FKBP39 Controls the Larval Stage JH Activity and Development in .

FK506-binding protein 39kD (FKBP39) localizes in the nucleus and contains multiple functional domains. Structural analysis suggests that FKBP39 might function as a transcriptional factor and control juvenile hormone (JH) activity. Here, we show that FKBP39 expresses at a high level and localizes in the nucleolus of fat body cells during the first two larval stages and early third larval stage. The mutant displays delayed larval-pupal transition and an increased expression of , the main mediator of the JH pathway, at the early third larval stage. Moreover, the mutant has a fertility defect that is independent of JH activity. Interestingly, the expression of , the most widely used reference gene for qRT-PCR in Drosophila, significantly decreased in the mutant, suggesting that FKBP39 might regulate ribosome assembly. Taken together, our data demonstrate the expression pattern and physiological roles of FKBP39 in Drosophila.