Juvenile hormone acts through FoxO to promote <i>Cdc2</i> and <i>Orc5</i> transcription for polyploidy-dependent vitellogenesis
Zhongxia Wu, Qiongjie He, Baojuan Zeng, Haodan Zhou, Shutang Zhou
Abstract
Vitellogenin (Vg) is prerequisite to egg production and embryonic development after oviposition in oviparous animals. In many insects, juvenile hormone (JH) promotes fat body cell polyploidization for massive Vg synthesis required for maturation of multiple oocytes, but the underlying mechanisms remain poorly understood. Using the migratory locust Locusta migratoria as a model system, we report here that JH induces the dephosphorylation of Forkhead box O transcription factor (FoxO) through a signaling cascade including leucine carboxyl methyltransferase 1 (LCMT1) and protein phosphatase 2A (PP2A). JH promotes PP2A activity via LCMT1-mediated methylation, consequently triggering FoxO dephosphorylation. Dephosphorylated FoxO binds to the upstream of two endocycle-related genes, cell-division-cycle 2 (Cdc2) and origin-recognition-complex subunit 5 (Orc5) and activates their transcription. Depletion of FoxO, Cdc2 or Orc5 results in blocked polyploidization of fat body cells, accompanied by markedly reduced Vg expression, impaired oocyte maturation and arrested ovarian development. The results suggest that JH acts via LCMT1-PP2A-FoxO to regulate Cdc2 and Orc5 expression and enhance ploidy of fat body cells in preparation for large-scale Vg synthesis required for synchronous maturation of multiple eggs.