Combinatorial expression of ebony and tan generates body color variation from nymph through adult stages in the cricket, Gryllus bimaculatus

Pleiotropic effects of Ebony on pigmentation and development in the Asian multi-coloured ladybird beetle, Harmonia axyridis (Coleoptera: Coccinellidae)

Melanin plays a pivotal role in insect body pigmentation, significantly contributing to their adaptation to diverse biotic and abiotic environmental challenges. Several genes involved in insect melanin synthesis showed pleiotropic effects on insect development and reproduction. Among these, the N-β-alanyl dopamine synthetase gene (Ebony) is integral to the pigmentation process. However, the full spectrum of its pleiotropic impacts is not yet thoroughly understood. In this study, we identified and characterised the HaEbony gene in the Asian multi-coloured ladybird beetle (Harmonia axyridis) and found that HaEbony gene is a conserved gene within the Coleoptera order. We aimed to further explore the multiple roles of HaEbony in the physiology and behaviour in H. axyridis. The CRISPR/Cas9 system was applied to generate multiple HaEbony knockout allele (HaEbony+/-), showing nucleotide deletion in the G0 and G1 generations. Remarkably, the resultant HaEbony+/- mutants consistently displayed darker pigmentation than their wild-type counterparts across larval, pupal and adult stages. Furthermore, these HaEbony+/- individuals (G0) demonstrated an enhanced predatory efficiency, evidenced by a higher number of aphids consumed compared to the wild type. A significant finding was the reduced egg hatchability in both G0 and G1 generations of the HaEbony+/- group, highlighting a potential reproductive fitness cost associated with HaEbony deficiency. In conclusion, our study not only sheds light on the multifaceted roles of HaEbony in H. axyridis but also highlights the potential of employing CRISPR/Cas9-targeted modifications of the Ebony gene. Such genetic interventions could enhance the environmental adaptability and predatory efficacy of ladybirds, presenting a novel strategy in biological control application.

Evaluation of ebony as a potential selectable marker for genetic sexing in Aedes aegypti

BACKGROUND

Aedes aegypti is expected to invade previously unoccupied areas, mainly due to the climate change, the increase in travel and trade activities and the continuous transformation of the rural environment into urban areas. The sterile insect technique (SIT), which relies on the mass production and release of sterile males, is an environmentally friendly approach that can be applied for population control of Ae. aegypti. SIT programs can be greatly benefited by a genetic sexing strain (GSS) and a reliable sex sorting system to minimize any accidental female release. Visually detectable or conditionally lethal selectable markers can be used for the development of new GSSs. In this study, we evaluated the suitability and competence of a mutant Ae. aegypti ebony strain for the development of a new GSS. The ebony gene is known to be involved in the pigmentation pathway of several dipteran insects, including Ae. aegypti.

METHODS

An ebony gene knockout was developed though CRISPR/Cas9 mutagenesis. G0 individuals with the desired phenotype were crossed, and progeny were screened in every generation. PCR and sequencing were performed using gDNA from a pulled leg to determine the mutant genotype. Quality control tests, including pupae and adult recovery rates, male sex ratio and fecundity, were applied to the ebony mutant line to determine whether the mutation confers any fitness cost.

RESULTS

An Ae. aegypti ebony knockout mutant carrying a 5-bp deletion was obtained, which presented darker head and siphon phenotypes at the larval stage. However, genetic analysis revealed that this ebony mutation results in incomplete penetrance and variable expressivity. The establishment of a pure ebony mutant line was not possible because of the fitness costs conferred by the mutation.

CONCLUSIONS

In this study, the adequacy and suitability of the ebony gene as a selectable marker for the development of a GSS in Ae. aegypti were assessed. Despite its clear phenotype early in larval development, the homozygous mutant line presented phenotypic inconsistency and loss of fertility. These drawbacks clearly indicate that this particular mutation is not suitable for the development of a new GSS. Nonetheless, it cannot be excluded that a different mutation will lead to a different expression and penetrance profile and a viable homozygous mutant line.

Lineage-specific duplication and functional diversification of DOPA-decarboxylase genes in the Gryllidae family, as revealed in Gryllus bimaculatus

The DOPA-decarboxylase (DDC) gene is crucial for dopamine synthesis and influences various biological functions in insects, including body coloration, behavior, learning, and sleep. However, its evolutionary impact remains largely unexplored. This study reports on the tandem duplication of two bona fide ddc genes (ddc1 and ddc2) in the Gryllidae cricket family. We herein investigated the function of ddc1 and ddc2 using Gryllus bimaculatus (Gb) as a model. Our results revealed that Gb'ddc1 was expressed systemically, with its expression being higher immediately after molting compared to the stage following melanin pigmentation. In homozygous knockout mutants of Gb'ddc1, generated via CRISPR/Cas9, reduced body color pigmentation and had translucent cuticles, decreased dopamine levels, and over-accumulated DOPA. These mutants died shortly after hatching, likely due to cuticle defects, underscoring the essential role of dopamine, produced by Gb'ddc1, in melanin synthesis. Conversely, Gb'ddc2 expression was confined to the ovary and was not up-regulated after molting. Homozygous knockout mutants of Gb'ddc2 exhibited no body color defects, whereas hatchability and embryonic development rates were significantly reduced. Interestingly, dopamine levels in the ovaries were significantly elevated in Gb'ddc2 mutants. This suggests that normal ovarian dopamine levels, modulated by Gb'ddc2, are vital for fertility maintenance. The function of Gb'ddc2 differs from that of typical ddc, indicating neofunctionalization through evolutionary duplication. Overall, Gb'ddc1 and Gb'ddc2 have distinct functions, and precise regulation of ovarian dopamine levels using these two ddc genes may have enhanced cricket fertility.

Potential of Cricket Chitosan for Nanoparticle Development Through Ionotropic Gelation: Novel Source for Cosmeceutical Delivery Systems

BACKGROUND/OBJECTIVES

Crickets are recognized as an alternative source of chitosan. This study aimed to assess the potential of cricket-derived chitosan as a natural source to develop chitosan nanoparticles (CNPs).

METHODS

Chitosan were isolated from different cricket species, including Gryllus bimaculatus, Teleogryllus mitratus, and Acheta domesticus. The isolated chitosan were characterized by their functional groups, crystallographic and thermal properties, molecular structure, morphology, water solubility, molecular weight, binding capacity, irritation potential, and cytotoxicity in comparison to commercial shrimp-based chitosan. CNPs were developed through an ionotropic gelation method, followed by the evaluation of particle size, polydispersity index (PDI), and zeta potential.

RESULTS

The findings of this study indicate that chitosan can be successfully isolated from the three cricket species, with yields ranging from 4.35% to 5.22% w/w of the dried material. The characteristics of cricket-based chitosan were similar to those of commercial chitosan, except that the cricket-based chitosan displayed a higher crystallinity and a lower molecular weight. Additionally, CPNs were successfully produced from cricket-based chitosan using sodium citrate as a crosslinking agent. All cricket-based chitosan exhibited no irritation or cytotoxicity. Chitosan derived from A. domesticus however was found to be the most suitable to develop CPNs, as it produced the smallest particle size (522.0 ± 12.1 nm) with a comparatively narrow PDI (0.388 ± 0.026) and an acceptable positive zeta potential (34.2 ± 4.4 mV).

CONCLUSIONS

Cricket-derived chitosan compares favorably with crustacean-derived chitosan and showed potential for a range of applications, including the use as a nanocosmeceutical delivery system in topical and cosmetic formulations.

The white gene as a transgenesis marker for the cricket Gryllus bimaculatus

The cricket Gryllus bimaculatus is an emerging model insect of the order Orthoptera that is used in a wide variety of biological research themes. This hemimetabolous species appears highly complementary to Drosophila and other well-established holometabolous models. To improve transgenesis applications in G. bimaculatus, we have designed a transformation marker gene inspired from the widespread Drosophila mini-white+. Using CRISPR/Cas9, we first generated a loss-of-function mutant allele of the Gb-white gene (Gb-w), which exhibits a white eye coloration at all developmental stages. We then demonstrate that transgenic insertions of a piggyBac vector containing a 3xP3-Gb-w+ cassette rescue eye pigmentation. As an application, we used this vector to generate G. bimaculatus lines expressing a centromeric histone H3 variant (CenH3.1) fused to EGFP and validated EGFP-CenH3.1 detection at cricket centromeres. Finally, we demonstrate that Minos-based germline transformation and site-specific plasmid insertion with the ΦC31 integrase system function in G. bimaculatus.

CRISPR/Cas9-mediated ebony knockout causes melanin pigmentation and prevents moth Eclosion in Ectropis grisescens

Ectropis grisescens (Lepidoptera: Geometridae) is a destructive tea pest in China. Mimesis, characterized by changing body color, is an important trait of E. grisescens larvae. Hence, identifying melanin pathway-related genes may contribute to developing new pest control strategies. In the present study, we cloned Egebony, a gene potentially involved in melanin pigmentation in E. grisescens, and subsequently conducted CRISPR/Cas9-mediated targeted mutagenesis of Egebony to analyze its role in pigmentation and development. At the larvae, prepupae, and pupae stages, Egebony-knockout individuals exhibited darker pigmentation than the wild-type. However, Egebony knockout did not impact the colors of sclerotized appendants, including ocelli, setae, and claws. While mutant pupae could successfully develop into moths, they were unable to emerge from the puparium. Notably, embryo hatchability and larval survival of mutants remained normal. Further investigation indicated that mutant pupae exhibited significantly stronger shearing force than the wild-type, with the pigmented layer of mutant pupae appearing darker and thicker. Collectively, these results suggest that the loss of Egebony might increase the rigidity of the puparium and prevent moth eclosion. This study provides new insights into understanding the function and diversification of ebony in insect development and identifies a lethal gene that can be manipulated for developing effective pest control strategies.

The Fatty Acid Compositions, Irritation Properties, and Potential Applications of Teleogryllus mitratus Oil in Nanoemulsion Development

This study aimed to characterize and investigate the potential of the oils from Gryllus bimaculatus, Teleogryllus mitratus, and Acheta domesticus to be used in nanoemulsions. The oils were extracted by a cold press method and characterized for their fatty acid profiles. Their irritation effects on the chorioallantoic membrane (CAM) were evaluated, along with investigations of solubility and the required hydrophilic-lipophilic balance (RHLB). Various parameters impacting nanoemulsion generation using high-pressure homogenization were investigated. The findings revealed that G. bimaculatus yielded the highest oil content (24.58% w/w), followed by T. mitratus (20.96% w/w) and A. domesticus (15.46% w/w). Their major fatty acids were palmitic, oleic, and linoleic acids. All oils showed no irritation, suggesting safety for topical use. The RHLB values of each oil were around six-seven. However, they could be successfully developed into nanoemulsions using various surfactants. All cricket oils could be used for the nanoemulsion preparation, but T. mitratus yielded the smallest internal droplet size with acceptable PDI and zeta potential. Nanoemulsion was found to significantly enhance the antioxidant and anti-skin wrinkle of the T. mitratus oil. These findings pointed to the possible use of cricket oils in nanoemulsions, which could be used in various applications, including topical and cosmetic formulations.