Molecular cloning and expression patterns of the molt-regulating transcription factor HHR3 from Helicoverpa armigera.

Molt-regulating transcription factors, hormone receptor 3 (HR3), play important roles in regulating expression of tissue-specific genes involved in insect molting and metamorphosis. A 1668 bp cDNA encoding a molt-regulating transcription factor (HHR3) was cloned from Helicoverpa armigera, which encodes a protein made up of 556 amino acids. This 62 kDa protein was found to have an isoelectric point (pI) of 6.52. There was no signal peptide or N-glycosylation site found in this cDNA. A DNA-binding region signature of nuclear hormone receptor was found from amino acids 107-133. A possible outside to inside transmembrane helice was found from amino acids 72-90. Northern blots of the larvae revealed five bands of HHR3 named as band 0, 1, 2, 3 and 4 with molecular masses determined as 2.1, 2.6, 3.6, 4.5 and 5.5 kb, respectively. The expression patterns of HHR3 in vivo were variable with developmental stages and tissues. Results showed that band 1-4 of HHR3 was only briefly expressed during molting, which suggested these bands are involved in the regulation of molting cascade, whereas band 0 was expressed in both molting and feeding larvae. Band 1 and 2 of HHR3 could be induced from epidermis of newly molted 6th instar larvae by non-steroidal ecdysone agonist, RH-2485.