Differentiation of Somatic Cells, Stem Cells and Stem Cell Variants:In VitroModels

Abstract

Because conditions of culture in vitro cannot be identical to those in the living system, cell lines cultured in vitro are referred to as ‘model systems’. Not all cell types are capable of differentiation in vitro . Stem cells are of various types, including embryonic stem cells (ESC), mesenchymal stem cells (MSCs), induced pluripotent stem cells (iPSCs), cancer/leukaemia stem cells (CSCs/LSCs), etc. Procedures for studying differentiation in model systems depend on the type of culture that can be employed. Techniques employed include liquid suspension cultures, monolayer cultures and complex culture systems involving semisolid matrices or liquid overlay methods. Cells derived from various tissues can be maintained in culture known as ‘primary culture’. Only a rare human cell in a culture can undergo changes in its molecular machinery known as ‘immortalisation’ which allow it to propagate indefinitely. Recent developments include systems optimised for stem cell differentiation. Such in vitro culture techniques have applications to the study of differentiation in basic research and clinical applications. Key Concepts: Mammalian cells derived from many tissues, the subject of this article, can propagate outside of the body. Stem cells can differentiate, but provide a reservoir for development of functional cells of various types which is known as ‘lineage expansion’. Stem cells give rise to progenitor cells (PCs) which can differentiate into mature cells, but have a limited repertoire of lineages of differentiation. Mature cells can be induced to have the capabilities of stem cells and PCs by introduction of four or less transcription factors (TFs), for example, Oct4, Sox2, Klf4 and c‐Myc, under defined conditions. The cell environment – other cells, extracellular material – can favour lineage expansion into mature, functional cells and is called a ‘niche’.