Structural organization and expression analysis of the cdna encoding allatotropin in the cotton bollworm,Helicoverpa armigera

Abstract

The cDNA encoding allatotropin (AT), which stimulates juvenile hormone (JH) biosynthesis by the adult corpora allata (CA) of Lepidoptera, was cloned from Helicoverpa armigera (Har). Har-AT cDNA encodes a 135-amino acid polypeptide precursor containing a 13-amino acid AT sequence identical to Manduca sexta AT (Mas-AT). Three other H. armigera AT cDNAs encoding 172, 213, and 246 amino acids were also cloned. The four isoforms were produced by alternative splicing and termed Har-AT1, -AT2, -AT3, and -AT4, respectively. The basic organization of the Har-AT1 polypeptide precursor is similar to that of known ATs from other Lepidoptera with 80-97% identity at amino acid level. From the processing of the polypeptide precursor, three AT-like peptides named Har-ATL-I, -II, and -III were predicted. However, functions of the three AT-like peptides remain to be further elucidated. The evidence of Northern blots showed that a 0.7-kb Har-AT1 transcript is present in the brain and 0.7-kb Har-AT1 and 1.0-kb Har-AT4 transcripts are present in the abdominal ganglion (AG). Using quantitative RT-PCR, Har-AT mRNAs were detectable at much lower levels in other neural tissues, such as suboesophageal ganglion (SG) and thoracic ganglion (TG), but not in non-neural tissue, such as the epidermis, midgut, and fat body. We investigated the spatial and temporal expression of Har-AT gene in the central nervous system, and showed that expression patterns of four isoforms are distinct from each other. The results from immunocytochemistry showed that Har-AT transcript is located in the central nervous system, mainly in the brain and terminal abdominal ganglion (TAG). Thus, the AT gene products, besides affecting JH biosynthesis, might have broad influence on many biological processes in H. armigera.