title: Torso, a Drosophila receptor tyrosine kinase, plays a novel role in the larval fat body in regulating insulin signaling and body growth.
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.
authors.affiliation: Department of Life Science, Chung-Ang University, Seoul, 156-756, Korea.
authors.forename: Jong Woo
authors.initials: JW
authors.lastname: Jun
authors.affiliation: Department of Life Science, Chung-Ang University, Seoul, 156-756, Korea.
authors.forename: Gangsik
authors.initials: G
authors.lastname: Han
authors.affiliation: Department of Life Science, Chung-Ang University, Seoul, 156-756, Korea.
authors.forename: Hyun Myoung
authors.initials: HM
authors.lastname: Yun
authors.affiliation: Department of Life Science, Chung-Ang University, Seoul, 156-756, Korea.
authors.forename: Gang Jun
authors.initials: GJ
authors.lastname: Lee
authors.affiliation: Department of Life Science, Chung-Ang University, Seoul, 156-756, Korea. sghyun@cau.ac.kr.
authors.forename: Seogang
authors.initials: S
authors.lastname: Hyun
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D049628:Body Size; D004330:Drosophila / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D005216:Fat Body / Q000378:metabolism*; D007328:Insulin / Q000378:metabolism*; D007814:Larva / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D011679:Pupa / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D020794:Receptor Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism
chemical_list: D029721:Drosophila Proteins; D007328:Insulin; D012333:RNA, Messenger; D020794:Receptor Protein-Tyrosine Kinases; C080148:tor protein, Drosophila; D051057:Proto-Oncogene Proteins c-akt; D038762:Ribosomal Protein S6 Kinases, 70-kDa; C448959:ribosomal protein S6 kinase, 70kD, polypeptide 2
keywords: Body size; Drosophila; Fat body; Insulin signaling; Torso