Insulin/FOXO signaling regulates ovarian prostaglandins critical for reproduction

A germline-to-soma signal triggers an age-related decline of mitochondrial stress response

The abilities of an organism to cope with extrinsic stresses and activate cellular stress responses decline during aging. The signals that modulate stress responses in aged animals remain to be elucidated. Here, we discover that feeding Caenorhabditis elegans (C. elegans) embryo lysates to adult worms enabled the animals to activate the mitochondrial unfolded protein response (UPRmt) upon mitochondrial perturbations. This discovery led to subsequent investigations that unveil a hedgehog-like signal that is transmitted from the germline to the soma in adults to inhibit UPRmt in somatic tissues. Additionally, we find that the levels of germline-expressed piRNAs in adult animals markedly decreased. This reduction in piRNA levels coincides with the production and secretion of a hedgehog-like signal and suppression of the UPRmt in somatic cells. Building upon existing research, our study further elucidates the intricate mechanisms of germline-to-soma signaling and its role in modulating the trade-offs between reproduction and somatic maintenance within the context of organismal aging.

Forkhead box protein FOXK1 disrupts the circadian rhythm to promote breast tumorigenesis in response to insulin resistance

The dysregulation of circadian rhythm oscillation is a prominent feature of various solid tumors. Thus, clarifying the molecular mechanisms that maintain the circadian clock is important. In the present study, we revealed that the transcription factor forkhead box FOXK1 functions as an oncogene in breast cancer. We showed that FOXK1 recruits multiple transcription corepressor complexes, including NCoR/SMRT, SIN3A, NuRD, and REST/CoREST. Among them, the FOXK1/NCoR/SIN3A complex transcriptionally regulates a cohort of genes, including CLOCK, PER2, and CRY2, that are critically involved in the circadian rhythm. The complex promoted the proliferation of breast cancer cells by disturbing the circadian rhythm oscillation. Notably, the nuclear expression of FOXK1 was positively correlated with tumor grade. Insulin resistance gradually became more severe with tumor progression and was accompanied by the increased expression of OGT, which caused the nuclear translocation and increased expression of FOXK1. Additionally, we found that metformin downregulates FOXK1 and exports it from the nucleus, while HDAC inhibitors (HDACi) inhibit the FOXK1-related enzymatic activity. Combined treatment enhanced the expression of circadian clock genes through the regulation of FOXK1, thereby exerting an antitumor effect, indicating that highly nuclear FOXK1-expressing breast cancers are potential candidates for the combined application of metformin and HDACi.

Phenomenon of reproductive plasticity in ants

Ant colonies are organized in castes with distinct behaviors that together allow the colony to strive. Reproduction relies on one or a few queens that stay in the nest producing eggs, while females of the worker caste do not reproduce and instead engage in colony maintenance and brood caretaking. Yet, in spite of this clear separation of functions, workers can become reproductive under defined circumstances. Here, we review the context in which workers become reproductive, exhibiting asexual or sexual reproduction depending on the species. Remarkably, the activation of reproduction in these workers can be quite stable, with changes that include behavior and a dramatic extension of lifespan. We compare these changes between species that do or do not have a queen caste. We discuss how the mechanisms underlying reproductive plasticity include changes in hormonal functions and in epigenetic configurations. Further studies are warranted to elucidate not only how reproductive functions have been gradually restricted to the queen caste during evolution but also how reproductive plasticity remains possible in workers of some species.

A mutation in F-actin polymerization factor suppresses the distal arthrogryposis type 5 PIEZO2 pathogenic variant in Caenorhabditis elegans

The mechanosensitive PIEZO channel family has been linked to over 26 disorders and diseases. Although progress has been made in understanding these channels at the structural and functional levels, the underlying mechanisms of PIEZO-associated diseases remain elusive. In this study, we engineered four PIEZO-based disease models using CRISPR/Cas9 gene editing. We performed an unbiased chemical mutagen-based genetic suppressor screen to identify putative suppressors of a conserved gain-of-function variant pezo-1[R2405P] that in human PIEZO2 causes distal arthrogryposis type 5 (DA5; p. R2718P). Electrophysiological analyses indicate that pezo-1(R2405P) is a gain-of-function allele. Using genomic mapping and whole-genome sequencing approaches, we identified a candidate suppressor allele in the C. elegans gene gex-3. This gene is an ortholog of human NCKAP1 (NCK-associated protein 1), a subunit of the Wiskott-Aldrich syndrome protein (WASP)-verprolin homologous protein (WAVE/SCAR) complex, which regulates F-actin polymerization. Depletion of gex-3 by RNAi, or with the suppressor allele gex-3(av259[L353F]), significantly increased brood size and ovulation rate, as well as alleviating the crushed oocyte phenotype of the pezo-1(R2405P) mutant. Expression of GEX-3 in the soma is required to rescue the brood size defects in pezo-1(R2405P) animals. Actin organization and orientation were disrupted and distorted in the pezo-1 mutants. Mutation of gex-3(L353F) partially alleviated these defects. The identification of gex-3 as a suppressor of the pathogenic variant pezo-1(R2405P) suggests that the PIEZO coordinates with the cytoskeleton regulator to maintain the F-actin network and provides insight into the molecular mechanisms of DA5 and other PIEZO-associated diseases.

Transmembrane protein 120A (TMEM-120A/TACAN) coordinates with PIEZO channel during Caenorhabditis elegans reproductive regulation

Membrane protein TMEM120A (also known as TACAN) was presumed to be both a mechanically activated molecule and a lipid-modifying enzyme. TMEM120A has been identified as a negative regulator of the essential excitatory mechanosensitive protein PIEZO2. However, the extent to which TMEM120A mediates PIEZO2's activity during physiological processes remains largely unknown. In this study, we used the Caenorhabditis elegans reproductive tract to explore the functional contribution of tmem-120, the sole TMEM120A/B ortholog, and its genetic interaction with pezo-1 in vivo. tmem-120 was expressed throughout the C. elegans development, particularly in the germline, embryos, and spermatheca. A tmem-120 mutant with a full-length deletion (tmem-120Δ) displayed deformed germline, maternal sterility, and a reduced brood size. In vivo live imaging revealed that pinched zygotes were frequently observed in the uterus of tmem-120Δ mutant animals, suggesting damage during spermathecal contraction. We then employed the auxin-inducible degradation system to degrade TMEM-120 protein in all somatic tissues or the germline, both of which resulted in reduced brood sizes. These findings suggested that multiple inputs of tmem-120 from different tissues regulate reproduction. Lastly, the loss of tmem-120 alleviated the brood size reduction and defective sperm navigation behavior in the pezo-1Δ mutant. Overall, our findings reveal a role for tmem-120 in regulating reproductive physiology in C. elegans, and suggest an epistatic interaction between pezo-1 and tmem-120 when governing proper reproduction.

Comparative transcriptome analysis reveals key genes and pathways related to gonad development in the sea cucumber Apostichopus japonicus

The sea cucumber Apostichopus japonicus is an economically important marine species in China, and understanding the mechanisms underlying its gonad development is crucial for successful reproduction and breeding. In this study, we performed transcriptome comparisons and analyses of A. japonicus gonadal and non-gonadal tissues to identify genes and molecular pathways associated with gonadal development. We also supplemented the annotation of the A. japonicus genome. Collectively, results revealed a total of 941 ovary-specific genes and 2499 testis-specific genes through different expression analysis and WGCNA analysis. The most enriched pathways in ovary and testis were "DNA replication" and "purine metabolism", respectively. Additionally, we identified key candidate gene modules that control gonad development and germ cell maturation, with CDT1 and DYNC2LI1 serving as hub genes. Our findings provide important insights into the gonadal development system of A. japonicus and offer valuable references for further research on reproductive biology in this marine invertebrate species.

Mutation in F-actin Polymerization Factor Suppresses Distal Arthrogryposis Type 5 (DA5) PIEZO2 Pathogenic Variant in Caenorhabditis elegans

The mechanosensitive PIEZO channel family has been linked to over 26 disorders and diseases. Although progress has been made in understanding these channels at the structural and functional levels, the underlying mechanisms of PIEZO-associated diseases remain elusive. In this study, we engineered four PIEZO-based disease models using CRISPR/Cas9 gene editing. We performed an unbiased chemical mutagen-based genetic suppressor screen to identify putative suppressors of a conserved gain-of-function variant pezo-1[R2405P] that in human PIEZO2 causes distal arthrogryposis type 5 (DA5; p. R2718P). Electrophysiological analyses indicate that pezo-1(R2405P) is a gain-of-function allele. Using genomic mapping and whole genome sequencing approaches, we identified a candidate suppressor allele in the C. elegans gene gex-3. This gene is an ortholog of human NCKAP1 (NCK-associated protein 1), a subunit of the Wiskott-Aldrich syndrome protein (WASP)-verprolin homologous protein (WAVE/SCAR) complex, which regulates F-actin polymerization. Depletion of gex-3 by RNAi, or with the suppressor allele gex-3(av259[L353F]) , significantly restored the small brood size and low ovulation rate, as well as alleviated the crushed oocyte phenotype of the pezo-1(R2405P) mutant. Auxin-inducible degradation of GEX-3 revealed that only somatic-specific degradation of GEX-3 restored the reduced brood size in the pezo-1(R2405P) mutants. Additionally, actin organization and orientation were disrupted and distorted in the pezo-1 mutants. Mutation of gex-3(L353F) partially alleviated these defects. The identification of gex-3 as a suppressor of the pathogenic variant pezo-1(R2405P) suggests that the cytoskeleton plays an important role in regulating PIEZO channel activity and provides insight into the molecular mechanisms of DA5 and other PIEZO-associated diseases.

Comparative transcriptomic analysis reveals candidate genes for seasonal breeding in the male Lion-Head goose

1. Due to seasonal breeding, geese breeds from Southern China have low egg yield. The genetic makeup underlying performance of local breeds is largely unknown, and few studies have investigated this problem. This study integrated 21 newly generated and 50 publicly existing RNA-seq libraries, representing the hypothalamus, pituitary and testis, to identify candidate genes and importantly related pathways associated with seasonal breeding in male Lion-Head geese.2. In total, 19, 119 and 302 differentially expressed genes (DEGs) were detected in the hypothalamus, pituitary and testis, respectively, of male Lion-Head geese between non-breeding and breeding periods. These genes were significantly involved in the neuropeptide signalling pathway, gland development, neuroactive ligand-receptor interaction, JAK-STAT signalling pathway, cAMP signalling pathway, PI3K-Akt signalling pathway and Foxo signalling pathway.3. By integrating another 50 RNA-seq samples 4, 18 and 40 promising DEGs were confirmed in hypothalamus, pituitary and testis, respectively.4. HOX genes were identified as having important roles in the development of testis between non-breeding and breeding periods of male Lion-Head geese.

Prostaglandin F2α drives female pheromone signaling in cichlids, revealing a basis for evolutionary divergence in olfactory signaling

Pheromones play essential roles in reproduction in many species. Prostaglandin F_2α (PGF_2α) acts as a female reproductive hormone and as a sex pheromone in some species. An olfactory receptor (OR) for PGF_2α was recently discovered in zebrafish, but this signaling pathway is evolutionarily labile. To understand the evolution of signals that attract males to fertile females, we used the African cichlid Astatotilapia burtoni and found that adult males strongly prefer fertile female odors. Injection of a prostaglandin synthesis inhibitor abolishes this attractivity of fertile females, indicating these hormones are necessary for pheromonal signaling. Unlike zebrafish, A. burtoni males are insensitive to PGF_2α, but they do exhibit strong preference for females injected with PGF_2α. This attractiveness is independent of the PGF_2α hormonal receptor Ptgfr, indicating that this pheromone signaling derives from PGF_2α metabolization into a yet-undiscovered pheromone. We further discovered that fish that are insensitive to PGF_2α lack an ortholog for the OR Or114 that zebrafish use to detect PGF_2α. These results indicate that PGF_2α itself does not directly induce male preference in cichlids. Rather, it plays a vital role that primes females to become attractive via an alternative male OR.

The serotonin circuit that coordinates germline proliferation and egg laying with other reproductive functions in Caenorhabditis elegans

Behaviour and physiology are altered in reproducing animals, but neuronal circuits that regulate these changes remain largely unknown. Insights into mechanisms that regulate and possibly coordinate reproduction-related traits could be gleaned from the study of sex pheromones that can improve the reproductive success of potential mating partners. In Caenorhabditis elegans, the prominent male pheromone, ascr#10, modifies reproductive behaviour and several aspects of reproductive physiology in hermaphrodite recipients, including improving oocyte quality. Here we show that a circuit that contains serotonin-producing and serotonin-uptaking neurons plays a key role in mediating effects of ascr#10 on germline development and egg laying behaviour. We also demonstrate that increased serotonin signalling promotes proliferation of germline progenitors in adult hermaphrodites. Our results establish a role for serotonin in maintaining germline quality and highlight a simple neuronal circuit that acts as a linchpin that couples food intake, mating behaviour, reproductive output, and germline renewal and provisioning.

A Comparison of Prostaglandin Profile in Human Follicular Fluid Between White and Black/Hispanic Women

The aim of the study is to compare prostaglandin (PG) profiles in human follicular fluid between White and Black/Hispanic women using data from a previously published study. A retrospective cohort study of 5 White and 5 Black/Hispanic women who underwent oocyte retrieval was conducted. Human follicular fluid was obtained from the first follicle entered at time of oocyte retrieval for patients undergoing in vitro fertilization cycles (IVF). PG levels were compared using mass spectroscopy with known standards to quantify PG levels. Five White women were matched with 5 Black/Hispanic women with diagnosis. Both cohorts had similar levels of age, body mass index, and IVF cycle characteristics. There were no statistical differences in PG profiles (PGE2, PGF1α, PGF2α, or 8 iso-PGF1α). In this small repeat analysis of previously studied data, there were no differences noted in PG profiles in follicular fluid. Larger studies are needed to verify this finding. This study further demonstrates the lack of representation of minority patients in studies.

Sperm-Guiding Unconventional Prostaglandins in C. elegans: Synthesis and Signaling

Prostaglandins comprise a family of lipid signaling molecules derived from polyunsaturated fatty acids and are involved in a wide array of biological processes, including fertilization. Prostaglandin-endoperoxide synthase (a.k.a. cyclooxygenase or Cox) initiates prostaglandin synthesis from 20-carbon polyunsaturated fatty acids, such as arachidonic acid. Oocytes of Caenorhabditis elegans (C. elegans) have been shown to secrete sperm-guidance cues prostaglandins, independent of Cox enzymes. Both prostaglandin synthesis and signal transduction in C. elegans are environmentally modulated pathways that regulate sperm guidance to the fertilization site. Environmental factors such as food triggers insulin and TGF-β secretion and their levels regulate tissue-specific prostaglandin synthesis in C. elegans. This novel PG pathway is abundant in mouse and human ovarian follicular fluid, where their functions, mechanism of synthesis and pathways remain to be established. Given the importance of prostaglandins in reproductive processes, a better understanding of how diets and other environmental factors influence their synthesis and function may lead to new strategies towards improving fertility in mammals.

The brominated flame retardant, TBCO, impairs oocyte maturation in zebrafish (Danio rerio)

The brominated flame retardant, 1,2,5,6-tetrabromocyclooctane (TBCO), has been shown to decrease fecundity in Japanese medaka (Oryzias latipes) and there is indirect evidence from analysis of the transcriptome and proteome that this effect might be due to impaired oogenesis. An assay for disruption of oocyte maturation by chemical stressors has not been developed in Japanese medaka. Thus, using zebrafish (Danio rerio) as a model, objectives of the present study were to determine whether exposure to TBCO has effects on maturation of oocytes and to investigate potential mechanisms. Sexually mature female zebrafish were given a diet of 35.3 or 628.8 μg TBCO / g food for 14 days after which, stage IV oocytes were isolated to assess maturation in response to maturation inducing hormone. To explore potential molecular mechanisms, abundances of mRNAs of a suite of genes that regulate oocyte maturation were quantified by use of quantitative real-time PCR, and abundances of microRNAs were determined by use of miRNAseq. Ex vivo maturation of oocytes from fish exposed to TBCO was significantly less than maturation of oocytes from control fish. The percentage of oocytes which matured from control fish and those exposed to low and high TBCO were 89, 71, and 67%, respectively. Among the suite of genes known to regulate oocyte maturation, mRNA abundance of insulin like growth factor-3 was decreased by 1.64- and 3.44-fold in stage IV oocytes from females given the low and high concentrations of TBCO, respectively, compared to the control group. Abundances of microRNAs regulating the expression of proteins that regulate oocyte maturation, including processes related to insulin-like growth factor, were significantly different in stage IV oocytes from fish exposed to TBCO. Overall, results of this study indicated that impaired oocyte maturation might be a mechanism of reduced reproductive performance in TBCO-exposed fish. Results also suggested that effects of TBCO on oocyte maturation might be due to molecular perturbations on insulin-like growth factor signaling and expression of microRNAs.

Elucidating the Possible Role of FoxO in Depression

Forkhead box-O (FoxO) transcriptional factors perform essential functions in several physiological and biological processes. Recent studies have shown that FoxO is implicated in the pathophysiology of depression. Changes in the upstream mediators of FoxOs including brain-derived neurotrophic factor (BDNF) and protein kinase B have been associated with depressive disorder and the antidepressant agents are known to alter the phosphorylation of FoxOs. Moreover, FoxOs might be regulated by serotonin or noradrenaline signaling and the hypothalamic-pituitary-adrenal (HPA)-axis,both of them are associated with the development of the depressive disorder. FoxO also regulates neural morphology, synaptogenesis, and neurogenesis in the hippocampus, which accounts for the pathogenesis of the depressive disorder. The current article underlined the potential functions of FoxOs in the etiology of depressive disorder and formulate few essential proposals for further investigation. The review also proposes that FoxO and its signal pathway might establish possible therapeutic mediators for the management of depressive disorder.

Odorant and Taste Receptors in Sperm Chemotaxis and Cryopreservation: Roles and Implications in Sperm Capacitation, Motility and Fertility

Sperm chemotaxis, which guide sperm toward oocyte, is tightly associated with sperm capacitation, motility, and fertility. However, the molecular mechanism of sperm chemotaxis is not known. Reproductive odorant and taste receptors, belong to G-protein-coupled receptors (GPCR) super-family, cause an increase in intracellular Ca²⁺ concentration which is pre-requisite for sperm capacitation and acrosomal reaction, and result in sperm hyperpolarization and increase motility through activation of Ca²⁺-dependent Cl^¯ channels. Recently, odorant receptors (ORs) in olfactory transduction pathway were thought to be associated with post-thaw sperm motility, freeze tolerance or freezability and cryo-capacitation-like change during cryopreservation. Investigation of the roles of odorant and taste receptors (TRs) is important for our understanding of the freeze tolerance or freezability mechanism and improve the motility and fertility of post-thaw sperm. Here, we reviewed the roles, mode of action, impact of odorant and taste receptors on sperm chemotaxis and post-thaw sperm quality.

Mechanisms of TGFß in prostaglandin synthesis and sperm guidance in Caenorhabditis elegans

BACKGROUND

The transparent epidermis of Caenorhabditis elegans makes it an attractive model to study sperm motility and migration within an intact reproductive tract. C elegans synthesize specific F-series prostaglandins (PGFs) that are important for guiding sperm toward the spermatheca. These PGFs are synthesized from polyunsaturated fatty acid (PUFA) precursors, such as arachidonic acid (AA), via a novel pathway, independent of the classical cyclooxygenases (Cox) responsible for most PG synthesis. While the enzyme(s) responsible for PG synthesis has yet to be identified, the DAF-7 TGFß pathway has been implicated in modulating PG levels and sperm guidance.

RESULTS

We find that the reduced PGF levels in daf-1 type I receptor mutants are responsible for the sperm guidance defect. The lower level of PGs in daf-1 mutants is due in part to the inaccessibility of AA. Finally, lipid analysis and assessment of sperm guidance in daf-1;daf-3 double mutants suggest DAF-3 suppresses PG production and sperm accumulation at the spermatheca. Our data suggest that DAF-3 functions in the nervous system, and possibly the germline, to affect sperm guidance.

CONCLUSION

The C elegans TGFß pathway regulates many pathways to modulate PG metabolism and sperm guidance. These pathways likely function in the nervous system and possibly the germline.

The molecular tug of war between immunity and fertility: Emergence of conserved signaling pathways and regulatory mechanisms

Reproduction and immunity are energy intensive, intimately linked processes in most organisms. In women, pregnancy is associated with widespread immunological adaptations that alter immunity to many diseases, whereas, immune dysfunction has emerged as a major cause for infertility in both men and women. Deciphering the molecular bases of this dynamic association is inherently challenging in mammals. This relationship has been traditionally studied in fast-living, invertebrate species, often in the context of resource allocation between life history traits. More recently, these studies have advanced our understanding of the mechanistic underpinnings of the immunity-fertility dialogue. Here, we review the molecular connections between reproduction and immunity from the perspective of human pregnancy to mechanistic discoveries in laboratory organisms. We focus particularly on recent invertebrate studies identifying conserved signaling pathways and transcription factors that regulate resource allocation and shape the balance between reproductive status and immune health.

Ovarian Circular RNAs Associated with High and Low Fertility in Large White Sows during the Follicular and Luteal Phases of the Estrous Cycle

In this study, the ovarian tissues of Large White pigs were mined for novel circular RNAs (circRNAs), following which, their molecular characteristics and potential mechanisms for fertility regulation were examined. RNA sequencing was used for transcriptome analysis of ovarian follicles and corpora lutea in Large White sows with high (H) and low (L) fertility during the follicular (F) and luteal (L) phases of the estrous cycle. In total, 21,386 circRNA derived from 4535 host genes were identified. Differentially expressed circRNAs were detected in the LH vs. LL (1079) and in the FH vs. FL (1077) comparisons, and their host genes were enriched in steroid biosynthesis and forkhead box O (FOXO), thyroid hormone, cell cycle, and tumor growth factor (TGF)-beta signaling pathways. Protein–protein interaction networks were constructed on the basis of the host genes that were significantly enriched in pathways related to reproductive processes, with AKT3 and PP2CB serving as the hub genes in the networks of the LH vs. LL and FH vs. FL comparisons, respectively. The microRNA (miRNA) binding sites of the differentially expressed circRNAs were predicted, and 128 (LH vs. LL) and 113 (FH vs. FL) circRNA–miRNA pairs were identified. Finally, circRNA–miRNA negative regulatory networks were established on the basis of the gene expression profiles and bioinformatic analyses. In the current study, differentially expressed circRNAs were observed in ovarian tissues between the H and L fertility groups in both F and L phases of the estrous cycle, which suggested roles in pig fertility regulation. These findings provide new clues for elucidating fertility differences in pigs.

Synthesis and function of fatty acids and oxylipins, with a focus on Caenorhabditis elegans

Polyunsaturated fatty acids (PUFAs) exhibit a diverse range of important biological functions in most biological systems. These PUFAs can be oxygenated via enzymatic or free radical-mediated reactions to form bioactive oxygenated lipid mediators termed oxylipins. Eicosanoids are broad class of oxylipins that are transient and locally synthesized signalling molecules, including prostaglandins, leukotrienes, lipoxins and thromboxanes, which mediate various physiological responses, such as inflammation. In addition to arachidonic acid-derived eicosanoids, current developments in lipidomic methodologies have brought attention to vast number of oxylipins produced from other PUFAs, including omega-3. Although, the molecular mechanisms of how PUFAs and oxylipins contribute to majority of the fundamental biological processes are largely unclear, a model organism Caenorhabditis elegans remains a powerful model for exploring lipid metabolism and functions of PUFAs and oxylipins. For instance, the ability of C. elegans to modify fatty acid composition with dietary supplementation and genetic manipulation enables the dissection of the roles of omega-3 and omega-6 PUFAs in many biological processes that include aging, reproduction, and neurobiology. However, much remains to be elucidated concerning the roles of oxylipins, but thus far, C. elegans is well-known for the synthesis of vast set of cytochrome (CYP) eicosanoids. These CYP eicosanoids are extremely susceptible to changes in the relative bioavailability of the different PUFAs, thus providing a better insight into complex mechanisms connecting essential dietary fatty acids to various biological processes. Therefore, this review provides an overview of the synthesis and function of PUFAs and oxylipins in mammals. It also focusses on what is known regarding the production of PUFAs and oxylipins in C. elegans and their functions.

Vitellogenins - Yolk Gene Function and Regulation in Caenorhabditis elegans

Vitellogenins are a family of yolk proteins that are by far the most abundant among oviparous animals. In the model nematode Caenorhabditis elegans, the 6 vitellogenins are among the most highly expressed genes in the adult hermaphrodite intestine, which produces copious yolk to provision eggs. In this article we review what is known about the vitellogenin genes and proteins in C. elegans, in comparison with vitellogenins in other taxa. We argue that the primary purpose of abundant vitellogenesis in C. elegans is to support post-embryonic development and fertility, rather than embryogenesis, especially in harsh environments. Increasing vitellogenin provisioning underlies several post-embryonic phenotypic alterations associated with advancing maternal age, demonstrating that vitellogenins can act as an intergenerational signal mediating the influence of parental physiology on progeny. We also review what is known about vitellogenin regulation - how tissue-, sex- and stage-specificity of expression is achieved, how vitellogenins are regulated by major signaling pathways, how vitellogenin expression is affected by extra-intestinal tissues and how environmental experience affects vitellogenesis. Lastly, we speculate whether C. elegans vitellogenins may play other roles in worm physiology.

Signature profile of cyclooxygenase-independent F2 series prostaglandins in C. elegans and their role in sperm motility

We previously discovered that Caenorhabditis elegans synthesizes Cox-independent F-series prostaglandins (PGs). To delineate the Cox-independent prostaglandin pathways and evaluate their role in sperm motility in C. elegans, we developed a novel biochemical method for the rapid production of F-series PGs using arachidonic acid as the substrate and worm lysate as source of enzyme(s). Among the four F2-series PGs produced in the reaction, three of them were identified as 8-isoPGF2α, 5iPF2 VI, and PGF2α based on their retention times and MS/MS spectral comparison with standards using LC-MS/MS. PG production was not markedly affected by specific antioxidants, or Cox, Lox, and Cyp inhibitors, suggesting that these PGs are formed through a novel, biologically regulated mechanism in C. elegans. This study also assessed the ability of 8-isoPGF2α, 5iPF2 VI, PGF2α, and a mixture containing these PGs in a 0.5/0.08/1 ratio that reflects their synthetic composition to modulate sperm motility in fat-2 mutants. PGF2α and the PG mixture at 25 μM concentration significantly stimulated sperm velocity by 28% and 38%, whereas 8-isoPGF2α and 5iPF2 VI reduced the velocity by 21% and 30%, respectively, compared to vehicle control. These results indicate that the sperm motility effects of PGs are structure- and composition-dependent in C. elegans.

Measuring Sperm Guidance and Motility within the Caenorhabditis elegans Hermaphrodite Reproductive Tract

Successful fertilization is fundamental to sexual reproduction, yet little is known about the mechanisms that guide sperm to oocytes within the female reproductive tract. While in vitro studies suggest that sperm of internally fertilizing animals can respond to various cues from their surroundings, the inability to visualize their behavior inside the female reproductive tract creates a challenge for understanding sperm migration and mobility in its native environment. Here, we describe a method using C. elegans that overcomes this limitation and takes advantage of their transparent epidermis. C. elegans males stained with a mitochondrial  dye are mated with adult hermaphrodites, which act as modified females, and deposit fluorescently labeled sperm into the hermaphrodite uterus. The migration and motility of the labeled sperm can then be directly tracked using an epi-fluorescence microscope in a live hermaphrodite. In wild-type animals, approximately 90% of the labeled sperm crawl through the uterus and reach the fertilization site, or spermatheca. Images of the uterus can be taken 1 h after mating to assess the distribution of the sperm within the uterus and the percentage of sperm that have reached the spermatheca. Alternatively, time-lapse images can be taken immediately after mating to assess sperm speed, directional velocity and reversal frequency. This method can be combined with other genetic and molecular tools available for the C.elegans to identify novel genetic and molecular mechanisms that are important in regulating sperm guidance and motility within the female reproductive tract.

The Nematode Caenorhabditis elegans as a Model Organism to Study Metabolic Effects of ω-3 Polyunsaturated Fatty Acids in Obesity

Obesity is a complex disease that is influenced by several factors, such as diet, physical activity, developmental stage, age, genes, and their interactions with the environment. Obesity develops as a result of expansion of fat mass when the intake of energy, stored as triglycerides, exceeds its expenditure. Approximately 40% of the US population suffers from obesity, which represents a worldwide public health problem associated with chronic low-grade adipose tissue and systemic inflammation (sterile inflammation), in part due to adipose tissue expansion. In patients with obesity, energy homeostasis is further impaired by inflammation, oxidative stress, dyslipidemia, and metabolic syndrome. These pathologic conditions increase the risk of developing other chronic diseases including diabetes, hypertension, coronary artery disease, and certain forms of cancer. It is well documented that several bioactive compounds such as omega-3 polyunsaturated fatty acids (ω-3 PUFAs) are able to reduce adipose and systemic inflammation and blood triglycerides and, in some cases, improve glucose intolerance and insulin resistance in vertebrate animal models of obesity. A promising model organism that is gaining tremendous interest for studies of lipid and energy metabolism is the nematode Caenorhabditis elegans. This roundworm stores fats as droplets within its hypodermal and intestinal cells. The nematode's transparent skin enables fat droplet visualization and quantification with the use of dyes that have affinity to lipids. This article provides a review of major research over the past several years on the use of C. elegans to study the effects of ω-3 PUFAs on lipid metabolism and energy homeostasis relative to metabolic diseases.

Genetic Contributions to Ectopic Sperm Cell Migration in Caenorhabditis Nematodes

Reproductive barriers involving gametic incompatibilities can act to enhance population divergence and promote the persistence of species boundaries. Observing gametic interactions in internal fertilizing organisms, however, presents a considerable practical challenge to characterizing mechanisms of such gametic isolation. Here we exploit the transparency of Caenorhabditis nematodes to investigate gametic isolation mediated by sperm that can migrate to ectopic locations, with this sperm invasion capable of inducing female sterility and premature death. As a step toward identifying genetic factors and mechanisms associated with female susceptibility to sperm invasion, we characterized a panel of 25 C. elegans genetic mutants to test for effects on the incidence and severity of sperm invasion in both conspecific and inter-species matings. We found genetic perturbations to contribute to distinct patterns of susceptibility that identify ovulation dynamics and sperm guidance cues as modulators of ectopic sperm migration incidence and severity. Genotypes confer distinctive phenotypic sensitivities to the sperm from conspecific C. elegans males vs. heterospecific C. nigoni males, implicating evolution of functional divergence in the history of these species for components of sperm-reproductive tract interactions. Sexually-antagonistic co-evolution within species that drives divergent trait and molecular evolution between species provides a working model to explain mismatched species-specific gametic interactions that promote or mitigate ectopic sperm migration.

Evidence of evolutionary history and selective sweeps in the genome of Meishan pig reveals its genetic and phenotypic characterization

Background

Meishan is a pig breed indigenous to China and famous for its high fecundity. The traits of Meishan are strongly associated with its distinct evolutionary history and domestication. However, the genomic evidence linking the domestication of Meishan pigs with its unique features is still poorly understood. The goal of this study is to investigate the genomic signatures and evolutionary evidence related to the phenotypic traits of Meishan via large-scale sequencing.

Results

We found that the unique domestication of Meishan pigs occurred in the Taihu Basin area between the Majiabang and Liangzhu Cultures, during which 300 protein-coding genes have underwent positive selection. Notably, enrichment of the FoxO signaling pathway with significant enrichment signal and the harbored gene IGF1R were likely associated with the high fertility of Meishan pigs. Moreover, NFKB1 exhibited strong selective sweep signals and positively participated in hyaluronan biosynthesis as the key gene of NF-kB signaling, which may have resulted in the wrinkled skin and face of Meishan pigs. Particularly, three population-specific synonymous single-nucleotide variants occurred in PYROXD1, MC1R, and FAM83G genes; the T305C substitution in the MCIR gene explained the black coat of the Meishan pigs well. In addition, the shared haplotypes between Meishan and Duroc breeds confirmed the previous Asian-derived introgression and demonstrated the specific contribution of Meishan pigs.

Conclusions

These findings will help us explain the unique genetic and phenotypic characteristics of Meishan pigs and offer a plausible method for their utilization of Meishan pigs as valuable genetic resources in pig breeding and as an animal model for human wrinkled skin disease research.

CDK-11-Cyclin L is required for gametogenesis and fertility in C. elegans

CDK11, a member of the cyclin-dependent kinase family, has been implicated in a diverse array of functions including transcription, RNA processing, sister chromatid cohesion, spindle assembly, centriole duplication and apoptosis. Despite its involvement in many essential functions, little is known about the requirements for CDK11 and its partner Cyclin L in a developing multicellular organism. Here we investigate the function of CDK11 and Cyclin L during development of the nematode Caenorhabditis elegans. Worms express two CDK11 proteins encoded by distinct loci: CDK-11.1 is essential for normal male and female fertility and is broadly expressed in the nuclei of somatic and germ line cells, while CDK-11.2 is nonessential and is enriched in hermaphrodite germ line nuclei beginning in mid pachytene. Hermaphrodites lacking CDK-11.1 develop normally but possess fewer mature sperm and oocytes and do not fully activate the RAS-ERK pathway that is required for oocyte production in response to environmental cues. Most of the sperm and eggs that are produced in cdk-11.1 null animals appear to complete development normally but fail to engage in sperm-oocyte signaling suggesting that CDK-11.1 is needed at multiple points in gametogenesis. Finally, we find that CDK-11.1 and CDK-11.2 function redundantly during embryonic and postembryonic development and likely do so in association with Cyclin L. Our results thus define multiple requirements for CDK-11-Cyclin L during animal development.

Comprehensive profiling of prostaglandins in human ovarian follicular fluid using mass spectrometry

Prostaglandins are formed by enzymatic and non-enzymatic mechanisms. They have been detected in human ovarian follicular fluid (HFF), a medium rich in growth factors and nutrients important for oocyte growth and fertility. However, the comprehensive identification of HFF prostaglandins has not been addressed. Here we use hybrid triple quadrupole time-of-flight and triple quadrupole mass spectrometers to comprehensively analyze prostaglandins in HFF. We identified PGE1, PGE2, PGF2α, and other prostaglandins synthesized via prostaglandin-endoperoxide synthase (i.e. Cox) cascades. We also identified specific PGF2α isomers (F2-isoprostanes) and PGF3α analogs whose structures are inconsistent with Cox-dependent formation. A prospective cohort pilot study of infertility patient subtypes revealed two potential associations. F2-isoprostanes are decreased in the diminished ovarian reserve subtype and elevated PGF2α may be associated with decreased live birth. Other than PGF2α, only body mass index >25kg/m2 correlated with poor in vitro fertilization outcome. Our studies suggest that HFF contains prostaglandins formed from at least two mechanisms, which may correlate with distinct clinical parameters.

Integration of lncRNA-miRNA-mRNA reveals novel insights into oviposition regulation in honey bees

BACKGROUND

The honey bee (Apis mellifera) is a highly diverse species commonly used for honey production and pollination services. The oviposition of the honey bee queen affects the development and overall performance of the colony. To investigate the ovary activation and oviposition processes on a molecular level, a genome-wide analysis of lncRNAs, miRNAs and mRNA expression in the ovaries of the queens was performed to screen for differentially expressed coding and noncoding RNAs. Further analysis identified relevant candidate genes or RNAs.

RESULTS

The analysis of the RNA profiles in different oviposition phase of the queens revealed that 740 lncRNAs, 81 miRNAs and 5,481 mRNAs were differently expressed during the ovary activation; 88 lncRNAs, 13 miRNAs and 338 mRNAs were differently expressed during the oviposition inhibition process; and finally, 100 lncRNAs, four miRNAs and 497 mRNAs were differently expressed during the oviposition recovery process. In addition, functional annotation of differentially expressed RNAs revealed several pathways that are closely related to oviposition, including hippo, MAPK, notch, Wnt, mTOR, TGF-beta and FoxO signaling pathways. Furthermore, in the QTL region for ovary size, 73 differentially expressed genes and 14 differentially expressed lncRNAs were located, which are considered as candidate genes affecting ovary size and oviposition. Moreover, a core set of genes served as bridges among different miRNAs were identified through the integrated analysis of lncRNA-miRNA-mRNA network.

CONCLUSION

The observed dramatic expression changes of coding and noncoding RNAs suggest that they may play a critical role in honey bee queens' oviposition. The identified candidate genes for oviposition activation and regulation could serve as a resource for further studies of genetic markers of oviposition in honey bees.

The secreted MSP domain of C. elegans VAPB homolog VPR-1 patterns the adult striated muscle mitochondrial reticulum via SMN-1

The major sperm protein domain (MSPd) has an extracellular signaling function implicated in amyotrophic lateral sclerosis. Secreted MSPds derived from the C. elegans VAPB homolog VPR-1 promote mitochondrial localization to actin-rich I-bands in body wall muscle. Here we show that the nervous system and germ line are key MSPd secretion tissues. MSPd signals are transduced through the CLR-1 Lar-like tyrosine phosphatase receptor. We show that CLR-1 is expressed throughout the muscle plasma membrane, where it is accessible to MSPd within the pseudocoelomic fluid. MSPd signaling is sufficient to remodel the muscle mitochondrial reticulum during adulthood. An RNAi suppressor screen identified survival of motor neuron 1 (SMN-1) as a downstream effector. SMN-1 acts in muscle, where it colocalizes at myofilaments with ARX-2, a component of the Arp2/3 actin-nucleation complex. Genetic studies suggest that SMN-1 promotes Arp2/3 activity important for localizing mitochondria to I-bands. Our results support the model that VAPB homologs are circulating hormones that pattern the striated muscle mitochondrial reticulum. This function is crucial in adults and requires SMN-1 in muscle, likely independent of its role in pre-mRNA splicing.

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

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

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

Chemosensory and hyperoxia circuits in C. elegans males influence sperm navigational capacity

The sperm’s crucial function is to locate and fuse with a mature oocyte. Under laboratory conditions, Caenorhabditis elegans sperm are very efficient at navigating the hermaphrodite reproductive tract and locating oocytes. Here, we identify chemosensory and oxygen-sensing circuits that affect the sperm’s navigational capacity. Multiple Serpentine Receptor B (SRB) chemosensory receptors regulate Gα pathways in gustatory sensory neurons that extend cilia through the male nose. SRB signaling is necessary and sufficient in these sensory neurons to influence sperm motility parameters. The neuropeptide Y pathway acts together with SRB-13 to antagonize negative effects of the GCY-35 hyperoxia sensor on spermatogenesis. SRB chemoreceptors are not essential for sperm navigation under low oxygen conditions that C. elegans prefers. In ambient oxygen environments, SRB-13 signaling impacts gene expression during spermatogenesis and the sperm’s mitochondria, thereby increasing migration velocity and inhibiting reversals within the hermaphrodite uterus. The SRB-13 transcriptome is highly enriched in genes implicated in pathogen defense, many of which are expressed in diverse tissues. We show that the critical time period for SRB-13 signaling is prior to spermatocyte differentiation. Our results support the model that young C. elegans males sense external environment and oxygen tension, triggering long-lasting downstream signaling events with effects on the sperm’s mitochondria and navigational capacity. Environmental exposures early in male life may alter sperm function and fertility.

Habitat loss, disease, climate change, and pollution are thought to negatively affect animal fertility. Sperm are a potential target, but the molecular mechanisms are not understood. The nematode C. elegans is a powerful genetic model to investigate the relationship between environment and male fertility. The hermaphrodite’s transparent epidermis permits the direct visualization of migrating male sperm and fertilization. In this study, we identified multiple serpentine receptor B (SRB) chemosensory receptors that are expressed in amphid sensory neurons, which extend cilia through the male nose. These SRB chemoreceptors are necessary to produce sperm that are efficient at navigating the hermaphrodite reproductive tract to the fertilization site. We show that SRB-13 signaling counteracts the negative effect of GCY-35 O₂ sensor activity, thereby maintaining sperm mitochondrial function and navigational capacity in hyperoxic conditions. Of particular interest, SRB-13 acts in early larval stage males prior to testis maturation. We propose that young males respond to specific stressful environments by altering SRB neural circuits, which in turn impact sperm mitochondrial function and motility. This chemosensory mechanism may be part of a systemic response in C. elegans males to external environment and oxygen levels.

Sequestration of polyunsaturated fatty acids in membrane phospholipids of Caenorhabditis elegans dauer larva attenuates eicosanoid biosynthesis for prolonged survival

Mechanistic basis governing the extreme longevity and developmental quiescence of dauer juvenile, a "non-ageing" developmental variant of Caenorhabditis elegans, has remained largely obscure. Using a lipidomic approach comprising multiple reaction monitoring transitions specific to distinct fatty acyl moieties, we demonstrated that in comparison to other developmental stages, the membrane phospholipids of dauer larva contain a unique enrichment of polyunsaturated fatty acids (PUFAs). Esterified PUFAs in phospholipids exhibited temporal accumulation throughout the course of dauer endurance, followed by sharp reductions prior to termination of diapause. Reductions in esterified PUFAs were accompanied by concomitant increases in unbound PUFAs, as well as their corresponding downstream oxidized derivatives (i.e. eicosanoids). Global phospholipidomics has unveiled that PUFA sequestration in membrane phospholipids denotes an essential aspect of dauer dormancy, principally via suppression of eicosanoid production; and a failure to upkeep membrane lipid homeostasis is associated with termination of dauer endurance.

Sperm Navigation Mechanisms in the Female Reproductive Tract

Fertilization, the union of an oocyte and a sperm, is a fundamental process that restores the diploid genome and initiates embryonic development. For the sperm, fertilization is the end of a long journey, one that starts in the male testis before transitioning to the female reproductive tract's convoluted tubule architecture. Historically, motile sperm were thought to complete this journey using luck and numbers. A different picture of sperm has emerged recently as cells that integrate complex sensory information for navigation. Chemical, physical, and thermal cues have been proposed to help guide sperm to the waiting oocyte. Molecular mechanisms are being delineated in animal models and humans, revealing common features, as well as important differences. Exposure to pheromones and nutritional signals can modulate guidance mechanisms, indirectly impacting sperm motility performance and fertility. These studies highlight the importance of sensory information and signal transduction in fertilization.

Post-translational modifications of FOXO family proteins (Review)

The Forkhead box O (FOXO) protein family is predominantly involved in apoptosis, oxidative stress, DNA damage/repair, tumor angiogenesis, glycometabolism, regulating life span and other important biological processes. Its activity is affected by a variety of posttranslational modifications (PTMs), including phosphorylation, acetylation, ubiquitination, methylation and glycosylation. When cells are subjected to different environments, the corresponding PTMs act on the FOXO protein family, to change transcriptional activity or subcellular localization, and the expression of downstream target genes, will ultimately affect the biological behavior of the cells. In this review, we will discuss the biological characteristics of FOXO protein PTMs.

Specific polyunsaturated fatty acids modulate lipid delivery and oocyte development in C. elegans revealed by molecular-selective label-free imaging

Polyunsaturated fatty acids (PUFAs) exhibit critical functions in biological systems and their importance during animal oocyte maturation has been increasingly recognized. However, the detailed mechanism of lipid transportation for oocyte development remains largely unknown. In this study, the transportation of yolk lipoprotein (lipid carrier) and the rate of lipid delivery into oocytes in live C. elegans were examined for the first time by using coherent anti-Stokes Raman scattering (CARS) microscopy. The accumulation of secreted yolk lipoprotein in the pseudocoelom of live C. elegans can be detected by CARS microscopy at both protein (~1665 cm⁻¹) and lipid (~2845 cm⁻¹) Raman bands. In addition, an image analysis protocol was established to quantitatively measure the levels of secreted yolk lipoprotein aberrantly accumulated in PUFA-deficient fat mutants (fat-1, fat-2, fat-3, fat-4) and PUFA-supplemented fat-2 worms (the PUFA add-back experiments). Our results revealed that the omega-6 PUFAs, not omega-3 PUFAs, play a critical role in modulating lipid/yolk level in the oocytes and regulating reproductive efficiency of C. elegans. This work demonstrates the value of using CARS microscopy as a molecular-selective label-free imaging technique for the study of PUFA regulation and oocyte development in C. elegans.

Current advances in the functional studies of fatty acids and fatty acid-derived lipids in C. elegans

Fatty acids and fatty acid-derived lipids (FAs/FADLs) play essential roles in many living organisms, including contributions to membrane structure and signaling transduction. Aberrant metabolism of FAs/FADLs often causes diseases and health problems. However, the detailed mechanistic studies of specific FAs/FADLs in vivo are limited. C. elegans has been an effective model system for FA/ FADL studies due to its powerful genetics and conserved lipid biosynthetic pathways. The recently developed high-throughput analytic tools also enable sophisticated profiling of lipids molecules in C. elegans, which is critical for understanding their specific functions. Here we review a subset of current advances in FA/FADL functional studies in C. elegans.

Reversible reprotoxic effects of manganese through DAF-16 transcription factor activation and vitellogenin downregulation in Caenorhabditis elegans

AIMS

Vitellogenesis is the yolk production process which provides the essential nutrients for the developing embryos. Yolk is a lipoprotein particle that presents lipids and lipid-binding proteins, referred to as vitellogenins (VIT). The Caenorhabditis elegans nematode has six genes encoding VIT lipoproteins. Several pathways are known to regulate vitellogenesis, including the DAF-16 transcription factor. Some reports have shown that heavy metals, such as manganese (Mn), impair brood size in C. elegans; however the mechanisms associated with this effect have yet to be identified. Our aim was to evaluate Mn's effects on C. elegans reproduction and better understand the pathways related to these effects.

MAIN METHODS

Young adult larval stage worms were treated for 4h with Mn in 85mM NaCl and Escherichia coli OP50 medium.

KEY FINDINGS

Mn reduced egg-production and egg-laying during the first 24h after the treatment, although the total number of progenies were indistinguishable from the control group levels. This delay may have occurred due to DAF-16 activation, which was noted only after the treatment and was not apparent 24h later. Moreover, the expression, protein levels and green fluorescent protein (GFP) fluorescence associated with VIT were decreased soon after Mn treatment and recovered after 24h.

SIGNIFICANCE

Combined, these data suggest that the delay in egg-production is likely regulated by DAF-16 and followed by the inhibition of VIT transport activity. Further studies are needed to clarify the mechanisms associated with Mn-induced DAF-16 activation.

Using Caenorhabditis elegans to Uncover Conserved Functions of Omega-3 and Omega-6 Fatty Acids

The nematode Caenorhabditis elegans is a powerful model organism to study functions of polyunsaturated fatty acids. The ability to alter fatty acid composition with genetic manipulation and dietary supplementation permits the dissection of the roles of omega-3 and omega-6 fatty acids in many biological process including reproduction, aging and neurobiology. Studies in C. elegans to date have mostly identified overlapping functions of 20-carbon omega-6 and omega-3 fatty acids in reproduction and in neurons, however, specific roles for either omega-3 or omega-6 fatty acids are beginning to emerge. Recent findings with importance to human health include the identification of a conserved Cox-independent prostaglandin synthesis pathway, critical functions for cytochrome P450 derivatives of polyunsaturated fatty acids, the requirements for omega-6 and omega-3 fatty acids in sensory neurons, and the importance of fatty acid desaturation for long lifespan. Furthermore, the ability of C. elegans to interconvert omega-6 to omega-3 fatty acids using the FAT-1 omega-3 desaturase has been exploited in mammalian studies and biotechnology approaches to generate mammals capable of exogenous generation of omega-3 fatty acids.

Sex Pheromones of C. elegans Males Prime the Female Reproductive System and Ameliorate the Effects of Heat Stress

Pheromones are secreted molecules that mediate animal communications. These olfactory signals can have substantial effects on physiology and likely play important roles in organismal survival in natural habitats. Here we show that a blend of two ascaroside pheromones produced by C. elegans males primes the female reproductive system in part by improving sperm guidance toward oocytes. Worms have different physiological responses to different ratios of the same two molecules, revealing an efficient mechanism for increasing coding potential of a limited repertoire of molecular signals. The endogenous function of the male sex pheromones has an important side benefit. It substantially ameliorates the detrimental effects of prolonged heat stress on hermaphrodite reproduction because it increases the effectiveness with which surviving gametes are used following stress. Hermaphroditic species are expected to lose female-specific traits in the course of evolution. Our results suggest that some of these traits could have serendipitous utility due to their ability to counter the effects of stress. We propose that this is a general mechanism by which some mating-related functions could be retained in hermaphroditic species, despite their expected decay.

The Caenorhabditis elegans metabolome contains over a hundred ascaroside molecules. Most of them have no known function, or no function at all, but some act as pheromones. Two of these molecules, ascr#10 and ascr#3, are produced in different proportions by males and hermaphrodites. We report that when a hermaphrodite senses a male-specific mixture of these molecules, it changes several aspects of its reproductive physiology, including signaling that guides sperm toward oocytes. During evolution from an ancestor that had both males and females, C. elegans hermaphrodites lost several female-specific traits, but their reproductive system retained the ability to respond to male pheromones. This greatly aids them during recovery from heat stress. We suggest that serendipitous side benefits of female-specific traits could be a general cause of their retention during evolution.

Comparative Lipidomics of Caenorhabditis elegans Metabolic Disease Models by SWATH Non-Targeted Tandem Mass Spectrometry

Tandem mass spectrometry (MS/MS) with Sequential Window Acquisition of all Theoretical (SWATH) mass spectra generates a comprehensive archive of lipid species within an extract for retrospective, quantitative MS/MS analysis. Here we apply this new technology in Caenorhabditis elegans (C. elegans) to identify potential lipid mediators and pathways. The DAF-1 type I TGF-β and DAF-2 insulin receptors transmit endocrine signals that couple metabolic status to fertility and lifespan. Mutations in daf-1 and daf-2 reduce prostaglandin-endoperoxide synthase (i.e., Cox)-independent prostaglandin synthesis, increase triacylglyceride storage, and alter transcription of numerous lipid metabolism genes. However, the extent to which DAF-1 and DAF-2 signaling modulate lipid metabolism and the underlying mechanisms are not well understood. MS/MS^ALL with SWATH analysis across the groups identified significant changes in numerous lipids, including specific triacylglycerols, diacylglycerols, and phosphatidylinositols. Examples are provided, using retrospective neutral loss and precursor ion scans as well as MS/MS spectra, to help identify annotated lipids and search libraries for lipids of interest. As proof of principle, we used comparative lipidomics to investigate the prostaglandin metabolism pathway. SWATH data support an unanticipated model: Cox-independent prostaglandin synthesis may involve lysophosphatidylcholine and other lyso glycerophospholipids. This study showcases the power of comprehensive, retrospectively searchable lipid archives as a systems approach for biological discovery in genetic animal models.

Epoxides Derived from Dietary Dihomo-Gamma-Linolenic Acid Induce Germ Cell Death in C. elegans

Dietary fats are not created equally, slight differences in structure lead to crucial differences in function. Muticellular organisms use polyunsaturated fatty acid as substrates to produce potent signaling molecules crucial for many physiological processes, including reproduction. Here we explored the mechanism responsible for germ cell loss induced by dietary supplementation of dihomo-gamma-linolenic acid (DGLA, 20:3n-6) in the roundworm Caenorhabditis elegans. In this study we found that C. elegans CYP-33E2 activity produces a range of epoxy and hydroxy metabolites from dietary DGLA. Knockdown of cyp-33E2 suppressed the DGLA-induced sterility phenotype. Additionally, direct exposure of two specific DGLA-derived epoxy products, 8,9- and 14,15-epoxyeicosadienoic acids, produced germ cell abnormalities in the C. elegans gonad. We propose that sterility is mediated by the production of toxic DGLA-derived epoxides that trigger germ cell destruction. These studies are the first to establish a biological activity for a CYP-produced metabolite of DGLA.

Neural Regulatory Pathways of Feeding and Fat in Caenorhabditis elegans

The compact nervous system of Caenorhabditis elegans and its genetic tractability are features that make this organism highly suitable for investigating energy balance in an animal system. Here, we focus on molecular components and organizational principles emerging from the investigation of pathways that largely originate in the nervous system and regulate feeding behavior but also peripheral fat regulation through neuroendocrine signaling. We provide an overview of studies aimed at understanding how C. elegans integrate internal and external cues in feeding behavior. We highlight some of the similarities and differences in energy balance between C. elegans and mammals. We also provide our perspective on unresolved issues, both conceptual and technical, that we believe have hampered critical evaluation of findings relevant to fat regulation in C. elegans.

COMP-1 promotes competitive advantage of nematode sperm

Competition among sperm to fertilize oocytes is a ubiquitous feature of sexual reproduction as well as a profoundly important aspect of sexual selection. However, little is known about the cellular mechanisms sperm use to gain competitive advantage or how these mechanisms are regulated genetically. In this study, we utilize a forward genetic screen in Caenorhabditis elegans to identify a gene, comp-1, whose function is specifically required in competitive contexts. We show that comp-1 functions in sperm to modulate their migration through and localization within the reproductive tract, thereby promoting their access to oocytes. Contrary to previously described models, comp-1 mutant sperm show no defects in size or velocity, thereby defining a novel pathway for preferential usage. Our results indicate not only that sperm functional traits can influence the outcome of sperm competition, but also that these traits can be modulated in a context-dependent manner depending on the presence of competing sperm.

Drosophila spermatid individualization is sensitive to temperature and fatty acid metabolism

Fatty acids are precursors of potent lipid signaling molecules. They are stored in membrane phospholipids and released by phospholipase A₂ (PLA₂). Lysophospholipid acyltransferases (ATs) oppose PLA₂ by re-esterifying fatty acids into phospholipids, in a biochemical pathway known as the Lands Cycle. Drosophila Lands Cycle ATs oys and nes, as well as 7 predicted PLA₂ genes, are expressed in the male reproductive tract. Oys and Nes are required for spermatid individualization. Individualization, which occurs after terminal differentiation, invests each spermatid in its own plasma membrane and removes the bulk of the cytoplasmic contents. We developed a quantitative assay to measure individualization defects. We demonstrate that individualization is sensitive to temperature and age but not to diet. Mutation of the cyclooxygenase Pxt, which metabolizes fatty acids to prostaglandins, also leads to individualization defects. In contrast, modulating phospholipid levels by mutation of the phosphatidylcholine lipase Swiss cheese (Sws) or the ethanolamine kinase Easily shocked (Eas) does not perturb individualization, nor does Sws overexpression. Our results suggest that fatty acid derived signals such as prostaglandins, whose abundance is regulated by the Lands Cycle, are important regulators of spermatogenesis.

Insights and challenges in using C. elegans for investigation of fat metabolism

C. elegans provides a genetically tractable system for deciphering the homeostatic mechanisms that underlie fat regulation in intact organisms. Here, we provide an overview of the recent advances in the C. elegans fat field with particular attention to studies of C. elegans lipid droplets, the complex links between lipases, autophagy, and lifespan, and analyses of key transcriptional regulatory mechanisms that coordinate lipid homeostasis. These studies demonstrate the ancient origins of mammalian and C. elegans fat regulatory pathways and highlight how C. elegans is being used to identify and analyze novel lipid pathways that are then shown to function similarly in mammals. Despite its many advantages, study of fat regulation in C. elegans is currently faced with a number of conceptual and methodological challenges. We critically evaluate some of the assumptions in the field and highlight issues that we believe should be taken into consideration when interpreting lipid content data in C. elegans.

Exploring developmental and physiological functions of fatty acid and lipid variants through worm and fly genetics

Lipids are more than biomolecules for energy storage and membrane structure. With ample structural variation, lipids critically participate in nearly all aspects of cellular function. Lipid homeostasis and metabolism are closely related to major human diseases and health problems. However, lipid functional studies have been significantly underdeveloped, partly because of the difficulty in applying genetics and common molecular approaches to tackle the complexity associated with lipid biosynthesis, metabolism, and function. In the past decade, a number of laboratories began to analyze the roles of lipid metabolism in development and other physiological functions using animal models and combining genetics, genomics, and biochemical approaches. These pioneering efforts have not only provided valuable insights regarding lipid functions in vivo but have also established feasible methodology for future studies. Here, we review a subset of these studies using Caenorhabditis elegans and Drosophila melanogaster.

Intense sperm-mediated sexual conflict promotes reproductive isolation in Caenorhabditis nematodes

Sperm from other species invade female tissues to cause sterility and death, helping to keep nematode species boundaries intact.

Conflict between the sexes over reproductive interests can drive rapid evolution of reproductive traits and promote speciation. Here we show that inter-species mating between Caenorhabditis nematodes sterilizes maternal individuals. The principal effectors of male-induced harm are sperm cells, which induce sterility and shorten lifespan by displacing conspecific sperm, invading the ovary, and sometimes breaching the gonad to infiltrate other tissues. This sperm-mediated harm is pervasive across species, but idiosyncrasies in its magnitude implicate both independent histories of sexually antagonistic coevolution within species and differences in reproductive mode (self-fertilizing hermaphrodites versus females) in determining its severity. Consistent with this conclusion, in androdioecious species the hermaphrodites are more vulnerable, the males more benign, or both. Patterns of assortative mating and a low incidence of invasive sperm occurring with conspecific mating are indicative of ongoing intra-specific sexual conflict that results in inter-species reproductive incompatibility.

The sexes have divergent reproductive interests, and conflict arising from this disparity can drive the rapid evolution of reproductive traits and promote speciation. Here we describe a unique reproductive barrier in Caenorhabditis nematodes that is induced by sperm. We found that mating between species can sterilize maternal worms and even cause premature death, and we were able to attribute this phenomenon directly to the sperm themselves. Sperm from other species can displace sperm from the same species and, in some cases, can invade inappropriate parts of the maternal reproductive system and even their non-reproductive tissues. We find that mating to males of another species harms females far more than does within-species mating. Overall, our observations are consistent with ongoing sexual conflict between the sexes within species, arising as a byproduct of sperm competition among the gametes of different males. Finally, patterns of assortative mating indicate that mating behaviours that reduce the likelihood of costly inter-species mating have evolved in this group of animals. These findings support an important role of sexual selection and gametic interactions contributing to reproductive boundaries between species, as predicted by evolutionary theory.

Neurosensory perception of environmental cues modulates sperm motility critical for fertilization

Environmental exposures affect gamete function and fertility, but the mechanisms are poorly understood. Here, we show that pheromones sensed by ciliated neurons in the Caenorhabditis elegans nose alter the lipid microenvironment within the oviduct, thereby affecting sperm motility. In favorable environments, pheromone-responsive sensory neurons secrete a transforming growth factor-β ligand called DAF-7, which acts as a neuroendocrine factor that stimulates prostaglandin-endoperoxide synthase [cyclooxygenase (Cox)]-independent prostaglandin synthesis in the ovary. Oocytes secrete F-class prostaglandins that guide sperm toward them. These prostaglandins are also synthesized in Cox knockout mice, raising the possibility that similar mechanisms exist in other animals. Our data indicate that environmental cues perceived by the female nervous system affect sperm function.

The regulation of spermatogenesis and sperm function in nematodes

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

FOXO transcription factors: their clinical significance and regulation

Members of the class O of forkhead box transcription factors (FOXO) have important roles in metabolism, cellular proliferation, stress resistance, and apoptosis. The activity of FOXOs is tightly regulated by posttranslational modification, including phosphorylation, acetylation, and ubiquitylation. Activation of cell survival pathways such as phosphoinositide-3-kinase/AKT/IKK or RAS/mitogen-activated protein kinase phosphorylates FOXOs at different sites which regulate FOXOs nuclear localization or degradation. FOXO transcription factors are upregulated in a number of cell types including hepatocytes, fibroblasts, osteoblasts, keratinocytes, endothelial cells, pericytes, and cardiac myocytes. They are involved in a number of pathologic and physiologic processes that include proliferation, apoptosis, autophagy, metabolism, inflammation, cytokine expression, immunity, differentiation, and resistance to oxidative stress. These processes impact a number of clinical conditions such as carcinogenesis, diabetes, diabetic complications, cardiovascular disease, host response, and wound healing. In this paper, we focus on the potential role of FOXOs in different disease models and the regulation of FOXOs by various stimuli.