Localizations of Laminin Chains Suggest Their Multifaceted Functions in Mouse Tooth Development

The human laminin family is composed of five alpha, four beta, and three gamma chains. Laminins are heterotrimers of alpha, beta, and gamma chains. Laminins play critical roles during organogenesis, mostly as basement membrane components. The expression of all and the localization of most laminin chains were characterized in mouse developing teeth. Primary laminin isoforms in basement membranes along the inner enamel epithelium before the secretory stage and outside of the outer enamel epithelium were laminins 111 (alpha 1 beta 1 gamma 1) and 511. The mouse laminin alpha 3 chain has two variants, alpha 3A and alpha 3B. Although a basement membrane structure is absent, laminin 3A32 was localized along the secretory surface of the secretory stage ameloblast Tomes' processes. Laminin 3A32 was localized along the atypical basement membrane of maturation stage ameloblasts and the specialized basement membrane of junctional epithelium facing the enamel surface. The endothelial basement membrane in the dental papilla and outside of the enamel organ contained laminins 411 and 511. Laminin 332 was detected in the extracellular matrix but not the basement membrane of the apical loop. Laminin 111 was localized in the extracellular matrix of the apical dental papilla without forming a visible basement membrane. These findings suggest the multifaceted functions of laminins in tooth development and set the foundation for functional investigations.