In order to regenerate a functional tissue following an injury or to replace a tissue destroyed by the consequences of a pathological disease, the differentiation of stem or progenitor cells must be accompanied by effective strategies to promote tissue morphogenesis. This proposal investigates the mechanisms that guide cell and tissue morphogenesis with the ultimate goal of applying the results to instruct the recapitulation of normal developmental processes in tissue repair and regeneration. The model for these studies is the embryonic lens, ideal for investigating the molecular mechanisms of morphogenesis because its cytoarchitecture defines its function. Morphogenesis of the lens must be precisely executed and its structure maintained in order for it to perform its function of focusing images on the retina. This proposal aims to discover the mechanisms responsible for the two principal morphogenetic events of lens development: 1) the elongation/convergent extension mechanism that establishes the highly elongated lens fiber cell phenotype and 2) the mechanism by which neighboring lens fiber cells are organized into an exact hexagonally packed cellular array. The studies are focused on N-cadherin junctions and their dynamic interactions with different cytoskeletal elements as key modulators of cell and tissue morphogenesis during development. For these studies we developed a number of important culture models including: 1) ex vivo mock cataract surgery cultures where it is possible to examine the response of the lens epithelium to a clinically relevant wounding in its native microenvironment and its ability to regenerate lens-like tissue, 2) primary cultures of lens epithelial cells that differentiate in culture to form mini-lens structures, and 3) epithelial explants where fiber cells both elongate and organize into a highly ordered tissue-like structure;in addition to N-cadherin fiber cell-specific knockouts. These models provide powerful tools with which to examine N-cadherin as a focal point where actin microfilaments, microtubules and intermediate filaments coordinate their function to direct lens morphogenesis with the following questions: What are the mechanisms that drive fiber cell elongation? How do neighboring lens fiber cells interact to form a functional structure? What regulates the organization of fiber cells into a hexagonal array? What stabilizes this unique cytoarchitecture of the lens? How do lens epithelial cells remodel their N-cadherin/cytoskeletal interactions for wound healing and tissue regeneration? The results of these proposed studies are expected to identify the underlying mechanisms responsible for establishing and maintaining cell and tissue cytoarchitecture, knowledge of which would provide substantive targets for guiding effective tissue regeneration in vivo.
The studies in this proposal examine the importance of dynamic interactions between N-cadherin junctions and the cytoskeleton in directing both cell and tissue morphogenesis, focusing on mechanisms that regulate the morphogenetic movement of cells in development and how these cells become arranged into highly ordered structures required for tissue function. This approach addresses one of the greatest challenges in Regenerative Medicine, how following an injury or in response to tissue damage resulting from a pathological disease, reparative cells can be induced to undergo morphogenetic differentiation and interact with their near neighbors to form a new tissue. Our studies are expected to provide functional targets for promoting tissue regeneration.
|Basu, Subhasree; Rajakaruna, Suren; Reyes, Beverly et al. (2014) Suppression of MAPK/JNK-MTORC1 signaling leads to premature loss of organelles and nuclei by autophagy during terminal differentiation of lens fiber cells. Autophagy 10:1193-211|
|Menko, A S; Bleaken, B M; Libowitz, A A et al. (2014) A central role for vimentin in regulating repair function during healing of the lens epithelium. Mol Biol Cell 25:776-90|
|Menko, A S; Bleaken, B M; Walker, J L (2014) Regional-specific alterations in cell-cell junctions, cytoskeletal networks and myosin-mediated mechanical cues coordinate collectivity of movement of epithelial cells in response to injury. Exp Cell Res 322:133-48|
|Leonard, Michelle; Zhang, Liping; Bleaken, Brigid M et al. (2013) Distinct roles for N-Cadherin linked c-Src and fyn kinases in lens development. Dev Dyn 242:469-84|
|Basu, Subhasree; Rajakaruna, Suren; Menko, A Sue (2012) Insulin-like growth factor receptor-1 and nuclear factor *B are crucial survival signals that regulate caspase-3-mediated lens epithelial cell differentiation initiation. J Biol Chem 287:8384-97|
|Leonard, Michelle; Zhang, Liping; Zhai, Ni et al. (2011) Modulation of N-cadherin junctions and their role as epicenters of differentiation-specific actin regulation in the developing lens. Dev Biol 349:363-77|
|Menko, A Sue; Andley, Usha P (2010) ?A-Crystallin associates with ?6 integrin receptor complexes and regulates cellular signaling. Exp Eye Res 91:640-51|
|Walker, Janice L; Zhai, Ni; Zhang, Liping et al. (2010) Unique precursors for the mesenchymal cells involved in injury response and fibrosis. Proc Natl Acad Sci U S A 107:13730-5|
|Walker, Janice; Menko, A Sue (2009) Integrins in lens development and disease. Exp Eye Res 88:216-25|
|Leonard, Michelle; Chan, Yim; Menko, A Sue (2008) Identification of a novel intermediate filament-linked N-cadherin/gamma-catenin complex involved in the establishment of the cytoarchitecture of differentiated lens fiber cells. Dev Biol 319:298-308|
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