The impacts of classical insect hormones on the expression profiles of a new digestive trypsin‐like protease (TLP) from the cotton bollworm, Helicoverpa armigera

Abstract

Trypsin proteinases perform important roles in the protein digestion of an insect midgut. A 1042 bp full-length cDNA was cloned from Helicoverpa armigera. The gene encoded a 32 kDa protein, with a predicted isoelectric point of 5.7. The amino acid sequence of the protein had a trypsin-like serine protease domain, and the gene was named Ha-TLP. The expression of the gene was tissue-specific and the transcript of Ha-TLP existed only in the midgut and was not found in the head-thorax, integument, fat body and haemocytes from 5th instar larvae, with similar expression levels between those in feeding larvae and in molting larvae. In the midgut, the gene transcription level declined from 6th instar 72 h after the larvae entered the wandering stage, and disappeared from 6th instar at 96 h until the pupal stage. By immunohistochemistry, Ha-TLP was detected in the cytoplasm of the midgut epithelial cells of the 6th instar feeding stage worms. The expression of Ha-TLP could be up-regulated by a juvenile hormone (JH) analog methoprene and down-regulated by 20-hydroxyecdysone (20E). These facts indicate that Ha-TLP was involved in food digestion during larval growth and probably up-regulated by JH and suppressed by extra 20E in vivo.