How cells assemble into complex arrangements that enable the specialized function of a tissue is a fundamental question in biology. For proper tissue assembly to occur, self-organization properties of cells must be coordinated with long-range signals that organize a tissue into the correct orientation, or polarity, within the body. Despite extensive research using genetic model organisms, the identity of these long-range polarizing signals remains unknown. As the field of regenerative medicine advances towards generating any cell type from multipotent stem cells, the discovery of long-range signals required for the proper three-dimensional organization of adult tissues will be essential. Tissue polarity or planar cell polarity (PCP) refers to the collective polarization of cells globally alon the epithelial plane, and genetic disruption of PCP results in severe developmental disorders such as neural tube defects, cystic kidney disease, hearing loss, ciliopathies, and heart defects. While a core set of PCP genes conserved across species is responsible for communicating directional signals from cell to cell over short distances, what biases polarity globally toward a particular direction over long distances is unknown. One possibility is that a secreted or extracellular signal expressed in a concentration gradient across a tissue could provide a global polarizing cue. Alternatively, physical interactions between polarizing cells and their underlying substratum, or mechanical forces exerted during morphogenesis could lead to global alignment of cell polarity. Identifying the source of long-range polarizing signals will solve a long-standin problem in the polarity field and profoundly impact the field of tissue engineering. The goal of this proposal is to identify the molecular and physical cues that orchestrate long-range tissue polarity and to decipher how cells asymmetrically reorganize in response to these directional cues. Using mammalian skin, one of the most strikingly polarized tissues in nature, a combination of genomic, proteomic, imaging, genetic, and biophysical approaches will be employed to: (1) Determine how graded directional cues bias tissue polarity in the epidermis; (2) Decipher the role of external forces in establishing long-range tissue polarity; and (3) Elucidate the mechanisms by which cells polarize in response to directional cues. Identifying the instructive cues that direct the proper three-dimensional organization of a tissue is the next step towards engineering functional organs in vitro. Ultimately, identification of the pathways controlling normal tissue development will help to understand how misregulation of these pathways leads to developmental defects and adult proliferative disorders.
Understanding how tissues are assembled and organized into complex three dimensional arrangements will directly impact the field of tissue engineering and regenerative medicine. Now that patient-specific, multipotent stem cells can be derived and differentiated towards many different cell types, identifying the instructive cues that direct the proper three-dimensional organization of a tissue is the next step towards engineering functional organs in vitro. Ultimately, identification of the pathways controlling normal tissue development will help to understand how misregulation of these pathways leads to developmental defects and adult proliferative disorders.
