Juvenile hormone and its receptor methoprene-tolerant promote ribosomal biogenesis and vitellogenesis in the Aedes aegypti mosquito

Jia-Lin Wang,Tusar T Saha,Yang Zhang,Changyu Zhang,Alexander S Raikhel

doi:10.1074/jbc.m116.761387

Abstract

Juvenile hormone (JH) controls many biological activities in insects, including development, metamorphosis, and reproduction. In the Aedes aegypti mosquito, a vector of dengue, yellow fever, chikungunya, and zika viruses, the metabolic tissue (the fat body, which is an analogue of the vertebrate liver) produces yolk proteins for developing oocytes. JH is important for the fat body to acquire competence for yolk protein production. However, the molecular mechanisms of how JH promotes mosquito reproduction are not completely understood. In this study we show that stimulation of the JH receptor methoprene-tolerant (Met) activates expression of genes encoding the regulator of ribosome synthesis 1 (RRS1) and six ribosomal proteins (two ribosomal large subunit proteins, two ribosomal small subunit proteins, and two mitochondrial ribosomal proteins). Moreover, RNAi-mediated depletion of RRS1 decreased biosynthesis of the ribosomal protein L32 (RpL32). Depletion of Met, RRS1, or RpL32 led to retardation of ovarian growth and reduced mosquito fecundity, which may at least in part have resulted from decreased vitellogenin protein production in the fat body. In summary, our results indicate that JH is critical for inducing the expression of ribosomal protein genes and demonstrate that RRS1 mediates the JH signal to enhance both ribosomal biogenesis and vitellogenesis.

Highlights

Juvenile hormone (JH) controls many biological activities in insects, including development, metamorphosis, and reproduction
Met RNA interference (RNAi) depletion suppressed the expression of genes involved in ribosome biogenesis We previously identified 2151 differentially expressed transcripts controlled by Met in the fat body of female A. aegypti mosquitoes at the end of the PE phase, with 1613 transcripts down-regulated and 538 up-regulated [19]
In vitro fat body culture demonstrated that Vg expression can only be stimulated by 20E in fat bodies dissected from the late stage of PE or from newly emerged mosquitoes on the condition that their fat bodies are preincubated with JH [7]

Summary

The abbreviations used are

Vitellogenin; YPP, yolk protein precursor; 20E, 20-hydroxyecdysone; JH, juvenile hormone; PE, posteclosion; CA, corpora allata; Met, methoprene-tolerant; bHLH, basic helix-loop-helix; PAS, Per-Arnt-Sim; Tai, Taiman; iMet, Met RNAi depletion; RRS1, regulator of ribosome synthesis 1; RpL32, ribosomal protein large subunit 32; qRT-PCR, quantitative real-time PCR; PBM, post blood meal; CHX, cycloheximide; Kr-h1, Krüppel homolog 1; Gce, germ cell-expressed; DmMet, Drosophila Met; DmTai, Drosophila Tai; dsRNA, double-stranded RNA; NI, non-injected; FISC, ␤FTZ-F1 interacting steroid receptor coactivator. Saha et al [19] performed a RNAi-based transcriptomic screen to identify genes co-regulated by Met and Hairy in the fat body. 1613 transcripts were shown to be activated, whereas 538 were suppressed after RNAi depletion of Met (iMet). In the current study we have shown that among 538 iMet-suppressed transcripts, many are those involved in ribosome biogenesis. We have demonstrated that A. aegypti RRS1 and six ribosomal protein genes are activated by Met, and Met directly regulates the transcription of RRS1. RNAi-mediated depletion of RRS1 resulted in a decreased level of ribosomal protein large subunit 32 (RpL32) protein. RRS1, or RpL32 depletion caused retardation of ovarian growth, which may at least partly result from a decreased Vg expression in the fat body. Our study provides new insight into JH-dependent ribosome proliferation and vitellogenesis

Results

Discussion

Experimental procedures