Identification of a juvenile hormone esterase binding protein gene and its developmental and hormone regulation in the silkworm, Bombyx mori

The regulation of the juvenile hormone (JH) titer is critical for insect development. Consequently, both regulators of JH such as juvenile hormone esterase (JHE; EC 3.1.1.1) and the appropriate regulation of these regulators are also critically important for development. To better characterize and understand JHE regulation, we identified a putative JHE binding protein gene named BmJHEBP in Bombyx mori. The full-length cDNA of BmJHEBP is 963 bp and encodes a 243 amino acid polypeptide. Its molecular weight is ∼29 kDa, as confirmed by Western blotting, and transcripts of BmJHEBP were found to be expressed in all tissues. The mRNA level of BmJHEBP in the fat body was high on day 1 of the fifth instar, followed by a decrease from day 2 to day 5; thereafter, the mRNA level increased simultaneously with an increase in the hemolymph ecdysteroid titer. This temporary expression pattern was similar to that of BmJHE in the fat body and of the JHE enzyme activity in the hemolymph. The BmJHEBP level in the fat body of male larvae was slightly higher than that of the fat body in female larvae. Moreover, this protein expression pattern is consistent with the qRT-PCR results. The in vitro fat body culture results indicate that the high titer JH III induced BmJHEBP mRNA expression, while the lower titer exhibited no significant difference at the mRNA level to the group cultivated with DMSO. These studies demonstrate that BmJHEBP might function in JHE transportation and degradation when the JH III titer is high. BmJHEBP was upregulated by 20E cultivation, but this cultivation induced less upregulation and later responses to the JH pulse. Thus, BmJHEBP is regulated by both JH and ecdysone in a balanced manner.