Mechanistic target of rapamycin complex 1 signaling regulates cell proliferation, cell survival, and differentiation in regenerating zebrafish fins.

Kentaro Hirose,Yutaka Kikuchi,Shunya Hozumi,Taishi Shiomi

doi:10.1186/s12861-014-0042-9

Abstract

BackgroundThe mechanistic target of rapamycin complex1 (mTORC1) signaling pathway has been implicated in functions of multicellular processes, including cell growth and metabolism. Although recent reports showed that many signaling pathways, including Activin, Bmp, Fgf, sonic hedgehog, Insulin-like growth factor (IGF), Notch, retinoic acid, and Wnt, are implicated in non-mammalian vertebrate regeneration, also known as epimorphic regeneration, mTORC1 function remains unknown.ResultsTo investigate the role of mTORC1 signaling pathway in zebrafish caudal fin, we examined the activation and function of mTORC1 signaling using an antibody against phosphorylated S6 kinase and a specific inhibitor, rapamycin. mTORC1 signaling is activated in proliferative cells of intra-ray and wound epidermal cells before blastema formation, as well as in proliferative blastema cells, wound epidermal cells, and osteoblasts during regenerative outgrowth. Before blastema formation, proliferation of intra-ray and wound epidermal cells is suppressed, but cell death is not affected by mTORC1 signaling inhibition with rapamycin. Moreover, rapamycin treatment inhibits blastema and wound epidermal cell proliferation and survival during blastema formation and regenerative outgrowth, as well as osteoblast proliferation and differentiation during regenerative outgrowth. We further determined that mTORC1 signaling is regulated through IGF-1 receptor/phosphatidylinositol-3 kinase and Wnt pathways during fin regeneration.ConclusionTaken together, our findings reveal that mTORC1 signaling regulates proliferation, survival, and differentiation of intra-ray cells, wound epidermis, blastema cells, and/or osteoblasts in various fin regeneration stages downstream of IGF and Wnt signaling pathways.Electronic supplementary materialThe online version of this article (doi:10.1186/s12861-014-0042-9) contains supplementary material, which is available to authorized users.

Highlights

The mechanistic target of rapamycin complex1 signaling pathway has been implicated in functions of multicellular processes, including cell growth and metabolism
Spatiotemporal dynamism of mechanistic target of rapamycin complex1 (mTORC1) signaling activation during fin regeneration To investigate the molecular mechanisms of regeneration, we analyzed the signaling pathways involved in zebrafish fin regeneration using various inhibitors and drugs
To analyze the activation of mTORC1 signaling during fin regeneration, spatiotemporal distribution of phosphorylated S6 kinase (p-S6K), an activated form of S6K, was first examined by immunohistochemistry

Summary

Introduction

The mechanistic target of rapamycin complex (mTORC1) signaling pathway has been implicated in functions of multicellular processes, including cell growth and metabolism. Recent reports showed that many signaling pathways, including Activin, Bmp, Fgf, sonic hedgehog, Insulin-like growth factor (IGF), Notch, retinoic acid, and Wnt, are implicated in non-mammalian vertebrate regeneration, known as epimorphic regeneration, mTORC1 function remains unknown. The adult zebrafish caudal fin is composed of multiple cell types, including fibroblast-like mesenchymal cells, osteoblasts, After 48 hpa, regenerative outgrowth starts and the ray blastema mainly consists of three distinct domains: the distal blastema, proliferative zone, and differentiation zone (72 hpa) [5,6]. The mTORC1 signaling pathway is involved in multicellular processes, including protein synthesis, lipid synthesis, glycolysis, and autophagy, and is inhibited by rapamycin [7,8]. The mTORC1 signaling pathway is involved in multicellular processes, including protein synthesis, lipid synthesis, glycolysis, and autophagy, and is inhibited by rapamycin [7,8]. mTORC1 signaling is known to regulate protein synthesis mainly through direct phosphorylation of S6 kinase (S6K) [7,8]

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