Our data indicates that rapamycin is able to reverse the effects of Smed-smg-1(RNAi) by decreasing proliferation and preventing the formation of outgrowths in about 50% of Smed-smg-1(RNAi) animals. Discussion mTOR signalling has central control of cell growth and proliferation in all eukaryotes www.selleckchem.com/products/nutlin-3a.html analyzed so far [31]. Consistent with mTOR signalling regulating growth, human genetic defects that are associated with upregulated mTOR activity manifest as abnormal cell growth and proliferation. Indeed, many negative regulators of mTOR signalling are known human tumour suppressors. As a result mTOR signalling is currently the most targeted signalling pathway in drug development for the treatment of cancers. It is known that mTOR signalling is essential for the early developmental programmes of metazoans.

For instance Drosophila or C. elegans TOR loss-of-function mutations leads to developmental arrest [38], [39] and homozygous mTOR?/? mouse embryos die shortly after implantation due to impaired cell proliferation in both embryonic and extra-embryonic compartments [40]�C[42]. mTOR itself forms the core of two different complexes and of these TOR complex 1 is thought to be responsible for regulating cell growth and proliferation [31]. We show that planarian Smed-tor, Smed-raptor and Smed-lst8 homologs of TOR, RAPTOR and LST8 respectively and members of TORC1, are necessary for blastema growth during regeneration (Figure 4 and Figure S12). RNAi experiments for Smed-tor and Smed-raptor result in a lack of the first mitotic peak and blastema during regeneration and show lower general levels of proliferation through the whole regenerative process.

Recently it has been shown that planarian amputation triggers two peaks in neoblast mitoses early in regeneration. The first mitotic peak is a body-wide response to any injury and the second response is induced only when injury results in missing tissue [8]. RNAi experiments for Smed-tor or Smed-raptor show that these animals lack the first mitotic peak of regeneration and thus lack a response to injury. Our results suggest both that the first mitotic peak is necessary for blastema formation and that this first mitotic peak requires the activation of mTOR signalling. The second mitotic peak is a response to missing tissue and it triggers neoblast differentiation [8].

Although reduced, Smed-tor and Smed-raptor RNAi planarians did show a second mitotic peak (Figure 4F) and some ability to restore missing structures at the wound site within old tissues without making a blastema (Figure 5C and 5D). The role of mTOR signalling in regeneration [43] and in the regulation of stem cells [44], [45] is just starting to be elucidated. Our results support a key role for mTOR signalling in controlling stem cell proliferation and growth Drug_discovery during regeneration. In this study we have also characterised the planarian homolog of hSMG-1.