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Torso, a Drosophila receptor tyrosine kinase, plays a novel role in the larval fat body in regulating insulin signaling and body growth

Journal of Comparative Physiology B volume 186, pages 701–709 (2016)Cite this article

Abstract

Torso is a receptor tyrosine kinase whose localized activation at the termini of the Drosophila embryo is mediated by its ligand, Trunk. Recent studies have unveiled a second function of Torso in the larval prothoracic gland (PG) as the receptor for the prothoracicotropic hormone, which triggers pupariation. As such, inhibition of Torso in the PG prolongs the larval growth period, thereby increasing the final pupa size. Here, we report that Torso also acts in the larval fat body, regulating body size in a manner opposite from that of Torso in PG. We confirmed the expression of torso mRNA in the larval fat body and its reduction by RNA interference (RNAi). Fat body-specific knockdown of torso, by either of the two independent RNAi transgenes, significantly decreased the final pupal size. We found that torso knockdown suppresses insulin/target of rapamycin (TOR) signaling in the fat body, as confirmed by repression of Akt and S6K. Notably, the decrease in insulin/TOR signaling and decrease of pupal size induced by the knockdown of torso were rescued by the expression of a constitutively active form of the insulin receptor or by the knockdown of FOXO. Our study revealed a novel role for Torso in the fat body with respect to regulation of insulin/TOR signaling and body size. This finding exemplifies the contrasting effects of the same gene expressed in two different organs on organismal physiology.

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Acknowledgments

We thank the Bloomington Drosophila Stock Center, the Vienna Drosophila RNAi Center and the Kyoto stock center for the fly stocks used in this study. This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF), funded by the Ministry of Education, Science and Technology (2014R1A2A1A11052915) and by a grant from the Korea Health Technology R&D Project through the Korea Health Industry Development Institute (KHIDI), funded by the Ministry of Health and Welfare, Republic of Korea (Grant Number: HI14C2380).

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    1. Department of Life Science, Chung-Ang University, Seoul, 156-756, Korea

      Jong Woo Jun, Gangsik Han, Hyun Myoung Yun, Gang Jun Lee & Seogang Hyun

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    1. Jong Woo Jun
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    2. Gangsik Han
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    3. Hyun Myoung Yun
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    Correspondence to Seogang Hyun.

    Additional information

    J. W. Jun, G. Han and H. M. Yun contributed equally to this study.

    Communicated by G. Heldmaier.

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    Jun, J.W., Han, G., Yun, H.M. et al. Torso, a Drosophila receptor tyrosine kinase, plays a novel role in the larval fat body in regulating insulin signaling and body growth. J Comp Physiol B 186, 701–709 (2016). https://doi.org/10.1007/s00360-016-0992-2

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    • DOI: https://doi.org/10.1007/s00360-016-0992-2

    Keywords

    • Torso
    • Fat body
    • Insulin signaling
    • Body size
    • Drosophila