The integrin-mediated adhesive complex in the ancestor of animals, fungi, and amoebae

The retromer and retriever systems are conserved and differentially expanded in parabasalids

Early endosomes sort transmembrane cargo either for lysosomal degradation or retrieval to the plasma membrane or the Golgi complex. Endosomal retrieval in eukaryotes is governed by the anciently homologous retromer or retriever complexes. Each comprises a core tri-protein subcomplex, membrane-deformation proteins and interacting partner complexes, together retrieving a variety of known cargo proteins. Trichomonas vaginalis, a sexually transmitted human parasite, uses the endomembrane system for pathogenesis. It has massively and selectively expanded its endomembrane protein complement, the evolutionary path of which has been largely unexplored. Our molecular evolutionary study of retromer, retriever and associated machinery in parabasalids and its free-living sister lineage of Anaeramoeba demonstrates specific expansion of the retromer machinery, contrasting with the retriever components. We also observed partial loss of the Commander complex and sorting nexins in Parabasalia but complete retention in Anaeramoeba. Notably, we identified putative parabasalid sorting nexin analogs. Finally, we report the first retriever protein localization in a non-metazoan group along with retromer protein localization in T. vaginalis.

Cell polarity in the protist-to-animal transition

A signature feature of the animal kingdom is the presence of epithelia: sheets of polarized cells that both insulate the organism from its environment and mediate interactions with it. Epithelial cells display a marked apico-basal polarity, which is highly conserved across the animal kingdom, both in terms of morphology and of molecular regulators. How did this architecture first evolve? Although the last eukaryotic common ancestor almost certainly possessed a simple form of apico-basal polarity (marked by the presence of one or several flagella at a single cellular pole), comparative genomics and evolutionary cell biology reveal that the polarity regulators of animal epithelial cells have a surprisingly complex and stepwise evolutionary history. Here, we retrace their evolutionary assembly. We suggest that the "polarity network" that polarized animal epithelial cells evolved by integration of initially independent cellular modules that evolved at distinct steps of our evolutionary ancestry. The first module dates back to the last common ancestor of animals and amoebozoans and involved Par1, extracellular matrix proteins, and the integrin-mediated adhesion complex. Other regulators, such as Cdc42, Dlg, Par6 and cadherins evolved in ancient unicellular opisthokonts, and might have first been involved in F-actin remodeling and filopodial dynamics. Finally, the bulk of "polarity proteins" as well as specialized adhesion complexes evolved in the metazoan stem-line, in concert with the newly evolved intercellular junctional belts. Thus, the polarized architecture of epithelia can be understood as a palimpsest of components of distinct histories and ancestral functions, which have become tightly integrated in animal tissues.

Adhesion of Dictyostelium Amoebae to Surfaces: A Brief History of Attachments

Dictyostelium amoebae adhere to extracellular material using similar mechanisms to metazoan cells. Notably, the cellular anchorage loci in Amoebozoa and Metazoa are both arranged in the form of discrete spots and incorporate a similar repertoire of intracellular proteins assembled into multicomponent complexes located on the inner side of the plasma membrane. Surprisingly, however, Dictyostelium lacks integrins, the canonical transmembrane heterodimeric receptors that dominantly mediate adhesion of cells to the extracellular matrix in multicellular animals. In this review article, we summarize the current knowledge about the cell-substratum adhesion in Dictyostelium, present an inventory of the involved proteins, and draw parallels with the situation in animal cells. The emerging picture indicates that, while retaining the basic molecular architecture common to their animal relatives, the adhesion complexes in free-living amoeboid cells have evolved to enable less specific interactions with diverse materials encountered in their natural habitat in the deciduous forest soil. Dissection of molecular mechanisms that underlay short lifetime of the cell-substratum attachments and high turnover rate of the adhesion complexes in Dictyostelium should provide insight into a similarly modified adhesion phenotype that accompanies the mesenchymal-amoeboid transition in tumor metastasis.

Ancient Origins of Cytoskeletal Crosstalk: Spectraplakin-like Proteins Precede the Emergence of Cortical Microtubule Stabilization Complexes as Crosslinkers

Adhesion between cells and the extracellular matrix (ECM) is one of the prerequisites for multicellularity, motility, and tissue specialization. Focal adhesions (FAs) are defined as protein complexes that mediate signals from the ECM to major components of the cytoskeleton (microtubules, actin, and intermediate filaments), and their mutual communication determines a variety of cellular processes. In this study, human cytoskeletal crosstalk proteins were identified by comparing datasets with experimentally determined cytoskeletal proteins. The spectraplakin dystonin was the only protein found in all datasets. Other proteins (FAK, RAC1, septin 9, MISP, and ezrin) were detected at the intersections of FAs, microtubules, and actin cytoskeleton. Homology searches for human crosstalk proteins as queries were performed against a predefined dataset of proteomes. This analysis highlighted the importance of FA communication with the actin and microtubule cytoskeleton, as these crosstalk proteins exhibit the highest degree of evolutionary conservation. Finally, phylogenetic analyses elucidated the early evolutionary history of spectraplakins and cortical microtubule stabilization complexes (CMSCs) as model representatives of the human cytoskeletal crosstalk. While spectraplakins probably arose at the onset of opisthokont evolution, the crosstalk between FAs and microtubules is associated with the emergence of metazoans. The multiprotein complexes contributing to cytoskeletal crosstalk in animals gradually gained in complexity from the onset of metazoan evolution.