Abstract
Simple SummaryFushi Tarazu Factor-1 (FTZ-F1) plays a crucial regulatory role in molting in insects. It is hypothesized that, by alternative transcription start and splicing, the FTZ-F1 gene generates two isomers (α- and βFTZ-F1) that exert isoform-specific roles in non-Drosophilid insects. In the present paper, we first unveiled that the same post-transcriptional processing in FTZ-F1 occurred in coleopterans, lepidopterans, dipterans and hymenopterans. We then found that αFTZ-F1 and βFTZ-F1 were actively transcribed throughout the development, from embryo to adult, in Henosepilachna vigintioctopunctata. Moreover, by RNA interference, we confirmed that both FTZ-F1 isoforms act as regulators in larval–larval molting and βFTZ-F1 is involved in the regulation of the larval–pupal transition.Fushi Tarazu Factor 1 (FTZ-F1), a member of the nuclear receptor superfamily, is the downstream factor of 20-hydroxyecdysone signaling. In Drosophila melanogaster, alternative transcription start and splicing in the FTZ-F1 gene generate αFTZ-F1 and βFTZ-F1 isoforms, which are vital for pair-rule segmentation in early embryogenesis and post-embryonic development, respectively. However, whether the same mRNA isoforms are present and exert the conservative roles remains to be clarified in other insects. In the present paper, we first mined the genomic data of representative insect species and unveiled that the same post-transcriptional processing in FTZ-F1 occurred in coleopterans, lepidopterans, dipterans and hymenopterans. Our expression data in Henosepilachna vigintioctopunctata, a serious polyphagous defoliator damaging a wide range of crops in Solanaceae and Cucurbitaceae, showed that both αFTZ-F1 and βFTZ-F1 were actively transcribed throughout the development, from embryo to adult. The RNA interference-aided knockdown of both isoforms completely arrested larval ecdysis from the third to the fourth instar, in contrast to the depletion of either isoform. In contrast, silencing βFTZ-F1, rather than αFTZ-F1, severely impaired the larval–pupal transformation. We accordingly propose that both FTZ-F1 isoforms are essential but mutually interchangeable for larval–larval molting, while βFTZ-F1 is necessary for the larval–pupal transition and sufficient to exert the role of both FTZ-F1s during larval–pupal metamorphosis in H. vigintioctopunctata.
Highlights
Introduction distributed under the terms andFushi Tarazu Factor 1 (FTZ-F1), a member of the NR5A class of the nuclear receptor superfamily, is the downstream player of the 20-hydroxyecdysone signaling pathway [1,2].FTZ-F1 has first been identified in Drosophila melanogaster [3]
It is hypothesized that ecdysozoan FTZ-F1 genes have similar structural organization, where αFTZ-F1 and βFTZ-F1 are generated through alternative transcription start and splicing
Our preliminary searches and RT-polymerase chain reaction (PCR) results in this study reveal that FTZ-F1 genes generate two isoforms, αFTZ-F1 and βFTZ-F1, in dipteran, coleopteran, lepidopteran and hymenopteran insects
Summary
Introduction distributed under the terms andFushi Tarazu Factor 1 (FTZ-F1), a member of the NR5A class of the nuclear receptor superfamily, is the downstream player of the 20-hydroxyecdysone signaling pathway [1,2].FTZ-F1 has first been identified in Drosophila melanogaster [3]. In D. melanogaster, alternative transcription start and splicing in FTZ-F1 generate two protein isoforms, named αFTZ-F1 and βFTZ-F1. They contain identical ligand-binding domains (LBD), but unique N-terminal A/B domains [12,13]. An aliquot (0.1 μL) of solution including 500 ng or 300 ng of dsRNA was injected into the newly ecdysed fourth- or third-instar larvae. Four biologically independent experiments were carried out using the newly ecdysed fourth- or third-instar larvae from different generations. Three replicates were sampled 2 and 3 days after the injection for qRT-PCR to test RNAi efficacy. Three replicates were used to observe the phenotypes during a 3-week trial period Another three replicates were collected 5 days after the initiation of the bioassay, dissected for observation under microscope
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