Hormonal regulation and effects of four environmental pollutants on vitellogenin gene transcription in the giant water bFfigug, Lethocerus deyrollei (Hemiptera: Belostomatidae)

摘要

The giant water bug, Lethocerus deyrollei has become an endangered species in Japan. For conservation of this insect, hormonal regulation and the potential involvement of environmental pollutants as endocrine disrupting chemicals (EDCs) in reproduction was investigated using vitellogenin (Vg), the major yolk protein precursor, gene as a biomarker. For this, the cDNA encoding Vg of L. deyrollei was cloned and the amino acid sequence was deduced. The Vg polypeptide sequence was deduced from the 5,865 bp cDNA, containing several well-conserved features of insect Vgs. SDS-PAGE showed two Vg subunit polypeptides of about 193 and 56 kDa in L. deyrollei. Northern blot analysis revealed that the Vg gene was transcribed specifically in the female fat body and Vg expression was induced when females in reproductive diapause were injected with juvenile hormone (JH) III and inhibited when they were injected with 20-hydroxyecdysone (20E), suggesting that the Vg gene is regulated by the JH in L. deyrollei. Dramatic induction or inhibition of Vg gene transcript was detected when diapausing females were injected with EDCs. 17 beta-estradiol and bisphenol A enhanced the expression but 4-t-octylphenol and 4-nonylphenol repressed it. These results indicate that EDCs may disrupt the reproductive physiology of L. deyrollei in nature, providing a first indication that environmental pollutants could be the cause of the rapid disappearance of this species from Japanese ecosystems.