Abstract
Juvenile hormone (JH) prevents metamorphosis during insect larval stages and promotes adult reproductive processes. Krüppel-homolog 1 (Kr-h1), a zinc finger transcription factor assumed to be induced by JH via the JH receptor methoprene-tolerant (Met), mediates the antimetamorphic effect of JH in insects, but its function in JH-mediated reproductive processes has not been fully explored. In this study, Met and Kr-h1 involved in the JH signaling pathway were first cloned and identified from the oriental fruit fly, Bactrocera dorsalis, an important pest infesting fruit and vegetables worldwide. Subsequent spatiotemporal expression analysis revealed that Met and Kr-h1 were both highly expressed in 7-day-old adults and fat body of female adults, respectively. Treatment with a JH analog (methoprene) significantly induced the expression of JH signaling and vitellogenin (Vg) genes and accelerated ovary development. RNA interference (RNAi) further revealed that either Met or Kr-h1 depletion at the adult stage of B. dorsalis impeded ovary development, with significantly lower egg production noted as well. In addition, rescue through methoprene application after RNAi stimulated the expression of JH signaling and Vg genes. Although there were still differences in ovary phenotype between rescued insects and the pre-RNAi control, ovary redevelopment with a larger surface area was observed, consistent with the spatiotemporal expression and phenotypes recorded in the original methoprene experiment. Our data reveal the involvement of Met and Kr-h1 in insect vitellogenesis and egg production, thus indicating the crucial role of the JH signaling pathway in insect reproduction.
Highlights
Juvenile hormone (JH) is one of the most important hormones regulating insect development, metamorphosis, and reproduction (Riddiford et al, 2010; Hiruma and Kaneko, 2013; Song et al, 2014)
The full-length cDNA sequences of Met and Krüppel-homolog 1 (Kr-h1) were cloned from B. dorsalis
Comparison with sequences of other insect species allowed the identification of bHLH and PAS domains in BdMet and eight putative zinc-finger domains in BdKr-h1
Summary
Juvenile hormone (JH) is one of the most important hormones regulating insect development, metamorphosis, and reproduction (Riddiford et al, 2010; Hiruma and Kaneko, 2013; Song et al, 2014). This hormone, which is present during larval molting to prevent immature insects from transforming into adults, reappears in adults to regulate female reproductive maturation. Methoprene-tolerant (Met), a receptor of JH, has recently been systematically characterized (Jindra et al, 2013); in contrast, the molecular mechanism underlying the JH signaling pathway is far from clear.
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