The development and maintenance of tissues and organs involves regulated formation and remodeling of the associated connective tissue. Connective tissues are composed of secreted extracellular matrix (ECM) proteins such as Fibronectin and Collagen, and cells bind and synthesize ECM via proteins called Integrins that are positioned on the surface of the cell. Excessive connective tissue formation following heart attack reduces heart function while insufficient ECM assembly can lead to cartilage degeneration. To understand how cells regulate ECM assembly, one needs to study this process in a living organism, and the zebrafish is simple experimental proxy for the human body. This project utilizes methods to genetically alter Integrin and Fibronectin activity and to visualize and measure the movement these proteins in live zebrafish embryos using laser microscopy. Cells also adhere to each other via proteins called Cadherins, and this study includes an investigation as to how cells coordinate binding between cells and between cells and connective tissue. The outcomes of the experiments are expected to shed light on how tissues form and maintain their integrity via connective tissue synthesis. Educationally, this research project involves training for an Associate Research Scientist, a PhD student as well as undergraduate students. The Principal Investigator also mentors a biotechnology class at The Sound School, part of the New Haven Public School system. This high school has extensive aquaculture programs, and the research group at Yale is helping the biotechnology students utilize zebrafish as part the course research project.
Animal tissues are composed of cells and a meshwork of proteins called the extracellular matrix (ECM). The ECM is synthesized and continually remodeled by cells during embryonic development, adult tissue maintenance and wound healing. Cells also have receptors that sense the composition of the ECM and can relay signals to control gene expression and cell behavior. We use zebrafish as a simple model system to understand how cells and ECM coalesce to form tissues during development. We specifically examined the somitic mesoderm which gives rise to the vertebral column and muscle of the adult. We found that proteins that hold cells together, called Cadherins, regulate ECM production via two mechanisms. Cadherins repress ECM production within the tissue, thus preventing inappropriate fibrosis. However, on the surface of the tissue, Cadherins promote ECM production. These two activities create a clear pattern in cross-sections of the tissue whereby ECM coats the surface of the tissue but is missing from the internal tissue. This normal pattern of tissue assembly helps drive the elongation of the vertebrate trunk. As this tissue develops further it is partitioned into repetitive units called somites. This repetitive pattern lays the foundation for the vertebral column, and the early pattern is stabilized by repetitive stripes of ECM synthesis. We characterized the process of ECM synthesis. This study revealed novel mechanisms regulating ECM synthesis during vertebrate development. The study has implications for controlling ECM synthesis in artificial, engineered tissues and in understanding mechanisms that may be mis-regulated in diseases associated with excessive ECM production.
