Larval Development Research Articles

Dietary supplementation with thymoquinone inhibits rotenone induced developmental toxicity in Drosophila melanogaster: Focus on ovary and larval development

Pesticide exposure has been associated with various health conditions like asthma, Parkinson’s disease, Alzheimer’s disease, genetic disorders, epigenetic changes, oxidative stress, and hormonal disruption. Recent evidence suggests that infants are more vulnerable to pesticides (such as rotenone) than adults. Although the disease has already been clinically characterized, no treatment has yet been developed to improve pathology or prevent developmental toxicity. Therefore, the purpose of this study was to investigate whether thymoquinone (TQ) from Nigella sativa seeds could ameliorate rotenone (ROT)-induced developmental damage in both Drosophila melanogaster ovary and third instar larvae. Female adult wild-type flies and third instar larvae (72 ± 2 h after egg laying) were exposed to ROT and/or TQ through food for 48 and 24 h respectively. Results indicate that co-exposure of TQ inhibits ROT-induced increased oxidative stress and alleviates abnormal antioxidant enzyme activities. Further, TQ alters developmental gene expression (Bacoid, Oscar, Nanos, and Gurken), impedes mitochondrial dysfunction, and reduces apoptosis in ROT induced ovary. In addition, TQ changes ROT induced abnormal crawling behaviour, cholinergic dysfunction, and dopamine depletion to normal levels in third instar larvae. Also, TQ reduces pupation and emergence time in ROT induced third instar larvae. The above findings demonstrate that ROT exposure during early developmental stages is inevitable, and TQ supplementation prevents developmental toxicity in the Drosophila ovary and third instar larvae. A diet enriched TQ provides a ray of hope in preventing ROT induced developmental toxicity.

Effect and Mechanism of Uric Acid in Regulating Larval Growth and Development of Drosophila Melanogaster

Objective To explore the effect and mechanism of uric acid (UA) in regulating the larval growth and development of Drosophila melanogaster. Methods A total of 1350 newly hatched first-instar larvae of wild-type Drosophila melanogaster (W1118) were collected,and the Drosophila melanogaster model of hyperuricemia was constructed with a high purine diet.The larvae were assigned into three groups (n=150):control (standard corn meal medium),low-dose adenine (corn meal medium containing 0.05% adenine),and high-dose adenine (corn meal medium containing 0.10% adenine),and two parallel groups were set up.The growth and development of larvae in each group was observed,and the UA and hormone levels were measured.In addition,the expression levels of genes involved in growth and development were determined. Results Compared with the control group,the low- and high-dose adenine groups showed elevated UA levels (both P<0.001) and prolonged developmental period (P=0.024,P<0.001).The high-dose adenine group showed decreased survival rate,pupation rate,and eclosion rate and elevated levels of juvenile hormone (JH) and 20-hydroxyecdysone (20E) (all P<0.001).The PCR results showed that compared with the control group,high-dose adenine upregulated the mRNA levels of reactive oxygen species (ROS),forkhead box O (FOXO),and mammalian target of rapamycin (mTOR) while downregulating the mRNA levels of Sestrin,mTOR complex 1(mTORC1),and AMP-activated protein kinase (all P<0.001). Conclusion High concentrations of UA may promote the expression of ROS/FOXO/mTORC1/mTOR signaling pathway by regulating the levels of JH and 20E,thereby inhibiting the larval growth and development of Drosophila melanogaster.

Larval development of a parasitoid depends on host ecdysteroids

Parasitoids often exhibit high flexibility in their development depending on stages of their host at the parasitism, yet little is known about the mechanism underlying such flexibility. In the study, we evaluated the larval development time of the parasitoid Exorista sorbillans (Diptera: Tachinidae) on the lepidopteran model insect Bombyx mori (Lepidoptera: Bombycidae). We found that the development duration of E. sorbillans larvae parasitizing on the late-developmental silkworms was significantly shorter than that of the larvae parasitizing on the early-developmental hosts. Intriguingly, the 2nd-3rd instar molting of parasitoid always occurred when the ecdysteroid titers in the host were increased to higher levels. Furthermore, inhibiting the release of ecdysteroids to parasitic abdomen by thorax-abdomen ligation of the host only repressed the 2nd-instar growth and molting of E. sorbillans larvae, but had no effect on their pupation. Meanwhile, the ecdysone synthesis and 20-hydroxyecdysone (20E) signaling in larval parasitoids were impeded after ligation treatment. Moreover, exogenous 20E application could largely rescue the defect in 2nd instar growth and molting through stimulating ecdysone synthesis and signaling in E. sorbillans. Our results indicate that the parasitoid requires the host ecdysteroids to stimulate 20E signaling and the subsequent 2nd- instar growth and molting. These findings will improve our understanding of the host utilization strategies of parasitoids, and contribute to the development of in vitro rearing procedures of tachinid parasitoids for biological control.

Exploring unified methods of killing and storing insect samples for forensic entomotoxicology using diazepam in Lucilia sericata (Meigen, 1826) (Diptera: Calliphoridae) larvae

Forensic entomologists use the maturity of necrophagous larvae to estimate the minimum post-mortem interval (PMImin), ideally taking account of effects that xenobiotics in the corpse may have on insect maturation. Forensic toxicologists may employ larvae to detect drugs in drug-related deaths when human samples are unavailable. Yet current pre-analytical practices of these two professions differ significantly, impeding the successful use of the same samples. Potential benefits of shared pre-analytical practices and opportunities for enhanced collaboration have yet to be fully explored. We employed Lucilia sericata (Meigen, 1826) (Diptera: Calliphoridae) larvae, grown in the presence of diazepam, to investigate the effects of two standard investigative practices on larvae for drug detection and for quantifying mass and length as proxies of age. Specimens were killed by either blanching or freezing and stored at -20℃ for either intermediate or long periods. Blanched larvae showed smaller changes in size and body integrity during storage, thereby producing the most reproducible estimates of PMImin. Consequently, data obtained from blanched larvae were used to evaluate the impact of diazepam on larval development. Diazepam exerted no significant effect on larval mass, and a weak effect on length. Diazepam recovery was significantly higher from blanched larvae, suggesting that freeze-killing causes drug loss. This model system demonstrates the value to forensic entomologists of the standard technique of blanching larvae, followed by storage at -20℃ for toxicological analysis. We recommend that forensic toxicologists consider blanching to kill larvae before storage at low temperatures, at least for certain drugs. This approach offers the dual benefit of high-quality specimens for both PMI estimation and drug detection.

Pesticides and Heavy Metal Toxicity in Fish and Possible Remediation – A Review

Abstract Pesticides and heavy metals are considered as potent contaminants in aquatic environment. Both contaminants are sourced into the aquatic ecosystems by various types of anthropogenic as well as natural practices. Such types of aquatic contamination drastically affect the normal activity of associated living organisms particularly fish. Both the pesticides and heavy metals toxicity cause several negative effects on fish growth, physiology, immune response, reproduction, embryonic and larval development as well as different histopathology of major organs including fish gill, kidney, liver, gonads, and intestine. Besides, the consumption of contaminated fish poses a serious health concern to associated consumers. Considering these serious issues, the current review is designed to investigate the toxic effects of pesticides and heavy metals on different aspects of fishes along with their possible sources, major types, and mode of action as well as role of medicinal herbs to mitigate their toxicity.

ECR Spotlight – Yanira Jiménez-Padilla

ECR Spotlight is a series of interviews with early-career authors from a selection of papers published in Journal of Experimental Biology and aims to promote not only the diversity of early-career researchers (ECRs) working in experimental biology but also the huge variety of animals and physiological systems that are essential for the ‘comparative’ approach. Yanira Jiménez-Padilla is an author on ‘ Live yeasts accelerate Drosophila melanogaster larval development’, published in JEB. Yanira is a PhD student in the lab of Brent J. Sinclair at Department of Biology, University of Western Ontario, Canada, investigating how gut microbes, especially yeasts, affect their host physiology.

Life History Strategies Drive Meso-Scale Distribution Patterns in Coastal Benthic Macroinvertebrates.

The environment shapes the spatial distribution of species, but species also comprise suites of traits which may indicate their adaptability to a specific environment. This forms the basis of trait biogeography studies. We thus examined how a species distribution is not only influenced by its environment and traits, but by interactions among its traits. Trait information was collected for 150 intertidal macroinvertebrates along a 3000 km environmental and biogeographic gradient on the South African coast. This information was analysed, as functional entities (FEs) were species performing similar functions that have the same trait values and were further condensed into two trait domains (Reproduction and Lifestyle). We then defined Life History Strategies (LHS) as specific combinations of Lifestyle and Reproduction FEs. Seven combinations of Lifestyle and Reproduction formed LHS that dominated total biomass. Some of these LHS were ubiquitous, while others showed geographic patterns across our west-east environmental gradient. For Lifestyle, filter-feeders exhibited high abundances on the East (subtropical, oligotrophic) and West (cool-temperate, eutrophic) extremes of the biogeographic gradient, but differed between the two in size at reproductive maturity and larval development type. This similarity in functionality of feeding mechanism and mobility with different reproductive strategies suggests a trait trade-off (investment in one trait reduces resources for others) between the Reproduction and Lifestyle domains. Within the Reproduction domain, gonochoristic, annual planktotrophic reproduction was common across bioregions, reflecting spin-offs (investment in one trait facilitates another trait) among these traits. Gonochoristic investment in less frequent episodic reproduction is another trade-off, with investment in large size and delayed maturation being a trade-off for many reproductive cycles. Overall, although our data supports the habitat templet model (i.e., the importance of environmental drivers), it further indicates that species distribution patterns observed along the South African coast reflect strong trait interactions and biomass patterns related to their LHS.

Sorption of PFOS onto polystyrene microplastics potentiates synergistic toxic effects during zebrafish embryogenesis and neurodevelopment

Microplastics (MPs) have become an emerging anthropogenic pollutant, and their ability to sorb contaminants potentially enhances the threats to the ecosystem. Only a few studies are available to understand the combined effects of microplastics and other pollutants. The present study investigated the sorption of perfluorooctane sulfonic acid (PFOS) onto polystyrene microplastics (PS-MPs) at varying concentrations, using molecular dynamics simulation (MDS) to preliminarily explore the adsorption behavior. The MDS results revealed negative interaction energies between PFOS and PS-MPs, underscoring PS-MPs' role as a potential adsorbent for PFOS in an aqueous solution. Thereafter, zebrafish embryos were employed to explore the toxic effects of combined exposure to PS-MPs and PFOS. Fluorescence and Scanning Electron Microscopy (SEM) suggested PS-MP accumulation individually and in combination with PFOS on the embryonic chorion membrane. As a result, the exposed group showed increased inner pore size of the chorionic membrane and accelerated heartbeat, indicating hypoxic conditions and hindered gaseous exchange. PS-MPs aggravated the toxicity of PFOS during larval development manifested by delayed hatching rate, increased mortality, and malformation rate. Additionally, increased ROS accumulation and altered antioxidant enzymatic status were observed in all the exposed groups suggesting perturbation of the redox state. Additionally, co-exposure of zebrafish larvae to PS-MPs and PFOS resulted in an abrupt behavioral response, which decreased AChE activity and altered neurotransmitter levels. Taken together, our results emphasize that PS-MPs can act as a potential vector for PFOS, exerting synergistic toxic effects in the aquatic environment, and hence their health risks cannot be ignored.

Temperature dependent sensitivity of the harpacticoid copepod Nitokra spinipes to marine algal toxins

Harmful algal blooms (HABs) – proliferated algae densities, often producing toxins – have increasingly been found in ocean and coastal areas. Recent studies show that rising temperatures contribute to HAB occurrence, but the broader influence of climate change on these outbreaks is less quantified. Of particular concern is the limited research on HAB toxin effects under varying temperatures, especially regarding primary consumers such as copepods, a crucial component of aquatic ecosystems. Therefore, we examined the impact of marine toxins on the harpacticoid copepod Nitokra spinipes, a model organism for marine ecotoxicology, in the context of climate change. We evaluated the toxicity of four purified, commonly occurring algal toxins, at three different temperatures in the laboratory. First, adult females were exposed to a concentration series of toxins at 15, 20, and 25 °C for 48 hours. EC50 values of domoic acid ranged from 8.79 ± 1.93 μg L-1 to 25.97 ± 11.96 μg L-1. Nauplii, aged 48 to 72 hours, were exposed at 18, 20 and 22 °C for the same duration. Less sensitive compared to adults, the EC50 of domoic acid in this case varied from 57.26 ± 6.82 μg L-1 to 97.24 ± 6.45 μg L-1. Both results indicated a temperature-dependent EC50. For the chronic toxicity tests, larval development ratio (LDR), brood size and inter-brood time of domoic acid (DA), yessotoxin (YTX), saxitoxin (STX), and microcystin-LR (MC-LR) were examined at 18, 20 and 22 °C. We observed that with increasing temperatures, LDR increased, whereas brood size significantly decreased as DA, YTX or STX concentrations rose. No interaction between temperature and algal toxins was found but a temperature dependent sensitivity of copepods towards DA, YTX and STX was revealed. Our research provides insights into the effects of long-term exposure to algal toxins on marine copepods and the potential impacts of climate warming.

Predatory potential of Coccinella undecimpunctata L. (Coleoptera, Coccinellidae) on Aphis craccivora Koch. (Hemiptera, Aphididae) in Ladakh, India

Predatory potential of all instar larvae and adults of Coccinella undecimpunctata (Coleoptera, Coccinellidae), using Aphis craccivora Koch (Hemiptera, Aphididae) was assessed in laboratory settings. The study, conducted with varying aphid densities in rearing jars, showed a significant increase in prey consumption as aphid density rose. Furthermore, prey consumption heightened with larval development, with 4th instars devouring more aphids compared to earlier instars. Female adults exhibited greater aphid consumption than males. Deploying both 4th instar larvae and adults could enhance pest suppression.

Can microplastic contamination affect the wing morphology and wingbeat frequency of Aedes aegypti (Diptera: Culicidae) mosquitoes?

Microplastics (MPs) are increasingly widespread in the environment, which raises questions about their potential effects at different biological levels. It is essential to assess the impacts on biodiversity, and it is also crucial to understand whether the presence of MPs can interfere with the biological traits of species of relevance in public health. Considering that the life-history traits of mosquitoes, such as size and the wingbeat frequency (WBF), are related to its vector competence, here, we study the effects of 106 particles L-1 (as expected concentration of MPs on the environment, using the polyethylene type) on WBF, as well as wing morphology, testing the Culicidae species found across all continents, Aedes aegypti, as an indicator. Results show that larvae survival and development were not affected by the tested concentration of MP. Geometric morphometrics showed some asymmetry in female mosquito wings, which were also smaller for individuals reared in MP suspension. As for WBF, results did not indicate any significant differences between females. Male mosquitoes, however, showed alterations in WBF and wing morphology, suggesting possible sex-specific reactions to microplastic exposure. Also, the combination of morphological parameters analyzed as covariates (wing centroid size and body weight) did not significantly affect WBF for both female and male mosquitoes. Overall, this study shows an inaugural investigation of the effects of MP on wing size and WBF on Ae. aegypti, shedding light on these parameters tested for a current pollution issue and its impact on a virus vector.

Влияние плотности посадки на личиночное развитие камышовой жабы (Epidalea calamita) (по результатам лабораторных исследований)

The Natterjack toad (Epidalea calamita) is widespread in Europe, but it is reducing in numbers, especially in the north and east of its range. The paper presents the results of studying the effect of initial stocking density on survival, development duration and body length of E. calamita larvae in laboratory conditions. The experiments used containers with the same bottom area (1092 cm2), but with different water levels (14 and 28 cm). Larvae were grown at different stocking densities per unit volume (1–3 larvae/L) of water and per unit area of the bottom (82.4–494.5 larvae/m2). The studied larvae have very high survival rate (90.7–100.0%) and show no differences in this parameter in groups in all variants of cultivation. Animals from the lowest density groups were characterized by the shortest developmental duration. With an increase in the stocking density per unit volume of water and bottom area the larval development duration increased. There was a negative correlation of body length with the initial stocking density per unit volume of water (r=-0.52) and bottom area (r=-0.62). The stocking density per the bottom area affected greater the larval developmental duration and body length of juvenile toads, than the stocking density per unit water volume. The authors note that it is advisable to grow E. calamita larvae in laboratory conditions at maximum stocking density (3 larvae/L and 494.5 larvae/m2), as this allows for a greater number of juvenile toads.

Development observed in the field of the Antarctic bivalve mollusc Aequiyoldia eightsii at Signy Island, South Orkney Islands

ABSTRACT The embryonic development of marine ectotherms has been shown to be strongly temperature dependent across the world's oceans. However, at the coldest sites, in the polar regions, development is even slower than would be predicted on the basis of the temperature dependence of development in warmer waters, and this is thought to be a consequence of changes in physical characteristics of cytoplasm near 0 °C—such as viscosity and osmolyte packing that slow protein folding and increase the likelihood of interference by charged particles, and their effect on protein synthesis. The overwhelming majority of studies of rates of embryonic development have been laboratory-based, with animals either collected directly from the sea and spawned in the laboratory or held first in the laboratory and preconditioned to set environments before spawning. Few studies have assessed development from regularly collected samples and assessed field development, especially from polar latitudes. Here we present data for the Antarctic bivalve mollusc Aequiyoldia eightsii, tracking its development from spawning on 25/26 May to hatching of pelagic veligers on 12 June and the disappearance of pediveliger larvae from the water column at the end of September or early October, 108–114 days later. Larval dry mass was constant at 16.7 µg (SE = 0.19) across the pelagic phase, except for the initial few days after hatching when it was 9.55 µg (SE = 0.60). The difference was likely the calcification of the larval shell. The development time to trochophore was 189 h, and this was in line with previous studies showing larval development at temperatures around 0 °C is around 4–22 times slower than would be predicted from the general effect of temperature on development rates.

Assessing Queen Cell Cups Priming from Combs of Different Honey Bee Species for Mass Rearing of Apis mellifera L. Queen Bee

Experiments were carried out at the Beekeeping-cum-Honey Production Unit, Department of Entomology, Bihar Agricultural University, Sabour, Bhagalpur, Bihar, India, during 2020-21. The study was aimed to evaluate queen cell cups prepared from combs of different bee species to find out a suitable technique for royal jelly production through mass queen bee rearing of Apis mellifera species. The worker bees of Apis mellifera (AM) exhibited a low preference for working with combs produced by Apis dorsata (AD) and Apis cerana (AC) for queen cell construction amongst evaluated combs. In contrast, when queen cell cups were made using AM combs, the worker bees attempted to build 100% of the cells. The time required by AM worker bees to complete queen cell construction on AM combs ranged from 7 to 15 days, however, they took 1.20 and 0.98 times longer to complete cells made with AD and AC combs, respectively. Similarly, queen bees showed reluctance to lay eggs in cells built on AD and AC combs. In queen cells constructed on AM combs, the queen bee began laying eggs on the second day after release into the nucleus hive and continued for five days, with an increasing trend in egg-laying activity. Among the different batches of eggs laid, the third batch was the most successful in respect of the larval growth and development. Additionally, larval growth showed a consistent upward trend during the first three days of observation for each laying batch. A. mellifera combs have been found to be more favourable for queen cell construction by worker bees, showing a strong preference for the queen's egg-laying performance, as well as optimal larval growth and development. Based on these findings, it is recommended that beekeepers may adopt this method to promote mass queen bee rearing and enhance royal jelly production.

Ultrastructure of Immatures Stages and Life Cycle of Helicobia aurescens (Diptera: Sarcophagidae: Sarcophaginae).

Helicobia aurescens is a flesh fly associated with pig and rat carcasses. This study aims to describe the life cycle at two temperatures (27 ± 1 °C and 29 ± 1 °C) and analyze the morphological characteristics of the eggs, larvae, and puparia of H. aurescens using scanning electron microscopy (SEM). Temperature is an abiotic factor that greatly influences the development of insects. The larval development of H. aurescens lasts longer at 27 ± 1 °C than it does at 29 ± 1 °C, affecting the growth of newly hatched larvae into adults. The females larviposited three times more at 27 °C than they did at 29 °C, and the number of days laying larvae was also greater. At 27 °C, they laid larvae for 38 days, whereas, at 29 °C, the females larviposited for 21 days. No hatching lines or median areas were detected on the exochorion with SEM, as in the other sarcophagid species. The first-instar larva is very similar to those of the other species. The second instar has anterior spiracles present on the first thoracic segment, with six or seven ramifications aligned regularly. On the third instar, these structures have eight ramifications in a regular row and are located dorsolaterally. The puparium morphology is similar to that of the third-instar larvae.

Story of an infection: Viral dynamics and host responses in the Caenorhabditis elegans-Orsay virus pathosystem.

Orsay virus (OrV) is the only known natural virus affecting Caenorhabditis elegans, with minimal impact on the animal's fitness due to its robust innate immune response. This study aimed to understand the interactions between C. elegans and OrV by tracking the infection's progression during larval development. Four distinct stages of infection were identified on the basis of viral load, with a peak in capsid-encoding RNA2 coinciding with the first signs of viral egression. Transcriptomic analysis revealed temporal changes in gene expression and functions induced by the infection. A specific set of up-regulated genes remained active throughout the infection, and genes correlated and anticorrelated with virus accumulation were identified. Responses to OrV mirrored reactions to other biotic stressors, distinguishing between virus-specific responses and broader immune responses. Moreover, mutants of early response genes and defense-related processes showed altered viral load progression, uncovering additional players in the antiviral defense response.

Functions and Mechanism of Thyroid Hormone Receptor Action During Amphibian Development.

Thyroid hormones and their receptors (TRs) play critical roles during vertebrate development. One of the most dramatic developmental processes regulated by thyroid hormones is frog metamorphosis, which mimics the postembryonic (perinatal) period in mammals. Here, we review some of the findings on the developmental functions of thyroid hormones and TRs as well as their associated mechanisms of action obtained from this model system. More than 2 decades ago, a dual function model was proposed for TR in anuran development. During larval development, unliganded receptors recruit corepressors to repress thyroid hormone response genes to prevent premature metamorphic changes. Subsequently, when thyroid hormone levels rise, liganded receptors recruit coactivators to activate thyroid hormone response genes, leading to metamorphic changes. Over the years, molecular and genetic approaches have provided strong support for this model and have shown that it is applicable to mammalian development as well as to understanding the diverse effects of thyroid hormones in normal physiology and diseases caused by thyroid hormone signaling dysfunction.

The ethanol extract of Sargassum duplicatum as an ovicidal agent against Aedes aegypti

Dengue hemorrhagic fever (DHF) is a major health concern in tropical and subtropical countries. Indonesia has DHF cases perennially every year. On the other hand, Indonesia is abundant with seaweed (Sargassum duplicatum), which can be found across its seashore. The macroalgae contains secondary metabolites with ovicidal activity; hence, it has the potential to be utilized in suppressing the Aedes aegypti. The aim of this study was to determine the ovicidal activity of S. duplicatum against the Ae. aegypti eggs. The algae were macerated with ethanol 70% before being subjected to qualitative phytochemical screenings. The ovicidal tests were conducted with an extract concentration of 50 ppm, 100 ppm, 500 ppm, 1000 ppm, and 1500 ppm, while distilled water was used as the control. The hatchability of Ae. aegypti was observed 24 hours a day for 4 days and the larval development was investigated under a microscope. Phytochemical screenings revealed that the extract was positive containing alkaloids, flavonoids, steroids, saponins, and phenols. The hatchability of Ae. aegypti eggs were significantly reduced following the S. duplicatum extract exposure for four days (p=0.000). The extract had LC50 of 828.653 ppm and LC50 of 1786.09 ppm for the ovicidal activity against Ae. aegypti eggs. The concentration of ethanol extract of S. duplicatum did not affect the mosquito development from larvae to adult stage (p=0.263). Further research is needed to explore the effect of specific compounds contained in the S. duplicatum and investigate their ovicidal potential.

MiRNA-mediated gene silencing in Drosophila larval development involves GW182-dependent and independent mechanisms.

MicroRNAs (miRNAs) regulate a wide variety of biological processes by silencing their target genes. Argonaute (AGO) proteins load miRNAs to form an RNA-induced silencing complex (RISC), which mediates translational repression and/or mRNA decay of the targets. A scaffold protein called GW182 directly binds AGO and the CCR4-NOT deadenylase complex, initiating the mRNA decay reaction. Although previous studies have demonstrated the critical role of GW182 in cultured cells as well as in cell-free systems, its biological significance in living organisms remains poorly explored, especially in Drosophila melanogaster. Here, we generated gw182-null flies using the CRISPR/Cas9 system and found that, unexpectedly, they can survive until an early second-instar larval stage. Moreover, in vivo miRNA reporters can be effectively repressed in gw182-null first-instar larvae. Nevertheless, gw182-null flies have defects in the expression of chitin-related genes and the formation of the larval trachea system, preventing them from completing larval development. Our results highlight the importance of both GW182-dependent and -independent silencing mechanisms in vivo.

Autism candidate gene rbm-26 (RBM26/27) regulates MALS-1 to protect against mitochondrial dysfunction and axon degeneration during neurodevelopment.

Mitochondrial dysfunction is thought to be a key component of neurodevelopmental disorders such as autism, intellectual disability, and ADHD. However, little is known about the molecular mechanisms that protect against mitochondrial dysfunction during neurodevelopment. Here, we address this question through the investigation of rbm-26, the C. elegans ortholog of the RBM27 autism candidate gene, which encodes an RNA-binding protein whose role in neurons is unknown. We report that RBM-26 (RBM26/27) protects against axonal defects by negatively regulating expression of the MALS-1 (MALSU1) mitoribosomal assembly factor. Autism-associated missense variants in RBM-26 cause a sharp decrease in RBM-26 protein expression along with defects in in axon overlap and axon degeneration that occurs during larval development. Using a biochemical screen, we identified the mRNA for the MALS-1 mitoribosomal assembly factor as a binding partner for RBM-26. Loss of RBM-26 function causes a dramatic overexpression of mals-1 mRNA and MALS-1 protein. Moreover, genetic analysis indicates that this overexpression of MALS-1 is responsible for the mitochondrial and axon degeneration defects in rbm-26 mutants. These observations reveal a mechanism that regulates expression of a mitoribosomal assembly factor to protect against axon degeneration during neurodevelopment.