Functional analysis of the circadian clock gene timeless in Tribolium castaneum

Beyond adult models: Tribolium castaneum larval timekeeping reveals unexpected robustness and insights into circadian clock

Circadian rhythms are self-sustained endogenous oscillations that are found in all living organisms. In insects, circadian rhythms control a wide variety of behavioral and physiological processes, including feeding, locomotion, mating, and metabolism. While the role of circadian rhythms in adult insects is well-understood, it is largely unexplored in larvae. This study investigates the potential for larval synchronized activity in the red flour beetle (Tribolium castaneum), a species exhibiting solitary and aggregation phases. We hypothesized that, similar to adults, larvae would exhibit a daily activity pattern governed by an endogenous circadian clock. We further predicted that the transition between the solitary and gregarious phases extends to unique temporal activity patterns. Our results revealed unique timekeeper gene expression in larvae, leading to a distinct daily rhythm characterized by nocturnal activity. Cues indicating on potential cannibalism did not change daily activity peak. However, the absence of these cues significantly reduced the proportion of rhythmic larvae and led to higher variation in peak activity, highlighting the crucial role of social interactions in shaping their rhythmicity. This study sheds light on the evolution and function of larval synchronization in group-living insects, offering novel insights into this complex behavior.

Circadian Activity and Clock Genes in Pachycrepoideus vindemmiae: Implications for Field Applications and Circadian Clock Mechanisms of Parasitoid Wasps

Despite the importance of circadian rhythms in insect behavior, our understanding of circadian activity and the molecular oscillatory mechanism in parasitoid wasp circadian clocks is limited. In this study, behavioral activities expected to be under the control of the endogenous circadian system were characterized in an ectoparasitoid wasp, Pachycrepoideus vindemmiae. Most adults exhibited emergence between late night and early morning, while mating only occurred during the daytime, with a peak at midday. Oviposition had three peaks in the early morning, late day, or early night and late night. Additionally, we identified eight putative clock genes from P. vindemmiae. The quantitative PCR (qPCR) results indicate that most clock genes showed significant rhythmic expressions. Our comparative analysis of clock genes in P. vindemmiae and 43 other parasitoid wasps revealed that none of the wasps possessed the timeless and cry1 genes commonly found in some other insect species, suggesting that the circadian clock system in parasitoid wasps is distinct from that in other non-Hymenoptera insects such as Drosophila. Thus, this study attempted to build the first hypothetical circadian clock model for a parasitoid wasp, thus generating hypotheses and providing a platform for the future functional characterization of P. vindemmiae clock genes as well as those of other parasitoid wasps. Finally, these findings on P. vindemmiae circadian activity will aid the development of effective field release programs for biological control, which can be tested under field conditions.

Mutation of the clock gene timeless disturbs diapause induction and adult emergence rhythm in Helicoverpa armigera

BACKGROUND

Circadian rhythms are physical and behavioral changes that follow the 24-h cycle of Earth's light and temperature and are regulated by clock genes. Timeless (Tim) has been identified as a canonical clock gene in some insects, however, its functions have been little studied in lepidopteran pests.

RESULTS

To investigate Tim (HaTim) gene function in Helicoverpa armigera, an important lepidopteran pest, we obtained the HaTim mutant using the CRISPR/Cas9 gene editing system. Our results showed that the transcript levels of HaTim rhythmically peaked at night in heads of the wild larvae and adult, and the diel expression of HaTim was sensitive to photoperiod and temperature. The expression rhythms of other clock genes, such as HaPer, HaCry1, HaCry2 and HaCwo, were disturbed in the HaTim mutant larvae, as that stage is a sensitivity period for diapause induction. Fifth-instar wild-type larvae could be induced to pupate in diapause under a short-day photoperiod and low temperature, however, fifth-instar HaTim mutant larvae could not be induced under the same conditions. In addition, the emergence of wild-type adults peaked early at night, but the rhythm was disturbed in the HaTim mutant with arrhythmic expression of some clock genes, such as HaPer, HaCry1 and HaCwo in adults.

CONCLUSION

Our results suggest that the clock gene Tim is involved in diapause induction and adult emergence in H. armigera, and is a potential target gene for controlling pest. © 2023 Society of Chemical Industry.

The red flour beetle T. castaneum: elaborate genetic toolkit and unbiased large scale RNAi screening to study insect biology and evolution

The red flour beetle Tribolium castaneum has emerged as an important insect model system for a variety of topics. With respect to studying gene function, it is second only to the vinegar fly D. melanogaster. The RNAi response in T. castaneum is exceptionally strong and systemic, and it appears to target all cell types and processes. Uniquely for emerging model organisms, T. castaneum offers the opportunity of performing time- and cost-efficient large-scale RNAi screening, based on commercially available dsRNAs targeting all genes, which are simply injected into the body cavity. Well established transgenic and genome editing approaches are met by ease of husbandry and a relatively short generation time. Consequently, a number of transgenic tools like UAS/Gal4, Cre/Lox, imaging lines and enhancer trap lines are already available. T. castaneum has been a genetic experimental system for decades and now has become a workhorse for molecular and reverse genetics as well as in vivo imaging. Many aspects of development and general biology are more insect-typical in this beetle compared to D. melanogaster. Thus, studying beetle orthologs of well-described fly genes has allowed macro-evolutionary comparisons in developmental processes such as axis formation, body segmentation, and appendage, head and brain development. Transgenic approaches have opened new ways for in vivo imaging. Moreover, this emerging model system is the first choice for research on processes that are not represented in the fly, or are difficult to study there, e.g. extraembryonic tissues, cryptonephridial organs, stink gland function, or dsRNA-based pesticides.

Identification and dynamic expression profiling of circadian clock genes in Spodoptera litura provide new insights into the regulation of sex pheromone communication

Spodoptera litura is an important pest that causes significant economic damage to numerous crops worldwide. Sex pheromones (SPs) mediate sexual communication in S. litura and show a characteristic degree of rhythmic activity, occurring mainly during the scotophase; however, the specific regulatory mechanisms remain unclear. Here, we employed a genome-wide analysis to identify eight candidate circadian clock genes in S. litura. Sequence characteristics and expression patterns were analyzed. Our results demonstrated that some circadian clock genes might regulate the biosynthesis and perception of SPs by regulating the rhythmic expression of SP biosynthesis-related genes and SP perception-related genes. Interestingly, all potential genes exhibited peak expression in the scotophase, consistent with the SP could mediate courtship and mating behavior in S. litura. Our findings are helpful in elucidating the molecular mechanism by which circadian clock genes regulate sexual communication in S. litura.

Social communication activates the circadian gene Tctimeless in Tribolium castaneum

Chemical communication via pheromones is an integral component in insect behavior, particularly for mate searching and reproduction. Aggregation pheromones, that attract conspecifics of both sexes, are particularly common and have been identified for hundreds of species. These pheromones are among the most ecologically selective pest suppression agents. In this study, we identified an activating effect of the aggregation pheromone of the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenibroidae) on a highly conserved circadian clock gene (Tctimeless). Tribolium castaneum is one of the most damaging cosmopolitan pest of flour and other stored food products. Its male produced aggregation pheromone, 4,8-dimethyldecanal (DMD), attracts both conspecific males and females and is used for pest management via monitoring and mating disruption. The Tctimeless gene is an essential component for daily expression patterns of the circadian clock and plays vital roles in eclosion, egg production, and embryonic development. In this study, we demonstrate that constant exposure to the species-specific aggregation pheromone led to Tctimeless up-regulation and a different pattern of rhythmic locomotive behavior. We propose that changing the well-adapted "alarm clock", using DMD is liable to reduce fitness and can be highly useful for pest management.

Functions of a C-type lectin with a single carbohydrate-recognition domain in the innate immunity and movement of the red flour beetle, Tribolium castaneum

C-type lectins (CTLs) are a superfamily of proteins found in almost all vertebrates and invertebrates. They play an important role in innate immune defences, development and epidermal structure. Here, a CTL with one carbohydrate-recognition domain containing a highly conserved Gln-Pro-Asp (QPD) motif was identified in Tribolium castaneum and given the name TcCTL5. Spatiotemporal analyses showed that Tcctl5 was highly expressed in the late pupa stage and mainly existed in the central nervous system and haemolymph. The transcript level of Tcctl5 was prominently induced after bacterial infection. Recombinant TcCTL5 proteins (rTcCTL5) were found to bind to lipopolysaccharide, peptidoglycan and tested bacteria and induce microbial agglutination in the presence of Ca²⁺ . Interestingly, when Tcctl5 was knocked down, the transcript level of antimicrobial peptides (AMPs) (attacin1, defensins3, coleoptericin1 and cecropins3) was prominently downregulated after induction with Gram-negative Escherichia coli. More interestingly, Tcctl5 was knocked down, leading to increased mortality and loss of locomotor activity, which exhibited less travel distances among early adults. These results demonstrate that Tcctl5 plays an important role in the innate immune reaction and the movement of T. castaneum. Thus, it may represent an alternative molecular target for pest control and thus reduce the use of pesticides in agricultural production.

Model and Non-model Insects in Chronobiology

The fruit fly Drosophila melanogaster is an established model organism in chronobiology, because genetic manipulation and breeding in the laboratory are easy. The circadian clock neuroanatomy in D. melanogaster is one of the best-known clock networks in insects and basic circadian behavior has been characterized in detail in this insect. Another model in chronobiology is the honey bee Apis mellifera, of which diurnal foraging behavior has been described already in the early twentieth century. A. mellifera hallmarks the research on the interplay between the clock and sociality and complex behaviors like sun compass navigation and time-place-learning. Nevertheless, there are aspects of clock structure and function, like for example the role of the clock in photoperiodism and diapause, which can be only insufficiently investigated in these two models. Unlike high-latitude flies such as Chymomyza costata or D. ezoana, cosmopolitan D. melanogaster flies do not display a photoperiodic diapause. Similarly, A. mellifera bees do not go into "real" diapause, but most solitary bee species exhibit an obligatory diapause. Furthermore, sociality evolved in different Hymenoptera independently, wherefore it might be misleading to study the social clock only in one social insect. Consequently, additional research on non-model insects is required to understand the circadian clock in Diptera and Hymenoptera. In this review, we introduce the two chronobiology model insects D. melanogaster and A. mellifera, compare them with other insects and show their advantages and limitations as general models for insect circadian clocks.

A C-type lectin with a single carbohydrate-recognition domain involved in the innate immune response of Tribolium castaneum

C-type lectins are one of the pattern-recognition proteins involved in innate immunity in invertebrates. Although there are 16 C-type lectin genes that have been identified in the genome of Tribolium castaneum, their functions and mechanisms in innate immunity remain unknown. Here, we identified one C-type lectin orthologue, TcCTL6 (TC003708), by sequencing random clones from the cDNA library of the coleopteran beetle, T. castaneum. TcCTL6 contains a 654 bp open reading frame encoding a protein of 217 amino acids that includes a single carbohydrate-recognition domain. The expression of TcCTL6 was significantly induced by Escherichia coli, Staphylococcus aureus and stimulation with carbohydrates, including lipopolysaccharide and peptidoglycan. A binding assay suggested that the recombinant TcCTL6 not only bound to lipopolysaccharide and peptidoglycan but also bound to Gram-positive (S. aureus, Bacillus subtilis and Bacillus thuringiensis) and Gram-negative bacteria (E. coli and Pseudomonas aeruginosa) in the presence of calcium ions. Furthermore, when TcCTL6 was knocked down by RNA interference, four antimicrobial peptides (attacin1, attacin2, coleoptericin1 and coleoptericin2) were significantly decreased. These results demonstrate that TcCTL6 plays a vital role in the immune response towards pathogen infection by influencing the expression of antimicrobial peptides and the agglutination of bacteria in the presence of calcium ions in T. castaneum.

Latrophilin participates in insecticide susceptibility through positively regulating CSP10 and partially compensated by OBPC01 in Tribolium castaneum

Latrophilin (LPH) is an adhesion G protein-coupled receptor (aGPCR) that participates in multiple essential physiological processes. Our previous studies have shown that lph is not only indispensable for the development and reproduction of red flour beetles (Tribolium castaneum), but also for their resistance against dichlorvos or carbofuran insecticides. However, the regulatory mechanism of lph-mediated insecticide susceptibility remains unclear. Here, we revealed that knockdown of lph in beetles resulted in opposing changes in two chemoreception genes, chemosensory protein 10 (CSP10) and odorant-binding protein C01 (OBPC01), in which the expression of TcCSP10 was downregulated, whereas the expression of TcOBPC01 was upregulated. TcCSP10 and TcOBPC01 were expressed at the highest levels in early pupal and late larval stages, respectively. High levels of expression of both these genes were observed in the heads (without antennae) of adults. TcCSP10 and TcOBPC01 were significantly induced by dichlorvos or carbofuran between 12 and 72 h (hrs) after exposure, suggesting that they are likely associated with increasing the binding affinity of insecticides, leading to a decrease in sensitivity to the insecticides. Moreover, once these two genes were knocked down, the susceptibility of the beetles to dichlorvos or carbofuran was enhanced. Additionally, RNA interference (RNAi) targeting of lph followed by exposure to dichlorvos or carbofuran also caused the opposing expression levels of TcCSP10 and TcOBPC01 compared to the expression levels of wild-type larvae treated with insecticides alone. All these results indicate that lph is involved in insecticide susceptibility through positively regulating TcCSP10; and the susceptibility could also further partially compensated for through the negative regulation of TcOBPC01 when lph was knockdown in the red flour beetle. Our studies shed new light on the molecular regulatory mechanisms of lph related to insecticide susceptibility.

Knockdown of timeless Disrupts the Circadian Behavioral Rhythms in Laodelphax striatellus (Hemiptera: Delphacidae)

Most living organisms developed the innate clock system to anticipate daily environmental changes and to enhance their chances of survival. timeless (tim) is a canonical clock gene. It has been extensively studied in Drosophila melanogaster (Diptera: Drosophilidae) as a key component of the endogenous circadian clock, but its role is largely unknown in some agriculture pests. Laodelphax striatellus (Fallén) (Hemiptera: Delphacidae), an important rice pest, exhibits a robust locomotor rhythm. In the present study, we cloned tim gene (ls-tim) from L. striatellus and investigated its function in the regulation of behavioral rhythms. Quantitative real-time polymerase chain reaction revealed a circadian expression pattern of ls-tim under different light conditions with a trough in the photophase and a peak in the late scotophase. After the knockdown of ls-tim via RNA interference (RNAi), the adults showed an earlier onset of locomotor activity under light/dark cycles and became arrhythmic in constant darkness. ls-tim RNAi also abolished the timing of adult emergence that normally occurs in the early photophase. These results suggest that ls-tim is essential for the light-entrained circadian rhythms in L. striatellus and provide more insights into the endogenous clock network underlying the behavioral and physiological rhythms of this insect.