Type I and II classical cadherins help to determine the adhesive specificities of animal cells. Crystal-structure determination of ectodomain regions from three type II cadherins reveals adhesive dimers formed by exchange of N-terminal beta strands between partner extracellular cadherin-1 (EC1) domains. These interfaces have two conserved tryptophan side chains that anchor each swapped strand, compared with one in type I cadherins, and include large hydrophobic regions unique to type II interfaces. The EC1 domains of type I and type II cadherins appear to encode cell adhesive specificity in vitro. Moreover, perturbation of motor neuron segregation with chimeric cadherins depends on EC1 domain identity, suggesting that this region, which includes the structurally defined adhesive interface, encodes type II cadherin functional specificity in vivo.

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We review mean-field and fluctuation-dominated behaviors exhibited by the Seceder Model, which moves an evolving population to various critical states of self-organized segregation, delicately balancing opposed sociological pressures of conformity & dissent, and giving rise to rich ideological condensation phenomena. The secession exponent and finite societal Seceder limits are examined.This paper discusses recent research [1] on the Seceder Model [2], an intriguing far-from-equilibrium stochastic model of opinion dynamics in which the competing tendencies of conformity and dissent cause an evolving population to fragment, disperse, and coalesce, forming distinct groups characterized by free and frequent interchange of individuals. We imagine a population that is ultimately economic, sociological, or political in character, with interactions based upon shared investment strategies, cultural opinions, or electoral inclinations. This is in sharp contrast to many well-known examples of inanimate cluster formation found in Nature (e.g., in the astrophysical context-Saturnian rings, globular clusters, Virgo galactic supercluster, etc.), where the underlying forces are physical in origin; here, the interactions are based upon signaling, opinion, and information exchange. The Seceder Model bears close spiritual

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