As methodological achievements, we can highlight the molecular cloning of nuclear receptors of the ecdysteroid cascade, membrane receptors involved in vitellogenesis and transcription factors involved in juvenile hormone action.
Transcripts of all these genes encoding enzymes of the JH biosynthetic pathway were detected in the CA-CC complex (). This is consistent with the high rates of JH biosynthesis in the CA and high titers of JH in the hemolymph of foragers . The expression of several of these genes was undetectable, or detected at only basal levels in fat body (fpps5, fpps6, scd, mt, mfe,), ovaries (hmgs, hmgr, ippi, fpps1, scd, famet, mt, mfe, mat), or in the brain (fpps1, fpps6, mt, mfe, mat). Expression profiles of the FPPS codifying genes in tissues and organs of forager bees were compared separately. As fpps3 turned out to be highly expressed in the CA-CC complex ( - insert) this suggests that it is the bona fide farnesyl diphosphate synthase gene involved in JH biosynthesis in honey bees.
Roles of juvenile hormones in adult insects
AB - The effects of the social environment and age on juvenile hormone (JH) and reproduction were investigated by measuring ovarian development, hemolymph levels of JH III, and rates of JH biosynthesis from the same individual bumble bees (Bombus terrestris). Differences in social environment were associated with differences in rates of JH biosynthesis, JH titer and ovarian development. Young queenless workers had a higher rate of JH biosynthesis, JH titer and ovarian development than queenright (QR) workers of similar age. Dominant workers in QR colonies had a higher rate of JH biosynthesis, JH titer and ovarian development than low ranked workers of similar size. There was a positive correlation between JH titer and ovarian development, but no correlation between rate of JH biosynthesis and ovarian development or between JH biosynthesis and JH titer. Both JH titer and rate of JH biosynthesis increased with age from emergence to 3 days of age, but 6- day-old workers, egg-laying workers, and actively reproducing queens had high JH titers and highly developed ovaries but low rates of JH biosynthesis. These results show that reproduction in B. terrestris is strongly affected by the social environment and the influence of the environment on reproduction is mediated by JH. Our data also indicate that the rate of JH biosynthesis measured in vitro is not a reliable indicator of JH titer or ovarian development in B. terrestris; possible reasons are discussed.
Juvenile hormone biosynthesis during sexual maturation …
The expression of 24 of the 25 annotated JH biosynthesis genes was assayed in RNA extracts from CA-CC complexes, remaining brain tissue, fat body, and ovary. All genes were expressed in the CA-CC complexes, placing in evidence their putative role in JH biosynthesis. Transcription for most of the genes was also evidenced in the other tissues, which is not surprising, considering that the mevalonate pathway enzymes are required not only for JH production but also for the production of other bioactive terpenoids and for the farnesylation of proteins . In contrast, two genes involved in JH-specific steps, those encoding O-methyltransferase (mt) and methyl farnesoate epoxidase (mfe), were specifically expressed in the CA-CC complexes.
juvenile hormone biosynthesis - QM SBCS
Methyl farnesoate is the immediate precursor of JH in insects and has hormonal functions in crustaceans . Farnesoic acid O-methyltransferase (FAMeT) and JH acid O-methyltransferase (JHAMT) (called here MT) are described as catalyzing the methylation of farnesoic acid to methyl farnesoate with S-adenosyl-L-methionine functioning as cofactor . In the fruit fly, D. melanogaster, a recombinant FAMeT (rFAMeT) was cloned, expressed, and a specific antiserum was generated. Immunohistochemical analysis confirmed the presence of FAMeT in the CA portion of the ring gland, but rFAMeT presented no enzymatic activity in a radiochemical assay, inferring that D. melanogaster FAMeT has little, if any role in sesquiterpenoid biosynthesis . Notwithstanding, the DmJHAMT gene is predominantly expressed in the fly CA. Moreover, the recombinant protein was capable of catalyzing the methylation/esterification of JH-III acid or farnesoic acid in the presence of S-adenosyl-L-methionine . Subsequently, Marchal et al. , using the locust Schistocerca gregaria as a model, showed that JHAMT, and not FAMeT, is the enzyme involved in JH synthesis. In the honey bee genome we found orthologs for both, famet and mt genes, and when assaying their expression by means of RT-qPCR we found that mt transcripts were specifically detected in CA-CC complex, whereas famet was transcribed more ubiquitously, as is also the case in the highly eusocial stingless bee Melipona quadrifasciata. This leads us to infer that mt and not famet is the gene encoding a functional methyltransferase activity in the honey bee CA.