Integrin-Mediated Adhesion in the Unicellular Holozoan Capsaspora owczarzaki

Abstract

In animals, cell-matrix adhesions are essential for cell migration, tissue organization, and differentiation, which have central roles in embryonic development [1Berrier A.L. Yamada K.M. Cell-matrix adhesion.J. Cell. Physiol. 2007; 213: 565-573Crossref PubMed Scopus (702) Google Scholar, 2Bulgakova N.A. Klapholz B. Brown N.H. Cell adhesion in Drosophila: versatility of cadherin and integrin complexes during development.Curr. Opin. Cell Biol. 2012; 24: 702-712Crossref PubMed Scopus (43) Google Scholar, 3Hynes R.O. Cell adhesion: old and new questions.Trends Cell Biol. 1999; 9: M33-M37Abstract Full Text Full Text PDF PubMed Scopus (254) Google Scholar, 4Hynes R.O. Zhao Q. The evolution of cell adhesion.J. Cell Biol. 2000; 150: F89-F96Crossref PubMed Google Scholar, 5Maartens A.P. Brown N.H. Anchors and signals: the diverse roles of integrins in development.Curr. Top. Dev. Biol. 2015; 112: 233-272Crossref PubMed Scopus (33) Google Scholar, 6Winograd-Katz S.E. Fässler R. Geiger B. Legate K.R. The integrin adhesome: from genes and proteins to human disease.Nat. Rev. Mol. Cell Biol. 2014; 15: 273-288Crossref PubMed Scopus (393) Google Scholar]. Integrins are the major cell surface adhesion receptors mediating cell-matrix adhesion in animals. They are heterodimeric transmembrane proteins that bind extracellular matrix (ECM) molecules on one side and connect to the actin cytoskeleton on the other [7Hynes R.O. Integrins: bidirectional, allosteric signaling machines.Cell. 2002; 110: 673-687Abstract Full Text Full Text PDF PubMed Scopus (6849) Google Scholar]. Given the importance of integrin-mediated cell-matrix adhesion in development of multicellular animals, it is of interest to discover when and how this machinery arose during evolution. Comparative genomic analyses have shown that core components of the integrin adhesome pre-date the emergence of animals [8Brown M.W. Sharpe S.C. Silberman J.D. Heiss A.A. Lang B.F. Simpson A.G.B. Roger A.J. Phylogenomics demonstrates that breviate flagellates are related to opisthokonts and apusomonads.Proc. Biol. Sci. 2013; 280: 20131755Crossref PubMed Scopus (102) Google Scholar, 9de Mendoza A. Suga H. Permanyer J. Irimia M. Ruiz-Trillo I. Complex transcriptional regulation and independent evolution of fungal-like traits in a relative of animals.eLife. 2015; 4: e08904Crossref PubMed Google Scholar, 10Hehenberger E. Tikhonenkov D.V. Kolisko M. Del Campo J. Esaulov A.S. Mylnikov A.P. Keeling P.J. Novel predators reshape holozoan phylogeny and reveal the presence of a two-component signaling system in the ancestor of animals.Curr. Biol. 2017; 27: 2043-2050.e6Abstract Full Text Full Text PDF PubMed Scopus (53) Google Scholar, 11Sebé-Pedrós A. Ruiz-Trillo I. Integrin-mediated adhesion complex: cooption of signaling systems at the dawn of Metazoa.Commun. Integr. Biol. 2010; 3: 475-477Crossref PubMed Google Scholar]; however, whether it mediates cell adhesion in non-metazoan taxa remains unknown. Here, we investigate cell-substrate adhesion in Capsaspora owczarzaki, the closest unicellular relative of animals with the most complete integrin adhesome [11Sebé-Pedrós A. Ruiz-Trillo I. Integrin-mediated adhesion complex: cooption of signaling systems at the dawn of Metazoa.Commun. Integr. Biol. 2010; 3: 475-477Crossref PubMed Google Scholar, 12Sebé-Pedrós A. Roger A.J. Lang F.B. King N. Ruiz-Trillo I. Ancient origin of the integrin-mediated adhesion and signaling machinery.Proc. Natl. Acad. Sci. USA. 2010; 107: 10142-10147Crossref PubMed Scopus (178) Google Scholar]. Previous work described that the life cycle of C. owczarzaki (hereafter, Capsaspora) includes three distinct life stages: adherent; cystic; and aggregative [13Sebé-Pedrós A. Irimia M. Del Campo J. Parra-Acero H. Russ C. Nusbaum C. Blencowe B.J. Ruiz-Trillo I. Regulated aggregative multicellularity in a close unicellular relative of metazoa.eLife. 2013; 2: e01287Crossref PubMed Scopus (106) Google Scholar]. Using an adhesion assay, we show that, during the adherent life stage, C. owczarzaki adheres to surfaces using actin-dependent filopodia. We show that integrin β2 and its associated protein vinculin localize as distinct patches in the filopodia. We also demonstrate that substrate adhesion and integrin localization are enhanced by mammalian fibronectin. Finally, using a specific antibody for integrin β2, we inhibited cell adhesion to a fibronectin-coated surface. Our results suggest that adhesion to the substrate in C. owczarzaki is mediated by integrins. We thus propose that integrin-mediated adhesion pre-dates the emergence of animals.

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