AUTHOR=Shen Chen-Hui , Xu Qing-Yu , Fu Kai-Yun , Guo Wen-Chao , Jin Lin , Li Guo-Qing 

TITLE=Two Splice Isoforms of Leptinotarsa Ecdysis Triggering Hormone Receptor Have Distinct Roles in Larva-Pupa Transition

JOURNAL=Frontiers in Physiology

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2020.593962

DOI=10.3389/fphys.2020.593962

ISSN=1664-042X

ABSTRACT=<p>Insect ecdysis triggering hormone (ETH) receptors (ETHRs) are rhodopsin-like G protein-coupled receptors. Upon binding its ligand ETH, ETHR initiates a precisely programed ecdysis behavior series and physiological events. In <italic>Drosophila melanogaster</italic>, the <italic>ethr</italic> gene produces two functionally distinct splicing isoforms, <italic>ethra</italic> and <italic>ethrb</italic>. ETH/ETHRA activates eclosion hormone (EH), kinin, crustacean cardioactive peptide (CCAP), and bursicon (burs and pburs) neurons, among others, in a rigid order, to elicit the behavioral sequences and physiological actions for ecdysis at all developmental stages, whereas ETH/ETHRB is required at both pupal and adult ecdysis. However, the role of ETHRB in regulation of molting has not been clarified in any non-drosophila insects. In the present paper, we found that 20-hydroxyecdysone (20E) signaling triggers the expression of both <italic>ethra</italic> and <italic>ethrb</italic> in a Coleopteran insect pest, the Colorado potato beetle <italic>Leptinotarsa decemlineata</italic>. RNA interference (RNAi) was performed using double-stranded RNAs (dsRNAs) targeting the common (ds<italic>ethr</italic>) or isoform-specific (ds<italic>ethra</italic>, ds<italic>ethrb</italic>) regions of <italic>ethr</italic>. RNAi of ds<italic>ethr</italic>, ds<italic>ethra</italic>, or ds<italic>ethrb</italic> by the final-instar larvae arrested larva development. The arrest was not rescued by feeding 20E. All the <italic>ethra</italic> depleted larvae stopped development at prepupae stage; the body cavity was expanded by a large amount of liquid. Comparably, more than 80% of the <italic>ethrb</italic> RNAi larvae developmentally halted at the prepupae stage. The remaining <italic>Ldethrb</italic> hypomorphs became pupae, with blackened wings and highly-expressed <italic>burs</italic>, <italic>pburs</italic> and four melanin biosynthesis genes. Therefore, ETHRA and ETHRB play isoform-specific roles in regulation of ecdysis during larva-pupa transition in <italic>L. decemlineata</italic>.</p>