Characterization of the Cadherin–Catenin Complex of the Sea AnemoneNematostella vectensisand Implications for the Evolution of Metazoan Cell–Cell Adhesion

Abstract

The cadherin–catenin complex (CCC) mediates cell–cell adhesion in bilaterian animals by linking extracellular cadherin-based adhesions to the actin cytoskeleton. However, it is unknown whether the basic organization of the complex is conserved across all metazoans. We tested whether protein interactions and actin-binding properties of the CCC are conserved in a nonbilaterian animal, the sea anemone Nematostella vectensis. We demonstrated that N. vectensis has a complete repertoire of cadherin–catenin proteins, including two classical cadherins, one α-catenin, and one β-catenin. Using size-exclusion chromatography and multi-angle light scattering, we showed that α-catenin and β-catenin formed a heterodimer that bound N. vectensis Cadherin-1 and -2. Nematostella vectensis α-catenin bound F-actin with equivalent affinity as either a monomer or an α/β-catenin heterodimer, and its affinity for F-actin was, in part, regulated by a novel insert between the N- and C-terminal domains. Nematostella vectensis α-catenin inhibited Arp2/3 complex-mediated nucleation of actin filaments, a regulatory property previously thought to be unique to mammalian αE-catenin. Thus, despite significant differences in sequence, the key interactions of the CCC are conserved between bilaterians and cnidarians, indicating that the core function of the CCC as a link between cell adhesions and the actin cytoskeleton is ancestral in the eumetazoans.

Cadherin switch marks germ layer formation in the diploblastic sea anemone Nematostella vectensis

“…The two investigated cadherin genes code for large proteins with 31 EC domains each, largely confirming previous predictions from the genome (Hulpiau and van Roy, 2011) and gene models based on our transcriptome assembly (Fredman et al, 2013). This significantly extends the structure of the recently published gene model for Cdh3 (termed Cad1 in (Clarke et al, 2016). Thus, cnidarians as well as other non-bilaterians have substantially larger classical cadherins than most bilaterians and their extracellular domain structure is reminiscent of the FAT-like proteins (Hulpiau and van Roy, 2009;Hulpiau and van Roy, 2011).…”

“…This would result in an mRNA of > 15 kb and predict a protein size of about 480 kDalton. However, in a recent publication, two cadherins (called Cadherin 1 and Cadherin 2) with 14 and 30 Cadherin repeats, respectively, were reported (Clarke et al, 2016). To resolve this discrepancy, we used numerous primers derived from the predictions of Hulpiau and van Roy and our gene models from RNAseq (Fredman et al, 2013), cloned the large transcript in overlapping pieces of about 2-3 kb.…”

“…A recent biochemical study showed that the intracellular domain of the classical cadherins can form a ternary complex with α-catenin and β-catenin (Clarke et al, 2016). To explore further the molecular composition of the adherens junctions, we co-stained the embryos with the antibody against Cdh3 and β-catenin.…”

Diverse cell junctions with unique molecular composition in tissues of a sponge (Porifera)

“…As we begin to examine cell adhesion in non-bilaterian lineages, there appears to be more mechanistic diversity than anticipated. For example, the cnidarian Nematostella vectensis has a conserved classical cadherin/catenin complex (Clarke et al, 2016), but β-catenin is not always detected at cadherin-positive cell-cell adhesions in tissues (Pukhlyakova et al, n.d.;Salinas-Saavedra et al, 2018). Likewise, sequence analyses of ctenophores indicate that they lack conserved cadherin/β-catenin interaction motifs (Belahbib et al, 2018), and a recent study indicates that β-catenin is altogether absent at cell-cell contacts in Mnemiopsis leidyi (Salinas-Saavedra et al, n.d.).…”

“…However, experimental studies of cell junction composition and function are largely restricted to bilaterian animals, such as the roundworm Caenorhabditis elegans, the fruit fly Drosophila melanogaster, and vertebrates. Recent studies demonstrate conserved roles for adherens junction proteins in cnidarians, as well (Clarke et al, 2019(Clarke et al, , 2016Pukhlyakova et al, n.d.).…”