In vertebrates, peptide growth factors such as EGF (Epidermal growth factor) and IGFs (Insulin-like growth factors) regulate cell growth, metabolism, differentiation and proliferation. The pleiotropic effects of growth factors are mediated by specific tyrosine kinase receptors, whose activation leads to activation of complex signal transduction pathways involving a cascade of kinase-driven reactions.
In invertebrate model systems, genetic studies have identified specific nucleotide sequences homologous to vertebrate growth factors as well as growth factor-like peptides; however, the biochemical events involved in the response of most invertebrate groups to these regulatory peptides are largely unknown. Isolated cells from the marine bivalve Mytilus sp. have proven useful as an experimental model to study the possible effects of heterologous growth factors on invertebrates and to investigate the signal transduction pathways involved in the physiological response of these organisms. Here the data obtained so far with EGF, IGF- 1 and insulin are summarized, revealing that, in mussel cells, growth factors exert pleiotropic effects on growth and metabolism. The response of mussel cells to different peptides involves different signalling pathways, leading to activation of specific tyrosine kinase receptors, induction of calcium transients, eicosanoid production, activation of Mitogen-Activated Protein Kinases (MAPKs) and of Signal Transducers and Activators of Transcription (STATs). The results add force to the concept that the physiological role of growth factors is highly conserved in evolution and show that bivalve cells are a suitable model for the comparative study of cell signalling in invertebrates..
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