Expression of the juvenile hormone esterase gene in the Colorado potato beetle, Leptinotarsa decemlineata: photoperiodic and juvenile hormone analog response

Abstract

Metamorphosis and reproduction in insects are controlled by juvenile hormone (JH). One of the factors, which regulate the JH titer in the hemolymph, is the activity of juvenile hormone esterase (JHE). JHE from the Colorado potato beetle, Leptinotarsa decemlineata, consists of two 57 kDa subunits. In this study, the JHE-cDNA was used as a probe to examine where and when the gene is transcribed as well as how gene expression responds to photoperiodic treatment and to topical application with a JH analog, pyriproxyfen. JHE transcripts were almost exclusively found in RNA extracts from fat body tissue in both larvae and adults. JHE-mRNA levels in the fat body correlated positively with levels of JHE activity in the hemolymph. In the last larval instar, high levels of JHE-mRNA were found in the feeding stage. In adults, reared under short-day conditions, JHE-mRNA levels were high between day 2 and day 9, which correlated with high JHE activity in the hemolymph. During these conditions, the JH titer decreases in preparation for pupation and diapause, respectively. The JHE-mRNA levels and JHE activity in the hemolymph were higher in short-day than in reproductive long-day adults. If the JH analog pyriproxyfen was applied to animals of the last larval instar on day 0 or day 3, JHE gene expression was enhanced. In contrast, if pyriproxyfen was applied to short-day adults on day 1 or day 4, the mRNA levels and the JHE activity in the hemolymph were suppressed to levels similar to those found in long-day adults. Thus, transcription of JHE is dependent on developmental stage, tissue, photoperiod and the level of its substrate JH.