The integrins are a superfamily of the major cell adhesion receptors that bind primarily to extracellular matrix ligands, typically short peptide motifs such as arginine-glycine-aspartate – RGD, but can also bind to cell-surface ligands and soluble ligands. Integrin heterodimers bind and interact with several other proteins forming the integrin-mediated adhesion and two-way signalling complex. This complex consists of alpha-actinin and talin which bind to the cytoplasmic C-terminal tail of the integrin and paxillin and vinculin which bind to talin and alphaactinin. Moreover, the IPP complex composed of ILK, PINCH (particularly interesting Cys-His-rich protein) and parvin acts as a connection between integrins and the actin cytoskeleton.Until very recently integrin-mediated adhesion and signalling machinery was thought to be specific to Metazoa (animals) as they had not been identified in any other group and as their mmost important function – binding to the proteins of the extracellular matrix – is only possible in the metazoans.Recently, integrins and other components of the integrin-mediated adhesion and signalling machinery have been identified in unicellular organisms; such as in the filasterean Capsaspora owczarzaki, a close relative of metazoans and choanoflagellates. However, nothing is known about the function of integrins in the unicellular context.The aim of this project is to investigate the function of integrins and other components of the integrin-mediated adhesion and signalling machinery in the unicellular metazoan relatives. The results will enable us to understand 1) the ancestral function of integrins and 2) how the functions changed during the transition to multicellular metazoans.These findings will significantly improve the general understanding of the mechanisms and principles of functional adaptations, diversifications and co-options of genes through evolution.