Examination of the Missense Mutation (rs74653330, Ala481Thr) of the Oculocutaneous Albinism 2 Gene to the Facial Skin Characteristics

ObjectiveA melanin pathway gene, oculocutaneous albinism 2 (OCA2) operates the first step of the melanin synthesis pathway and is known to associate with the albinism and pigmentation. Our previous study identified a significant association (p-value<5x10-8) between a OCA2 missense mutation (rs74653330, Ala481thr) and skin pigmentation. Since melanin pigment protects the skin from damage by ultraviolet light and we hypothesize that the rs74653330 SNP effect on the skin phenotypes not only the melanin, but also the other skin characteristics such as wrinkle formation, moisture level and sebum levels. We examined the association of the rs74653330 SNP to 19 skin characteristics consisting of wrinkle, moisture, melanin, erythema, brightness, and sebum using eight cosmetological instruments. ResultsThe rs74653330 SNP showed significant association with melanin phenotypes, specifically in young and middle groups. The melanin levels of pigmented area showed more melanin in middle age group but less in old group. Also, the rs74653330 SNP affect to wrinkle formation and sebum secretion. Conclusively, the analyses in this study clearly indicate that rs74653330 SNP affects to the melanin related skin phenotypes, and to the wrinkle formation or sebum secretion.

RNAi and CRISPR/Cas9 as Functional Genomics Tools in the Neotropical Stink Bug, Euschistus heros

The Neotropical brown stink bug, Euschistus heros, is one of the most important stink bug pests in leguminous plants in South America. RNAi and CRISPR/Cas9 are important and useful tools in functional genomics, as well as in the future development of new integrated pest management strategies. Here, we explore the use of these technologies as complementing functional genomic tools in E. heros. Three genes, abnormal wing disc (awd), tyrosine hydroxylase (th) and yellow (yel), known to be involved in wing development (awd) and the melanin pathway (th and yel) in other insects, were chosen to be evaluated using RNAi and CRISPR/Cas9 as tools. First, the genes were functionally characterized using RNAi knockdown technology. The expected phenotype of either deformed wing or lighter cuticle pigmentation/defects in cuticle sclerotization was observed for awd and th, respectively. However, for yel, no obvious phenotype was observed. Based on this, yel was selected as a target for the development of a CRISPR/Cas9 workflow to study gene knockout in E. heros. A total of 719 eggs were injected with the Cas9 nuclease (300 ng/µL) together with the sgRNA (300 ng/µL) targeting yel. A total of six insects successfully hatched from the injected eggs and one of the insects showed mutation in the target region, however, the phenotype was still not obvious. Overall, this study for the first time provides a useful CRISPR/Cas9 gene editing methodology to complement RNAi for functional genomic studies in one of the most important and economically relevant stink bug species.

speck, First Identified in Drosophila melanogaster in 1910, Is Encoded by the Arylalkalamine N-Acetyltransferase (AANAT1) Gene

The pigmentation mutation speck is a commonly used recombination marker characterized by a darkly pigmented region at the wing hinge. Identified in 1910 by Thomas Hunt Morgan, speck was characterized by Sturtevant as the most “workable” mutant in the rightmost region of the second chromosome and eventually localized to 2-107.0 and 60C1-2. Though the first speck mutation was isolated over 110 years ago, speck is still not associated with any gene. Here, as part of an undergraduate-led research effort, we show that speck is encoded by the Arylalkylamine N-acetyltransferase 1 (AANAT1) gene. Both alleles from the Morgan lab contain a retrotransposon in exon 1 of the RB transcript of the AANAT1 gene. We have also identified a new insertion allele and generated multiple deletion alleles in AANAT1 that all give a strong speck phenotype. In addition, expression of AANAT1 RNAi constructs either ubiquitously or in the dorsal portion of the developing wing generates a similar speck phenotype. We find that speck alleles have additional phenotypes, including ectopic pigmentation in the posterior pupal case, leg joints, cuticular sutures and overall body color. We propose that the acetylated dopamine generated by AANAT1 decreases the dopamine pool available for melanin production. When AANAT1 function is decreased, the excess dopamine enters the melanin pathway to generate the speck phenotype.

Molecular evolution and developmental expression of melanin pathway genes in Lepidoptera

ABSTRACTPigmentation is involved in a wide array of biological functions across insect orders, including body patterning, thermoregulation, and immunity. The melanin pathway, in particular, has been characterized in several species. However, molecular evolution of the genes involved in this pathway is poorly characterized, and their roles in pigmentation of early developmental stages are just beginning to be explored in non-model organisms. We traced the molecular evolution of six melanin pathway genes in 53 species of Lepidoptera covering butterflies and moths, and representing over 100 million years of diversification. We compared the rates of synonymous and nonsynonymous substitutions within and between these genes to study signatures of selection at the level of individual sites, genes, and branches of the gene tree. We found that molecular evolution of all six genes was governed by strong purifying selection. Yet, a number of sites showed signs of being under positive selection, including in the highly conserved domain regions of three genes. Further, we traced the expression of these genes across developmental stages, tissues, and sexes in the Papilio polytes butterfly using a developmental transcriptome dataset. We observed that the expression patterns of the genes in P. polytes largely reflected their known tissue-specific function in other species. The expression of sequentially acting genes in the melanin pathway was correlated. Interestingly, four out of six melanin pathway genes (ebony, pale, aaNAT, and DDC) showed a sexually dimorphic pattern of developmental heterochrony; i.e., females showed peak activity much earlier in pupal development compared to that of males. Our evolutionary and developmental analyses suggest that the vast diversity of wing patterning and pigmentation in Lepidoptera may have been aided largely by differential developmental regulation of genes in a highly conserved pathway, in which the sequence evolution of individual genes is highly constrained.

speck, first identified in Drosophila melanogaster in 1910, is encoded by the Arylalkalamine N-acetyltransferase (AANAT1) gene

The pigmentation mutation speck is a commonly used recombination marker characterized by a darkly pigmented region at the wing hinge. Identified in 1910 by Thomas Hunt Morgan, speck was characterized by Sturtevant as the most 'workable' mutant in the rightmost region of the second chromosome and eventually localized to 2-107.0 and 60C1-2. Though the first speck mutation was isolated over 115 years ago, speck is still not associated with any gene. Here, as part of an undergraduate-led research effort, we show that speck is encoded by the Arylalkylamine N-acetyltransferase 1 (AANAT1) gene. Both alleles from the Morgan lab contain a retrotransposon in exon 1 of the RB transcript of the AANAT1 gene. We have also identified a new insertion allele and generated multiple deletion alleles in AANAT1 that all give a strong speck phenotype. In addition, expression of AANAT1 RNAi constructs either ubiquitously or in the dorsal portion of the developing wing generates a similar speck phenotype. We find that speck alleles have additional phenotypes, including ectopic pigmentation in the posterior pupal case, leg joints, cuticular sutures and overall body color. We propose that the acetylated dopamine generated by AANAT1 decreases the dopamine pool available for melanin production. When AANAT1 function is decreased, the excess dopamine enters the melanin pathway to generate the speck phenotype.

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.