induction-evaluation-inbreeding-crosses-using-ant-vollenhovia

Induction and Evaluation of Inbreeding Crosses Using the Ant, <em>Vollenhovia Emeryi</em>

The genetic and molecular components of the sex-determination cascade have been extensively studied in the honeybee, Apis mellifera, a hymenopteran model ...

Utsunomiya University

Steroid hormone receptor family provides an example of evolution of diverse transcription factors through whole-genome duplication (WGD). However, little is known about how their functions have been evolved after the duplication. Teleosts present a good model to investigate an accurate evolutionary history of protein function after WGD, because a teleost-specific WGD (TSGD) resulted in a variety of duplicated genes in modern fishes. This study focused on the evolution of androgen receptor (AR) gene, as two distinct paralogs, ARα and ARβ, have evolved in teleost lineage after TSGD. ARα showed a unique intracellular localization with a higher transactivation response than that of ARβ. Using site-directed mutagenesis and computational prediction of protein-ligand interactions, we identified two key substitutions generating a new functionality of euteleost ARα. The substitution in the hinge region contributes to the unique intracellular localization of ARα. The substitution on helices 10/11 in the ligand-binding domain possibly modulates hydrogen bonds that stabilize the receptor-ligand complex leading to the higher transactivation response of ARα. These substitutions were conserved in Acanthomorpha (spiny-rayed fish) ARαs, but not in an earlier branching lineage among teleosts, Japanese eel. Insertion of these substitutions into ARs from Japanese eel recapitulates the evolutionary novelty of euteleost ARα. These findings together indicate that the substitutions generating a new functionality of teleost ARα were fixed in teleost genome after the divergence of the Elopomorpha lineage. Our findings provide a molecular explanation for an adaptation process leading to generation of the hyperactive AR subtype after TSGD. 

Neofunctionalization of Androgen Receptor by Gain-of-Function Mutations in Teleost Fish Lineage.

The American alligator (Alligator mississippiensis) displays temperature-dependent sex determination (TSD), in which incubation temperature during embryonic development determines the sexual fate of the individual. However, the molecular mechanisms governing this process remain a mystery, including the influence of initial environmental temperature on the comprehensive gonadal gene expression patterns occurring during TSD.

RNA-seq analysis of the gonadal transcriptome during Alligator mississippiensis temperature-dependent sex determination and differentiation.

Embryo development in arthropods is accompanied by a series of moltings. A cladoceran crustacean Daphnia magna molts three times before reaching first instar neonate during embryogenesis. Previous studies argued ecdysteroids might regulate D. magna embryogenesis. However, no direct evidence between innate ecdysteroids fluctuation and functions has been forthcoming. Recently, we identified genes involved in ecdysteroid synthesis called, neverland (neverland1 and neverland 2) and shade and in the ecdysteroid degradation (Cyp18a1). To understand the physiological roles of ecdysteroids in D. magna embryos, we performed expression and functional analyzes of those genes. Examining innate ecdysteroids titer during embryogenesis showed two surges of ecdysteroids titer at 41 and 61 h after oviposition. The first and second embryonic moltings occurred at each ecdysteroid surge. Expression of neverland1 and shade began to increase before the first peak in ecdysteroid. Knockdown of neverland1 or shade by RNAi technique caused defects in embryonic moltings and subsequent development. The ecdysteroids titer seemingly decreased in nvd1-knowckdown embryos. Knockdown of Cyp18a1 resulted in early embryonic lethality before the first molting. Our in situ hybridization analysis revealed that nvd1 was prominently expressed in embryonic gut epithelium suggesting the site for an initial step of ecdysteroidgenesis, a conversion of cholesterol to 7-dehydrocholesterol and possibly for ecdysone production. Taken together, de novo ecdysteroid synthesis by nvd1 in the gut epithelial cells stimulates molting, which is indispensable for D. magna embryo development. These findings identify neverland as a possible target for chemicals, including various pesticides that are known to disrupt molting, development and reproduction. Copyright © 2016 John Wiley & Sons, Ltd.

Neverland regulates embryonic moltings through the regulation of ecdysteroid synthesis in the water flea Daphnia magna, and may thus act as a target for chemical disruption of molting.

One of the defining features of the evolutionary success of insects is the morphological diversification of their appendages, especially mouthparts. Although most insects share a common mouthpart ground plan, there is remarkable diversity in the relative size and shapes of these appendages among different insect lineages. One of the most prominent examples of mouthpart modification can be found in the enlargement of mandibles in stag beetles (Coleoptera, Insecta). In order to understand the proximate mechanisms of mouthpart modification, we investigated the function of appendage-patterning genes in mandibular enlargement during extreme growth of the sexually dimorphic mandibles of the stag beetle Cyclommatus metallifer. Based on knowledge from Drosophila and Tribolium studies, we focused on seven appendage patterning genes (Distal-less (Dll), aristaless (al), dachshund (dac), homothorax (hth), Epidermal growth factor receptor (Egfr), escargot (esg), and Keren (Krn). In order to characterize the developmental function of these genes, we performed functional analyses by using RNA interference (RNAi). Importantly, we found that RNAi knockdown of dac resulted in a significant mandible size reduction in males but not in female mandibles. In addition to reducing the size of mandibles, dac knockdown also resulted in a loss of the serrate teeth structures on the mandibles of males and females. We found that al and hth play a significant role during morphogenesis of the large male-specific inner mandibular tooth. On the other hand, knockdown of the distal selector gene Dll did not affect mandible development, supporting the hypothesis that mandibles likely do not contain the distal-most region of the ancestral appendage and therefore co-option of Dll expression is unlikely to be involved in mandible enlargement in stag beetles. In addition to mandible development, we explored possible roles of these genes in controlling the divergent antennal morphology of Coleoptera.

The function of appendage patterning genes in mandible development of the sexually dimorphic stag beetle.

The cultured cell-based in vitro assay using the stringency of ligand-receptor interactions is typically useful for screening certain hormone agonists from among a very large number of molecules. However, ligands are frequently altered or modified through evolution; indeed, even in the same receptor orthologs, different ligand sensitivity profiles are considered to arise among species and/or taxa. Such ligand transition has been observed in juvenile hormone (JH), one of the most important endocrine factors in arthropods. To understand the molecular basis of ligand selectivity alteration in hormone receptors, we compared the amino acid sequences and ligand selectivity of the JH receptor, Methoprene-tolerant (Met), among three insects (Drosophila melanogaster, Aedes aegypti and Tribolium castaneum) and one crustacean (Daphnia pulex). Compared with D. pulex, we found that the receptors of the three insects showed a higher sensitivity to JH III, which is the major innate JH ligand in insects. Furthermore, point mutation analysis in Met sequences revealed a candidate amino acid residue that is important for increasing JH sensitivity in insects. Amino acid mutations in Met may have affected changes in ligand selectivity intermittently over the course of the evolution of the JH-signaling pathway. These findings are useful to improve the existing (developing) cultured cell-based assay system and may shed light on the relationship between functional diversification in hormonal signaling and the molecular evolution of hormone receptors. Copyright © 2017 John Wiley & Sons, Ltd.

Comparative luciferase assay for establishing reliable in vitro screening system of juvenile hormone agonists.

The two essential insect hormones, ecdysteroids and juvenile hormones, are possessed not only by insects, but also widely by arthropods, and regulate various developmental and physiological processes. In contrast to the abundant information about molecular endocrine mechanisms in insects, the knowledge of non-insect arthropod endocrinology is still limited. In this review, we summarize recent reports about the molecular basis of these two major insect hormones in the freshwater microcrustacean Daphnia, a keystone taxon in limnetic ecology and a bioindicator in environmental studies. Comprehensive comparisons of endocrine signaling pathways between insects and daphnids may shed light on the regulatory mechanisms of various biological phenomena and, moreover, evolutionary processes of arthropod species.

Ecdysteroid and juvenile hormone biosynthesis, receptors and their signaling in the freshwater microcrustacean Daphnia.

Elaborate regulation of insect metamorphosis is the consequence of physiological cooperation among multiple endocrine factors such as juvenile hormones (JHs) and ecdysteroids. Hormone-induced transcription factors play important roles in substantive interactions between hormonal signaling pathways. In insects, zinc finger transcription factor Krüppel homolog 1 (Kr-h1) is a key gene of the endocrine signaling pathway in which it is directly upregulated by JH receptor Methoprene-tolerant (Met) in the presence of JH and then regulates multiple downstream factors, including components of the ecdysteroid signaling pathway. Although JH also plays a role in various biological phenomena in other arthropod species, little is known about the molecular basis of the JH signaling pathway. Here we cloned Kr-h1 from a branchiopod crustacean, Daphnia pulex, (DappuKr-h1) and analyzed its expression profile and developmental function together with consideration of its relationship to the JH signaling pathway. We suggest that DappuKr-h1 lacks JH responsiveness and regulatory relationship with the JH receptor. Moreover our loss-of-function analysis revealed that maternal mRNA of DappuKr-h1 plays a critical role in early development independent from the JH signaling pathway. These findings provide insights about whether and how the JH signaling pathway influenced evolution, leading to greater diversity in phylum Arthropoda.

Juvenile hormone-independent function of Krüppel homolog 1 in early development of water flea Daphnia pulex.

A female diploid, male haploid sex determination system (haplodiploidy) is found in hymenopteran taxa, such as ants, wasps, bees and sawflies. In this system, a single, complementary sex-determination (sl-CSD) locus functions as the primary sex-determination signal. In the taxa that has evolved this system, females and males are heterozygous and hemi/homozygous at the CSD locus, respectively. While the sl-CSD system enables females to alter sex ratios in the nest, it carries a high cost in terms of inbreeding, as individuals that are homozygous at the CSD locus become sterile diploid males. To counter this risk, some of hymenopteran species have evolved a multi-locus CSD (ml-CSD) system, which effectively reduces the proportion of sterile males. However, the mechanism by which these multiple primary signals are integrated and how they affect the terminal sex-differentiation signal of the molecular cascade have not yet been clarified. To resolve these questions, we examined the molecular cascade in the Japanese ant Vollenhovia emeryi, which we previously confirmed has two CSD loci. Here, we showed that the sex-determination gene, doublesex (dsx), which is highly conserved among phylogenetically distant taxa, is responsible for integrating two CSD signals in V. emeryi. After identifying and characterizing dsx, genotypes containing two CSD loci and splicing patterns of dsx were found to correspond to the sexual phenotype, suggesting that two primary signals are integrated into dsx. These findings will facilitate future molecular and functional studies of the sex determination cascade in V. emeryi, and shed light on the evolution and diversification of sex determination systems in insects.

The doublesex gene integrates multi-locus complementary sex determination signals in the Japanese ant, Vollenhovia emeryi.

Environmental waters are polluted by various chemicals originating from human activities. Recently, the environmental risk of juvenile hormones (JHs) to aquatic microcrustaceans has been recognized by risk assessors and researchers. JH is a major arthropod hormone that regulates molting and reproduction and has analogs that have been used as insect growth regulators. JHs are known to disturb the sex determination system of Daphnia, which is a keystone animal in limnetic ecosystems and is not the target of extermination. To assess the risk of contaminant chemicals and to protect biodiversity, reliable methods for detecting such chemicals are essential. In this study, we attempted to establish a practical in vitro reporter assay system for detecting chemicals with JH activity. Using a newly constructed reporter vector (modified from the JH response element of Tribolium castaneum Krüppel homolog 1, which is a major JH responsive gene in insects), strong JH-dependent transcriptional activity (>40-fold activation) was found in Chinese hamster ovary cells that express JH receptors of Daphnia pulex. Dose-response analysis conducted on several JH and non-JH chemicals revealed that the established reporter assay system has strict specificity to JH chemicals, and the half maximum effective concentration (EC ) was between 10 and 10  m. These results suggest that the new system is a rapid and economical method for assessing the environmental risk of JH-active chemicals.

Hitoshi Miyakawa

Center for Bioscience Research and Education

Utsunomiya University

Induction and Evaluation of Inbreeding Crosses Using the Ant, Vollenhovia Emeryi