Caenorhabditis elegans HUS-1 is a DNA damage checkpoint protein required for genome stability and EGL-1-mediated apoptosis

Torenia sp. Extracts Contain Multiple Potent Antitumor Compounds with Nematocidal Activity, Triggering an Activated DNA Damage Checkpoint and Defective Meiotic Progression

Previously, we analyzed 316 herbal extracts to evaluate their potential nematocidal properties in Caenorhabditis elegans. In this study, our attention was directed towards Torenia sp., resulting in reduced survival and heightened larval arrest/lethality, alongside a noticeable decrease in DAPI-stained bivalent structures and disrupted meiotic progression, thus disrupting developmental processes. Notably, Torenia sp. extracts activated a DNA damage checkpoint response via the ATM/ATR and CHK-1 pathways, hindering germline development. LC-MS analysis revealed 13 compounds in the Torenia sp. extracts, including flavonoids, terpenoids, tanshinones, an analog of resveratrol, iridoids, carotenoids, fatty acids, and alkaloids. Of these, 10 are known for their antitumor activity, suggesting the potential of Torenia species beyond traditional gardening, extending into pharmaceutical and therapeutic applications.

Outcomes of BRCA pre-implantation genetic testing according to the parental mutation origin: a cohort study

BACKGROUND

The process of gamete formation and early embryonic development involves rapid DNA replication, chromosome segregation and cell division. These processes may be affected by mutations in the BRCA1/2 genes. The aim of this study was to evaluate BRCA mutation inheritance and its effect on early embryonic development according to the parental origin of the mutation. The study question was approached by analyzing in vitro fertilization cycles (IVF) that included pre-implantation testing (PGT-M) for a BRCA gene mutation.

METHODS

This retrospective cohort study compared cycles of pre-implantation genetic testing for mutations (PGT-M) between male and female patients diagnosed with BRCA 1/2 mutations (cases), to a control group of two other mutations with dominant inheritance (myotonic dystrophy (MD) and polycystic kidney disease (PKD)). Results were compared according to mutation type and through a generalized linear model analysis.

RESULTS

The cohort included 88 PGT-M cycles (47 BRCA and 41 non-BRCA) among 50 patients. Maternal and paternal ages at oocyte retrieval were comparable between groups. When tested per cycle, FSH dose, maximum estradiol level, oocytes retrieved, number of zygotes, and number of embryos available for biopsy and affected embryos, were not significantly different among mutation types. All together 444 embryos were biopsied: the rate of affected embryos was comparable between groups. Among BRCA patients, the proportion of affected embryos was similar between maternal and paternal mutation origin (p = 0.24). In a generalized linear model analysis, the relative oocyte yield in maternal BRCA patients was significantly lower (0.7, as related to the non BRCA group)(p < 0.001). Zygote formation and blastulation were not affected by the BRCA gene among paternal cases (P = 0.176 and P = 0.293 respectively), nor by paternal versus maternal BRCA carriage (P = 0.904 and P = 0.149, respectively).

CONCLUSIONS

BRCA PGT-M cycles performed similarly compared to non-BRCA cycles. Inheritance rate and cycle parameters were not affected by the parental origin of the mutation.

Polyethylene nanoplastics cause reproductive toxicity associated with activation of both estrogenic hormone receptor NHR-14 and DNA damage checkpoints in C. elegans

As the most commercial polymer, the polyethylene nanoparticle (PE-NP) has been discharged into the environment and poses potential risks to organisms. However, the possible reproductive toxicity of PE-NP and underlying mechanisms remain largely unknown. In this study, Caenorhabditis elegans was employed as the animal model to effects of PE-NP (100 nm) and their leachates on reproduction and underlying mechanisms. Nematodes were exposed to PE-NP at 0.1-100 μg/L from L1-larvae to adult day 1 (approximately 4.5 days). Both brood size and number of fertilized eggs in uterus were decreased by 10 and 100 μg/L PE-NP, but could not be affected by their leachates. In addition, number of mitotic cells, length, and area of gonad were reduced by 10 and 100 μg/L PE-NP, but were not altered by their leachates. Accompanied with alteration in expressions of genes (egl-1, ced-9, ced-4, and ced-3) governing cell apoptosis, germline apoptosis was enhanced by PE-NP. Meanwhile, DNA damage was involved in the enhancement germline apoptosis after PE-NP exposure. PE-NP further increased expression of nhr-14 encoding estrogenic hormone receptor, and RNAi of nhr-14 suppressed PE-NP reproductive toxicity. Moreover, RNAi of nhr-14 decreased expression of egl-1, ced-4, ced-3, and mrt-2 in PE-NP exposed nematodes. Therefore, exposure to PE-NPs rather than in their leachates potentially caused reproductive toxicity by activating both estrogenic hormone receptor NHR-14 and DNA damage checkpoints (CLK-2, HUS-1, and MRT-2) in nematodes. These findings provide important insights into the exposure risk of PE-NPs on reproduction of environmental organisms.

Exploring the Impact of Onobrychis cornuta and Veratrum lobelianum Extracts on C. elegans: Implications for MAPK Modulation, Germline Development, and Antitumor Properties

In an era of increasing interest in the potential health benefits of medicinal foods, the need to assess their safety and potential toxicity remains a critical concern. While these natural remedies have garnered substantial attention for their therapeutic potential, a comprehensive understanding of their effects on living organisms is essential. We examined 316 herbal extracts to determine their potential nematocidal attributes in Caenorhabditis elegans. Approximately 16% of these extracts exhibited the capacity to induce diminished survival rates and larval arrest, establishing a correlation between larval arrest and overall worm viability. Certain extracts led to an unexpected increase in male nematodes, accompanied by a discernible reduction in DAPI-stained bivalent structures and perturbed meiotic advancement, thereby disrupting the conventional developmental processes. Notably, Onobrychis cornuta and Veratrum lobelianum extracts activated a DNA damage checkpoint response via the ATM/ATR and CHK-1 pathways, thus hindering germline development. Our LC-MS analysis revealed jervine in V. lobelianum and nine antitumor compounds in O. cornuta. Interestingly, linoleic acid replicated phenotypes induced by O. cornuta exposure, including an increased level of pCHK-1 foci, apoptosis, and the MAPK pathway. Mutants in the MAPK pathway mitigated the decline in worm survival, underscoring its importance in promoting worm viability. This study reveals complex interactions between herbal extracts and C. elegans processes, shedding light on potential antitumor effects and mechanisms. The findings provide insights into the complex landscape of herbal medicine's impact on a model organism, offering implications for broader applications.

The dynamic subcellular localisation of Rad1 is cell cycle dependent in Leishmania major

The subcellular localisation of Rad1, a subunit of the Leishmania major 9-1-1 complex, remains unexplored. Herein, we reveal that Rad1 localises predominantly to the nucleus. Upon hydroxyurea treatment, the diffuse nuclear localisation of Rad1 becomes more punctate, suggesting that Rad1 is responsive to replication stress. Moreover, Rad1 localisation correlates with cell cycle progression. In the majority of G1 to early S-phase cells, Rad1 localises predominantly to the nucleus. As cells progress from late-S phase to mitosis, Rad1 relocalizes to both the nucleus and the cytoplasm in ∼90 % of cells. This pattern of distribution is different from Rad9 and Hus1, which remain nuclear throughout the cell cycle, suggesting Leishmania Rad1 may regulate 9-1-1 activities and/or perform relevant functions outside the 9-1-1 complex.

Telomeric repeat evolution in the phylum Nematoda revealed by high-quality genome assemblies and subtelomere structures

Telomeres are composed of tandem arrays of telomeric-repeat motifs (TRMs) and telomere-binding proteins (TBPs), which are responsible for ensuring end-protection and end-replication of chromosomes. TRMs are highly conserved owing to the sequence specificity of TBPs, although significant alterations in TRM have been observed in several taxa, except Nematoda. We used public whole-genome sequencing data sets to analyze putative TRMs of 100 nematode species and determined that three distinct branches included specific novel TRMs, suggesting that evolutionary alterations in TRMs occurred in Nematoda. We focused on one of the three branches, the Panagrolaimidae family, and performed a de novo assembly of four high-quality draft genomes of the canonical (TTAGGC) and novel TRM (TTAGAC) isolates; the latter genomes revealed densely clustered arrays of the novel TRM. We then comprehensively analyzed the subtelomeric regions of the genomes to infer how the novel TRM evolved. We identified DNA damage-repair signatures in subtelomeric sequences that were representative of consequences of telomere maintenance mechanisms by alternative lengthening of telomeres. We propose a hypothetical scenario in which TTAGAC-containing units are clustered in subtelomeric regions and pre-existing TBPs capable of binding both canonical and novel TRMs aided the evolution of the novel TRM in the Panagrolaimidae family.

DNA damage signals from somatic uterine tissue arrest oogenesis through activated DAF-16

Germ line integrity is crucial for progeny fitness. Organisms deploy the DNA damage response (DDR) signaling to protect the germ line from genotoxic stress, facilitating the cell-cycle arrest of germ cells and DNA repair or their apoptosis. Cell-autonomous regulation of germ line quality in response to DNA damage is well studied; however, how quality is enforced cell non-autonomously on sensing somatic DNA damage is less known. Using Caenorhabditis elegans, we show that DDR disruption, only in the uterus, when insulin/IGF-1 signaling (IIS) is low, arrests oogenesis in the pachytene stage of meiosis I, in a FOXO/DAF-16 transcription factor-dependent manner. Without FOXO/DAF-16, germ cells of the IIS mutant escape the arrest to produce poor-quality oocytes, showing that the transcription factor imposes strict quality control during low IIS. Activated FOXO/DAF-16 senses DDR perturbations during low IIS to lower ERK/MPK-1 signaling below a threshold to promote germ line arrest. Altogether, we elucidate a new surveillance role for activated FOXO/DAF-16 that ensures optimal germ cell quality and progeny fitness in response to somatic DNA damage.

Long-term exposure to 6-PPD quinone reduces reproductive capacity by enhancing germline apoptosis associated with activation of both DNA damage and cell corpse engulfment in Caenorhabditis elegans

Recently, 6-PPD quinone (6-PPDQ), a derivative of tire antioxidant 6-PPD, was reported to have acute toxicity for organisms. However, the possible reproductive toxicity of 6-PPDQ is still largely unclear. In this study, the reproductive toxicity of 6-PPDQ after long-term exposure was further investigated in Caenorhabditis elegans. Exposure to 1 and 10 μg/L 6-PPDQ reduced the reproductive capacity. Meanwhile, exposure to 1 and 10 μg/L 6-PPDQ enhanced the germline apoptosis, which was accompanied by upregulation of ced-3, ced-4, and egl-1 expressions and downregulation of ced-9 expression. The observed increase in germline apoptosis in 1 and 10 μg/L 6-PPDQ exposed nematodes was associated with the enhancement in DNA damage and increase in expressions of related genes of cep-1, clk-2, hus-1, and mrt-2. The detected enhancement in germline apoptosis in 1 and 10 μg/L 6-PPDQ exposed nematodes was further associated with the increase in expressions of ced-1 and ced-6 governing the cell corpse engulfment process. Molecular docking analysis indicated the binding potentials of 6-PPDQ with three DNA damage checkpoints (CLK-2, HUS-1, and MRT-2) and corpse-recognizing phagocytic receptor CED-1. Therefore, our data suggested the toxicity on reproductive capacity by 6-PPDQ at environmentally relevant concentrations by enhancing DNA damage- and cell corpse engulfment-induced germline apoptosis in organisms.

SKN-1/Nrf2-dependent regulation of mitochondrial homeostasis modulates transgenerational toxicity induced by nanoplastics with different surface charges in Caenorhabditis elegans

The toxic effects of nanoplastics on transgenerational toxicity in environmental organisms and the involved mechanisms remain poorly comprehended. This study aimed to identify the role of SKN-1/Nrf2-dependent regulation of mitochondrial homeostasis in response to transgenerational toxicity caused by changes in nanoplastic surface charges in Caenorhabditis elegans (C. elegans). Our results revealed that compared with the wild-type control and PS exposed groups, exposure to PS-NH₂ or PS-SOOOH at environmentally relevant concentrations (ERC) of ≥ 1 μg/L caused transgenerational reproductive toxicity, inhibited mitochondrial unfolded protein responses (UPR) by downregulating the transcription levels of hsp-6, ubl-5, dve-1, atfs-1, haf-1, and clpp-1, membrane potential by downregulating phb-1 and phb-2, and promoted mitochondrial apoptosis by downregulating ced-4 and ced-3 and upregulating ced-9, DNA damage by upregulating hus-1, cep-1, egl-1, reactive oxygen species (ROS) by upregulating nduf-7 and nuo-6, ultimately resulting in mitochondrial homeostasis. Additionally, further study indicated that SKN-1/Nrf2 mediated antioxidant response to alleviate PS-induced toxicity in the P0 generation and dysregulated mitochondrial homeostasis to enhance PS-NH₂ or PS-SOOOH-induced transgenerational toxicity. Our study highlights the momentous role of SKN-1/Nrf2 mediated mitochondrial homeostasis in the response to nanoplastics caused transgenerational toxicity in environmental organisms.

Multi-generation reproductive toxicity of RDX and the involved signal pathways in Caenorhabditis elegans

As one of the most frequently used explosives, hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) can cause persistent pollution in the environment, leading to the potential ecological threat crossing the generations. In this study, we employed Caenorhabditis elegans to explore the toxic effects of RDX on the parental and offspring worms and the involved signaling pathways. Exposure up to 1000 ng/mL of RDX produced a significant increase in reactive oxygen species (ROS) production, germ cell apoptosis, and decrease in eggs laid. Various mutants were used to demonstrate the RDX-induced apoptosis signaling pathway, and the metabolism of RDX in the nematodes was found related to cytochrome P450 and GST through RNA sequencing. Exposure of parental worms to RDX produced significant reproductive toxicity in F1 and F2, but was recovered in F3 and F4. The transgenerational effects were associated with the decreased expression of met-2, spr-5, and set-2. Our findings revealed the signaling pathways related to the reproductive toxicity caused by RDX in C. elegans and their future generations, which provided the basis for further exploration of the ecological risks of energetic compounds in the environment.

Adverse health effects and mechanisms of microplastics on female reproductive system: a descriptive review

Microplastics (MPs), with a diameter of less than 5 mm, include polymers such as polystyrene, polypropylene, and polyethylene. The MPs occur in different morphologies including fragments, beads, fibers, and films that are swallowed by fresh water and land-based animals and enter their food chain, where they produce hazardous effects such as uterine toxicity, infertility, and neurotoxicity. The aim of this review is to explore the effects of polystyrene MPs (PS-MPs) on the female reproductive system and understand the mechanisms by which they produce reproductive toxicity. Several studies suggested that the exposure to PS-MPs increased the probability of larger ovaries with fewer follicles, decreased the number of embryos produced, and decreased the number of pregnancies in female mice. It also changed sex hormone levels and caused oxidative stress, which could have an impact on fertility and reproduction. Exposure to PS-MPs caused the death of granulosa cells through apoptosis and pyroptosis via activation of the NLRP3/caspase pathway and disruption of the Wnt-signaling pathway. Activation of TL4/NOX2 caused the uterine fibrosis resulting in endometrium thinning. The PS-MPs had a negative impact on ovarian capacity, oocyte maturation, and oocyte quality. Furthermore, the PS-MPs disrupted the hypothalamus-pituitary-gonadal axis in marine animals, resulting in a decrease in hatching rate and offspring body size, causing trans-generational effects. It also reduced fecundity and produced germ-line apoptosis. The main focus of this review was to explore the different mechanisms and pathways through which PS-MPs adversely impact the female reproductive system.

Paeoniflorin attenuates polystyrene nanoparticle-induced reduction in reproductive capacity and increase in germline apoptosis through suppressing DNA damage checkpoints in Caenorhabditis elegans

Due to high sensitivity to environmental exposures, Caenorhabditis elegans is helpful for toxicity evaluation and toxicological study of pollutants. Using this animal model, we investigated the reproductive toxicity of 20 nm polystyrene nanoparticle (PS-NP) in the range of μg/L and the following pharmacological intervention of paeoniflorin. After exposure from L1-larvae to young adults, 10-100 μg/L PS-NP could cause the reduction in reproductive capacity reflected by the endpoints of brood size and number of fertilized eggs in uterus. Meanwhile, the enhancements in germline apoptosis analyzed by AO staining and germline DNA damage as shown by alteration in HUS-1::GFP signals were detected in 10-100 μg/L PS-NP exposed nematodes, suggesting the role of DNA damage-induced germline apoptosis in mediating PS-NP toxicity on reproductive capacity. Following the exposure to 100 μg/L PS-NP, posttreatment with 25-100 mg/L paeoniflorin increased the reproductive capacity and inhibited both germline apoptosis and DNA damage. In addition, in 100 μg/L PS-NP exposed nematodes, treatment with 100 mg/L paeoniflorin modulated the expressions of genes governing germline apoptosis as indicated by the decrease in ced-3, ced-4, an egl-1 expressions and the increase in ced-9 expression. After exposure to 100 μg/L PS-NP, treatment with 100 mg/L paeoniflorin also decreased expressions of genes (cep-1, clk-2, hus-1, and mrt-2) governing germline DNA damage. Molecular docking analysis further demonstrated the binding potential of paeoniflorin with three DNA damage checkpoints (CLK-2, HUS-1, and MRT-2). Therefore, our data suggested the toxicity of PS-NP in the range of μg/L on reproductive capacity after exposure from L1-larvae to young adults, which was associated with the enhancement in DNA damage-induced germline apoptosis. More importantly, the PS-NP-induced reproductive toxicity on nematodes could be inhibited by the following paeoniflorin treatment.

Role of transcription factors in apoptotic cells clearance

The human body generates 10-100 billion cells every day, and the same number of cells die to maintain homeostasis. The genetically controlled, autonomously ordered cell death mainly proceeds by apoptosis. Apoptosis is an important way of programmed cell death in multicellular organisms, timely and effective elimination of apoptotic cells plays a key role in the growth and development of organisms and the maintenance of homeostasis. During the clearance of apoptotic cells, transcription factors bind to specific target promoters and act as activators or repressors to regulate multiple genes expression, how transcription factors regulate apoptosis is an important and poorly understood aspect of normal development. This paper summarizes the regulatory mechanisms of transcription factors in the clearance of apoptotic cells to date.

Reproductive toxicity and underlying mechanisms of fine particulate matter (PM2.5) on Caenorhabditis elegans in different seasons

Although numerous studies have investigated that atmospheric fine particulate matter (PM_2.5) can be toxic to environmental organisms, the research on the reproductive toxicity of PM_2.5 is limited, and the key toxic components and underlying mechanisms remain unknown. In this work, PM_2.5 samples of four seasons in Nanjing from March 1, 2021, to February 28, 2022 were collected and the chemical components were analyzed. Caenorhabditis elegans (C. elegans) was employed to conduct the toxicological testing. The reproductive toxicity of PM_2.5 to C. elegans in different seasons was evaluated by multiple reproductive endpoints. Exposure to high concentrations of PM_2.5 significantly decreased the brood size and the number of fertilized eggs in utero. PM_2.5 exposure also increased the number of germ cell corpses and caused abnormal expression of apoptosis-related genes (ced-9, ced-4, and ced-3), which confirmed that PM_2.5 induced germline apoptosis. In addition, PM_2.5 exposure significantly increased the production of reactive oxygen species (ROS) in C. elegans and the fluorescence intensity of HUS-1 protein in of transgenic strain WS1433. Meanwhile, the expression of genes related to DNA damage (cep-1, clk-2, egl-1, and hus-1) and oxidative stress (mev-1, isp-1, and gas-1) also significantly altered in C. elegans, suggesting induction of DNA damage and oxidative stress. According to Pearson correlation analyses, DNA damage and oxidative stress were significantly correlated with multiple reproductive endpoints in C. elegans. Thus, it was speculated that PM_2.5 caused reproductive dysfunction and germ cell apoptosis in C. elegans may be by inducing ROS and DNA damage. In addition, heavy metals in PM_2.5 were significantly correlated with multiple endpoints at physiological and biochemical, suggesting that the heavy metals might be an important contributor to the reproductive toxicity induced by PM_2.5.

Caenorhabditis elegans NHR-14/HNF4α regulates DNA damage-induced apoptosis through cooperating with cep-1/p53

Background

Nuclear hormone receptors are involved in transcriptional regulation and many important cellular processes including development and metabolism. However, its role in DNA damage-induced apoptosis remains elusive.

Methods

Synchronized young adult animals were irradiated with different doses of gamma-Ray, and then put back to culture at 20 °C. Germline cell apoptosis was scored at different time point.

Results

Deletion of nhr-14 led to decreased DNA damage-induced germline apoptosis, but not the physiological programmed cell death. We also demonstrate that nhr-14 functions downstream of the DNA damage checkpoint pathway. Moreover, we show that nhr-14 regulates egl-1 and ced-13 transcription upon DNA damage. Mechanistically, NHR-14 forms a complex with CEP-1/p53 and binds directly to the egl-1 promoter to promote egl-1 transcription..

Conclusions

Our results indicate that NHR-14/HNF4α cooperates with CEP-1/p53 to regulate DNA damage-induced apoptosis.

Graphic abstract

Tetrachlorobisphenol A mediates reproductive toxicity in Caenorhabditis elegans via DNA damage-induced apoptosis

Tetrachlorobisphenol A (TCBPA), an alternative to tetrabromobisphenol A (TBBPA), is ubiquitous in the environment and could potentially impact the reproductive system of organisms. However, the mechanisms underlying TCBPA-mediated reproductive effects remain unclear. Herein, we exposed Caenorhabditis elegans (C. elegans, L4 larvae) to TCBPA at environmentally relevant doses (0-100 μg/L) for 24 h. Exposure to TCBPA at concentrations of 1-100 μg/L impaired fertility of C. elegans, as indicated by brood size. After staining, the number of germline cells decreased in a dose-dependent manner, whereas germline cell corpses increased in exposed nematodes (10-100 μg/L TCBPA). Moreover, the expression of genes related to the germline apoptosis pathway was regulated following exposure to 100 μg/L TCBPA, indicating the potential role of DNA damage in TCBPA-induced apoptosis. Apoptosis was nearly abolished in ced-4 and ced-3 mutants and blocked in hus-1, egl-1, cep-1, and ced-9 mutants. Numerous foci were detected in TCBPA (100 μg/L)-exposed hus-1::GFP strains. These results indicate that TCBPA induces hus-1-mediated DNA damage and further causes apoptosis via a cep-1-dependent pathway. Our data provide evidence that TCBPA causes reproductive toxicity via DNA damage-induced apoptosis.

Reproductive toxicity by exposure to low concentrations of pesticides in Caenorhabditis elegans

In view of the recurrent applications of pesticides in agricultural producing countries, the increased presence of these substances in the environment raise a demand for the evaluation of adverse effects on non-target organisms. This study assesses the impact of exposure to five pesticides suspected of being endocrine disruptors (atrazine, 2,4-dichlorophenoxyacetic acid, mancozeb, chlorpyrifos and cypermethrin) on the reproductive development of the nematode Caenorhabditis elegans. To this end, nematodes in the L4 larval stage were exposed to different concentrations of pesticides for 24 h and the consequences on brood size, percentage of gravid nematodes, expression of reproductive-related genes and vitellogenin trafficking and endocytosis were measured. Moreover, 17β-estradiol was used as an estrogenic control for endocrine disrupting compounds throughout the work. The results showed that all the pesticides disturbed to some extent one or more of the evaluated endpoints. Remarkably, we found that atrazine, 2,4-dichlorophenoxyacetic acid and chlorpyrifos produced comparable responses to 17β-estradiol suggesting that these pesticides may have estrogen-like endocrine disrupting activity. Atrazine and 17β-estradiol, as well as 2,4-dichlorophenoxyacetic acid and chlorpyrifos to a lesser extent, decreased the brood size, affected vitellogenin trafficking and endocytosis, and changed the expression of several reproductive-related genes. Conversely, mancozeb and cypermethrin had the least impact on the evaluated endpoint. Cypermethrin affected the brood size at the highest concentration tested and mancozeb altered the distribution of vitellogenin only in approximately 10% of the population. However, both products overexpressed hus-1 and vit-2 genes, indicating that an induction of stress could interfere with the normal development of the nematode. In conclusion, our work proved that C. elegans is a useful biological model to identify the effects of estrogen-like endocrine disruptor compounds, and the sublethal endpoints proposed may serve as an important contribution on evaluating environmental pollutants.

Green synthesis of broccoli-derived carbon quantum dots as effective photosensitizers for the PDT effect testified in the model of mutant Caenorhabditis elegans

The clinical application of photodynamic therapy (PDT) is still limited because of the drawbacks of the traditional photosensitizers, such as low singlet oxygen (¹O₂) quantum yield and the problem of photobleaching. Herein, carbon quantum dots (CQDs) derived from broccoli natural biomass as a carbon source were fabricated via a simple hydrothermal method and showed outstanding PDT ability as an effective photodynamic agent tested in Caenorhabditis elegans (C. elegans) models. The as-prepared broccoli-derived CQDs (BCQDs) showed excellent water solubility and optical properties and could generate singlet oxygen (¹O₂) effectively under irradiated light with a wavelength of 660 nm. The in vivo experiment revealed that the PDT efficiency of the BCQDs was dependent on the induction of germline apoptosis through the cep-1/p53 pathway. Further investigation confirmed the DNA damage of the worm by the BCQDs after sufficient light irradiation, which was tested by measuring the egl-1-fold induction in hus-1(op244), and cep-1(w40) mutants that have a loss of function in the genes involved in DNA damage response such as hus-1 (DNA checkpoint gene) and cep-1/p53 (tumor suppressor). The lack of germline apoptosis in the loss of function mutants egl-1(n487), hus-1(op244), and cep-1(w40) exposed to light irradiation compared with the control proved the necessity of these genes in DNA damage-induced germline apoptosis. Therefore, this work has not only provided a new photodynamic agent but also introduced C. elegans as an easy and high-throughput model for the rapid evaluation of the efficiency of PDT.

3,3'-Diindolylmethane Supplementation Maintains Oocyte Quality by Reducing Oxidative Stress and CEP-1/p53-Mediated Regulation of Germ Cells in a Reproductively Aged Caenorhabditis elegans Model

In recent decades, maternal age at first birth has increased, as has the risk of infertility due to rapidly declining oocyte quality with age. Therefore, an understanding of female reproductive aging and the development of potential modulators to control oocyte quality are required. In this study, we investigated the effects of 3,3'-diindolylmethane (DIM), a natural metabolite of indole-3-cabinol found in cruciferous vegetables, on fertility in a Caenorhabditis elegans model. C. elegans fed DIM showed decreased mitochondrial dysfunction, oxidative stress, and chromosomal aberrations in aged oocytes, and thus reduced embryonic lethality, suggesting that DIM, a dietary natural antioxidant, improves oocyte quality. Furthermore, DIM supplementation maintained germ cell apoptosis (GCA) and germ cell proliferation (GCP) in a CEP-1/p53-dependent manner in a reproductively aged C. elegans germ line. DIM-induced GCA was mediated by the CEP-1-EGL-1 pathway without HUS-1 activation, suggesting that DIM-induced GCA is different from DNA damage-induced GCA in the C. elegans germ line. Taken together, we propose that DIM supplementation delays the onset of reproductive aging by maintaining the levels of GCP and GCA and oocyte quality in a reproductively aged C. elegans.

The p53 network: cellular and systemic DNA damage responses in cancer and aging

The tumor protein TP53 gene, encoding the cellular tumor antigen p53, is the single most frequently mutated gene in human cancers. p53 plays a central role in responding to DNA damage and determines the outcome of the DNA damage checkpoint response by regulating cell cycle arrest and apoptosis. As a consequence of this function, dysfunctional p53 results in cells that, despite a damaged genome, continue to proliferate thus fueling malignant transformation. New insights have recently been gained into the complexity of the p53 regulation of the DNA damage response (DDR) and how it impacts a wide variety of cellular processes. In addition to cell-autonomous signaling mechanisms, non-cell-autonomous regulatory inputs influence p53 activity, which in turn can have systemic consequences on the organism. New inroads have also been made toward therapeutic targeting of p53 that for a long time has been anticipated.

Reproductive toxicity of UV-photodegraded polystyrene microplastics induced by DNA damage-dependent cell apoptosis in Caenorhabditis elegans

Although many studies have investigated the toxic effects of polystyrene microplastics (PS-MPs), toxicity of natural aged of PS-MPs to soil organisms remains unclear. The photodegradation of virgin PS-MPs under UV irradiation was investigated, and reproductive toxicity of pristine and UV-photodegraded PS-MPs at environmental concentrations (0.1-100 μg/L) was examined to Caenorhabditis elegans. Using brood size and egg ejection rate as endpoints, acute exposure to aged PS-MPs resulted in more severe reproductive toxicity than pristine PS-MPs. Exposure to 100 μg/L aged PS-MPs significantly increased the number of HUS-1::GFP foci and the expression of genes required for DNA damage, such as clk-2, cep-1, and egl-1, suggesting induction of DNA damage. Additionally, the number of cell corpses and apoptosis-related gene expression (e.g., ced-3, ced-4, and ced-9) were significantly altered, indicating induction of apoptosis. Germline apoptosis induced by aged PS-MPs was altered in egl-1, hus-1, cep-1, ced-3, ced-4, and ced-9 mutants. Thus, the reproductive toxicity of aged PS-MPs may be due to DNA damage-induced cell apoptosis, and the HUS-1-CEP-1-EGL-1-CED-9-CED-4-CED-3 signalling pathway is involved in regulating cell apoptosis in nematodes.

Release of CHK-2 from PPM-1.D anchorage schedules meiotic entry

Transition from the stem/progenitor cell fate to meiosis is mediated by several redundant posttranscriptional regulatory pathways in Caenorhabditis elegans. Interfering with all three branches causes tumorous germ lines. SCFPROM-1 comprises one branch and mediates a scheduled degradation step at entry into meiosis. prom-1 mutants show defects in the timely initiation of meiotic prophase I events, resulting in high rates of embryonic lethality. Here, we identify the phosphatase PPM-1.D/Wip1 as crucial substrate for PROM-1. We report that PPM-1.D antagonizes CHK-2 kinase, a key regulator for meiotic prophase initiation, including DNA double-strand breaks, chromosome pairing, and synaptonemal complex formation. We propose that PPM-1.D controls the amount of active CHK-2 via both catalytic and noncatalytic activities; notably, noncatalytic regulation seems to be crucial at meiotic entry. PPM-1.D sequesters CHK-2 at the nuclear periphery, and programmed SCFPROM-1-mediated degradation of PPM-1.D liberates the kinase and promotes meiotic entry.

Somatic PMK-1/p38 signaling links environmental stress to germ cell apoptosis and heritable euploidy

Inheritance of stable and euploid genomes is a prerequisite for species maintenance. The DNA damage response in germ cells controls the integrity of heritable genomes. Whether and how somatic stress responses impact the quality control of germline genomes has remained unclear. Here, we show that PMK-1/p38-mediated stress signaling in intestinal cells is required for germ cell apoptosis amid ionizing radiation (IR)-induced or meiotic DNA double strand breaks (DSBs) in C. elegans. We demonstrate that intestinal PMK-1/p38 signaling regulates the germ cell death in response to environmental stress. The PMK-1/p38 target SYSM-1 is secreted from the intestine into the germline to trigger apoptosis of meiotic pachytene cells. Compromised PMK-1/p38 signaling in intestinal cells leads to stress-induced aneuploidy in the consequent generation. Our data suggest that somatic stress surveillance controls heritable genome integrity and euploidy.

Sublethal toxicity of graphene oxide in Caenorhabditis elegans under multi-generational exposure

Nanomaterials have received increasing attentions owing to their potential hazards to the environment and human health; however, the multi-generational toxicity of graphene oxide under consecutive multi-generational exposure scenario still remains unclear. In the present study, Caenorhabditis elegans as an in vivo model organism was employed to explore the multi-generational toxicity effects of graphene oxide and the underlying mechanisms. Endpoints including development and lifespan, locomotion behaviors, defecation cycle, brood sizes, and oxidative response were evaluated in the parental generation and subsequent five filial generations. After continuous exposure for several generations, worms grew smaller and lived shorter. The locomotion behaviors were reduced across the filial generations and these reduced trends were following the impairments of locomotion-related neurons. In addition, the extended defecation cycles from the third filial generation were in consistency with the relative size reduction of the defecation related neuron. Simultaneously, the fertility function of the nematode was impaired under consecutive exposure as reduced brood sizes and oocytes numbers, increased apoptosis of germline, and aberrant expression of reproductive related genes ced-3, ced-4, ced-9, egl-1 and ced-13 were detected in exposed worms. Furthermore, the antioxidant enzyme, SOD-3 was significantly increased in the parent and filial generations. Thus, continuous multi-generational exposure to graphene oxide caused damage to the neuron development and the reproductive system in nematodes. These toxic effects could be reflected by indicators such as growth inhibition, shortened lifespan, and locomotion behavior impairment and induced oxidative response.

Study on the reproductive toxicity and mechanism of tri-n-butyl phosphate (TnBP) in Caenorhabditis elegans

Tri-n-butyl phosphate (TnBP), a typical alkyl organophosphate ester is widely used as an emerging flame retardant for polybrominated diphenyl ethers alternatives, but the potential toxicity and mechanism are unclear. In this study, the reproductive toxicity of TnBP and its related mechanisms were explored using the Caenorhabditis elegans (C. elegans) model. After TnBP (100-1000 μg/L) exposure, brood size and the number of fertilized eggs in the uterus in C. elegans were significantly reduced, the relative area of gonad arm and the number of total germline cells in C. elegans were significantly reduced, germ cell apoptosis and germ cell DNA damage in C. elegans were significantly increased, the level of ROS in C. elegans was significantly increased. Furthermore, TnBP exposure caused abnormal gene expressions of cell apoptosis (ced-9, ced-4 and ced-3), DNA damage (hus-1, clk-2, cep-1 and egl-1) and oxidative stress (mev-1 and gas-1). TnBP exposure can lead to reproductive ability decreased and gonad development impaired in C. elegans, the mechanism of TnBP reduced reproductive ability may be related to germ cell apoptosis, germ cell DNA damage and oxidative stress. Environmental exposure to TnBP may have potential reproductive toxicity.

Germ cell apoptosis is critical to maintain Caenorhabditis elegans offspring viability in stressful environments

Maintaining reproduction in highly variable, often stressful, environments is an essential challenge for all organisms. Even transient exposure to mild environmental stress may directly damage germ cells or simply tax the physiology of an individual, making it difficult to produce quality gametes. In Caenorhabditis elegans, a large fraction of germ cells acts as nurse cells, supporting developing oocytes before eventually undergoing so-called physiological germ cell apoptosis. Although C. elegans apoptosis has been extensively studied, little is known about how germline apoptosis is influenced by ecologically relevant environmental stress. Moreover, it remains unclear to what extent germline apoptosis contributes to maintaining oocyte quality, and thus offspring viability, in such conditions. Here we show that exposure to diverse environmental stressors, likely occurring in the natural C. elegans habitat (starvation, ethanol, acid, and mild oxidative stress), increases germline apoptosis, consistent with previous reports on stress-induced apoptosis. Using loss-of-function mutant alleles of ced-3 and ced-4, we demonstrate that eliminating the core apoptotic machinery strongly reduces embryonic survival when mothers are exposed to such environmental stressors during early adult life. In contrast, mutations in ced-9 and egl-1 that primarily block apoptosis in the soma but not in the germline, did not exhibit such reduced embryonic survival under environmental stress. Therefore, C. elegans germ cell apoptosis plays an essential role in maintaining offspring fitness in adverse environments. Finally, we show that ced-3 and ced-4 mutants exhibit concomitant decreases in embryo size and changes in embryo shape when mothers are exposed to environmental stress. These observations may indicate inadequate oocyte provisioning due to the absence of germ cell apoptosis. Taken together, our results show that the central genes of the apoptosis pathway play a key role in maintaining gamete quality, and thus offspring fitness, under ecologically relevant environmental conditions.

Review of Biological Effects of Acute and Chronic Radiation Exposure on Caenorhabditis elegans

Knowledge regarding complex radiation responses in biological systems can be enhanced using genetically amenable model organisms. In this manuscript, we reviewed the use of the nematode, Caenorhabditis elegans (C. elegans), as a model organism to investigate radiation’s biological effects. Diverse types of experiments were conducted on C. elegans, using acute and chronic exposure to different ionizing radiation types, and to assess various biological responses. These responses differed based on the type and dose of radiation and the chemical substances in which the worms were grown or maintained. A few studies compared responses to various radiation types and doses as well as other environmental exposures. Therefore, this paper focused on the effect of irradiation on C. elegans, based on the intensity of the radiation dose and the length of exposure and ways to decrease the effects of ionizing radiation. Moreover, we discussed several studies showing that dietary components such as vitamin A, polyunsaturated fatty acids, and polyphenol-rich food source may promote the resistance of C. elegans to ionizing radiation and increase their life span after irradiation.

Preservation of lagging strand integrity at sites of stalled replication by Pol α-primase and 9-1-1 complex

During genome duplication, the replication fork encounters a plethora of obstacles in the form of damaged bases, DNA-cross-linked proteins, and secondary structures. How cells protect DNA integrity at sites of stalled replication is currently unknown. Here, by engineering "primase deserts" into the Caenorhabditis elegans genome close to replication-impeding G-quadruplexes, we show that de novo DNA synthesis downstream of the blocked fork suppresses DNA loss. We next identify the pol α-primase complex to limit deletion mutagenesis, a conclusion substantiated by whole-genome analysis of animals carrying mutated POLA2/DIV-1. We subsequently identify a new role for the 9-1-1 checkpoint clamp in protecting Okazaki fragments from resection by EXO1. Together, our results provide a mechanistic model for controlling the fate of replication intermediates at sites of stalled replication.

DNA topoisomerase 3 is required for efficient germ cell quality control

An important quality control mechanism eliminates meiocytes that have experienced recombination failure during meiosis. The culling of defective oocytes in Caenorhabditis elegans meiosis resembles late oocyte elimination in female mammals. Here we show that topoisomerase 3 depletion generates DNA lesions in both germline mitotic and meiotic compartments that are less capable of triggering p53 (cep-1)–dependent apoptosis, despite the activation of DNA damage and apoptosis signaling. Elimination of nonhomologous, alternative end joining and single strand annealing repair factors (CKU-70, CKU-80, POLQ-1, and XPF-1) can alleviate the apoptosis block. Remarkably, the ability of single mutants in the other members of the Bloom helicase-topoisomerase-RMI1 complex to elicit apoptosis is not compromised, and depletion of Bloom helicase in topoisomerase 3 mutants restores an effective apoptotic response. Therefore, uncontrolled Bloom helicase activity seems to direct DNA repair toward normally not used repair pathways, and this counteracts efficient apoptosis. This implicates an as-yet undescribed requirement for topoisomerase 3 in mounting an effective apoptotic response to ensure germ cell quality control.

Worms, Fat, and Death: Caenorhabditis elegans Lipid Metabolites Regulate Cell Death

Caenorhabditis elegans is well-known as the model organism used to elucidate the genetic pathways underlying the first described form of regulated cell death, apoptosis. Since then, C. elegans investigations have contributed to the further understanding of lipids in apoptosis, especially the roles of phosphatidylserines and phosphatidylinositols. More recently, studies in C. elegans have shown that dietary polyunsaturated fatty acids can induce the non-apoptotic, iron-dependent form of cell death, ferroptosis. In this review, we examine the roles of various lipids in specific aspects of regulated cell death, emphasizing recent work in C. elegans.

DNA repair, recombination, and damage signaling

DNA must be accurately copied and propagated from one cell division to the next, and from one generation to the next. To ensure the faithful transmission of the genome, a plethora of distinct as well as overlapping DNA repair and recombination pathways have evolved. These pathways repair a large variety of lesions, including alterations to single nucleotides and DNA single and double-strand breaks, that are generated as a consequence of normal cellular function or by external DNA damaging agents. In addition to the proteins that mediate DNA repair, checkpoint pathways have also evolved to monitor the genome and coordinate the action of various repair pathways. Checkpoints facilitate repair by mediating a transient cell cycle arrest, or through initiation of cell suicide if DNA damage has overwhelmed repair capacity. In this chapter, we describe the attributes of Caenorhabditis elegans that facilitate analyses of DNA repair, recombination, and checkpoint signaling in the context of a whole animal. We review the current knowledge of C. elegans DNA repair, recombination, and DNA damage response pathways, and their role during development, growth, and in the germ line. We also discuss how the analysis of mutational signatures in C. elegans is helping to inform cancer mutational signatures in humans.

A DNA Damage-Repair Dynamic Model for HRS/IRR Effects of C.elegans Induced by Neutron Irradiation

Neutron irradiation which could trigger severe biological effects, is being applied in nuclear plants, radiotherapy, and aerospace gradually. Low dose hyper-radiosensitivity response of low Linear Energy Transfer (LET) irradiation on the cell survival has become a matter of great interest since its discovery, but a few research have been done on this response induced by neutron irradiation. To investigate this response induced by neutron irradiation, Caenorhabditis elegans (C. elegans) was irradiated by neutron irradiation. The surviving fraction of C. elegans on the 12th day after irradiation was analyzed, which showed a hyper-radiosensitive response at low doses and followed by an increase in survival fraction at slightly higher doses. The finding of this work that neutron irradiation decreased the surviving fraction in a non-dose-dependent manner was different from previous low-LET irradiation studies. To understand the experimental results, a DNA damage-repair model was introduced. By comparing experimental results with theoretical analyses, we suggest that the low dose hyper-radiosensitivity response of neutron irradiation may possible related to different radiation types and DNA damage recognition proteins and immune system of C. elegans.

DNA Damaged Induced Cell Death in Oocytes

The production of haploid gametes through meiosis is central to the principle of sexual reproduction. The genetic diversity is further enhanced by exchange of genetic material between homologous chromosomes by the crossover mechanism. This mechanism not only requires correct pairing of homologous chromosomes but also efficient repair of the induced DNA double-strand breaks. Oocytes have evolved a unique quality control system that eliminates cells if chromosomes do not correctly align or if DNA repair is not possible. Central to this monitoring system that is conserved from nematodes and fruit fly to humans is the p53 protein family, and in vertebrates in particular p63. In mammals, oocytes are stored for a long time in the prophase of meiosis I which, in humans, can last more than 50 years. During the entire time of this arrest phase, the DNA damage checkpoint remains active. The treatment of female cancer patients with DNA damaging irradiation or chemotherapeutics activates this checkpoint and results in elimination of the oocyte pool causing premature menopause and infertility. Here, we review the molecular mechanisms of this quality control system and discuss potential therapeutic intervention for the preservation of the oocyte pool during chemotherapy.

The SDHB Arg230His mutation causing familial paraganglioma alters glycolysis in a new Caenorhabditis elegans model

The conserved B-subunit of succinate dehydrogenase (SDH) participates in the tricarboxylic acid cycle (TCA) cycle and mitochondrial electron transport. The Arg230His mutation in SDHB causes heritable pheochromocytoma/paraganglioma (PPGL). In Caenorhabditiselegans, we generated an in vivo PPGL model (SDHB-1 Arg244His; equivalent to human Arg230His), which manifests delayed development, shortened lifespan, attenuated ATP production and reduced mitochondrial number. Although succinate is elevated in both missense and null sdhb-1(gk165) mutants, transcriptomic comparison suggests very different causal mechanisms that are supported by metabolic analysis, whereby only Arg244His (not null) worms demonstrate elevated lactate/pyruvate levels, pointing to a missense-induced, Warburg-like aberrant glycolysis. In silico predictions of the SDHA-B dimer structure demonstrate that Arg230His modifies the catalytic cleft despite the latter's remoteness from the mutation site. We hypothesize that the Arg230His SDHB mutation rewires metabolism, reminiscent of metabolic reprogramming in cancer. Our tractable model provides a novel tool to investigate the metastatic propensity of this familial cancer and our approach could illuminate wider SDH pathology.This article has an associated First Person interview with the first author of the paper.

SUMO promotes longevity and maintains mitochondrial homeostasis during ageing in Caenorhabditis elegans

The insulin/IGF signalling pathway impacts lifespan across distant taxa, by controlling the activity of nodal transcription factors. In the nematode Caenorhabditis elegans, the transcription regulators DAF-16/FOXO and SKN-1/Nrf function to promote longevity under conditions of low insulin/IGF signalling and stress. The activity and subcellular localization of both DAF-16 and SKN-1 is further modulated by specific posttranslational modifications, such as phosphorylation and ubiquitination. Here, we show that ageing elicits a marked increase of SUMO levels in C. elegans. In turn, SUMO fine-tunes DAF-16 and SKN-1 activity in specific C. elegans somatic tissues, to enhance stress resistance. SUMOylation of DAF-16 modulates mitochondrial homeostasis by interfering with mitochondrial dynamics and mitophagy. Our findings reveal that SUMO is an important determinant of lifespan, and provide novel insight, relevant to the complexity of the signalling mechanisms that influence gene expression to govern organismal survival in metazoans.

In vivo assessment of reactive oxygen species production and oxidative stress effects induced by chronic exposure to gamma radiation in Caenorhabditis elegans

In the current study, effects of chronic exposure to ionizing gamma radiation were assessed in the radioresistant nematode Caenorhabditis elegans in order to understand whether antioxidant defences (AODs) could ameliorate radical formation, or if increased ROS levels would cause oxidative damage. This analysis was accompanied by phenotypical as well as molecular investigations, via assessment of reproductive capacity, somatic growth and RNA-seq analysis. The use of a fluorescent reporter strain (sod1::gfp) and two ratiometric biosensors (HyPer and Grx1-roGFP2) demonstrated increased ROS production (H₂O₂) and activation of AODs (SOD1 and Grx) in vivo. The data showed that at dose-rates ≤10 mGy h^-1 defence mechanisms were able to prevent the manifestation of oxidative stress. In contrast, at dose-rates ≥40 mGy h^-1 the continuous formation of radicals caused a redox shift, which lead to oxidative stress transcriptomic responses, including changes in mitochondrial functions, protein degradation, lipid metabolism and collagen synthesis. Moreover, genotoxic effects were among the most over-represented functions affected by chronic gamma irradiation, as indicated by differential regulation of genes involved in DNA damage, DNA repair, cell-cycle checkpoints, chromosome segregation and chromatin remodelling. Ultimately, the exposure to gamma radiation caused reprotoxic effects, with >20% reduction in the number of offspring per adult hermaphrodite at dose-rates ≥40 mGy h^-1, accompanied by the down-regulation of more than 300 genes related to reproductive system, apoptosis, meiotic functions and gamete development and fertilization.

Quercetin and Its Mixture Increase the Stress Resistance of Caenorhabditis elegans to UV-B

Ultraviolet B (UV-B, 280–320 nm) radiation causes complex molecular reactions in cells, including DNA damage, oxidative stress, and apoptosis. This study designed a mixture consisting of quercetin, luteolin and lycopene and used Caenorhabditis elegans as a model to study the resistance of these natural chemicals to UV-B. Specifically, we have confirmed that quercetin and its mixture can increase the resistance of Caenorhabditis elegans to UV-B through lifespan test, reactive oxygen species level assay, germ cell apoptosis test, embryonic lethal test and RT-qPCR experiments. The results show that quercetin and its mixture prolonged the lifespan of UV-B-irradiated Caenorhabditis elegans and reduced abnormal levels of reactive oxygen species, embryo death, and apoptosis induced by UV-B. The protective effect of quercetin and its mixture may be attributed to its down-regulation of HUS-1, CEP-1, EGL-1 and CED-13. Therefore, the results of this research could help the development of UV-B radiation protection agents.

Antioxidant CoQ10 Restores Fertility by Rescuing Bisphenol A-Induced Oxidative DNA Damage in the Caenorhabditis elegans Germline

Endocrine-disrupting chemicals are ubiquitously present in our environment, but the mechanisms by which they adversely affect human reproductive health and strategies to circumvent their effects remain largely unknown. Here, we show in Caenorhabditis elegans that supplementation with the antioxidant Coenzyme Q10 (CoQ10) rescues the reprotoxicity induced by the widely used plasticizer and endocrine disruptor bisphenol A (BPA), in part by neutralizing DNA damage resulting from oxidative stress. CoQ10 significantly reduces BPA-induced elevated levels of germ cell apoptosis, phosphorylated checkpoint kinase 1 (CHK-1), double-strand breaks (DSBs), and chromosome defects in diakinesis oocytes. BPA-induced oxidative stress, mitochondrial dysfunction, and increased gene expression of antioxidant enzymes in the germline are counteracted by CoQ10. Finally, CoQ10 treatment also reduced the levels of aneuploid embryos and BPA-induced defects observed in early embryonic divisions. We propose that CoQ10 may counteract BPA-induced reprotoxicity through the scavenging of reactive oxygen species and free radicals, and that this natural antioxidant could constitute a low-risk and low-cost strategy to attenuate the impact on fertility by BPA.

Somatic Niche Cells Regulate the CEP-1/p53-Mediated DNA Damage Response in Primordial Germ Cells

Genome integrity in primordial germ cells (PGCs) is a prerequisite for fertility and species maintenance. In C. elegans, PGCs require global-genome nucleotide excision repair (GG-NER) to remove UV-induced DNA lesions. Failure to remove the lesions leads to the activation of the C. elegans p53, CEP-1, resulting in mitotic arrest of the PGCs. We show that the eIF4E2 translation initiation factor IFE-4 in somatic gonad precursor (SGP) niche cells regulates the CEP-1/p53-mediated DNA damage response (DDR) in PGCs. We determine that the IFE-4 translation target EGL-15/FGFR regulates the non-cell-autonomous DDR that is mediated via FGF-like signaling. Using hair follicle stem cells as a paradigm, we demonstrate that the eIF4E2-mediated niche cell regulation of the p53 response in stem cells is highly conserved in mammals. We thus reveal that the somatic niche regulates the CEP-1/p53-mediated DNA damage checkpoint in PGCs. Our data suggest that the somatic niche impacts the stability of heritable genomes.

Amino modification enhances reproductive toxicity of nanopolystyrene on gonad development and reproductive capacity in nematode Caenorhabditis elegans

Although amino modified nanopolystyrene could cause toxicity on environmental organisms, the effect of amino modification on nanopolystyrene toxicity is still largely unclear. We here employed Caenorhabditis elegans as an animal model to compare the effects between pristine and amino modified nanopolystyrene particles in inducing reproductive toxicity. Nanopolystyrene (35 nm) could cause the damage on gonad development as indicated by the endpoints of number of total germline cells, length of gonad arm, and relative area of gonad arm. Nanopolystyrene exposure also reduced the reproductive capacity as reflected by the endpoints of brood size and number of fertilized eggs in uterus. Moreover, amino modification enhanced nanopolystyrene toxicity on both the gonad development and the reproductive capacity. Additionally, induction of germline apoptosis and formation of germline DNA damage contributed to the enhancement of nanopolystyrene toxicity in reducing reproductive capacity by amino modification. Our results highlight the potential environmental risk of amino modified nanopolystyrene in inducing reproductive toxicity on gonad development and reproductive capacity of environmental organisms.

Gliadin Intake Causes Disruption of the Intestinal Barrier and an Increase in Germ Cell Apoptosis in A Caenorhabditis Elegans Model

Gliadin is a major protein component of gluten and causes gluten toxicity through intestinal stress. We previously showed that gliadin intake induces oxidative stress in the intestine and reduces fertility in a Caenorhabditis elegans model. To elucidate the possible link between intestinal stress and reproduction, changes in the intestine and germ cells of C. elegans after gliadin intake were examined at the molecular level. Gliadin intake increased reactive oxygen species (ROS) production in the intestine, decreased intestinal F-actin levels, and increased germ cell apoptosis. These gliadin-triggered effects were suppressed by antioxidant treatment. These results suggest that ROS production in the intestine induced by gliadin intake causes disruption of intestinal integrity and increases germ cell apoptosis. Gliadin-induced germ cell apoptosis (GIGA) was suppressed by depletion of cep-1, ced-13, egl-1, or mpk-1. However, HUS-1 was not activated, suggesting that GIGA is activated through the mitogen-activated protein kinase (MAPK) pathway and is CEP-1-dependent but is a separate pathway from that controlling the DNA damage response. Taken together, our results suggest that gliadin causes intestinal barrier disruption through ROS production and interacts with the germ cells to reduce fertility through GIGA.

ALG-2/AGO-Dependent mir-35 Family Regulates DNA Damage-Induced Apoptosis Through MPK-1/ERK MAPK Signaling Downstream of the Core Apoptotic Machinery in Caenorhabditis elegans

MicroRNAs (miRNAs) associate with argonaute (AGO) proteins to post-transcriptionally modulate the expression of genes involved in various cellular processes. Herein, we show that loss of the Caenorhabditis elegans AGO gene alg-2 results in rapid and significantly increased germ cell apoptosis in response to DNA damage inflicted by ionizing radiation (IR). We demonstrate that the abnormal apoptosis phenotype in alg-2 mutant animals can be explained by reduced expression of mir-35 miRNA family members. We show that the increased apoptosis levels in IR-treated alg-2 or mir-35 family mutants depend on a transient hyperactivation of the C. elegans ERK1/2 MAPK ortholog MPK-1 in dying germ cells. Unexpectedly, MPK-1 phosphorylation occurs downstream of caspase activation and depends at least in part on a functional cell corpse-engulfment machinery. Therefore, we propose a refined mechanism, in which an initial proapoptotic stimulus by the core apoptotic machinery initiates the engulfment process, which in turn activates MAPK signaling to facilitate the demise of genomically compromised germ cells.

Vital roles of PCNA K165 modification during C. elegans gametogenesis and embryogenesis

In eukaryotes, the DNA damage bypass pathway is promoted by ubiquitylation of PCNA at the conserved lysine 164. Using CRISPR-Cas9 system, we introduced amino acid substitution at K165 of C. elegans PCNA that corresponds to K164 in other characterised organisms and examined the contribution of this residue at a variety of stages during development. In the presence of UV-induced DNA lesions, PCNA-K165 is crucial for not only the early embryonic stages but also during larval development, implicating its functions for a broad time period during animal development. We also show that, without induction of DNA damage, concomitant inhibition of PCNA ubiquitylation and checkpoint activation causes abnormal gametogenesis events and severely impairs reproduction of worms. Our findings suggest a conserved function of PCNA ubiquitylation in tolerance of UV-induced damage and also propose that PCNA ubiquitylation contributes to gametogenesis during unperturbed C. elegans development.

Monte-Carlo dosimetry and real-time imaging of targeted irradiation consequences in 2-cell stage Caenorhabditis elegans embryo

Charged-particle microbeams (CPMs) provide a unique opportunity to investigate the effects of ionizing radiation on living biological specimens with a precise control of the delivered dose, i.e. the number of particles per cell. We describe a methodology to manipulate and micro-irradiate early stage C. elegans embryos at a specific phase of the cell division and with a controlled dose using a CPM. To validate this approach, we observe the radiation-induced damage, such as reduced cell mobility, incomplete cell division and the appearance of chromatin bridges during embryo development, in different strains expressing GFP-tagged proteins in situ after irradiation. In addition, as the dosimetry of such experiments cannot be extrapolated from random irradiations of cell populations, realistic three-dimensional models of 2 cell-stage embryo were imported into the Geant4 Monte-Carlo simulation toolkit. Using this method, we investigate the energy deposit in various chromatin condensation states during the cell division phases. The experimental approach coupled to Monte-Carlo simulations provides a way to selectively irradiate a single cell in a rapidly dividing multicellular model with a reproducible dose. This method opens the way to dose-effect investigations following targeted irradiation.

Progression of Meiosis Is Coordinated by the Level and Location of MAPK Activation Via OGR-2 in Caenorhabditis elegans

During meiosis, a series of evolutionarily conserved events allow for reductional chromosome division, which is required for sexual reproduction. Although individual meiotic processes have been extensively studied, we currently know far less about how meiosis is regulated and coordinated. In the Caenorhabditis elegans gonad, mitogen-activated protein kinase (MAPK) signaling drives oogenesis while undergoing spatial activation and deactivation waves. However, it is currently unclear how MAPK activation is governed and how it facilitates the progression of oogenesis. Here, we show that the oocyte and germline-related 2 (ogr-2) gene affects proper progression of oogenesis. Complete deletion of ogr-2 results in delayed meiotic entry and late spatial onset of double-strand break repair. Elevated levels of apoptosis are observed in this mutant, independent of the meiotic canonical checkpoints; however, they are dependent on the MAPK terminal member MPK-1/ERK. MPK-1 activation is elevated in diplotene in ogr-2 mutants and its aberrant spatial activation correlates with stages where meiotic progression defects are evident. Deletion of ogr-2 significantly reduces the expression of lip-1, a phosphatase reported to repress MPK-1, which is consistent with OGR-2 localization at chromatin in germ cells. We suggest that OGR-2 modulates the expression of lip-1 to promote the timely progression of meiosis through MPK-1 spatial deactivation.

A conserved CCM complex promotes apoptosis non-autonomously by regulating zinc homeostasis

Apoptotic death of cells damaged by genotoxic stress requires regulatory input from surrounding tissues. The C. elegans scaffold protein KRI-1, ortholog of mammalian KRIT1/CCM1, permits DNA damage-induced apoptosis of cells in the germline by an unknown cell non-autonomous mechanism. We reveal that KRI-1 exists in a complex with CCM-2 in the intestine to negatively regulate the ERK-5/MAPK pathway. This allows the KLF-3 transcription factor to facilitate expression of the SLC39 zinc transporter gene zipt-2.3, which functions to sequester zinc in the intestine. Ablation of KRI-1 results in reduced zinc sequestration in the intestine, inhibition of IR-induced MPK-1/ERK1 activation, and apoptosis in the germline. Zinc localization is also perturbed in the vasculature of krit1-/- zebrafish, and SLC39 zinc transporters are mis-expressed in Cerebral Cavernous Malformations (CCM) patient tissues. This study provides new insights into the regulation of apoptosis by cross-tissue communication, and suggests a link between zinc localization and CCM disease.

Transgenerational effects of diesel particulate matter on Caenorhabditis elegans through maternal and multigenerational exposure

Diesel particulate matter (DPM) is a dominant contaminant in fine particulate matters (PM_2.5) and has been proved to induce serious harmful effects to human beings, including lung cancer, allergic, and chronic bronchitis. However, little attention has been paid to understand the transgenerational effects of DPM. In the present study, we focused on the transgenerational effects of DPM in the model organism Caenorhabditis elegans (C. elegans) exposed in either maternal generation (F0) or consecutive generations (F0-F5). In maternal exposure manner, 0.1 and 1.0 µg/mL DPM significantly increased the germ cell apoptosis at F0 generation, while the number of apoptotic germ cells at F1-F5 generation were gradually recovered back to control level. The brood size were significantly reduced by DPM at F2 generation and recovered to control level at F3-F5 generations. In continuous exposure manner, although 0.1 and 1.0 µg/mL DPM induced significant germ cell apoptosis in F0 generation, there was no difference between F0 and other generations. Continuous exposure to DPM at 0.1 and 1.0 µg/mL impaired the brood size in F2 to F5 generations. Using a series of loss-of-function mutant strains, we found that cep-1 (w40), hus-1 (op241), and mitogen-activated protein kinase (MAPK) related signaling pathway genes were involved in DPM-induced apoptosis. Our results clearly demonstrated that the adverse effects of DPM could be passed on through long-term multigenerational exposure and DNA damage checkpoint genes and MAPK signal pathway played an essential role in response to DPM induced development and reproduction toxicity.

MiR-35 buffers apoptosis thresholds in the C. elegans germline by antagonizing both MAPK and core apoptosis pathways

Apoptosis is a genetically programmed cell death process with profound roles in development and disease. MicroRNAs modulate the expression of many proteins and are often deregulated in human diseases, such as cancer. C. elegans germ cells undergo apoptosis in response to genotoxic stress by the combined activities of the core apoptosis and MAPK pathways, but how their signalling thresholds are buffered is an open question. Here we show mir-35–42 miRNA family play a dual role in antagonizing both NDK-1, a positive regulator of MAPK signalling, and the BH3-only pro-apoptotic protein EGL-1 to regulate the magnitude of DNA damage-induced apoptosis in the C. elegans germline. We show that while miR-35 represses EGL-1 by promoting transcript degradation, repression of NDK-1 may be through sequestration of the transcript to inhibit translation. Importantly, dramatic increase in NDK-1 expression was observed in cells about to die. In the absence of miR-35, increased NDK-1 activity enhanced MAPK signalling that lead to significant increases in germ cell death. Our findings demonstrate that NDK-1 acts upstream of (or in parallel to) EGL-1, and that miR-35 targets both egl-1 and ndk-1 to fine-tune cell killing in response to genotoxic stress.

MINA-1 and WAGO-4 are part of regulatory network coordinating germ cell death and RNAi in C. elegans

Post-transcriptional control of mRNAs by RNA-binding proteins (RBPs) has a prominent role in the regulation of gene expression. RBPs interact with mRNAs to control their biogenesis, splicing, transport, localization, translation, and stability. Defects in such regulation can lead to a wide range of human diseases from neurological disorders to cancer. Many RBPs are conserved between Caenorhabditis elegans and humans, and several are known to regulate apoptosis in the adult C. elegans germ line. How these RBPs control apoptosis is, however, largely unknown. Here, we identify mina-1(C41G7.3) in a RNA interference-based screen as a novel regulator of apoptosis, which is exclusively expressed in the adult germ line. The absence of MINA-1 causes a dramatic increase in germ cell apoptosis, a reduction in brood size, and an impaired P granules organization and structure. In vivo crosslinking immunoprecipitation experiments revealed that MINA-1 binds a set of mRNAs coding for RBPs associated with germ cell development. Additionally, a system-wide analysis of a mina-1 deletion mutant compared with wild type, including quantitative proteome and transcriptome data, hints to a post-transcriptional regulatory RBP network driven by MINA-1 during germ cell development in C. elegans. In particular, we found that the germline-specific Argonaute WAGO-4 protein levels are increased in mina-1 mutant background. Phenotypic analysis of double mutant mina-1;wago-4 revealed that contemporary loss of MINA-1 and WAGO-4 strongly rescues the phenotypes observed in mina-1 mutant background. To strengthen this functional interaction, we found that upregulation of WAGO-4 in mina-1 mutant animals causes hypersensitivity to exogenous RNAi. Our comprehensive experimental approach allowed us to describe a phenocritical interaction between two RBPs controlling germ cell apoptosis and exogenous RNAi. These findings broaden our understanding of how RBPs can orchestrate different cellular events such as differentiation and death in C. elegans.