Abstract
Co-ordination of function between multiple cells, mediated by hormones or growth factors, is a crucial requirement for multicellularity. Phosphoinositides, generated by lipid kinase activity, are second messengers that mediate such signalling. Phosphatidylinositol 5-phosphate 4-kinase (PIP4K) is a lipid kinase that phosphorylates phosphatidylinositol 5-phosphate (PI5P) to generate phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2]. A comprehensive bioinformatics analysis of the tree of life, revealed that PIP4K is a metazoan-specific enzyme, but with homologues in choanoflagellates. We find that PIP4K from the sponge Amphimedon queenslandica (AqPIP4K), regarded as the earliest evolved metazoan, shows biochemical activity highly conserved with human PIP4K. Further, AqPIP4K was able to rescue the reduced cell size, growth and development of a Drosophila PIP4K mutant. These phenotypes are regulated through activity of the insulin receptor, a member of the receptor tyrosine kinase family, that is unique to metazoans. Overall, our work defines PIP4K as part of a signal transduction motif required to regulate receptor tyrosine kinase signalling for intercellular communication in the earliest forms of metazoans.
