Evolution of juvenile hormone esterase in insects

Juvenile hormones (JH) belong to the family of sesquiterpenoid hormones which play vital roles in regulating molting, metamorphosis, pheromone biosynthesis, and reproductive maturation in insects.  Because it is a major insect hormone, its titers are precisely regulated at a perfect balance between its synthesis in corpora allata and its degradation in hemolymph by juvenile hormone esterase (JHE), which belongs to a family of choline/carboxylesterases (CCEs).  The genes encoding for JHE or putative JHEs have been sequenced from Lepidoptera, Diptera, Hemiptera, Hymenoptera, Orthoptera, and Coleoptera, and a few recent studies have reported that many insects have multiple JHE-like genes.  What is intriguing is the fact that JH exists only in 6 major isoforms (JH0, JHI, JHII, JHIII, and JH bisepoxide) in insects, but there is a wide variety of JHE isoforms found across insects. In order to investigate why there are so many more JHEs that can degrade a small number of conserved JH isoforms, we analyze 98 mRNA sequences, 21 ESTs, and 138 amino acid sequences for JHE in a phylogenetic framework. We comment on the divergence of JHE in relation to the phylogeny of insects and postulate on the evolution and maintenance of JHE in insects.