<i>Dead ringer</i> acts as a major regulator of juvenile hormone biosynthesis in insects

In holometabolous insects, proper control of the production of juvenile hormone (JH), which maintains larval traits, is crucial for successful metamorphosis. JH is produced specifically in the corpora allata (CA) via the functioning of a set of JH biosynthetic enzymes (JHBEs). Expression of JHBE genes in the CA is coordinated except for JH acid methyltransferase (<i>JHAMT</i>), which functions in the last step of JH biosynthesis. Here, we sought to determine the mechanism that enables this coordinated expression, assuming the presence of a central regulator of JHBE genes. Comparison of transcriptomes in the CA during active and inactive stages revealed the presence of 3 transcription factors, whose expression patterns matched those of JHBE genes. We propose that one of these, Dead ringer (<i>Dri</i>), is the central up-regulator of CA-specific JHBE genes including <i>JHAMT</i>, based on the following findings: (ⅰ) Knockdown of <i>Dri</i> in the larvae caused precocious metamorphosis, which was rescued by the exogenous application of JH analog, and (ⅱ) knockdown of <i>Dri</i> decreased the expression of most CA-specific JHBE genes examined. Furthermore, RNAi-based reverse genetics indicated that <i>Dri</i> works most upstream in the control of CA-specific JHBE genes, and that shutdown of <i>JHAMT</i>, which occurs independent of other JHBE genes prior to the onset of metamorphosis, can be hypothetically explained by the presence of an unidentified repressor. Our study suggests that <i>Dri</i>, which has been known to regulate embryonic development in a wide range of animals, is conferred a new role in holometabolous insects, i.e. central regulation of CA-specific JHBE genes.