[Stem cell-fed maturational lineages and epithelial organogenesis]

Stem cell-fed maturational lineages have long known to exist in rapidly proliferating tissues such as bone marrow, gut and epidermis. Recent studies support the hypothesis that stem cell-fed maturational lineages occur also in quiescent tissues. In this review is presented evidence for this hypothesis using liver as one of the model systems representative of quiescent tissues. In addition, studies are summarized indicating that control of growth and tissue-specific gene expression is dependent on maturational lineage mechanisms operating dynamically and sometimes synergistically in combination with gradients of regulatory signals that include hormones, growth factors and extracellular matrix components. Tissue engineering for optimal maintenance of cells and tissues ex vivo and for the development of bioartificial organs will depend on use of cells at specific maturational lineage stages, seeding them onto substrata of specific mixtures of extracellular matrix components, and culturing them in hormonally and nutritionally defined media.