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

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.

Zebrafish fin and heart: what's special about regeneration?

“…While epicardium, endocardium and coronary vessels also regenerate [16][17][18]19 ], the majority of studies published so far have concentrated on the cellular and molecular mechanisms of cardiomyocyte regeneration. Genetic lineage tracing has shown that cardiomyocytes regenerate from spared differentiated cardiomyocytes, which dedifferentiate and re-enter the cell cycle (Figure 1a) 54], Activin [55], Calcineurin [56 ], Hippo (YAP) [57], and mTor [58], while heart regeneration requires PDGF [59], TGFb [34,60], Jak/Stat [61 ], Neuregulin [62] and NF-kB [63].…”

Effects of rapamycin on life span and on expression of TOR and S6K in Brachionus calyciflorus (Rotifera)

“…We speculate that the corresponding changes in expression had an impact on the TORC1 targets, p70 S6 kinase (S6K) and eIF4E-binding protein-1 4E-BP1, which regulate translation of mRNA. Inhibition of TORC1 signaling from 24 to 72 h after amputation in a zebrafish fin regeneration model suppressed cell proliferation through the inhibition of S6K activation (Hirose et al 2014). Thus, we speculate that it suppressed cell proliferation through the inhibition of S6K activation in B. calyciflorus.…”

“…A surprising discovery was that the TOR expression levels reached a maximum 20-fold increase (p < 0.001) and S6K reached a 15-fold increase (p < 0.001). Rapamycin inhibition of p70S6K and cell cycle activity is closely associated with many different key cellular processes, but in a cell-free system, a rapamycin-PKBP complex did not inhibit p70S6K activity, which showed that there was no direct interaction between rapamycin and p70S6K (Hirose et al 2014).…”

mTOR Signaling at the Crossroad between Metazoan Regeneration and Human Diseases

“…Following caudal fin amputation in zebrafish, TOR signaling, reflected by the levels of the phosphorylated form of S6K (S6 Kinase), is active in wound epidermal cells, osteoblasts and proliferative proximal region of the blastema [17] (Figure 2a). During regenerative outgrowth, mTORC1 inhibition (with rapamycin treatment) suppresses blastema formation.…”