Molecular genetics and enzyme regulation of epoxide hydrolases in the cabbage looper, Trichoplusia ni

A full-length epoxide hydrolase (EH) cDNA (TmEH-2; NCBI accession #AF035482) was isolated from a Trichoplusia ni digestive system cDNA library made from fifth (last) stadium larvae. When TmEH-2 was compared to a previously reported T. ni EH cDNA (TmEH-1) from fat body, the two were 67 and 73% identical at nucleic acid and amino acid levels, respectively. In an EH phylogenetic tree constructed from amino acid sequence alignments, TmEH-1, TmEH-2 and other known insect EHs were more closely related to the microsomal than soluble EHs of other organisms. Contrary to previous conceptions, it also was determined with multiple sequence alignments that not all membrane-bound microsomal EHs contain identical amino acid residues at the proposed catalytic site. To evaluate the tissue specificity of TmEH-1 and TmEH-2 expression, total RNA from T. ni fat body or gut was assayed by Northern blot using TmEH-1 and TmEH-2 gene-specific probes. Although TmEH-1 and TmEH-2 were isolated from fat body and gut, respectively, each was expressed in both tissues. TmEH-1 was subcloned into a baculovirus system for in vivo expression in T. ni larvae. Following injections with non-occluded virus, the TmEH-1 baculovirus accelerated toxicity significantly compared to a non-transformed control baculovirus.; Juvenile hormone (JH) III esterase and JH III EH in vitro activity was compared in whole body T. ni homogenates at each stage of development. Both enzymes contributed to JH metabolism throughout development, although JH esterase was significantly higher than EH activity at nearly all time points assayed. With virgin adults, females had significantly higher JH esterase and EH activity than males. After fifth stadium larvae were starved, both enzymes declined significantly compared to fed insects. Induction or inhibition of EH and JH esterase activity in larvae also was analyzed following topical or oral administration of selected insect hormones (JH III and methoprene) or xenobiotics (trans- and cis-stilbene oxides, phenobarbital, clofibrate, cholesterol 5-alpha,6-alpha-epoxide and 3-octylthio-1,1,1-trifluoropropan-2-one). Results shed light on the regulation of EH activity in T. ni.