In oviparous animals, vitellogenesis is prerequisite to egg production and embryonic growth after oviposition. For successful insect vitellogenesis and oogenesis, vitellogenin (Vg) synthesized in the fat body (homologue to vertebrate liver and adipose tissue) must pass through the intercellular channels, a condition known as patency in the follicular epithelium, to reach the surface of oocytes. This process is controlled by juvenile hormone (JH) in many insect species, but the underlying mechanisms remain elusive. Previous work has suggested the possible involvement of Na ؉ /K ؉ -ATPase in patency initiation, but again, the regulatory cascade of Na ؉ /K ؉ -ATPase for patency initiation has been lacking. Using the migratory locust Locusta migratoria as a model system, we report here that RNAi-mediated knockdown of gene coding for Na ؉ /K ؉ -ATPase, inhibition of its phosphorylation, or suppression of its activity causes loss of patency, resulting in blocked Vg uptake, arrested oocyte maturation, and impaired ovarian growth. JH triggers G proteincoupled receptor (GPCR), receptor tyrosine kinase (RTK), phospholipase C (PLC), inositol trisphosphate receptor (IP3R), and protein kinase C (PKC) to phosphorylate Na ؉ /K ؉ -ATPase ␣-subunit at amino acid residue Ser 8 , consequently activating Na ؉ /K ؉ -ATPase for the induction of patency in vitellogenic follicular epithelium. Our results thus point to a previously unidentified mechanism by which JH induces the phosphorylation and activation of Na ؉ /K ؉ -ATPase via a signaling cascade of GPCR, RTK, PLC, IP3R, and PKC. The findings advance our understanding of JH regulation in insect vitellogenesis and oogenesis.

Vitellogenin receptor (VgR) plays a pivotal role in ovarian vitellogenin (Vg) uptake and vertical transmission of pathogenic microbes and Wolbachia symbionts. However, the regulatory mechanisms of VgR action as an endocytic receptor and translocation from oocyte cytoplasm to the membrane remain poorly understood. Here, by using the migratory locust Locusta migratoria as a model system, we report that juvenile hormone (JH) promotes VgR phosphorylation at Ser1361 in the second EGF-precursor homology domain. A signaling cascade including GPCR, PLC, extracellular calcium, and PKC-ι is involved in JH-stimulated VgR phosphorylation. This posttranslational regulation is a prerequisite for VgR binding to Vg on the external surface of the oocyte membrane and subsequent VgR/Vg endocytosis. Acidification, a condition in endosomes, induces VgR dephosphorylation along with the dissociation of Vg from VgR. Phosphorylation modification is also required for VgR recycling from oocyte cytoplasm to the membrane. Additionally, VgR phosphorylation and its requirement for Vg uptake and VgR recycling are evolutionarily conserved in other representative insects including the cockroach Periplaneta americana and the cotton bollworm Helicoverpa armigera. This study fills an important knowledge gap of low-density lipoprotein receptors in posttranslational regulation, endocytosis, and intracellular recycling.