Amphioxus IGF-like peptide induces mouse muscle cell development via binding to IGF receptors and activating MAPK and PI3K/Akt signaling pathways.

Insulin-like growth factors (IGFs) are identified in all vertebrates. An insulin/IGF hybrid polypeptide has also been identified in protochordate amphioxus. However, whether this hybrid polypeptide functions as vertebrate IGFs remains unknown. Here we established a primary culture system of mouse muscle satellite cells as an in vitro model to investigate the effects of amphioxus IGF-like molecule on muscle cell development. Like human IGF, recombinant IGF-like molecule was able to stimulate the proliferation of mouse muscle cells. Besides, it was able to bind to the cells and the partially purified IGF receptors from mouse muscle cells. Moreover, recombinant IGF-like molecule was capable of activating MAPK and PI3K/Akt pathways by stimulating phosphorylation of MAPK and Akt. This interaction of amphioxus IGF-like molecule with mammalian (mouse) IGF receptors and its induction of similar downstream signaling pathways add substantially to the hypothesis of the presence of IGF signaling in the common ancestor of protochordate/vertebrates.