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Fig. 2. Cell-cell adhesion molecules involved in gastrulation. Classical cadherins are integral membrane proteins characterized by five extracellular (EC) domains that mediate homophilic, trans or cis binding (Pokutta and Weis, 2007). The cytoplasmic domains of all classical cadherins contain binding sites for β-catenin (β-cat) and the catenin-relative p120, and associate with the actin cytoskeleton, possibly through Eplin. They are regulated by non-canonical Wnt signalling or by the small GTPase Rdn1, which induces cadherin endocytosis in Rab5⁺ vesicles by binding to the cytoplasmic domain of FLRT3. Protocadherins have an additional EC domain and lack cytoplasmic p120 and β-cat binding sites. The cytoplasmic tail of Xenopus paraxial protocadherin C (XPAPC) contains several other binding sites that mediate intracellular signalling and interfere with non-canonical Wnt (PCP) signalling. Flamingo (Fmi) is an atypical seven-pass transmembrane (TM) cadherin-related protein, with eight or nine EC-domains, several EGF and two Laminin G domains, and a cytoplasmic domain that mediates intracellular signalling. Ca²⁺-independent cell-cell adhesion molecules that are required for gastrulation movements include Bves and Echinoid. Xenopus and Drosophila Bves and Popeye family members have relatively short EC domains, a three-pass TM and a long intracellular domain (Lin et al., 2007; Ripley et al., 2006). Echinoid, a Drosophila nectin-like immunoglobulin cell-adhesion molecule (Ig-CAM), clusters with classical cadherins via their cytoplasmic binding partners afadin and -catenin. ANR5, ankyrin repeats domain protein 5; EGF, epidermal growth factor; Fz7, Frizzled 7.

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