Identification, mRNA expression and functional analysis of several yellow family genes in Tribolium castaneum

Genome-wide identification of yellow gene family in Hermetia illucens and functional analysis of yellow-y by CRISPR/Cas9

The yellow gene family plays a crucial role in insect pigmentation. It has potential for use as a visible marker gene in genetic manipulation and transgenic engineering in several model and non-model insects. Sadly, yellow genes have rarely been identified in Stratiomyidae species and the functions of yellow genes are relatively unknown. In the present study, we first manually annotated and curated 10 yellow genes in the black soldier fly (BSF), Hermetia illucens (Stratiomyidae). Then, the conserved amino acids in the major royal jelly proteins (MRJPs) domain, structural architecture and phylogenetic relationship of yellow genes in BSF were analyzed. We found that the BSF yellow-y, yellow-c and yellow-f genes are expressed at all developmental stages, especially in the prepupal stage. Using the clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) system, we successfully disrupted yellow-y, yellow-c and yellow-f in the BSF. Consequently, the mutation of yellow-y clearly resulted in a pale-yellow body color in prepupae, pupae and adults, instead of the typical black body color of the wild type. However, the mutation of yellow-c or yellow-f genes did not result in any change in color of the insects, when compared with the wild type. Our study indicates that the BSF yellow-y gene plays a role in body pigmentation, providing an optimal marker gene for the genetic manipulation of BSF.

RNAi of yellow-y, required for normal cuticle pigmentation, impairs courtship behavior and oviposition in the German cockroach (Blattella germanica)

The insect cuticle plays a key role in maintaining the insect's physiological function and behavior. Herein, the yellow-y protein is required to produce black melanin, and is expressed in a pattern that correlates with the distribution of this pigment. However, yellow-y can also have other functions, for instance, in insect behavior, but not much is known. In this study, we have studied the yellow-y gene in one important model and pest species, namely the German cockroach (Blattella germanica), which is to our knowledge the first time reported. In essence, we identified the yellow-y gene (BgY-y) and characterized its function by using RNA interference (RNAi). Silencing of BgY-y gene led to different developmental abnormalities (body weight and wings) in both genders. Specifically, there was an abundant decrease in melanin, turning the body color in pale yellow and the cuticle softer and more transparent. Interestingly, we also observed that the knockdown of BgY-y impaired the male cockroaches to display a weaker response to female-emitted contact sex pheromones, and also that the oviposition ability was weakened in the RNAi females. This study comprehensively analyzed the biological functions of the yellow-y gene in German cockroaches from the perspectives of development, body color, courtship behavior and oviposition, and as a consequence, this may opens new avenues to explore it as a novel pest control gene.

Characterization of essential eggshell proteins from Aedes aegypti mosquitoes

BACKGROUND

Up to 40% of the world population live in areas where mosquitoes capable of transmitting the dengue virus, including Aedes aegypti, coexist with humans. Understanding how mosquito egg development and oviposition are regulated at the molecular level may provide new insights into novel mosquito control strategies. Previously, we identified a protein named eggshell organizing factor 1 (EOF1) that when knocked down with RNA interference (RNAi) resulted in non-melanized and fragile eggs that did not contain viable embryos.

RESULTS

In this current study, we performed a comprehensive RNAi screen of putative A. aegypti eggshell proteins to identify additional proteins that interact with intracellular EOF1. We identified several proteins essential for eggshell formation in A. aegypti and characterized their phenotypes through a combination of molecular and biochemical approaches. We found that Nasrat, Closca, and Polehole structural proteins, together with the Nudel serine protease, are indispensable for eggshell melanization and egg viability. While all four proteins are predominantly expressed in ovaries of adult females, Nudel messenger RNA (mRNA) expression is highly upregulated in response to blood feeding. Furthermore, we identified four additional secreted eggshell enzymes that regulated mosquito eggshell formation and melanization. These enzymes included three dopachrome-converting enzymes (DCEs) and one cysteine protease. All eight of these eggshell proteins were essential for proper eggshell formation. Interestingly, their eggshell surface topologies in response to RNAi did not phenocopy the effect of RNAi-EOF1, suggesting that additional mechanisms may influence how EOF1 regulates eggshell formation and melanization.

CONCLUSIONS

While our studies did not identify a definitive regulator of EOF1, we did identify eight additional proteins involved in mosquito eggshell formation that may be leveraged for future control strategies.

Phenotypic and genetic characterization of Africanized Apis mellifera colonies with natural tolerance to Varroa destructor and contrasting defensive behavior

Africanized Apis mellifera colonies with promising characteristics for beekeeping have been detected in northern Argentina (subtropical climate) and are considered of interest for breeding programs. Integral evaluation of this feral material revealed high colony strength and resistance/tolerance to brood diseases. However, these Africanized honeybees (AHB) also showed variable negative behavioral traits for beekeeping, such as defensiveness, tendency to swarm and avoidance behavior. We developed a protocol for the selection of AHB stocks based on defensive behavior and characterized contrasting colonies for this trait using NGS technologies. For this purpose, population and behavioral parameters were surveyed throughout a beekeeping season in nine daughter colonies obtained from a mother colony (A1 mitochondrial haplotype) with valuable characteristics (tolerance to the mite Varroa destructor, high colony strength and low defensiveness). A Defensive Behavior Index was developed and tested in the colonies under study. Mother and two daughter colonies displaying contrasting defensive behavior were analyzed by ddRADseq. High-quality DNA samples were obtained from 16 workers of each colony. Six pooled samples, including two replicates of each of the three colonies, were processed. A total of 12,971 SNPs were detected against the reference genome of A. mellifera, 142 of which showed significant differences between colonies. We detected SNPs in coding regions, lncRNA, miRNA, rRNA, tRNA, among others. From the original data set, we also identified 647 SNPs located in protein-coding regions, 128 of which are related to 21 genes previously associated with defensive behavior, such as dop3 and dopR2, CaMKII and ADAR, obp9 and obp10, and members of the 5-HT family. We discuss the obtained results by considering the influence of polyandry and paternal lineages on the defensive behavior in AHB and provide baseline information to use this innovative molecular approach, ddRADseq, to assist in the selection and evaluation of honey bee stocks showing low defensive behavior for commercial uses.

Ovariole-specific Yellow-g and Yellow-g2 proteins are required for fecundity and egg chorion rigidity in the red flour beetle, Tribolium castaneum

Most insects reproduce by laying eggs that have an eggshell/chorion secreted by follicle cells, which serves as a protective barrier for developing embryos. Thus, eggshell formation is vital for reproduction. Insect yellow family genes encode for secreted extracellular proteins that perform different, context-dependent functions in different tissues at various stages of development involving, for example, cuticle/eggshell coloration and morphology, molting, courtship behavior and embryo hatching. In this study we investigated the function of two of this family's genes, yellow-g (TcY-g) and yellow-g2 (TcY-g2), on the formation and morphology of the eggshell of the red flour beetle, Tribolium castaneum. Real-time PCR analysis revealed that both TcY-g and TcY-g2 were specifically expressed in the ovarioles of adult females. Loss of function produced by injection of double-stranded RNA (dsRNA) for either TcY-g or TcY-g2 gene resulted in failure of oviposition. There was no effect on maternal survival. Ovaries dissected from those dsRNA-treated females exhibited ovarioles containing not only developing oocytes but also mature eggs in their egg chambers. However, the ovulated eggs were collapsed and ruptured, resulting in swollen lateral oviducts and calyxes. TEM analysis showed that lateral oviducts were filled with electron-dense material, presumably from some cellular content leakage out of the collapsed eggs. In addition, morphological abnormalities in lateral oviduct epithelial cells and the tubular muscle sheath were evident. These results support the hypothesis that both TcY-g and TcY-g2 proteins are required for maintaining the rigidity and integrity of the chorion, which is critical for resistance to mechanical stress and/or rehydration during ovulation and egg activation in the oviducts of T. castaneum. Because Yellow-g and Yellow-g2 are highly conserved among insect species, both genes are potential targets for development of gene-based insect pest population control methods.

Differential expression of Phlebotomus tobbi Adler, Theodor & Lourie, 1930 (Diptera: Psychodidae) genes under different environmental conditions

Phlebotomus tobbi is a widely distributed sand fly species in Turkey and is the proven vector of Leishmania infantum and several Phleboviruses. Information regarding the genetic basis of phenotypic plasticity is crucial for managing vector-borne diseases, as the changing environmental conditions have consequences for the survival of arthropods and the disease agents they transmit. However, limited data is available on the impacts of environmental conditions on the traits associated with sand fly survival, reproduction, and vectorial competence. The present study aimed to reveal the changes in the expression levels of three selected P. tobbi genes using laboratory-reared and wild-caught populations. A nervous system protein, Cacophony (PtCac), related to the life history traits of sand flies, and two sand fly salivary protein genes, PtSP32 and PtSP38, influence the infection of the vertebrate hosts, were assessed. Sand flies were maintained at 23 °C and 27 °C in the laboratory to evaluate the relationship between temperature and the expressed phenotypes. Field collections were carried out in three climatically distinct regions of Turkey to establish the regional differences in the gene expression levels of natural P. tobbi populations. In the laboratory, PtCac expression increased with the temperature. However, PtCac expression was negatively correlated with local temperature and humidity conditions. No differences were detected in the PtSP32 gene expression levels of both laboratory-reared and wild-caught females, but a negative correlation was observed with relative humidity in natural populations. Although the expression levels of PtSP38 did not differ among the females collected from distinct regions, a positive correlation was detected in the laboratory-reared colony. The findings indicated that changes in environmental conditions could drive the expression levels of P. tobbi genes, which influence population dynamics and the transmission risk of the disease.

RNAi-Mediated Manipulation of Cuticle Coloration Genes in Lygus hesperus Knight (Hemiptera: Miridae)

Cuticle coloration in insects is a consequence of the accumulation of pigments in a species-specific pattern. Numerous genes are involved in regulating the underlying processes of melanization and sclerotization, and their manipulation can be used to create externally visible markers of successful gene editing. To clarify the roles for many of these genes and examine their suitability as phenotypic markers in Lygus hesperus Knight (western tarnished plant bug), transcriptomic data were screened for sequences exhibiting homology with the Drosophila melanogaster proteins. Complete open reading frames encoding putative homologs for six genes (aaNAT, black, ebony, pale, tan, and yellow) were identified, with two variants for black. Sequence and phylogenetic analyses supported preliminary annotations as cuticle pigmentation genes. In accord with observable difference in color patterning, expression varied for each gene by developmental stage, adult age, body part, and sex. Knockdown by injection of dsRNA for each gene produced varied effects in adults, ranging from the non-detectable (black 1, yellow), to moderate decreases (pale, tan) and increases (black 2, ebony) in darkness, to extreme melanization (aaNAT). Based solely on its expression profile and highly visible phenotype, aaNAT appears to be the best marker for tracking transgenic L. hesperus.

Yellow-b, -c, -d, and -h are required for normal body coloration of Henosepilachna vigintioctopunctata

The involvement of yellow genes y-b, y-c, y-e, and y-h in cuticle tanning has poorly been clarified. In the present paper, six putative yellow (y-y, y-b, y-c, y-e y-f, and y-h) genes were identified in Henosepilachna vigintioctopunctata. Hvy-b, Hvy-c, Hvy-e, and Hvy-h were abundantly transcribed at early larval and late pupal stages, especially in the epidermis. Accordingly, RNA interference (RNAi) experiments were performed by an injection of dsy-b, dsy-c, dsy-e, or dsy-h into the second instar larvae and 1-day-old pupae. The head capsule, scoli and strumae, and legs in the fourth-instar larvae became blacker; the blackish spots in the pupae were darkened and widened after RNAi of Hvy-b, compared with those of dsegfp-treated controls. Depletion of Hvy-b at the 1-day-old pupal stage expanded two pair of black markings on the sternum of the metathorax, and darkened the black patched on the sterna of the abdomen segments I-VI in the resultant adults. Depletion of Hvy-e caused darker pigmented adult body and elytral cuticles than those of dsegfp-introduced controls. However, there was no obvious difference in pigmentation of the black markings. Hvy-h-deficient larvae displayed dark yellow body color, whereas the body color of the dsegfp-injected control was pale yellow. There was no obvious difference in coloration of larval specific-black markings or pupal cuticle between dsHvy-h- and dsegfp-treated animals. Moreover, silence of Hvy-c at the second instar larval stage lightened black markings in the resulting larvae and pupae, but had no influence on pale yellow body color. Our results demonstrated their different roles of the four yellow genes during body pigmentation: HvY-b and HvY-c, respectively, inhibit and facilitate the coloration within dark markings, whereas HvY-e and HvY-h, respectively, repress the pigmentation in adult and larval body cuticles outside the black patches in H. vigintioctopunctata.

Drosophila yellow-h encodes dopaminechrome tautomerase: A new enzyme in the eumelanin biosynthetic pathway

Melanin is a widely distributed phenolic pigment that is biosynthesized from tyrosine and its hydroxylated product, dopa, in all animals. However, recent studies reveal a significant deviation from this paradigm, as insects appear to use dopamine rather than dopa as the major precursor of melanin. This observation calls for a reconsideration of the insect melanogenic pathway. While phenoloxidases and laccases can oxidize dopamine for dopaminechrome production, the fate of dopaminechrome remains undetermined. Dopachrome decarboxylase/tautomerase, encoded by yellow-f/f2 of Drosophila melanogaster, can convert dopaminechrome into 5,6-dihydroxyindole, but the same enzyme from other organisms does not act on dopaminechrome, suggesting the existence of a specific dopaminechrome tautomerase (DPT). We now report the identification of this novel enzyme that biosynthesizes 5,6-dihydroxyindole from dopaminechrome in Drosophila. Dopaminechrome tautomerase acted on both dopaminechrome and N-methyl dopaminechrome but not on dopachrome or other aminochromes tested. Our biochemical and molecular studies reveal that this enzyme is encoded by the yellow-h gene, a member of the yellow gene family, and advance our understanding of the physiological functions of this gene family. Identification and characterization of DPT clarifies the precursor for melanin biosynthetic pathways and proves the existence of an independent melanogenic pathway in insects that utilizes dopamine as the primary precursor.

Expression profiles of tyrosine metabolic pathway genes and functional analysis of DOPA decarboxylase in puparium tanning of Bactrocera dorsalis (Hendel)

BACKGROUND

Tanning is an important physiological process with critical roles in cuticle pigmentation and sclerotization. Previous studies have shown that insect cuticle tanning is closely associated with the tyrosine metabolism pathway, which consists of a series of enzymes.

RESULTS

In this study, 24 tyrosine metabolism pathway genes were identified in the oriental fruit fly Bactrocera dorsalis (Hendel) genome. Gene expression profiles throughout 15 developmental stages of B. dorsalis were established based on our previous RNA sequencing data, and we found that 13 enzyme genes could be involved in the process of pupariation. Accordingly, a tyrosine-mediated tanning pathway during the pupariation of B. dorsalis was predicted and a critical enzyme, 3,4-dihydroxyphenylalanine (DOPA) decarboxylase (DDC), was used to explore its possible roles in formation of the puparium. First, a real-time quantitative polymerase chain reaction confirmed that BdDDC had an epidermis-specific expression pattern, and was highly expressed during larval metamorphosis in B. dorsalis. Subsequent disruption of BdDDC by feeding 5-day-old larvae with DDC inhibitor (l-α-methyl-DOPA) could lead to: (i) a significant decrease in BdDDC enzyme activity and dopamine concentration; (ii) defects in puparium pigmentation; (iii) impairment of the morphology and less thickness of the puparium; and (iv) lower pupal weight and obstacles to eclosion.

CONCLUSION

This study provided a potential tyrosine metabolic pathway that was responsible for insect tanning during pupariation, and the BdDDC enzyme has been shown to have crucial roles in larval-pupal tanning of B. dorsalis. © 2021 Society of Chemical Industry.

Yellow-y Functions in Egg Melanization and Chorion Morphology of the Asian Tiger Mosquito, Aedes albopictus

The Asian tiger mosquito, Aedes albopictus, is one of the most serious public health pests, which can transmit various vector-borne diseases. Eggs from this mosquito species become dark black shortly after oviposition and exhibit high desiccation resistance. Some of the Yellow proteins that act as dopachrome conversion enzymes (DCEs) are involved in the tyrosine-mediated tanning (pigmentation and sclerotization) metabolic pathway that significantly accelerates melanization reactions in insects. In this research, we analyzed the function of one of the yellow genes, yellow-y (AalY-y), in eggshell/chorion melanization of Ae. albopictus eggs. Developmental and tissue-specific expression measured by real-time PCR showed that AalY-y transcripts were detected at all stages of development analyzed, with significantly higher levels in the ovaries from blood-fed adult females. Injection of double-stranded RNA for AalY-y (dsAalY-y) had no significant effect on fecundity. However, unlike dsEGFP-treated control eggs that become black by 2–3 h after oviposition (HAO), dsAalY-y eggs were yellow-brown at 2 HAO, and reddish-brown even at 48 HAO. dsEGFP eggs exhibited resistance to desiccation at 48 HAO, whereas approximately 50% of the dsAalY-y eggs collapsed when they were moved to a low humidity condition. In addition, TEM analysis revealed an abnormal morphology and ultrastructure of the outer-endochorion in the dsAalY-y eggs. These results support the hypothesis that AalY-y is involved in the tyrosine-induced melanin biosynthetic pathway, plays an important role in black melanization of the chorion and functions in conferring proper morphology of the outer-endochorion, a structure that is presumably required for egg desiccation resistance in Ae. albopictus.

Identification of yellow gene family and functional analysis of Spodoptera frugiperda yellow-y by CRISPR/Cas9

For a devastating agricultural pest, functional genomics promotes the finding of novel technology to control Spodoptera frugiperda, such as the genetics-based strategies. In the present study, 11 yellow genes were identified in Spodoptera frugiperda. The transcriptome analysis showed the tissue-specific expression of part yellow genes, which suggested the importance of yellow genes in some biological processes in S. frugiperda, such as pigmentation. Among these yellow genes, the expression profiles of yellow-y gene showed that it was expressed in all life stages. In order to realize the further study of yellow-y, we employed CRISPR/Cas9 system to knock out this gene. Following knock out, diverse phenotypes were observed, such as color changes in both larvae and adults. Different from the wild-type larvae and adults, G₀ mutants were yellowed since hatching. However, no color difference was observed with the pupal cuticle between the wild-type and mutant pupae before the 8th day. On the basis of the single-pair strategy of G0 generation, the yellow-y gene was proved to be a recessive gene. The G1 yellowish larvae with biallelic mutations displayed a relatively longer development period than wild-type, and often generated abnormal pupae and moths. The deletion of yellow-y also resulted in a decline in the fecundity. The results revealed that yellow-y gene was important for S. frugiperda pigmentation, as well as in its development and reproduction. Besides, the present study set up a standard procedure to knock out genes in S. frugiperda, which could be helpful for our understanding some key molecular processes, such as functional roles of detoxification genes as insecticide resistance mechanisms or modes of action of insecticides to facilitate the management of this insect pest.

CRISPR/Cas9-based functional analysis of yellow gene in the diamondback moth, Plutella xylostella

The diamondback moth, Plutella xylostella (L.), is an economically important pest of cruciferous crops worldwide. This pest is notorious for rapid evolution of the resistance to different classes of insecticides, making it increasingly difficult to control. Genetics-based control approaches, through manipulation of target genes, have been reported as promising supplements or alternatives to traditional methods of pest management. Here we identified a gene of pigmentation (yellow) in P. xylostella, Pxyellow, which encodes 1674 bp complementary DNA sequence with four exons and three introns. Using the clustered regularly interspersed palindromic repeats (CRISPR)/CRISPR-associated protein 9 system, we knocked out Pxyellow, targeting two sites in Exon III, to generate 272 chimeric mutants (57% of the CRISPR-treated individuals) with color-changed phenotypes of the 1st to 3rd instar larvae, pupae, and adults, indicating that Pxyellow plays an essential role in the body pigmentation of P. xylostella. Fitness analysis revealed no significant difference in the oviposition of adults, the hatchability of eggs, and the weight of pupae between homozygous mutants and wildtypes, suggesting that Pxyellow is not directly involved in regulation of growth, development, or reproduction. This work advances our understanding of the genetic and insect science molecular basis for body pigmentation of P. xylostella, and opens a wide avenue for development of the genetically based pest control techniques using Pxyellow as a screening marker.

CRISPR/Cas9 mediated knockout of Amyellow-y gene results in melanization defect of the cuticle in adult Apis mellifera

Visible genetic markers are critical to gene function studies using genome editing technology in insects. However, there is no report about visible phenotypic markers in Apis mellifera, which extremely influences the application of genomic editing in honey bees. Here, we cloned and characterized the Amyellow-y gene in A. mellifera. Stage expression profiles showed that Amyellow-y gene was highly expressed in 2-, 4-day-old pupae, and newly emerged bees, and a high expression level was detected in the leg, thorax, wing and sting. To understand its functional role in pigmentation, Amyellow-y edited honeybees were created using CRISPR/Cas9, and it was found that the black pigment was decreased in the cuticle of mosaic workers and mutant drones. In particular, mutant drones manifested an overall appearance of yellowish cuticle in the body and appendages, including antennae, wings and legs, indicating that mutagenesis induced by disruption of Amyellow-y with CRISPR/Cas9 are heritable. Furthermore, the expression levels of genes associated with melanin pigmentation was investigated in mutant and wild-type drones using quantitative reverse transcription PCR. Transcription levels of Amyellow-y and aaNAT decreased markedly in mutant drones than that in wild-type ones, whereas laccase 2 was significantly up-regulated. Our results provide the first evidence, to our knowledge, that CRISPR/Cas9 edited G1 mutant drones of A. mellifera have a dramatic body pigmentation defect that can be visualized in adults, suggesting that Amyellow-y may serve as a promising visible phenotypic marker for genome editing in honey bees.

Regional patterning and regulation of melanin pigmentation in insects

Insects display an immense diversity in melanin pigmentation, which is generated by the interplay between the regulatory genes (that provide general patterning information) and effector genes (that provide coloration of the pattern). However, recent studies encompassing several different orders (Hemiptera, Blattodea, Coleoptera, and Lepidoptera) have shown that knockdowns of melanin producing genes alone can generate distinct region-specific patterns. This review surveys the most recent studies to further document the regional patterning of effector genes, and highlights the new advances and their implications for future research.

Clustered Regularly Interspaced Short Palindromic Repeats/CRISPR-Associated Protein 9 Mediated Knockout Reveals Functions of the yellow-y Gene in Spodoptera litura

Yellow genes are thought to be involved in the melanin biosynthetic pathway and play a crucial role in pigmentation reactions in insects. However, little research has been done on yellow genes in lepidopteran pests. To clarify the function of one of the yellow genes (yellow-y) in Spodoptera litura, we cloned the full-length of yellow-y, and investigated its spatial and temporal expression profiles by quantitative real-time PCR (qPCR). It revealed that yellow-y was highly expressed in larva of fourth, fifth, and sixth instars, as well as in epidermis (Ep), fat bodies (FB), Malpighian tubes (MT), and midguts (MG) of the larvae; whereas it was expressed in very low levels in different tissues of adults, and was almost undetected in pupa. This expression profile suggests an important role of yellow-y in larvae, minor role in adults, and no role in pupae. To confirm this, we disrupted yellow-y using the clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9 (CRISPR/Cas9) system, and obtained G0 insects with mutation in yellow-y. The mutation in yellow-y clearly rendered the larvae body, a color yellower than that of wide type insects, and in addition, the mutation resulted in abnormal segmentation and molting for older larvae. The mutation of yellow-y also made various adult tissues (antennae, proboscis, legs, and wings) yellowish. However, the mutation had no effect on pigmentation of the pupal cuticle. Taken together, our study clearly demonstrated the role of yellow-y not only in the body pigmentation of larvae and adults, and but also in segmentation and molting of larvae, providing new insights into the physiology of larval development, as well as a useful marker gene for genome editing based studies.

Functional conservation and diversification of yellow-y in lepidopteran insects

The diverse colors and patterns found in Lepidoptera are important for success of these species. Similar to the wings of adult butterflies, lepidopteran larvae exhibit diverse color variations to adapt to their habitats. Compared with butterfly wings, however, less attention has been paid to larval body colorations and patterns. In the present study, we focus on the yellow-y gene, which participates in the melanin synthesis pathway. We conducted CRISPR/Cas9-mediated targeted mutagenesis of yellow-y in the tobacco cutworm Spodoptera litura. We analyzed the role of S. litura yellow-y in pigmentation by morphological observation and discovered that yellow-y is necessary for normal black pigmentation in S. litura. We also showed species- and tissue-specific requirements of yellow-y in pigmentation in comparison with those of Bombyx mori yellow-y mutants. Furthermore, we found that almost none of the yellow-y mutant embryos hatched unaided. We provide evidence that S. litura yellow-y has a novel important function in egg hatching, in addition to pigmentation. The present study will enable a greater understanding of the functions and diversification of the yellow-y gene in insects.

Involvement of the transcription factor E75 in adult cuticular formation in the red flour beetle Tribolium castaneum

Insect adult metamorphosis generally proceeds with undetectable levels of juvenile hormone (JH). In adult development of the red flour beetle Tribolium castaneum, biosynthesis of adult cuticle followed by its pigmentation and sclerotization occurs, and dark coloration of the cuticle becomes visible in pharate adults. Here, we examined the molecular mechanism of adult cuticular formation in more detail. We noticed that an exogenous JH mimic (JHM) treatment of Day 0 pupae did not inhibit pigmentation or sclerotization, but instead, induced precocious pigmentation of adult cuticle two days in advance. Quantitative RT-PCR analyses revealed that ecdysone-induced protein 75B (E75) is downregulated in JHM-treated pupae. Meanwhile, tyrosine hydroxylase (Th), an enzyme involved in cuticular pigmentation and sclerotization, was precociously induced, whereas a structural cuticular protein CPR27 was downregulated, by exogenous JHM treatment. RNA interference-mediated knockdown of E75 resulted in precocious adult cuticular pigmentation, which resembled the phenotype caused by JHM treatment. Notably, upregulation of Th as well as suppression of CPR27 were observed with E75 knockdown. Meanwhile, JHM treatment suppressed the expression of genes involved in melanin synthesis, such as Yellow-y and Laccase 2, but E75 knockdown did not result in marked reduction in their expression. Taken together, these results provided insights into the regulatory mechanisms of adult cuticular formation; the transcription of genes involved in adult cuticular formation proceeds in a proper timing with undetectable JH, and exogenous JHM treatment disturbs their transcription. For some of these genes such as Th and CPR27, E75 is involved in transcriptional regulation. This study shed light on the molecular mode of action of JHM as insecticides; exogenous JHM treatment disturbed the expression of genes involved in the adult cuticular formation, which resulted in lethality as pharate adults.

Yellow-g and Yellow-g2 proteins are required for egg desiccation resistance and temporal pigmentation in the Asian tiger mosquito, Aedes albopictus

Eggs from Aedes mosquitoes exhibit desiccation resistance that helps them to survive and spread as human disease vectors throughout the world. Previous studies have suggested that eggshell/chorion melanization and/or serosal cuticle formation are important for desiccation resistance. In this study, using dsRNAs for target genes, we analyzed the functional importance of two ovary-specific yellow genes, AalY-g and AalY-g2, in the resistance to egg desiccation of the Asian tiger mosquito, Aedes albopictus, a species in which neither the timing of the melanization nor temporal development of the serosal cuticle is correlated with desiccation resistance. Injections of dsAalY-g, dsAalY-g2 or dsAalY-g/g2 (co-injection) into adult females have no effect on their fecundity. However, initial melanization is delayed by 1-2 h with the eggshells eventually becoming black similar to that observed in eggs from dsEGFP-injected control females. In addition, the shape of the eggs from dsAalY-g, -g2 and -g/g2-treated females is abnormally crescent-shaped and the outermost exochorion is more fragile and partially peeled off. dsEGFP control eggs, like those from the wild-type strain, acquire resistance to desiccation between 18 and 24 h after oviposition (HAO). In contrast, ~80% of the 24 HAO dsAalY-g and dsAalY-g2 eggs collapse when they are transferred to a low humidity environment. In addition, there is no electron-dense outer endochorion evident in either dsAalY-g or dsAalY-g2 eggs. These results support the hypothesis that AalY-g and AalY-g2 regulate the timing of eggshell darkening and are required for integrity of the exochorion as well as for rigidity, normal morphology and formation of the outer endochorion, a structure that apparently is critical for desiccation resistance of the Ae. albopictus egg.

Superficially Similar Adaptation Within One Species Exhibits Similar Morphological Specialization but Different Physiological Regulations and Origins

Animals have developed numerous strategies to contend with environmental pressures. We observed that the same adaptation strategy may be used repeatedly by one species in response to a certain environmental challenge. The ladybird Harmonia axyridis displays thermal phenotypic plasticity at different developmental stages. It is unknown whether these superficially similar temperature-induced specializations share similar physiological mechanisms. We performed various experiments to clarify the differences and similarities between these processes. We examined changes in the numbers and sizes of melanic spots in pupae and adults, and confirmed similar patterns for both. The dopamine pathway controls pigmentation levels at both developmental stages of H. axyridis. However, the aspartate-β-alanine pathway controls spot size and number only in the pupae. An upstream regulation analysis revealed the roles of Hox genes and elytral veins in pupal and adult spot formation. Both the pupae and the adults exhibited similar morphological responses to temperatures. However, they occurred in different body parts and were regulated by different pathways. These phenotypic adaptations are indicative of an effective thermoregulatory system in H. axyridis and explains how insects contend with certain environmental pressure based on various control mechanisms.

Gene functions in adult cuticle pigmentation of the yellow mealworm, Tenebrio molitor

In many arthropod species including insects, the cuticle tanning pathway for both pigmentation and sclerotization begins with tyrosine and is responsible for production of both melanin- and quinoid-type pigments, some of which are major pigments for body coloration. In this study we identified and cloned cDNAs of the yellow mealworm, Tenebrio molitor, encoding seven key enzymes involved in this pathway including tyrosine hydroxylase (TmTH), DOPA decarboxylase (TmDDC), laccase 2 (TmLac2), Yellow-y (TmY-y), arylalkylamine N-acetyltransferase (TmAANAT1), aspartate 1-decarboxylase (TmADC) and N-β-alanyldopamine synthase (Tmebony). Expression profiles of these genes during development were analyzed by real-time PCR, revealing development-specific patterns of expression. Loss of function mediated by RNAi of either 1) TmTH or TmLac2, 2) TmDDC or TmY-y, and 3) TmAANAT1, TmADC or Tmebony resulted in pale/white, light yellow/brown and dark/black adult body coloration, respectively. In addition, there are three distinct layer/regional pigmentation differences in rigid types of adult cuticle, a brownish outer exocuticle (EX), a dark pigmented middle mesocuticle (ME) and a transparent inner endocuticle (EN). Decreases in pigmentation of the EX and/or ME layers were observed after RNAi of TmDDC or TmY-y. In TmADC- or Tmebony-deficient adults, a darker pigmented EX layer was observed. In TmAANAT1-deficient adults, trabeculae formed between the dorsal and ventral elytral cuticles as well as the transparent EN layer became highly pigmented. These results demonstrate that knocking down the level of gene expression of specific enzymes of this tyrosine metabolic pathway leads to abnormal pigmentation in individual layers and substructure of the rigid adult exoskeleton of T. molitor.

Modular cis-regulatory logic of yellow gene expression in silkmoth larvae

Colour patterns in butterflies and moths are crucial traits for adaptation. Previous investigations have highlighted genes responsible for pigmentation (ie yellow and ebony). However, the mechanisms by which these genes are regulated in lepidopteran insects remain poorly understood. To elucidate this, molecular studies involving dipterans have largely analysed the cis-regulatory regions of pigmentation genes and have revealed cis-regulatory modularity. Here, we used well-developed transgenic techniques in Bombyx mori and demonstrated that cis-regulatory modularity controls tissue-specific expression of the yellow gene. We first identified which body parts are regulated by the yellow gene via black pigmentation. We then isolated three discrete regulatory elements driving tissue-specific gene expression in three regions of B. mori larvae. Finally, we found that there is no apparent sequence conservation of cis-regulatory regions between B. mori and Drosophila melanogaster, and no expression driven by the regulatory regions of one species when introduced into the other species. Therefore, the trans-regulatory landscapes of the yellow gene differ significantly between the two taxa. The results of this study confirm that lepidopteran species use cis-regulatory modules to control gene expression related to pigmentation, and represent a powerful cadre of transgenic tools for studying evolutionary developmental mechanisms.

Three Melanin Pathway Genes, TH, yellow, and aaNAT, Regulate Pigmentation in the Twin-Spotted Assassin Bug, Platymeris biguttatus (Linnaeus)

Pigmentation plays a vital role in insect survival and reproduction. Many melanin pathway genes have been studied in holometabolous insects; however, they have only been studied in two hemimetabolous insect genera, Oncopeltus and Periplaneta. Here we analyzed three melanin pathway genes (TH, yellow, and aaNAT) using RNA interference (RNAi) in another hemimetabolous insect, namely the twin-spotted assassin bug, Platymeris biguttatus. TH was highly expressed in freshly molted nymphs and adults. TH RNAi resulted in a complete loss of black pigment, with yellow coloration maintained. Therefore, black pigment in this assassin bug is solely generated from the melanin pathway, whereas yellow pigment is generated from other unknown pigmentation pathways. yellow and aaNAT were highly expressed in the white spot of the hemelytra. Downregulation of yellow caused a brown phenotype with high mortality, indicating an important role of yellow functions in cuticle formation and in the process of converting melanin from brown to black. Interestingly, aaNAT RNAi caused not only loss of white pigment, but also loss of yellow and red pigments. This phenotype of aaNAT has not been reported in other insects. Our results provide new information for understanding the melanin pathway in which aaNAT is essential for the formation of colorless patterns.

Proteomics reveals localization of cuticular proteins in Anopheles gambiae

Anopheles gambiae devotes over 2% of its protein coding genes to its 298 structural cuticular proteins (CPs). This paper provides new LC-MS/MS data on two adult structures, proboscises and palps, as well as three larval samples - 4th instar larvae, just their terminal segment, and a preparation enriched in their tracheae. These data were combined with our previously published results of proteins from five other adult structures, whole adults, and two preparations chosen for their relatively clean cuticle, the larval head capsules left behind after ecdysis and the pupal cuticles left behind after adult eclosion. Peptides from 28 CPs were recovered in all adult structures; 24 CPs were identified for the first time, 6 of these were members of the TWDL family. Most newly identified proteins came from the larval sources. Based solely on peptide recovery, from our data and from other investigators, most available on VectorBase, there were only 4 CPs that were restricted to a single adult structure. More were restricted to a single metamorphic stage, 14 in larvae, 0 in pupae and 32 in adults. Expression data from our earlier RT-qPCR studies reduces these numbers. Charting restriction of CPs to stage or structure is a step forward in establishing their specific roles.

Identification of a transcription factor that functions downstream of corazonin in the control of desert locust gregarious body coloration

Corazonin (Crz) is a neuropeptide that controls phase-dependent body color polyphenism in locusts. The Crz signaling pathway is responsible for the development of gregarious black patterns in nymphs and determination of the morphometric ratio F/C (F = hind femur length, C = maximum head width) in adults. However, little information is available regarding the mediator and effector proteins regulated by Crz. In this study, we identified a novel transcription factor, Loct, which functions downstream of Crz in Schistocerca gregaria and Locusta migratoria. In S. gregaria, we detected a variant of Loct lacking the N-terminal region. Protein-protein interaction assays showed that both the long and short Loct variants formed a complex with themselves. LOCT knockdown in gregarious nymphs reduced the intensity of their black patterning, but did not affect F/C ratios in adults. LOCT was exclusively expressed in the integument of gregarious nymphs, suggesting that Loct is involved in melanin production. In addition, we found that the melanization-associated protein Yellow (YEL) and the albino-related takeout protein (ALTO) are expressed in the integument and function downstream of Crz. However, Crz injection failed to influence LOCT, YEL, and ALTO expression. Therefore, additional factors probably cooperate with Crz to induce these genes. The gene expression profiles of YEL and ALTO in LOCT-knockdown nymphs suggest that Loct does not directly control the transcription of YEL or ALTO. In summary, we present a working model of the Crz pathway, which is active in crowded S. gregaria nymphs.

Identification of yellow gene family in Agrotis ipsilon and functional analysis of Aiyellow-y by CRISPR/Cas9

The yellow gene family has been identified in several model insects, but yellow genes were poorly identified in non-model insects and the functions of yellow genes are largely unknown. In this study, we identified seven yellow genes in an important agricultural pest Agrotis ipsilon. Each gene encodes a protein containing a major royal jelly domain. Phylogenetic analysis defined these genes as yellow-y, -b, -b2, -c, -d, -e, and -h, respectively. The A. ipsilon yellow genes yellow-b, -b2, and -c were stably expressed in all developmental stages and tissues analyzed, whereas the other four yellow genes had unique expression patterns, suggesting distinct physiological roles of each gene. Using the CRISPR/Cas9 system, we successfully disrupted yellow-y in A. ipsilon and obtained G₀ insects with somatic mutations. Unlike the black of wild-type newly hatched larvae and of adults, the mutants were yellow, although in the pupal stage mutant coloration did not differ from wild-type coloration. This phenotype was inherited by G₁ offspring. The G₀ mutants did not show any growth deficiency compared with control insects; however, a dehydration-like phenotype was observed in newly hatched G₁ larvae from sibling crossed mutants. Our results indicate that A. ipsilon yellow-y gene plays a role in body pigmentation and also might function in waterproofing.

CRISPR-Cas9 targeted disruption of the yellow ortholog in the housefly identifies the brown body locus

The classic brown body (bwb) mutation in the housefly Musca domestica impairs normal melanization of the adult cuticle. In Drosophila melanogaster, a reminiscent pigmentation defect results from mutations in the yellow gene encoding dopachrome conversion enzyme (DCE). Here, we demonstrate that the bwb locus structurally and functionally represents the yellow ortholog of Musca domestica, MdY. In bwb Musca strains, we identified two mutant MdY alleles that contain lesions predicted to result in premature truncation of the MdY open reading frame. We targeted wildtype MdY by CRISPR-Cas9 RNPs and generated new mutant alleles that fail to complement existing MdY alleles, genetically confirming that MdY is the bwb locus. We further found evidence for Cas9-mediated interchromosomal recombination between wildtype and mutant bwb alleles. Our work resolves the molecular identity of the classic bwb mutation in Musca domestica and establishes the feasibility of Cas9-mediated genome editing in the Musca model.

Genetic Basis of Melanin Pigmentation in Butterfly Wings

Despite the variety, prominence, and adaptive significance of butterfly wing patterns, surprisingly little is known about the genetic basis of wing color diversity. Even though there is intense interest in wing pattern evolution and development, the technical challenge of genetically manipulating butterflies has slowed efforts to functionally characterize color pattern development genes. To identify candidate wing pigmentation genes, we used RNA sequencing to characterize transcription across multiple stages of butterfly wing development, and between different color pattern elements, in the painted lady butterfly Vanessa cardui This allowed us to pinpoint genes specifically associated with red and black pigment patterns. To test the functions of a subset of genes associated with presumptive melanin pigmentation, we used clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 genome editing in four different butterfly genera. pale, Ddc, and yellow knockouts displayed reduction of melanin pigmentation, consistent with previous findings in other insects. Interestingly, however, yellow-d, ebony, and black knockouts revealed that these genes have localized effects on tuning the color of red, brown, and ochre pattern elements. These results point to previously undescribed mechanisms for modulating the color of specific wing pattern elements in butterflies, and provide an expanded portrait of the insect melanin pathway.

The evolutionary origination of a novel expression pattern through an extreme heterochronic shift

The evolutionary origins of morphological structures are thought to often depend upon the redeployment of old genes into new developmental settings. Although many examples of cis-regulatory divergence have shown how pre-existing patterns of gene expression have been altered, only a small number of case studies have traced the origins of cis-regulatory elements that drive new expression domains. Here, we elucidate the evolutionary history of a novel expression pattern of the yellow gene within the Zaprionus genus of fruit flies. We observed a unique pattern of yellow transcript accumulation in the wing disc during the third larval instar, a stage that precedes its typical expression pattern associated with cuticular melanization by about a week. The region of the Zaprionus wing disc that expresses yellow subsequently develops into a portion of the thorax, a tissue for which yellow expression has been reported for several fruit fly species. Tests of GFP reporter transgenes containing the Zaprionus yellow regulatory region revealed that the wing disc pattern arose by changes in the cis-regulatory region of yellow. Moreover, the wing disc enhancer activity of yellow depends upon a short conserved sequence with ancestral thoracic functions, suggesting that the pupal thorax regulatory sequence was genetically reprogrammed to drive expression that commences much earlier during development. These results highlight how novel domains of gene expression may arise by extreme shifts in timing during the origins of novel traits.

Cuticle formation and pigmentation in beetles

Adult beetles (Coleoptera) are covered primarily by a hard exoskeleton or cuticle. For example, the beetle elytron is a cuticle-rich highly modified forewing structure that shields the underlying hindwing and dorsal body surface from a variety of harmful environmental factors by acting as an armor plate. The elytron comes in a variety of colors and shapes depending on the coleopteran species. As in many other insect species, the cuticular tanning pathway begins with tyrosine and is responsible for production of a variety of melanin-like and other types of pigments. Tanning metabolism involves quinones and quinone methides, which also act as protein cross-linking agents for cuticle sclerotization. Electron microscopic analyses of rigid cuticles of the red flour beetle, Tribolium castaneum, have revealed not only numerous horizontal chitin-protein laminae but also vertically oriented columnar structures called pore canal fibers. This structural architecture together with tyrosine metabolism for cuticle tanning is likely to contribute to the rigidity and coloration of the beetle exoskeleton.

Distribution of cuticular proteins in different structures of adult Anopheles gambiae

Anopheles gambiae devotes over 2% (295) of its protein coding genes to structural cuticular proteins (CPs) that have been classified into 13 different families plus ten low complexity proteins not assigned to families. Small groups of genes code for identical proteins reducing the total number of unique cuticular proteins to 282. Is the large number because different structures utilize different CPs, or are all of the genes widely expressed? We used LC-MS/MS to learn how many products of these genes were found in five adult structures: Johnston's organs, the remainder of the male antennae, eye lenses, legs, and wings. Data were analyzed against both the entire proteome and a smaller database of just CPs. We recovered unique peptides for 97 CPs and shared peptides for another 35. Members of 11 of the 13 families were recovered as well as some unclassified. Only 11 CPs were present exclusively in only one structure while 43 CPs were recovered from all five structures. A quantitative analysis, using normalized spectral counts, revealed that only a few CPs were abundant in each structure. When the MS/MS data were run against the entire proteome, the majority of the top hits were to CPs, but peptides were recovered from an additional 467 proteins. CP peptides were frequently recovered from chitin-binding domains, confirming that protein-chitin interactions are not mediated by covalent bonds. Comparison with three other MS/MS analyses of cuticles or cuticle-rich structures augmented the current analysis. Our findings provide new insights into the composition of different mosquito structures and reveal the complexity of selection and utilization of genes coding for structural cuticular proteins.

Characterization and analysis of a de novo transcriptome from the pygmy grasshopper Tetrix japonica

The pygmy grasshopper Tetrix japonica is a common insect distributed throughout the world, and it has the potential for use in studies of body colour polymorphism, genomics and the biology of Tetrigoidea (Insecta: Orthoptera). However, limited biological information is available for this insect. Here, we conducted a de novo transcriptome study of adult and larval T. japonica to provide a better understanding of its gene expression and develop genomic resources for future work. We sequenced and explored the characteristics of the de novo transcriptome of T. japonica using Illumina HiSeq 2000 platform. A total of 107 608 206 paired-end clean reads were assembled into 61 141 unigenes using the trinity software; the mean unigene size was 771 bp, and the N50 length was 1238 bp. A total of 29 225 unigenes were functionally annotated to the NCBI nonredundant protein sequences (Nr), NCBI nonredundant nucleotide sequences (Nt), a manually annotated and reviewed protein sequence database (Swiss-Prot), Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases. A large number of putative genes that are potentially involved in pigment pathways, juvenile hormone (JH) metabolism and signalling pathways were identified in the T. japonica transcriptome. Additionally, 165 769 and 156 796 putative single nucleotide polymorphisms occurred in the adult and larvae transcriptomes, respectively, and a total of 3162 simple sequence repeats were detected in this assembly. This comprehensive transcriptomic data for T. japonica will provide a usable resource for gene predictions, signalling pathway investigations and molecular marker development for this species and other pygmy grasshoppers.

Transcriptome analysis of the painted lady butterfly, Vanessa cardui during wing color pattern development

BACKGROUND

Butterfly wing color patterns are an important model system for understanding the evolution and development of morphological diversity and animal pigmentation. Wing color patterns develop from a complex network composed of highly conserved patterning genes and pigmentation pathways. Patterning genes are involved in regulating pigment synthesis however the temporal expression dynamics of these interacting networks is poorly understood. Here, we employ next generation sequencing to examine expression patterns of the gene network underlying wing development in the nymphalid butterfly, Vanessa cardui.

RESULTS

We identified 9, 376 differentially expressed transcripts during wing color pattern development, including genes involved in patterning, pigmentation and gene regulation. Differential expression of these genes was highest at the pre-ommochrome stage compared to early pupal and late melanin stages. Overall, an increasing number of genes were down-regulated during the progression of wing development. We observed dynamic expression patterns of a large number of pigment genes from the ommochrome, melanin and also pteridine pathways, including contrasting patterns of expression for paralogs of the yellow gene family. Surprisingly, many patterning genes previously associated with butterfly pattern elements were not significantly up-regulated at any time during pupation, although many other transcription factors were differentially expressed. Several genes involved in Notch signaling were significantly up-regulated during the pre-ommochrome stage including slow border cells, bunched and pebbles; the function of these genes in the development of butterfly wings is currently unknown. Many genes involved in ecdysone signaling were also significantly up-regulated during early pupal and late melanin stages and exhibited opposing patterns of expression relative to the ecdysone receptor. Finally, a comparison across four butterfly transcriptomes revealed 28 transcripts common to all four species that have no known homologs in other metazoans.

CONCLUSIONS

This study provides a comprehensive list of differentially expressed transcripts during wing development, revealing potential candidate genes that may be involved in regulating butterfly wing patterns. Some differentially expressed genes have no known homologs possibly representing genes unique to butterflies. Results from this study also indicate that development of nymphalid wing patterns may arise not only from melanin and ommochrome pigments but also the pteridine pigment pathway.

A Pathway Analysis of Melanin Patterning in a Hemimetabolous Insect

Diversity in insect pigmentation, encompassing a wide range of colors and spatial patterns, is among the most noticeable features distinguishing species, individuals, and body regions within individuals. In holometabolous species, a significant portion of such diversity can be attributed to the melanin synthesis genes, but this has not been formally assessed in more basal insect lineages. Here we provide a comprehensive analysis of how a set of melanin genes (ebony, black, aaNAT, yellow, and tan) contributes to the pigmentation pattern in a hemipteran, Oncopeltus fasciatus For all five genes, RNA interference depletion caused alteration of black patterning in a region-specific fashion. Furthermore, the presence of distinct nonblack regions in forewings and hindwings coincides with the expression of ebony and aaNAT in these appendages. These findings suggest that the region-specific phenotypes arise from regional employment of various combinations of the melanin genes. Based on this insight, we suggest that melanin genes are used in two distinct ways: a "painting" mode, using predominantly melanin-promoting factors in areas that generally lack black coloration, and, alternatively, an "erasing" mode, using mainly melanin-suppressing factors in regions where black is the dominant pigment. Different combinations of these strategies may account for the vast diversity of melanin patterns observed in insects.

The genetic control of aposematic black pigmentation in hemimetabolous insects: insights from Oncopeltus fasciatus

Variations in body pigmentation, encompassing both the range of specific colors as well as the spatial arrangement of those colors, are among the most noticeable and lineage-specific insect features. However, the genetic mechanisms responsible for generating this diversity are still limited to several model species that are primarily holometabolous insects. To address this lack of knowledge, we utilize Oncopeltus fasciatus, an aposematic hemimetabolous insect, as a new model to study insect pigmentation. First, to determine the genetic regulation of black pigment production in Oncopeltus, we perform an RNAi analysis on three core genes involved in the melanin pathway, tyrosine hydroxylase (TH), dopa decarboxylase (DDC), and laccase 2 (lac2). The black pigmentation is affected in all instances, showing that the black pigments in this species are derived from the melanin pathway. The results of the DDC RNAi are particularly informative because they reveal that it is Dopamine melanin, not DOPA melanin, which is the predominant component of black pigments in Oncopeltus. Second, we test whether pigmentation follows a two-step model where the spatial pre-mapping of enzymatic activity is followed by vein-dependent transportation of melanin substances. We confirm the existence of the first step by observing that premature wings develop black pigmentation when exposed to melanin precursors. In addition, we provide evidence for the second step by showing that wing melanin patterning is disrupted when vein transportation is halted. These findings bring novel insights from a hemimetabolous species and establish a framework for subsequent studies on the mechanisms of pigment production and patterning responsible for variations in insect coloration.

Establishing an in vivo assay system to identify components involved in environmental RNA interference in the western corn rootworm

The discovery of environmental RNA interference (RNAi), in which gene expression is suppressed via feeding with double-stranded RNA (dsRNA) molecules, opened the door to the practical application of RNAi-based techniques in crop pest management. The western corn rootworm (WCR, Diabrotica virgifera virgifera) is one of the most devastating corn pests in North America. Interestingly, WCR displays a robust environmental RNAi response, raising the possibility of applying an RNAi-based pest management strategy to this pest. Understanding the molecular mechanisms involved in the WCR environmental RNAi process will allow for determining the rate limiting steps involved with dsRNA toxicity and potential dsRNA resistance mechanisms in WCR. In this study, we have established a two-step in vivo assay system, which allows us to evaluate the involvement of genes in environmental RNAi in WCR. We show that laccase 2 and ebony, critical cuticle pigmentation/tanning genes, can be used as marker genes in our assay system, with ebony being a more stable marker to monitor RNAi activity. In addition, we optimized the dsRNA dose and length for the assay, and confirmed that this assay system is sensitive to detect well-known RNAi components such as Dicer-2 and Argonaute-2. We also evaluated two WCR sid1- like (sil) genes with this assay system. This system will be useful to quickly survey candidate systemic RNAi genes in WCR, and also will be adaptable for a genome-wide RNAi screening to give us an unbiased view of the environmental/systemic RNAi pathway in WCR.

A Major Facilitator Superfamily protein encoded by TcMucK gene is not required for cuticle pigmentation, growth and development in Tribolium castaneum

Insect cuticle pigmentation and sclerotization (tanning) are vital physiological processes for insect growth, development and survival. We have previously identified several colorless precursor molecules as well as enzymes involved in their biosynthesis and processing to yield the mature intensely colored body cuticle pigments. A recent study indicated that the Bombyx mori (silkmoth) gene, BmMucK, which encodes a protein orthologous to a Culex pipiens quiquefasciatus (Southern house mosquito) cis,cis, muconate transporter, is a member of the "Major Facilitator Superfamily" (MFS) of transporter proteins and is associated with the appearance of pigmented body segments of naturally occurring body color mutants of B. mori. While RNA interference of the BmMucK gene failed to result in any observable phenotype, RNAi using a dsRNA for an orthologous gene from the red flour beetle, Tribolium castaneum, was reported to result in molting defects and darkening of the cuticle and some body parts, leading to the suggestion that orthologs of MucK genes may differ in their functions among insects. To verify the role and essentiality of the ortholog of this gene in development and body pigmentation function in T. castaneum we obtained cDNAs for the orthologous gene (TcMucK) from RNA isolated from the GA-1 wild-type strain of T. castaneum. The sequence of a 1524 nucleotides-long cDNA for TcMucK which encodes the putatively full-length protein, was assembled from two overlapping RT-PCR fragments and the expression profile of this gene during development was analyzed by real-time PCR. This cDNA encodes a 55.8 kDa protein consisting of 507 amino acid residues and includes 11 putative transmembrane segments. Transcripts of TcMucK were detected throughout all of the developmental stages analyzed. The function of this gene was explored by injection of two different double-stranded RNAs targeting different regions of the TcMucK gene (dsTcMucKs) into young larvae to down-regulate transcripts during subsequent stages of insect development until the adult stage. RNA interference of TcMucK had no observable effects on larval, pupal or adult pigmentation. In addition, it did not affect larval-larval, larval-pupal and pupal-adult molting or survival. Thus, in contrast to the results of Zhao et al. (2012), our study demonstrates that TcMucK is not essential for growth, development or cuticle pigmentation of T. castaneum.

Sexually dimorphic body color is regulated by sex-specific expression of yellow gene in ponerine ant, Diacamma sp

Most hymenopteran species exhibit conspicuous sexual dimorphism due to ecological differences between the sexes. As hymenopteran genomes, under the haplodiploid genetic system, exhibit quantitative differences between sexes while remaining qualitatively identical, sexual phenotypes are assumed to be expressed through sex-specific gene usage. In the present study, the molecular basis for expression of sexual dimorphism in a queenless ant, Diacamma sp., which exhibits a distinct color dimorphism, was examined. Worker females of the species appear bluish-black, while winged males exhibit a yellowish-brown body color. Initially, observations of the pigmentation processes during pupal development revealed that black pigmentation was present in female pupae but not in males, suggesting that sex-specific melanin synthesis was responsible for the observed color dimorphism. Therefore, five orthologs of the genes involved in the insect melanin synthesis (yellow, ebony, tan, pale and dopa decarboxylase) were subcloned and their spatiotemporal expression patterns were examined using real-time quantitative RT-PCR. Of the genes examined, yellow, which plays a role in black melanin synthesis in insects, was expressed at higher levels in females than in males throughout the entire body during the pupal stage. RNA interference of yellow was then carried out in order to determine the gene function, and produced females with a more yellowish, brighter body color similar to that of males. It was concluded that transcriptional regulation of yellow was responsible for the sexual color dimorphism observed in this species.

Characterization of sulfakinin and sulfakinin receptor and their roles in food intake in the red flour beetle Tribolium castaneum

Sulfakinins (SK) are multifunctional neuropeptides widely found in insects that are structurally and functionally homologous to the mammalian gastrin/cholecystokinin (CCK) neuropeptides. CCK is involved in various biological processes such as the feeding regulation where it induces satiety. In this project we characterized SK and SK receptor (SKR) of an important pest and model beetle insect, the red flour beetle Tribolium castaneum, with the aim to better understand the SK signaling pathway and its function in food intake. The sk gene encoded a SK precursor with 113 amino acids and the skr gene a seven-transmembrane SKR with 554 amino acids. Both genes were expressed in the larval, pupal and adult stages with different expression levels in tested tissues. By RNA interference, sk dsRNA and skr dsRNA reduced the expression of the corresponding target gene by 80-90% and 30-50%, respectively, and stimulated food intake in the larvae. In parallel, we injected insects with a SK analog reducing food intake. In conclusion, the data are discussed in relation to the SK signaling pathway and its physiological-endocrinological role in regulating food intake and potential usage in the control of important pest insects.

Molecular and biochemical characterization of the major royal jelly protein in bumblebees suggest a non-nutritive function

Honeybee queens are generated on purpose by extensive feeding with a glandular secretion termed royal jelly. Major royal jelly proteins (MRJPs) are the dominant proteinaceous component of royal jelly. One of them, MRJP1, was found to play a central role in honeybee queen development. Genes encoding MRJPs were reported to originate from a single originator, and several of them have evolved nutritive function. Phylogenetic analysis provides evidence that the same originator has multiplied independently in Nasonia and ant lineages. Here we show that bumblebees represent a transition species preserving a single-copy pre-multiplication stage of MRJP evolution. By exploring the single-copy BtRJPL gene, we found striking similarities with MRJPs of the honeybee such as gene structure and expression regulation. At the same time it turned out that BtRJPL does not fulfill criteria for functioning as a nutritive protein. Instead we found evidence that BtRJPL is involved in food digestion or modification, which appears to be the original MRJP function, at least in this lineage. Thus, the evolutionary pattern of MRJPs in hymenopterans constitutes an excellent example of a functional diversification combined with the origin of new properties followed by intensive gene duplication events.

Transcriptome analysis reveals novel patterning and pigmentation genes underlying Heliconius butterfly wing pattern variation

Background

Heliconius butterfly wing pattern diversity offers a unique opportunity to investigate how natural genetic variation can drive the evolution of complex adaptive phenotypes. Positional cloning and candidate gene studies have identified a handful of regulatory and pigmentation genes implicated in Heliconius wing pattern variation, but little is known about the greater developmental networks within which these genes interact to pattern a wing. Here we took a large-scale transcriptomic approach to identify the network of genes involved in Heliconius wing pattern development and variation. This included applying over 140 transcriptome microarrays to assay gene expression in dissected wing pattern elements across a range of developmental stages and wing pattern morphs of Heliconius erato.

Results

We identified a number of putative early prepattern genes with color-pattern related expression domains. We also identified 51 genes differentially expressed in association with natural color pattern variation. Of these, the previously identified color pattern “switch gene” optix was recovered as the first transcript to show color-specific differential expression. Most differentially expressed genes were transcribed late in pupal development and have roles in cuticle formation or pigment synthesis. These include previously undescribed transporter genes associated with ommochrome pigmentation. Furthermore, we observed upregulation of melanin-repressing genes such as ebony and Dat1 in non-melanic patterns.

Conclusions

This study identifies many new genes implicated in butterfly wing pattern development and provides a glimpse into the number and types of genes affected by variation in genes that drive color pattern evolution.

Draft genome of the globally widespread and invasive Argentine ant (Linepithema humile)

Ants are some of the most abundant and familiar animals on Earth, and they play vital roles in most terrestrial ecosystems. Although all ants are eusocial, and display a variety of complex and fascinating behaviors, few genomic resources exist for them. Here, we report the draft genome sequence of a particularly widespread and well-studied species, the invasive Argentine ant (Linepithema humile), which was accomplished using a combination of 454 (Roche) and Illumina sequencing and community-based funding rather than federal grant support. Manual annotation of >1,000 genes from a variety of different gene families and functional classes reveals unique features of the Argentine ant's biology, as well as similarities to Apis mellifera and Nasonia vitripennis. Distinctive features of the Argentine ant genome include remarkable expansions of gustatory (116 genes) and odorant receptors (367 genes), an abundance of cytochrome P450 genes (>110), lineage-specific expansions of yellow/major royal jelly proteins and desaturases, and complete CpG DNA methylation and RNAi toolkits. The Argentine ant genome contains fewer immune genes than Drosophila and Tribolium, which may reflect the prominent role played by behavioral and chemical suppression of pathogens. Analysis of the ratio of observed to expected CpG nucleotides for genes in the reproductive development and apoptosis pathways suggests higher levels of methylation than in the genome overall. The resources provided by this genome sequence will offer an abundance of tools for researchers seeking to illuminate the fascinating biology of this emerging model organism.

Both UDP N-acetylglucosamine pyrophosphorylases of Tribolium castaneum are critical for molting, survival and fecundity

A bioinformatics search of the genome of the red flour beetle, Tribolium castaneum, resulted in the identification of two genes encoding proteins closely related to UDP-N-acetylglucosamine pyrophosphorylases (UAPs), which provide the activated precursor, UDP-N-acetylglucosamine, for the synthesis of chitin, glycoproteins and glycosylphosphoinositide (GPI) anchors of some membrane proteins as well as for the modification of other substrates. This is in contrast to other arthropods whose genomes have been completely sequenced, all of which have only a single copy of this gene. The two T. castaneum UAP genes, TcUAP1 and TcUAP2, share both nucleotide and amino acid sequence identities of about 60%. RT-PCR analysis revealed that the two genes differ in their developmental and tissue-specific patterns of expression. RNA interference (RNAi) indicated roles for TcUAP1 and TcUAP2 at the molt and intermolt stages, respectively: RNAi for TcUAP1 resulted in specific arrest at the larval-larval, larval-pupal or pupal-adult molts, depending on time of injection of double-stranded RNAs, whereas RNAi for TcUAP2 prevented larval growth or resulted in pupal paralysis. Analysis of elytral cuticle indicated loss of structural integrity and chitin staining after RNAi for TcUAP1, but not after RNAi for TcUAP2. Loss of peritrophic matrix (PM)-associated chitin was also observed following RNAi for TcUAP1, but not after RNAi for TcUAP2. Down-regulation of transcripts for either TcUAP gene at the mature adult stage resulted in cessation of oviposition in females, as well as fat body depletion and eventual death in both sexes. These results demonstrate that both TcUAP genes are critical for beetle development and survival, but that only TcUAP1 is clearly associated with synthesis of cuticular or PM chitin. However, both of these genes appear to have additional critical role(s) unrelated to chitin synthesis, presumably in the glycosylation of proteins and/or secondary metabolites.

Nomadic enhancers: tissue-specific cis-regulatory elements of yellow have divergent genomic positions among Drosophila species

cis-regulatory DNA sequences known as enhancers control gene expression in space and time. They are central to metazoan development and are often responsible for changes in gene regulation that contribute to phenotypic evolution. Here, we examine the sequence, function, and genomic location of enhancers controlling tissue- and cell-type specific expression of the yellow gene in six Drosophila species. yellow is required for the production of dark pigment, and its expression has evolved largely in concert with divergent pigment patterns. Using Drosophila melanogaster as a transgenic host, we examined the expression of reporter genes in which either 5' intergenic or intronic sequences of yellow from each species controlled the expression of Green Fluorescent Protein. Surprisingly, we found that sequences controlling expression in the wing veins, as well as sequences controlling expression in epidermal cells of the abdomen, thorax, and wing, were located in different genomic regions in different species. By contrast, sequences controlling expression in bristle-associated cells were located in the intron of all species. Differences in the precise pattern of spatial expression within the developing epidermis of D. melanogaster transformants usually correlated with adult pigmentation in the species from which the cis-regulatory sequences were derived, which is consistent with cis-regulatory evolution affecting yellow expression playing a central role in Drosophila pigmentation divergence. Sequence comparisons among species favored a model in which sequential nucleotide substitutions were responsible for the observed changes in cis-regulatory architecture. Taken together, these data demonstrate frequent changes in yellow cis-regulatory architecture among Drosophila species. Similar analyses of other genes, combining in vivo functional tests of enhancer activity with in silico comparative genomics, are needed to determine whether the pattern of regulatory evolution we observed for yellow is characteristic of genes with rapidly evolving expression patterns.