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Roles of and cross-talk between ecdysteroid and sesquiterpenoid pathways in embryogenesis of branchiopod crustacean Daphnia magna.

ABSTRACT: The ecdysteroid and sesquiterpenoid pathways control growth, developmental transition, and embryogenesis in insects. However, the function of orthologous genes and the cross-talk between both pathways remain largely uncharacterized in non-insect arthropods. Spook (Spo) and Juvenile hormone acid o-methyltransferase (Jhamt) have been suggested to function as rate-limiting factors in ecdysteroid and sesquiterpenoid biosynthesis, respectively, in insects. In this study, we report on the functions of Spo and Jhamt and the cross-talk between them in embryos of the branchiopod crustacean Daphnia magna. Spo expression was activated at the onset of gastrulation, with the depletion of Spo transcript by RNAi resulting in developmental arrest at this stage. This phenotype could be partially rescued by supplementation with 20-hydroxyecdysone, indicating that Spo may play the same role in ecdysteroid biosynthesis in early embryos, as reported in insects. After hatching, Spo expression was repressed, while Jhamt expression was activated transiently, despite its silencing during other embryonic stages. Jhamt RNAi showed little effect on survival, but shortened the embryonic period. Exposure to the sesquiterpenoid analog Fenoxycarb extended the embryonic period and rescued the Jhamt RNAi phenotype, demonstrating a previously unidentified role of sesquiterpenoid in the repression of precocious embryogenesis. Interestingly, the knockdown of Jhamt resulted in the derepression of ecdysteroid biosynthesis genes, including Spo, similar to regulation during insect hormonal biosynthesis. Sesquiterpenoid signaling via the Methoprene-tolerant gene was found to be responsible for the repression of ecdysteroid biosynthesis genes. It upregulated an ortholog of CYP18a1 that degrades ecdysteroid in insects. These results illuminate the conserved and specific functions of the ecdysteroid and sesquiterpenoid pathways in Daphnia embryos. We also infer that the common ancestor of branchiopod crustaceans and insects exhibited antagonism between the two endocrine hormones before their divergence 400 million years ago.

SUBMITTER: Adhitama N

PROVIDER: S-EPMC7546464 | biostudies-literature | 2020

REPOSITORIES: biostudies-literature

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Roles of and cross-talk between ecdysteroid and sesquiterpenoid pathways in embryogenesis of branchiopod crustacean Daphnia magna.

Adhitama Nikko N Kato Yasuhiko Y Matsuura Tomoaki T Watanabe Hajime H

PloS one 20201009 10

The ecdysteroid and sesquiterpenoid pathways control growth, developmental transition, and embryogenesis in insects. However, the function of orthologous genes and the cross-talk between both pathways remain largely uncharacterized in non-insect arthropods. Spook (Spo) and Juvenile hormone acid o-methyltransferase (Jhamt) have been suggested to function as rate-limiting factors in ecdysteroid and sesquiterpenoid biosynthesis, respectively, in insects. In this study, we report on the functions of ...[more]

PMID: 33035251

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Project description:Ecdysteroids initiate signaling along multiple pathways that regulate various aspects of development, maturation, and reproduction in arthropods. Signaling often involves the induction of downstream transcription factors that either positively or negatively regulate aspects of the pathway. We tested the hypothesis that crustaceans express the nuclear receptors HR3 (ortholog to vertebrate ROR) and E75 (ortholog to vertebrate rev-erb) in response to ecdysteroid signaling. HR3 and E75 cDNAs were cloned from the crustacean Daphnia magna. The DNA-binding domain and ligand-binding domain of the daphnid HR3 were 95% and 61% identical to those of Drosophila melanogaster. The DNA-binding domain and ligand-binding domain of the daphnid E75 were 100% and 71% identical to those of D. melanogaster. Both receptors exhibited structural characteristics of binding to DNA as a monomer. The expression of these receptor mRNAs was evaluated through the adult molt cycle and during embryo development. E75 levels were relatively constant throughout the adult molt cycle and through embryo development. HR3 levels were comparable to those of E75 during the initial phases of the adult molt cycle but were elevated approximately 30-fold at a time in the cycle co-incident with the pre-molt surge in ecdysteroid levels. HR3 mRNA levels in embryos also varied co-incident with ecdysteroid levels. To substantiate a role of ecdysteroids in the expression of HR3, daphnids were continuously exposed to 20-hydroxyecdysone and changes in gene expression were measured. HR3 levels were significantly induced by 20-hydroxyecdysone; while E75 levels were minimally affected. These results are consistent with the premise that transcription of HR3 is regulated by ecdysteroids in the crustacean D. magna and that HR3 likely serves as a mediator of ecdysteroid regulatory action in crustaceans. The marginal induction of E75 by 20-hydroxyecdysone may represent limited, tissue or cell-type-specific induction of this transcription factor.

Dataset Information

Roles of and cross-talk between ecdysteroid and sesquiterpenoid pathways in embryogenesis of branchiopod crustacean Daphnia magna.

Publications

Roles of and cross-talk between ecdysteroid and sesquiterpenoid pathways in embryogenesis of branchiopod crustacean Daphnia magna.

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