Bombyx ortholog of the Drosophila eye color gene brown controls riboflavin transport in Malpighian tubules

Knockdowns of red Malphigian tubules reveal pigmentation roles in the milkweed bug

Classical Drosophila eye color mutations have unearthed a toolkit of genes that have permitted candidate gene studies of the outstanding diversity of coloration patterns in other insects. The gene underlying the eye color phenotypes of the red Malphigian tubules (red) fly mutant was mapped to a LysM domain gene of unknown molecular function. Here, we used RNAi to test the role of a red ortholog in the pigmentation of the milkweed bug Oncopeltus fasciatus, and contrast its effect with the ommochrome biosynthetic pathway gene vermilion (ver). Pigmentation was reduced in the cuticle of embryonic legs and first instar abdomens following parental RNAi against red, but not against ver, likely reflecting an effect on pterin biogenesis. Nymphal RNAi of red and ver both resulted in adult eye depigmentation, consistent with an effect on ommochrome content. These results suggest red loss-of-function impacts biochemically distinct types of pigments, and we discuss its putative role in the biogenesis of lysosome-related organelles such as ommochromasomes and pterinosomes.

RNAi-induced knockdown of white gene in the southern green stink bug (Nezara viridula L.)

The southern green stink bug (SGSB) Nezara viridula L. is one of the most common stink bug species in the United States and can cause significant yield loss in a variety of crops. A suitable marker for the assessment of gene-editing tools in SGSB has yet to be characterized. The white gene, first documented in Drosophila, has been a useful target to assess the efficiency of introduced mutations in many species as it controls pigmentation processes and mutants display readily identifiable phenotypes. In this study we used the RNAi technique to investigate functions and phenotypes associated with the white ortholog in the SGSB and to validate white as a marker for genetic transformation in this species. This study revealed that white may be a suitable marker for germline transformation in the SGSB as white transcript knockdown was not lethal, did not impair embryo development and provided a distinguishable phenotype. Our results demonstrated that the white ortholog in SGSB is involved in the pathway for ommochrome synthesis and suggested additional functions of this gene such as in the integument composition, management of hemolymph compounds and riboflavin mobilization.

Atypical strategies for cuticle pigmentation in the blood-feeding hemipteran Rhodnius prolixus

Pigmentation in insects has been linked to mate selection and predator evasion, thus representing an important aspect for natural selection. Insect body color is classically associated to the activity of tyrosine pathway enzymes, and eye color to pigment synthesis through the tryptophan and guanine pathways, and their transport by ABC proteins. Among the hemiptera, the genetic basis for pigmentation in kissing bugs such as Rhodnius prolixus, that transmit Chagas disease to humans, has not been addressed. Here we report the functional analysis of R. prolixus eye and cuticle pigmentation genes. Consistent with data for most insect clades, we show that knockdown for yellow results in a yellow cuticle, while scarlet and cinnabar knockdowns display red eyes as well as cuticle phenotypes. In addition, tyrosine pathway aaNATpreto knockdown resulted in a striking dark cuticle that displays no color pattern or UV reflectance. In contrast, knockdown of ebony and tan, that encode NBAD branch tyrosine pathway enzymes, did not generate the expected dark and light brown phenotypes, respectively, as reported for other insects. We hypothesize that R. prolixus, which requires tyrosine pathway enzymes for detoxification from the blood diet, evolved an unusual strategy for cuticle pigmentation based on the preferential use of a color erasing function of the aaNATpreto tyrosine pathway branch. We also show that genes classically involved in the generation and transport of eye pigments regulate red body color in R. prolixus. This is the first systematic approach to identify the genes responsible for the generation of color in a blood-feeding hemiptera, providing potential visible markers for future transgenesis.

Comparative Proteomics of Coxiella like Endosymbionts (CLEs) in the Symbiotic Organs of Rhipicephalus sanguineus Ticks

Maternally transmitted obligatory endosymbionts are found in the female gonads as well as in somatic tissue and are expected to provide missing metabolite to their hosts. These deficiencies are presumably complemented through specific symbiotic microorganisms such as Coxiella-like endosymbionts (CLEs) of Rhipicephalus ticks. CLEs are localized in specialized host tissue cells within the Malpighian tubules (Mt) and the ovaries (Ov) from which they are maternally transmitted to developing oocytes. These two organs differ in function and cell types, but the role of CLEs in these tissues is unknown. To probe possible functions of CLEs, comparative proteomics was performed between Mt and Ov of R. sanguineus ticks. Altogether, a total of 580 and 614 CLE proteins were identified in Mt and Ov, respectively. Of these, 276 CLE proteins were more abundant in Mt, of which 12 were significantly differentially abundant. In Ov, 290 CLE proteins were more abundant, of which 16 were significantly differentially abundant. Gene Ontology analysis revealed that most of the proteins enriched in Mt are related to cellular metabolic functions and stress responses, whereas in Ov, the majority were related to cell proliferation suggesting CLEs function differentially and interdependently with host requirements specific to each organ. The results suggest Mt CLEs provide essential nutrients to its host and Ov CLEs promote proliferation and vertical transmission to tick progeny. IMPORTANCE Here we compare the Coxiella-like endosymbionts (CLEs) proteomes from Malpighian tubule (Mt) and the ovaries (Ov) of the brown dog tick Rhipicephalus sanguineus. Our results support the hypothesis that CLEs function interdependently with host requirements in each of the organs. The different functional specificity of CLE in the same host suggest that metabolic capabilities evolved according to the constrains imposed by the specific organ function and requirements. Our findings provide specific CLE protein targets that can be useful for future studies of CLE biology with a focus on tick population control.

Barriers and Promises of the Developing Pigment Organelle Field

Many colors and patterns in nature are regulated by the packaging and processing of intracellular pigment-containing organelles within cells. Spanning both molecular and tissue-level spatial scales with chemical and physical (structural) elements of coloration, pigment organelles represent an important but largely understudied feature of every biological system capable of coloration. Although vertebrate melanosomes have historically been the best-known and most studied pigment organelle, recent reports suggest a surge in studies focusing on other pigment organelles producing a variety of non-melanic pigments, optic crystals and structural colors through their geometric arrangement. In this issue, we showcase the importance these integrative and comparative studies and discuss their results which aid in our understanding of organelle form and function in their native environment. Specifically, we highlight how pigment organelles can be studied at different scales of organization, across multiple species in biology, and with an interdisciplinary approach to better understand the biological and chemical mechanisms underlying color. This type of comparative approach provides evidence for a common origin and identity of membrane-bound pigment organelles not only in vertebrates, as was originally postulated 40 years ago, but in all animals. This indicates that we have much to gain by studying a variety of pigment organelles, as the specific biological context may provide important and unique insights into various aspects of its life. We conclude by highlighting some barriers to this research and discussing strategies to overcome them through a discussion of future directions for pigment organelle research.

Functional analysis of ABCG and ABCH transporters from the red flour beetle, Tribolium castaneum

BACKGROUND

ATP-binding cassette transporter (ABC transporter) subfamilies ABCA-C and ABCG-H have been implicated in insecticide detoxification, mostly based on findings of elevated gene expression in response to insecticide treatment. We previously characterized TcABCA-C genes from the model beetle and pest Tribolium castaneum and demonstrated that TcABCA and TcABCC genes are involved in the elimination of diflubenzuron, because RNA interference (RNAi)-mediated gene silencing increased susceptibility. In this study, we focused on the potential functions of TcABCG and TcABCH genes in insecticide detoxification.

RESULTS

When we silenced the expression of TcABCG-H genes using RNAi, we noticed a previously unreported developmental RNAi phenotype for TcABCG-4F, which is characterized by 50% mortality and ecdysial arrest during adult moult. When we knocked down the Drosophila brown orthologue TcABCG-XC, we did not obtain apparent eye colour phenotypes but did observe a loss of riboflavin uptake by Malpighian tubules. Next, we determined the expression profiles of all TcABCG-H genes in different tissues and developmental stages and analysed transcript levels in response to treatment with four chemically unrelated insecticides. We found that some genes were specifically upregulated after insecticide treatment. However, when we determined insecticide-induced mortalities in larvae that were treated by double-stranded RNA injection to silence those TcABCG-H genes that were upregulated, we did not observe a significant increase in susceptibility to insecticides.

CONCLUSION

Our findings suggest that the observed insecticide-dependent induction of TcABCG-H gene expression reflects an unspecific stress response, and hence underlines the significance of functional studies on insecticide detoxification. © 2021 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Genome-wide identification and gene-editing of pigment transporter genes in the swallowtail butterfly Papilio xuthus

Background

Insect body coloration often functions as camouflage to survive from predators or mate selection. Transportation of pigment precursors or related metabolites from cytoplasm to subcellular pigment granules is one of the key steps in insect pigmentation and usually executed via such transporter proteins as the ATP-binding cassette (ABC) transmembrane transporters and small G-proteins (e.g. Rab protein). However, little is known about the copy numbers of pigment transporter genes in the butterfly genomes and about the roles of pigment transporters in the development of swallowtail butterflies.

Results

Here, we have identified 56 ABC transporters and 58 Rab members in the genome of swallowtail butterfly Papilio xuthus. This is the first case of genome-wide gene copy number identification of ABC transporters in swallowtail butterflies and Rab family in lepidopteran insects. Aiming to investigate the contribution of the five genes which are orthologous to well-studied pigment transporters (ABCG: white, scarlet, brown and ok; Rab: lightoid) of fruit fly or silkworm during the development of swallowtail butterflies, we performed CRISPR/Cas9 gene-editing of these genes using P. xuthus as a model and sequenced the transcriptomes of their morphological mutants. Our results indicate that the disruption of each gene produced mutated phenotypes in the colors of larvae (cuticle, testis) and/or adult eyes in G0 individuals but have no effect on wing color. The transcriptomic data demonstrated that mutations induced by CRISPR/Cas9 can lead to the accumulation of abnormal transcripts and the decrease or dosage compensation of normal transcripts at gene expression level. Comparative transcriptomes revealed 606 ~ 772 differentially expressed genes (DEGs) in the mutants of four ABCG transporters and 1443 DEGs in the mutants of lightoid. GO and KEGG enrichment analysis showed that DEGs in ABCG transporter mutants enriched to the oxidoreductase activity, heme binding, iron ion binding process possibly related to the color display, and DEGs in lightoid mutants are enriched in glycoprotein binding and protein kinases.

Conclusions

Our data indicated these transporter proteins play an important role in body color of P. xuthus. Our study provides new insights into the function of ABC transporters and small G-proteins in the morphological development of butterflies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07400-z.

The road to lysosome-related organelles: Insights from Hermansky-Pudlak syndrome and other rare diseases

Lysosome-related organelles (LROs) comprise a diverse group of cell type-specific, membrane-bound subcellular organelles that derive at least in part from the endolysosomal system but that have unique contents, morphologies and functions to support specific physiological roles. They include: melanosomes that provide pigment to our eyes and skin; alpha and dense granules in platelets, and lytic granules in cytotoxic T cells and natural killer cells, which release effectors to regulate hemostasis and immunity; and distinct classes of lamellar bodies in lung epithelial cells and keratinocytes that support lung plasticity and skin lubrication. The formation, maturation and/or secretion of subsets of LROs are dysfunctional or entirely absent in a number of hereditary syndromic disorders, including in particular the Hermansky-Pudlak syndromes. This review provides a comprehensive overview of LROs in humans and model organisms and presents our current understanding of how the products of genes that are defective in heritable diseases impact their formation, motility and ultimate secretion.

RNA interference-mediated knockdown of eye coloration genes in the western tarnished plant bug (Lygus hesperus Knight)

Insect eye coloration arises from the accumulation of various pigments. A number of genes that function in the biosynthesis (vermilion, cinnabar, and cardinal) and importation (karmoisin, white, scarlet, and brown) of these pigments, and their precursors, have been identified in diverse species and used as markers for transgenesis and gene editing. To examine their suitability as visible 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 all seven genes were identified. Bioinformatic-based sequence and phylogenetic analyses supported initial annotations as eye coloration genes. Consistent with their proposed role, each of the genes was expressed in adult heads as well as throughout nymphal and adult development. Adult eyes of those injected with double-stranded RNAs (dsRNAs) for karmoisin, vermilion, cinnabar, cardinal, and scarlet were characterized by a red band along the medial margin extending from the rostral terminus to the antenna. In contrast, eyes of insects injected with dsRNAs for both white and brown were a uniform light brown. White knockdown also produced cuticular and behavioral defects. Based on its expression profile and robust visible phenotype, cardinal would likely prove to be the most suitable marker for developing gene editing methods in Lygus species.

CRISPR-Cas9: A New Addition to the Drug Metabolism and Disposition Tool Box

Clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR associated protein 9 (Cas9), i.e., CRISPR-Cas9, has been extensively used as a gene-editing technology during recent years. Unlike earlier technologies for gene editing or gene knockdown, such as zinc finger nucleases and RNA interference, CRISPR-Cas9 is comparably easy to use, affordable, and versatile. Recently, CRISPR-Cas9 has been applied in studies of drug absorption, distribution, metabolism, and excretion (ADME) and for ADME model generation. To date, about 50 papers have been published describing in vitro or in vivo CRISPR-Cas9 gene editing of ADME and ADME-related genes. Twenty of these papers describe gene editing of clinically relevant genes, such as ATP-binding cassette drug transporters and cytochrome P450 drug-metabolizing enzymes. With CRISPR-Cas9, the ADME tool box has been substantially expanded. This new technology allows us to develop better and more predictive in vitro and in vivo ADME models and map previously underexplored ADME genes and gene families. In this mini-review, we give an overview of the CRISPR-Cas9 technology and summarize recent applications of CRISPR-Cas9 within the ADME field. We also speculate about future applications of CRISPR-Cas9 in ADME research.

A reexamination on the deficiency of riboflavin accumulation in Malpighian tubules in larval translucent mutants of the silkworm, Bombyx mori

A variety of insects accumulate high contents of riboflavin (vitamin B₂) in their Malpighian tubules (MTs). Although this process is known to be genetically controlled, the mechanism is not known. In the 1940s and the 1950s, several studies showed that riboflavin contents were low in the MTs of some Bombyx mori (silkworm) mutants with translucent larval skin mutations (e.g., w-3, od, oa, and otm) and that genes responsible for these translucent mutations also affected riboflavin accumulation in the MTs. Since the 2000s, it has been shown that the w-3 gene encodes an ABC transporter, whereas genes responsible for od, oa, and otm mutations encode for the biogenesis of lysosome-related organelles. These findings suggest that some genes of ABC transporters and biogenesis of lysosome-related organelles may control the accumulation of riboflavin in MTs. Therefore, we reexamined the effects that translucent mutations have on the accumulation of riboflavin in MTs by using the translucent and wild-type segregants in mutant strains to measure the specific effect that each gene has on riboflavin accumulation (independent of genomic background). We used nine translucent mutations (w-3^oe, oa, od, otm, Obs, oy, or, oh, and obt) even though the genes responsible for some of these mutations (Obs, oy, or, oh, and obt) have not yet been isolated. Through observation of larval MTs and measurements of riboflavin content using high-performance liquid chromatography, we found that the oa, od, otm, and or mutations were responsible for low contents of riboflavin in MTs, whereas the Obs and oy mutations did not affect riboflavin accumulation. This indicates that the molecular mechanism for riboflavin accumulation is similar but somewhat different than the mechanism responsible for uric acid accumulation in epidermal cells. We found that the genes responsible for oa, od, and otm mutations were consistent with those already established for uric acid accumulation in larval epidermis. This suggests that these three genes control riboflavin accumulation in MTs through a mechanism similar to that of uric acid accumulation, although we do not yet know why the or mutation also controls riboflavin accumulation.

Biogenesis of zinc storage granules in Drosophila melanogaster

Membrane transporters and sequestration mechanisms concentrate metal ions differentially into discrete subcellular microenvironments for use in protein cofactors, signalling, storage or excretion. Here we identify zinc storage granules as the insect's major zinc reservoir in principal Malpighian tubule epithelial cells of Drosophila melanogaster The concerted action of Adaptor Protein-3, Rab32, HOPS and BLOC complexes as well as of the white-scarlet (ABCG2-like) and ZnT35C (ZnT2/ZnT3/ZnT8-like) transporters is required for zinc storage granule biogenesis. Due to lysosome-related organelle defects caused by mutations in the homologous human genes, patients with Hermansky-Pudlak syndrome may lack zinc granules in beta pancreatic cells, intestinal paneth cells and presynaptic vesicles of hippocampal mossy fibers.