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Laminins are a family of multifunctional macromolecules, ubiquitous in basement
membranes, and represent the most abundant structural noncollagenous
glycoproteins of these highly specialised extracellular matrices. Their
discovery started with the difficult task of isolating molecules produced by
cultivated cells or extracted from tissues. The development of molecular biology
techniques has facilitated and accelerated the identification and the
characterisation of new laminin variants making it feasible to identify
full-length polypeptides which have not been purified. Further, genetically
engineered laminin fragments can be generated for studies of their
structure-function relationship, permitting the demonstration that laminins are
involved in multiple interactions with themselves, with other components of the
basal lamina, and with cells. It endows laminins with a central role in the
formation, the architecture, and the stability of basement membranes. In
addition, laminins may both separate and connect different tissues, i.e. the
parenchymal and the interstitial connective tissues. Laminins also provide
adjacent cells with a mechanical scaffold and biological information either
directly by interacting with cell surface components, or indirectly by trapping
growth factors. In doing so they trigger and control cellular functions.
Recently, the structural and biological diversity of the laminins has started to
be elucidated by gene targeting and by the identification of laminin defects in
acquired or inherited human diseases. The consequent phenotypes highlight the
pivotal role of laminins in determining heterogeneity in basement membrane
functions.
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