From cells to organs: building polarized tissue

Abstract

How do animal cells assemble into tissues and organs? A diverse array of tissue structures and shapes can be formed by organizing groups of cells into different polarized arrangements and by coordinating their polarity in space and time. Conserved design principles underlying this diversity are emerging from studies of model organisms and tissues. We discuss how conserved polarity complexes, signalling networks, transcription factors, membrane-trafficking pathways, mechanisms for forming lumens in tubes and other hollow structures, and transitions between different types of polarity, such as between epithelial and mesenchymal cells, are used in similar and iterative manners to build all tissues.The defining feature of metazoa is that their cells are organized into multicellular tissues and organs. Although almost every eukaryotic cell is spatially asymmetric or polarized, polarity must be coordinated in space and time for individual cells to form a tissue 1 . Cell polarity involves the asymmetric organization of most of the physical aspects of the cell, including the cell surface, intracellular organelles and the cytoskeleton 2,3 . Analysis of the polarization of unicellular eukaryotes, such as yeast, has yielded enormous insights into the mechanisms that underlie the polarity of individual cells 3 . Formation of a tissue, however, requires an ensemble cast; the emergent properties of the tissue result from the combined roles of the individual cells that are involved. Accordingly, several biological processes, including cell division, cell death, shape changes, cell migration and differentiation, must be coordinated with the polarity requirements of a tissue to form an organ 4 .Evolutionarily, epithelia are the most archetypal polarized tissues in metazoa, with ~60% of mammalian cell types being of epithelial or epithelial-derived origin 5 . Accordingly, the best studied polarized tissue is the simple epithelium of the mammalian intestine and kidney, the cells of which are columnar in shape (that is, they are taller than they are wide). The apical surfaces of these cells provide the luminal interface and are specialized to regulate the exchange of materials, such as nutrients from the intestine. The lateral surfaces of these cells contact adjacent cells and have specialized junctions and cell-cell adhesion structures 3,6 (FIG. 1a). The basal surfaces of these cells contact the underlying basement membrane, extracellular matrix (ECM) and, ultimately, underlying blood vessels. The basal and lateral surfaces are fairly similar in composition and organization and are often referred to together as the basolateral surface. The apical and basolateral surfaces, however, have very different NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript compositions. In vertebrates, tight junctions (TJs) are found at the apical-most portion of the lateral surfaces, where the TJs form barriers both between the apical and basolateral surfaces and between adjacent cells, limiting paracellular permeability...

Spatiotemporal control of microtubule nucleation and assembly using magnetic nanoparticles

“…First, this study opens the way to the magnetic control of cellular polarization in vivo using nanoparticles 38 . Second, the approach is generic and could be extended to other signalling proteins, such as kinases, that exhibit non-trivial behaviours when they work collectively or are recruited by scaffolding proteins 39 .…”

AmotL2 disrupts apical–basal cell polarity and promotes tumour invasion

“…These include the Par3/Par6/aPKC and Crumbs/Pals1/PATJ proteins that define the apical membrane and Scribble/Lgl/Dlg that promote baso-lateral membrane formation 4 . The evolutionary conserved proteins localize asymmetrically before morphological polarization and mutually antagonize each other 5 . The maintenance of cell polarity is a highly dynamic process as interference with vesicle trafficking proteins such as Rab8 and Rab11 results in loss of already established cellular asymmetry [6][7][8] .…”

Bile acid stimulates hepatocyte polarization through a cAMP-Epac-MEK-LKB1-AMPK pathway

“…Polarization is essential for biliary secretion. The mechanisms of polarization are complex and include cytoskeletal, tight junctional, and intracellular trafficking components (2)(3)(4)(5). Loss of polarity causes bile secretory failure (cholestasis) and liver damage (6).…”