Ebony plays an important role in egg hatching and 30k protein expression of silkworm (Bombyx mori)

QiufengN is a silkworm strain. During the feeding process of QiufengN, a mutant of black pupal cuticle QiufengNBP was found. Some silkworm pupae of the mutant were unable to easily molt during pupation, and some silkworm eggs produced by developed normally but larvae were unable to break out of the eggshells. These phenomena had not been observed in other black pupa mutants. Genetic analysis showed that the melanization trait of QiufengNBP is controlled by a recessive gene located on the autosome and follows Mendelian inheritance. Results of positional cloning and qRT-PCR showed that the occurrence of black pupae was caused by the mutation of the ebony gene on chromosome 26. 2-DE analysis of the pupal cuticle of QiufengN and QiufengNBP found that the 30K protein, the main storage protein for the growth and development of silkworms and an important energy substance for embryonic development, has changed significantly. In addition, the expression level of Bombyx mori hatching enzyme (BmHEL), which can soften the eggshell during the hatching process of silkworm, was significantly higher in the eggs of black pupae before and after hatching than in normal eggs. The mutation of ebony makes hatching difficult for silkworms, and increases in BmHEL is needed to soften the eggshell. This study showed that ebony may have important effects on the formation of silkworm pigment and egg hatching, and its formation mechanism is complex and deserves further study.

CRISPR/Cas9-based functional characterization of the pigmentation gene ebony in Plutella xylostella

Body pigmentation is an important character of insects in adapting to biotic and abiotic environmental challenges. Additionally, based on the relative ease of screening, several genes involved in insect melanization have been used in classic genetic studies or as visual markers in constructing transgenic insects. Here, a homologue of the Bombyx mori melanization-inhibiting gene ebony, associated with the conversion of dopamine to N-β-alanyl dopamine, was identified in a global pest, Plutella xylostella. The CRISPR/Cas9 system was applied to generate multiple Pxebony knockout alleles which were crossed to produce a Pxebony knockout strain, showing darker pigmentation in larvae, pupae and adults, compared with wildtype. Interestingly, we observed that Pxebony heterozygotes displayed an intermediate darkened phenotype, indicating partial dominance between the knockout and wildtype alleles. The fitness costs of Pxebony deficiency were also assessed in the mutant strain, indicating that embryo hatchability and larval survival were significantly reduced, while the eclosion rate was not obviously affected. Our work provides a potential target for exploring CRISPR-based genetics-control systems in this economically important pest lepidopteran.

Melanic pigmentation and light preference within and between two Drosophila species

Environmental adaptation and species divergence often involve suites of co-evolving traits. Pigmentation in insects presents a variable, adaptive, and well-characterized class of phenotypes for which correlations with multiple other traits have been demonstrated. In Drosophila, the pigmentation genes ebony and tan have pleiotropic effects on flies' response to light, creating the potential for correlated evolution of pigmentation and vision. Here, we investigate differences in light preference within and between two sister species, Drosophila americana and D. novamexicana, which differ in pigmentation in part because of evolution at ebony and tan and occupy environments that differ in many variables including solar radiation. We hypothesized that lighter pigmentation would be correlated with a greater preference for environmental light and tested this hypothesis using a habitat choice experiment. In a first set of experiments, using males of D. novamexicana line N14 and D. americana line A00, the light-bodied D. novamexicana was found slightly but significantly more often than D. americana in the light habitat. A second experiment, which included additional lines and females as well as males, failed to find any significant difference between D. novamexicana-N14 and D. americana-A00. Additionally, the other dark line of D. americana (A04) was found in the light habitat more often than the light-bodied D. novamexicana-N14, in contrast to our predictions. However, the lightest line of D. americana, A01, was found substantially and significantly more often in the light habitat than the two darker lines of D. americana, thus providing partial support for our hypothesis. Finally, across all four lines, females were found more often in the light habitat than their more darkly pigmented male counterparts. Additional replication is needed to corroborate these findings and evaluate conflicting results, with the consistent effect of sex within and between species providing an especially intriguing avenue for further research.

CRISPR/Cas9-mediated ebony knockout results in puparium melanism in Spodoptera litura

Insect body pigmentation and coloration are critical to adaption to the environment. To explore the mechanisms that drive pigmentation, we used the clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) genome editing system to target the ebony gene in the non-model insect Spodoptera litura. Ebony is crucial to melanin synthesis in insects. By directly injecting Cas9 messenger RNA and ebony-specific guide RNAs into S. litura embryos, we successfully induced a typical ebony-deficient phenotype of deep coloration of the puparium and induction of melanin formation during the pupal stage. Polymerase chain reaction-based genotype analysis demonstrated that various mutations had occurred at the sites targeted in ebony. Our study clearly demonstrates the function of ebony in the puparium coloration and also provides a potentially useful marker gene for functional studies in S. litura as well as other lepidopteran pests.

Pleiotropic Effects of ebony and tan on Pigmentation and Cuticular Hydrocarbon Composition in Drosophila melanogaster

Pleiotropic genes are genes that affect more than one trait. For example, many genes required for pigmentation in the fruit fly Drosophila melanogaster also affect traits such as circadian rhythms, vision, and mating behavior. Here, we present evidence that two pigmentation genes, ebony and tan, which encode enzymes catalyzing reciprocal reactions in the melanin biosynthesis pathway, also affect cuticular hydrocarbon (CHC) composition in D. melanogaster females. More specifically, we report that ebony loss-of-function mutants have a CHC profile that is biased toward long (>25C) chain CHCs, whereas tan loss-of-function mutants have a CHC profile that is biased toward short (<25C) chain CHCs. Moreover, pharmacological inhibition of dopamine synthesis, a key step in the melanin synthesis pathway, reversed the changes in CHC composition seen in ebony mutants, making the CHC profiles similar to those seen in tan mutants. These observations suggest that genetic variation affecting ebony and/or tan activity might cause correlated changes in pigmentation and CHC composition in natural populations. We tested this possibility using the Drosophila Genetic Reference Panel (DGRP) and found that CHC composition covaried with pigmentation as well as levels of ebony and tan expression in newly eclosed adults in a manner consistent with the ebony and tan mutant phenotypes. These data suggest that the pleiotropic effects of ebony and tan might contribute to covariation of pigmentation and CHC profiles in Drosophila.

Enhancing Ebony? Common Associations With a cis-Regulatory Haplotype for Drosophila melanogaster Thoracic Pigmentation in a Japanese Population and Australian Populations

The molecular underpinnings of pigmentation diversity in Drosophila have recently emerged as a model for understanding how the evolution of different cis-regulatory variants results in common adaptive phenotypes within species. We compared sequence variation in a 5' regulatory region harboring a modular enhancer containing a ∼0.7-kb core element contributing to abdominal melanisation in African, and a ∼0.5-kb core element contributing to thoracic pigmentation in D. melanogaster from Japan, to tropical and temperate populations from eastern Australia previously shown to be divergent in thoracic pigmentation and ebony expression. The Australian populations exhibited strong association with the core enhancer polymorphism cluster in complete association with Dark and Light phenotypes from Iriomote, Japan. Moreover, the Iriomote Light and Dark core enhancer haplotypes are common to the Australian populations in the direction predicted by pigmentation phenotype. We also confirmed the Japanese patterns of linkage disequilibrium and association of the tropical inversion In(3R)Payne with the Light enhancer haplotype in the Australian tropical light population. A worldwide survey of the ∼0.5-kb ebony control region SNPs and haplotypes in a subset of the Drosophila Genome Nexus (DGN) populations suggest origins in the sub-Saharan ancestral region surrounding Zambia and subsequent invasion following colonization out of Africa. A previous study demonstrated complex within and between population genetic architecture for abdominal pigmentation which is also correlated with thoracic pigmentation in melanized DGN sub-Saharan populations; however, the ∼0.5-kb ebony control region was not associated and both haplotypes are common even in the most intensely pigmented D. melanogaster from high altitude Ethiopia. In the Australian populations, the strong phenotypic association with the enhancer SNPs and haplotypes that at least partly regulates ebony expression in the Iriomote population, our previous work demonstrating opposing clines for thoracic pigmentation and ebony expression, where the expression cline parallels the In(3R)Payne cline, and the concerted evolution of pigmentation intensity and ebony expression under rapid experimental evolution, all point to a common adaptive evolutionary pathway in distinct populations.

The Drosophila simulans Y chromosome interacts with the autosomes to influence male fitness

The Y chromosome should degenerate because it cannot recombine. However, male-limited transmission increases selection efficiency for male-benefit alleles on the Y, and therefore, Y chromosomes should contribute significantly to variation in male fitness. This means that although the Drosophila Y chromosome is small and gene-poor, Y-linked genes are vital for male fertility in Drosophila melanogaster and the Y chromosome has large male fitness effects. It is unclear whether the same pattern is seen in the closely related Drosophila simulans. We backcrossed Y chromosomes from three geographic locations into five genetic backgrounds and found strong Y and genetic background effects on male fertility. There was a significant Y-background interaction, indicating substantial epistasis between the Y and autosomal genes affecting male fertility. This supports accumulating evidence that interactions between the Y chromosome and the autosomes are key determinants of male fitness.

The Genetic Basis of Pigmentation Differences Within and Between Drosophila Species

In Drosophila, as well as in many other plants and animals, pigmentation is highly variable both within and between species. This variability, combined with powerful genetic and transgenic tools as well as knowledge of how pigment patterns are formed biochemically and developmentally, has made Drosophila pigmentation a premier system for investigating the genetic and molecular mechanisms responsible for phenotypic evolution. In this chapter, we review and synthesize findings from a rapidly growing body of case studies examining the genetic basis of pigmentation differences in the abdomen, thorax, wings, and pupal cases within and between Drosophila species. A core set of genes, including genes required for pigment synthesis (eg, yellow, ebony, tan, Dat) as well as developmental regulators of these genes (eg, bab1, bab2, omb, Dll, and wg), emerge as the primary sources of this variation, with most genes having been shown to contribute to pigmentation differences both within and between species. In cases where specific genetic changes contributing to pigmentation divergence were identified in these genes, the changes were always located in noncoding sequences and affected cis-regulatory activity. We conclude this chapter by discussing these and other lessons learned from evolutionary genetic studies of Drosophila pigmentation and identify topics we think should be the focus of future work with this model system.

Divergent enhancer haplotype of ebony on inversion In(3R)Payne associated with pigmentation variation in a tropical population of Drosophila melanogaster

The pattern and intensity of pigmentation have direct impact on individual fitness through various ecological factors. In a Drosophila melanogaster population from southern Japan, thoracic trident pigmentation intensity of most of the strains could be classified into Dark or Light-type. The expression level variation of the ebony gene correlated well with this phenotype and the allelic differences in expression indicated that the variation is partly due to cis-regulatory changes. In the ∼13 kb gene region, we identified 17 nucleotide sites and 2 indels that were in complete association with the thoracic trident pigmentation intensity. Interestingly, 11 out of 19 sites located within ∼0.5 kb of the core epidermis enhancer. These sites had no obvious association with the abdominal pigmentation intensity in the previously analysed African populations from Uganda and Kenya, which suggested that multiple potential mutational pathways in the cis-regulatory control region of a single gene could lead to similar phenotypic variation within this species. We also found that the Light-type enhancer haplotype is strongly linked to a cosmopolitan inversion, In(3R)Payne, which is predominant in warmer climatic regions in both hemispheres. The sequence pattern suggested that the strong linkage may be due to selective forces related to thermal adaptation. The inferred selection for lighter pigmentation in the Japanese population is in the opposite direction of the previously reported case of selection for darker individuals in African populations. Nevertheless, both adaptive changes involved cis-regulatory changes of ebony, which shows that this gene is likely to be a common target of natural selection.