Regulation of cadherin junctions during mouse submandibular gland development

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Abstract
Submandibular gland (SMG) development involves branching morphogenesis of the salivary epithelium into the surrounding mesenchyme, accompanied by proliferation and differentiation of immature salivary cells along acinar and ductal cell lineages. During development, salivary cell sorting and cell–cell adhesion are likely to be directed by cadherin adhesion receptors. We show that two classic cadherins, N- and E-cadherin, participate in SMG development. Early in embryonic morphogenesis, both cadherins displayed diffuse staining with regionalized localization to cell–cell borders. At this stage, significant pools of N- and E-cadherins were Triton-soluble, suggesting that fractions of these molecules were not localized to stable junctional complexes associated with the actin cytoskeleton. With cytodifferentiation, cadherins became progressively Triton-insoluble, and this correlated with their organization at cell–cell interfaces. In the cytodifferentiated SMG, N-cadherin was absent, whereas E-cadherin remained at cell–cell interfaces. Early in morphogenesis, β-catenin was also primarily Triton-soluble, and its association with the actin cytoskeleton and localization to the adherens junctions increased with cytodifferentiation. Greater recruitment of cadherins and β-catenin to cell–cell borders was paralleled by changes in membrane association of two Rho GTPases, Cdc42 and RhoA. N-cadherin was detected only at early stages of postnatal development, whereas E-cadherin and β-catenin became progressively Triton-insoluble during differentiation. Our results indicate that N-cadherin functions transiently in SMG development. On the other hand, E-cadherin and β-catenin appear to play different roles during tissue organization and cytodifferentiation. In early morphogenesis, E-cadherin and β-catenin are likely to participate in SMG remodeling, whereas during cytodifferentiation, they form stable cell–cell contacts, and may collaborate with Rho GTPases in the establishment and maintenance of salivary cell polarity.