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Target of rapamycin-mediated amino acid signaling in mosquito anautogeny.

ABSTRACT: Mosquitoes generate an enormous burden on human health worldwide. Disease-transmitting species use a reproductive strategy, termed anautogeny, that requires a blood meal to initiate egg maturation. Whereas this strategy is important for driving disease transmission, the molecular mechanisms underlying this phenomenon are still poorly understood. The production of yolk protein precursors (YPPs), a central event in egg maturation, is called vitellogenesis. YPPs are synthesized in the fat body, the insect analogue of the vertebrate liver. Mosquito vitellogenesis is regulated by the steroid hormone 20 hydroxyecdysone (20E). However, 20E alone is not capable of activating vitellogenesis in vivo. Here, we report that amino acid signaling through the nutrient-sensitive target of rapamycin (TOR) pathway is essential for the activation of YPP gene expression. An increase in extracellular amino acid levels, similar to the increase observed after a blood meal, is critical for 20E stimulation of YPP gene expression. Treatment with the TOR kinase inhibitor rapamycin significantly inhibits YPP expression. We used RNA interference to knockdown the expression of two key proteins of the TOR signaling pathway, TOR, and tuberous sclerosis complex 2. Knockdown of TOR inhibited amino acid stimulation while knockdown of tuberous sclerosis complex 2, a negative regulator of TOR signaling, resulted in enhanced YPP expression. Thus, amino acid-based TOR signaling regulates the activation of egg development after a blood meal, an adaptation to the unique life style of mosquitoes.

SUBMITTER: Hansen IA

PROVIDER: S-EPMC489984 | biostudies-literature | 2004 Jul

REPOSITORIES: biostudies-literature

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Target of rapamycin-mediated amino acid signaling in mosquito anautogeny.

Hansen Immo A IA Attardo Geoffrey M GM Park Jong-Hwa JH Peng Quan Q Raikhel Alexander S AS

Proceedings of the National Academy of Sciences of the United States of America 20040630 29

Mosquitoes generate an enormous burden on human health worldwide. Disease-transmitting species use a reproductive strategy, termed anautogeny, that requires a blood meal to initiate egg maturation. Whereas this strategy is important for driving disease transmission, the molecular mechanisms underlying this phenomenon are still poorly understood. The production of yolk protein precursors (YPPs), a central event in egg maturation, is called vitellogenesis. YPPs are synthesized in the fat body, the ...[more]

PMID: 15229322

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Project description:Heat stress (HS) is one of the most serious factors to negatively affect the lactation performance of dairy cows. Bovine mammary epithelial cells are important for lactation. It was demonstrated that HS decreases the lactation performance of dairy cows, partly through altering gene expression within bovine mammary epithelial tissue. However, the cellular metabolism mechanisms under HS remains largely unknown. The objective of this study was to determine whether HS induced changes in intracellular metabolites and gene transcription related to amino acid metabolism, amino acid transportation and the mTOR signaling pathway. Immortalized bovine mammary epithelial cell lines (MAC-T cells, n = 5 replicates/treatment) were incubated for 12 h at 37 °C (Control group) and 42 °C (HS group). Relative to the control group, HS led to a greater mRNA expression of heat shock protein genes HSF1, HSPB8, HSPA5, HSP90AB1 and HSPA1A. Compared with the control group, metabolomics using liquid chromatography tandem-mass spectrometry identified 417 differential metabolites with p < 0.05 and a variable importance in projection (VIP) score >1.0 in the HS group. HS resulted in significant changes to the intracellular amino acid metabolism of glutathione, phenylalanine, tyrosine, tryptophan, valine, leucine, isoleucine, arginine, proline, cysteine, methionine, alanine, aspartate and glutamate. HS led to a greater mRNA expression of the amino acid transporter genes SLC43A1, SLC38A9, SLC36A1, and SLC3A2 but a lower mRNA expression of SLC7A5 and SLC38A2. Additionally, HS influenced the expression of genes associated with the mTOR signaling pathway and significantly upregulated the mRNA expression of mTOR, AKT, RHEB, eIF4E and eEF2K but decreased the mRNA expression of TSC1, TSC2 and eEF2 relative to the control group. Compared with the control group, HS also led to greater mRNA expression of the CSN1S2 gene. Overall, our study indicates that bovine mammary epithelial cells may have the ability to resist HS damage and continue milk protein synthesis partly through enhanced intracellular amino acid absorption and metabolism and by activating the mTOR signaling pathway during HS.

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Target of rapamycin-mediated amino acid signaling in mosquito anautogeny.

Publications

Target of rapamycin-mediated amino acid signaling in mosquito anautogeny.

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