provide insight into the logic of disease neural circuitry, selective neuron vulnerability and neural-glial interactions. The ability to control the disorder cell-autonomously and in naturally occurring spontaneous animal models that recapitulate many aspects of the human disease allows for an unparalleled dissection of the disease neurobiology in vivo. Here, we review progress in mouse-model-based studies of NPC disease, specifically focusing on the subtype that is caused by a deficiency in NPC1, a sterol-binding late endosomal membrane protein involved in lipid trafficking. We also discuss recent findings and future directions in NPC disease research that are pertinent to understanding the cellular and molecular mechanisms underlying neurodegeneration in general.

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.

Steroid regulation of C. elegans diapause, developmental timing, and longevity

Hormones play a critical role in driving major stage transitions and developmental timing events in many species. In the nematode C. elegans the steroid hormone receptor, DAF-12, works at the confluence of pathways regulating developmental timing, stage specification, and longevity. DAF-12 couples environmental and physiologic signals to life history regulation, and it is embedded in a rich architecture governing diverse processes. Here, we highlight the molecular insights, extraordinary circuitry, and signaling pathways governing life stage transitions in the worm and how they have yielded fundamental insights into steroid regulation of biological time.

NSBP-1 mediates the effects of cholesterol on insulin/IGF-1 signaling in Caenorhabditis elegans

Nematode sterol-binding protein 1 (NSBP-1) is a homolog of nucleosome assembly protein 1 in mammals that is expressed widely in Caenorhabditis elegans. NSBP-1 mutants are biologically lethal, demonstrating the significance of the gene in growth and development. We investigated how cholesterol influences the insulin signaling pathway through this novel sterol-binding protein in C. elegans. Here we report that NSBP-1 influences many biological processes mediated by insulin signaling, such as longevity, dauer formation, fat storage, and resistance to oxidative stress. We found that NSBP-1 is phosphorylated by AKT-1 downstream of insulin signaling. In the absence of insulin signaling, NSBP-1 is translocated to the nucleus and binds to DAF-16, a FOXO transcription factor, in a cholesterol-dependent manner. Moreover, NSBP-1 and DAF-16 regulate a common set of genes that can directly modulate fat storage, longevity, and resistance to stress. Together, our results present a new steroid-binding molecule that can connect sterol signaling to insulin signaling through direct interaction with FOXO.

RNAseq analysis of the parasitic nematode Strongyloides stercoralis reveals divergent regulation of canonical dauer pathways

The infectious form of many parasitic nematodes, which afflict over one billion people globally, is a developmentally arrested third-stage larva (L3i). The parasitic nematode Strongyloides stercoralis differs from other nematode species that infect humans, in that its life cycle includes both parasitic and free-living forms, which can be leveraged to investigate the mechanisms of L3i arrest and activation. The free-living nematode Caenorhabditis elegans has a similar developmentally arrested larval form, the dauer, whose formation is controlled by four pathways: cyclic GMP (cGMP) signaling, insulin/IGF-1-like signaling (IIS), transforming growth factor β (TGFβ) signaling, and biosynthesis of dafachronic acid (DA) ligands that regulate a nuclear hormone receptor. We hypothesized that homologous pathways are present in S. stercoralis, have similar developmental regulation, and are involved in L3i arrest and activation. To test this, we undertook a deep-sequencing study of the polyadenylated transcriptome, generating over 2.3 billion paired-end reads from seven developmental stages. We constructed developmental expression profiles for S. stercoralis homologs of C. elegans dauer genes identified by BLAST searches of the S. stercoralis genome as well as de novo assembled transcripts. Intriguingly, genes encoding cGMP pathway components were coordinately up-regulated in L3i. In comparison to C. elegans, S. stercoralis has a paucity of genes encoding IIS ligands, several of which have abundance profiles suggesting involvement in L3i development. We also identified seven S. stercoralis genes encoding homologs of the single C. elegans dauer regulatory TGFβ ligand, three of which are only expressed in L3i. Putative DA biosynthetic genes did not appear to be coordinately regulated in L3i development. Our data suggest that while dauer pathway genes are present in S. stercoralis and may play a role in L3i development, there are significant differences between the two species. Understanding the mechanisms governing L3i development may lead to novel treatment and control strategies.

Parasitic nematodes infect over one billion people worldwide and cause many diseases, including strongyloidiasis, filariasis, and hookworm disease. For many of these parasites, including Strongyloides stercoralis, the infectious form is a developmentally arrested and long-lived thirdstage larva (L3i). Upon encountering a host, L3i quickly resume development and mature into parasitic adults. In the free-living nematode Caenorhabditis elegans, a similar developmentally arrested third-stage larva, known as the dauer, is regulated by four key cellular mechanisms. We hypothesized that similar cellular mechanisms control L3i arrest and activation. Therefore, we used deep-sequencing technology to characterize the S. stercoralis transcriptome (RNAseq), which allowed us to identify S. stercoralis homologs of components of these four mechanisms and examine their temporal regulation. We found similar temporal regulation between S. stercoralis and C. elegans for components of two mechanisms, but dissimilar temporal regulation for two others, suggesting conserved as well as novel modes of developmental regulation for L3i. Understanding L3i development may lead to novel control strategies as well as new treatments for strongyloidiasis and other diseases caused by parasitic nematodes.

Cholesterol, an essential molecule: diverse roles involving cytochrome P450 enzymes

Cholesterol is an essential molecule for eukaryotic life and is an important precursor for a wide range of physiological processes. Biosynthesis and homoeostasis of cholesterol are complex mechanisms that are tightly regulated and interlinked with activities of a number of cytochrome P450 enzymes. These P450s play central critical roles in cholesterol metabolism. Key roles include a rate-limiting reaction in the synthesis of cholesterol itself, and in the oxidative transformations of cholesterol into steroid hormones and bile acids. However, microbial P450s also have important roles that impinge directly on human cholesterol synthesis and oxidation. Recent data reveal that Mycobacterium tuberculosis (which infects more than one-third of the world's human population) uses P450s to initiate breakdown of host cholesterol as an energy source. Microbial P450s also catalyse industrially important transformations in the synthesis of cholesterol-lowering statin drugs, with clear benefits to humans. The present article reviews the various roles of P450s in human cholesterol metabolism, from endogenous P450s through to microbial oxidases that enable catabolism of human cholesterol, or facilitate production of statins that regulate cholesterol production with positive outcomes in cardiovascular disease.

A novel 3-hydroxysteroid dehydrogenase that regulates reproductive development and longevity

Endogenous small molecule metabolites that regulate animal longevity are emerging as a novel means to influence health and life span. In C. elegans, bile acid-like steroids called the dafachronic acids (DAs) regulate developmental timing and longevity through the conserved nuclear hormone receptor DAF-12, a homolog of mammalian sterol-regulated receptors LXR and FXR. Using metabolic genetics, mass spectrometry, and biochemical approaches, we identify new activities in DA biosynthesis and characterize an evolutionarily conserved short chain dehydrogenase, DHS-16, as a novel 3-hydroxysteroid dehydrogenase. Through regulation of DA production, DHS-16 controls DAF-12 activity governing longevity in response to signals from the gonad. Our elucidation of C. elegans bile acid biosynthetic pathways reveals the possibility of novel ligands as well as striking biochemical conservation to other animals, which could illuminate new targets for manipulating longevity in metazoans.

Hormonal signal amplification mediates environmental conditions during development and controls an irreversible commitment to adulthood

A dual mechanism regulates the developmental fate choice in C. elegans in response to population density: variation of the threshold of DA hormone required to commit to a certain fate and a positive feedback loop that amplifies this hormonal signal to ensure an organism-wide developmental fate choice.

Many animals can choose between different developmental fates to maximize fitness. Despite the complexity of environmental cues and life history, different developmental fates are executed in a robust fashion. The nematode Caenorhabditis elegans serves as a powerful model to examine this phenomenon because it can adopt one of two developmental fates (adulthood or diapause) depending on environmental conditions. The steroid hormone dafachronic acid (DA) directs development to adulthood by regulating the transcriptional activity of the nuclear hormone receptor DAF-12. The known role of DA suggests that it may be the molecular mediator of environmental condition effects on the developmental fate decision, although the mechanism is yet unknown. We used a combination of physiological and molecular biology techniques to demonstrate that commitment to reproductive adult development occurs when DA levels, produced in the neuroendocrine XXX cells, exceed a threshold. Furthermore, imaging and cell ablation experiments demonstrate that the XXX cells act as a source of DA, which, upon commitment to adult development, is amplified and propagated in the epidermis in a DAF-12 dependent manner. This positive feedback loop increases DA levels and drives adult programs in the gonad and epidermis, thus conferring the irreversibility of the decision. We show that the positive feedback loop canalizes development by ensuring that sufficient amounts of DA are dispersed throughout the body and serves as a robust fate-locking mechanism to enforce an organism-wide binary decision, despite noisy and complex environmental cues. These mechanisms are not only relevant to C. elegans but may be extended to other hormonal-based decision-making mechanisms in insects and mammals.

During development, many animals choose between mutually exclusive fates, such as workers, soldiers, or queens in bees or ants. The choice between states is uniform throughout the animal since mixtures of these fates are not observed in the wild. The nematode Caenorhabditis elegans larvae integrate environmental conditions and have two choices: mature into reproductive adults or arrest development as dauer larvae—a latent form that can survive harsh conditions. The decision between both fates is governed by the hormone dafachronic acid (DA), however its regulation during development in response to environmental conditions has been unclear. In this study we show how two mechanisms are responsible for the integration of environmental conditions and the coordination of the decision between many tissues. We first show that a threshold mechanism integrates population density with the internal amount of DA made in the head. A normal population density has a low threshold of DA needed for worms to become adults, whereas a high population density increases this threshold and leads worms to develop into dauer larvae. We then show that the low levels of DA released from the head are amplified in the hypodermis (the main body syncytial epithelium) via a positive feedback loop, coordinating the decision over the animal. Disruption of this positive feedback yields abnormal adults. We propose that the positive feedback serves as a fate-locking mechanism enforcing an organismal binary decision—either adult or dauer—despite noisy and uncertain environmental conditions.

CUP-1 is a novel protein involved in dietary cholesterol uptake in Caenorhabditis elegans

Sterols transport and distribution are essential processes in all multicellular organisms. Survival of the nematode Caenorhabditis elegans depends on dietary absorption of sterols present in the environment. However the general mechanisms associated to sterol uptake in nematodes are poorly understood. In the present work we provide evidence showing that a previously uncharacterized transmembrane protein, designated Cholesterol Uptake Protein-1 (ChUP-1), [corrected] is involved in dietary cholesterol uptake in C. elegans. Animals lacking ChUP-1 [corrected] showed hypersensitivity to cholesterol limitation and were unable to uptake cholesterol. A ChUP-1-GFP [corrected] fusion protein colocalized with cholesterol-rich vesicles, endosomes and lysosomes as well as the plasma membrane. Additionally, by FRET imaging, a direct interaction was found between the cholesterol analog DHE and the transmembrane "cholesterol recognition/interaction amino acid consensus" (CRAC) motif present in C. elegans ChUP-1. [corrected]. In-silico analysis identified two mammalian homologues of ChUP-1. [corrected]. Most interestingly, CRAC motifs are conserved in mammalian ChUP-1 [corrected] homologous. Our results suggest a role of ChUP-1 [corrected] in cholesterol uptake in C. elegans and open up the possibility for the existence of a new class of proteins involved in sterol absorption in mammals.

Regulation of neuronal APL-1 expression by cholesterol starvation

Background

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the deposition of β-amyloid plaques composed primarily of the amyloid-β peptide, a cleavage product of amyloid precursor protein (APP). While mutations in APP lead to the development of Familial Alzheimer's Disease (FAD), sporadic AD has only one clear genetic modifier: the ε4 allele of the apolipoprotein E (ApoE) gene. Cholesterol starvation in Caenorhabditis elegans leads to molting and arrest phenotypes similar to loss-of-function mutants of the APP ortholog, apl-1 (amyloid precursor-like protein 1), and lrp-1 (lipoprotein receptor-related protein 1), suggesting a potential interaction between apl-1 and cholesterol metabolism.

Methodology/Principal Findings

Previously, we found that RNAi knock-down of apl-1 leads to aldicarb hypersensitivity, indicating a defect in synaptic function. Here we find the same defect is recapitulated during lrp-1 knock-down and by cholesterol starvation. A cholesterol-free diet or loss of lrp-1 directly affects APL-1 levels as both lead to loss of APL-1::GFP fluorescence in neurons. However, loss of cholesterol does not affect global transcription or protein levels as seen by qPCR and Western blot.

Conclusions

Our results show that cholesterol and lrp-1 are involved in the regulation of synaptic transmission, similar to apl-1. Both are able to modulate APL-1 protein levels in neurons, however cholesterol changes do not affect global apl-1 transcription or APL-1 protein indicating the changes are specific to neurons. Thus, regulation of synaptic transmission and molting by LRP-1 and cholesterol may be mediated by their ability to control APL-1 neuronal protein expression.

Hormone signaling and phenotypic plasticity in nematode development and evolution

Phenotypic plasticity refers to the ability of an organism to adopt different phenotypes depending on environmental conditions. In animals and plants, the progression of juvenile development and the formation of dormant stages are often associated with phenotypic plasticity, indicating the importance of phenotypic plasticity for life-history theory. Phenotypic plasticity has long been emphasized as a crucial principle in ecology and as facilitator of phenotypic evolution. In nematodes, several examples of phenotypic plasticity have been studied at the genetic and developmental level. In addition, the influence of different environmental factors has been investigated under laboratory conditions. These studies have provided detailed insight into the molecular basis of phenotypic plasticity and its ecological and evolutionary implications. Here, we review recent studies on the formation of dauer larvae in Caenorhabditis elegans, the evolution of nematode parasitism and the generation of a novel feeding trait in Pristionchus pacificus. These examples reveal a conserved and co-opted role of an endocrine signaling module involving the steroid hormone dafachronic acid. We will discuss how hormone signaling might facilitate life-history and morphological evolution.

The mevalonate pathway in C. elegans

The mevalonate pathway in human is responsible for the synthesis of cholesterol and other important biomolecules such as coenzyme Q, dolichols and isoprenoids. These molecules are required in the cell for functions ranging from signaling to membrane integrity, protein prenylation and glycosylation, and energy homeostasis. The pathway consists of a main trunk followed by sub-branches that synthesize the different biomolecules. The majority of our knowledge about the mevalonate pathway is currently focused on the cholesterol synthesis branch, which is the target of the cholesterol-lowering statins; less is known about the function and regulation of the non-cholesterol-related branches. To study them, we need a biological system where it is possible to specifically modulate these metabolic branches individually or in groups. The nematode Caenorhabditis elegans (C. elegans) is a promising model to study these non-cholesterol branches since its mevalonate pathway seems very well conserved with that in human except that it has no cholesterol synthesis branch. The simple genetic makeup and tractability of C. elegans makes it relatively easy to identify and manipulate key genetic components of the mevalonate pathway, and to evaluate the consequences of tampering with their activity. This general experimental approach should lead to new insights into the physiological roles of the non-cholesterol part of the mevalonate pathway. This review will focus on the current knowledge related to the mevalonate pathway in C. elegans and its possible applications as a model organism to study the non-cholesterol functions of this pathway.

Invertebrate models of lysosomal storage disease: what have we learned so far?

The lysosomal storage diseases (LSDs) collectively account for death in 1 in 8,000 children. Although some forms are treatable, they are essentially incurable and usually are lethal in the first decade of life. The most intractable forms of LSD are those with neuronal involvement. In an effort to identify the pathological signaling driving pathology in the LSDs, invertebrate models have been developed. In this review, we outline our current understanding of LSDs and recent findings using invertebrate models. We outline strategies and pitfalls for the development of such models. Available models of LSD in Drosophila and Caenorhabditis elegans are uncovering roles for LSD-related proteins with previously unknown function using both gain-of-function and loss-of-function strategies. These models of LSD in Drosophila and C. elegans have identified potential pathogenic signaling cascades that are proving critical to our understanding of these lethal diseases.

Sterol regulation of metabolism, homeostasis, and development

Sterol metabolites are critical signaling molecules that regulate metabolism, development, and homeostasis. Oxysterols, bile acids (BAs), and steroids work primarily through cognate sterol-responsive nuclear hormone receptors to control these processes through feed-forward and feedback mechanisms. These signaling pathways are conserved from simple invertebrates to mammals. Indeed, results from various model organisms have yielded fundamental insights into cholesterol and BA homeostasis, lipid and glucose metabolism, protective mechanisms, tissue differentiation, development, reproduction, and even aging. Here, we review how sterols act through evolutionarily ancient mechanisms to control these processes.

A potential biochemical mechanism underlying the influence of sterol deprivation stress on Caenorhabditis elegans longevity

To investigate the biochemical mechanism underlying the effect of sterol deprivation on longevity in Caenorhabditis elegans, we treated parent worms (P0) with 25-azacoprostane (Aza), which inhibits sitosterol-to-cholesterol conversion, and measured mean lifespan (MLS) in F2 worms. At 25 μM (∼EC(50)), Aza reduced total body sterol by 82.5%, confirming sterol depletion. Aza (25 μM) treatment of wild-type (N2) C. elegans grown in sitosterol (5 μg/ml) reduced MLS by 35%. Similar results were obtained for the stress-related mutants daf-16(mu86) and gas-1(fc21). Unexpectedly, Aza had essentially no effect on MLS in the stress-resistant daf-2(e1370) or mitochondrial complex II mutant mev-1(kn1) strains, indicating that Aza may target both insulin/IGF-1 signaling (IIS) and mitochondrial complex II. Aza increased reactive oxygen species (ROS) levels 2.7-fold in N2 worms, but did not affect ROS production by mev-1(kn1), suggesting a direct link between Aza treatment and mitochondrial ROS production. Moreover, expression of the stress-response transcription factor SKN-1 was decreased in amphid neurons by Aza and that of DAF-28 was increased when DAF-6 was involved, contributing to lifespan reduction.

A circulatory transcriptional regulation among daf-9, daf-12, and daf-16 mediates larval development upon cholesterol starvation in Caenorhabditis elegans

C. elegans shows dauer-like larvae formation upon cholesterol starvation (CS), but the genetic epistasis among abnormal dauer formation (daf) genes during the process remains unclear. To clarify the genetic interactions among daf-9, daf-12, and daf-16 in this process, mRNA levels of these genes upon CS were measured. CS increased the mRNA levels of daf-9, daf-12, and daf-16. CS also induced DAF-16 nuclear localization, which was positively and negatively regulated by DAF-12 and DAF-9 activities, respectively. Activated DAF-16, a FOXO transcription factor, enhanced daf-12 but suppressed daf-9 expression, whereas DAF-9 inhibited daf-12 expression. Concomitantly, CS-induced larval arrest was regulated positively by DAF-12 and DAF-16, but negatively by DAF-9. The larval arrest in daf-9 mutant was suppressed by daf-12 RNAi, placing DAF-12 downstream of DAF-9. These results altogether suggest that circulatory mutual regulation among daf-9, daf-12, and daf-16 at the expression level mediates cholesterol signal to control larval development upon CS.

Steroid hormone regulation of C. elegans and Drosophila aging and life history

In the last two decades it has become clear that hormones and gene mutations in endocrine signaling pathways can exert major effects on lifespan and related life history traits in worms, flies, mice, and other organisms. While most of this research has focused on insulin/insulin-like growth factor-1 signaling, a peptide hormone pathway, recent work has shown that also lipophilic hormones play an important role in modulating lifespan and other life history traits. Here we review how steroid hormones, a particular group of lipophilic hormones, affect life history traits in the nematode worm (Caenorhabditis elegans) and the fruit fly (Drosophila melanogaster), with a particular focus on longevity. Interestingly, a comparison suggests that parallel endocrine principles might be at work in worms and flies in these species and that steroid hormones interact with the gonad to affect lifespan.

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.

Lipid transport and signaling in Caenorhabditis elegans

The strengths of the Caenorhabditis elegans model have been recently applied to the study of the pathways of lipid storage, transport, and signaling. As the lipid storage field has recently been reviewed, in this minireview we (1) discuss some recent studies revealing important physiological roles for lipases in mobilizing lipid reserves, (2) describe various pathways of lipid transport, with a particular focus on the roles of lipoproteins, (3) debate the utility of using C. elegans as a model for human dyslipidemias that impinge on atherosclerosis, and (4) describe several systems where lipids affect signaling, highlighting the particular properties of lipids as information-carrying molecules. We conclude that the study of lipid biology in C. elegans exemplifies the advantages afforded by a whole-animal model system where interactions between tissues and organs, and functions such as nutrient absorption, distribution, and storage, as well as reproduction can all be studied simultaneously.

MLT-10 defines a family of DUF644 and proline-rich repeat proteins involved in the molting cycle of Caenorhabditis elegans

Molting of nematodes involves the synthesis and removal of a collagen-rich exoskeleton. We describe Caenorhabditis elegans MLT-10, which defines a large family of DUF644 and proline-rich repeat proteins. We show that MLT-10 is released from the epidermis during molting and that MLT-10 is involved in renewal of the exoskeleton and development of the epidermis.

The molting cycle of nematodes involves the periodic synthesis and removal of a collagen-rich exoskeleton, but the underlying molecular mechanisms are not well understood. Here, we describe the mlt-10 gene of Caenorhabditis elegans, which emerged from a genetic screen for molting-defective mutants sensitized by low cholesterol. MLT-10 defines a large family of nematode-specific proteins comprised of DUF644 and tandem P-X₂-L-(S/T)-P repeats. Conserved nuclear hormone receptors promote expression of the mlt-10 gene in the hypodermis whenever the exoskeleton is remade. Further, a MLT-10::mCherry fusion protein is released from the hypodermis to the surrounding matrices and fluids during molting. The fusion protein is also detected in strands near the surface of animals. Both loss-of-function and gain-of-function mutations of mlt-10 impede the removal of old cuticles. However, the substitution mutation mlt-10(mg364), which disrupts the proline-rich repeats, causes the most severe phenotype. Mutations of mlt-10 are also associated with abnormalities in the exoskeleton and improper development of the epidermis. Thus, mlt-10 encodes a secreted protein involved in three distinct but interconnected aspects of the molting cycle. We propose that the molting cycle of C. elegans involves the dynamic assembly and disassembly of MLT-10 and possibly the paralogs of MLT-10.

The endocrine regulation of aging in Caenorhabditis elegans

In recent years, there has been significant growth in our understanding of the regulation of longevity. The most notable change is the identification and detailed description of a number of molecular pathways modulating the rate of aging. A good portion of this new data has come from studies using the genetic model organism Caenorhabditis elegans. In this review, we provide an overview of physiological systems that are involved in the modulation of aging in C. elegans, then discuss the known endocrine signaling systems that are likely to couple these systems together. Finally, we present a working model describing how aging may be regulated as a coordinated system, communicating through endocrine signals.