The role of the extracellular matrix in Kupffer's vesicle formation in zebrafish

An important step in the formation of all epithelial organs is the coordinated polarisation of their constituent cells. One of the factors thought to be crucial for this process is the extracellular matrix (ECM), which provides positional information for cells and directs polarity specification and epithelial cyst formation in 3D culture. However, in vivo evidence for the role of the ECM in epithelial tissue polarisation is scarce. To gain insight in the factors involved in establishing cell polarity during organogenesis, we are studying a group of epithelial cells called the Dorsal Forerunner Cells (DFCs) in zebrafish embryos. These cells migrate as a cluster towards the vegetal pole of the developing embryo, where they involute. During this process they polarise, and make foci that open up to form a ciliated lumen called Kupffer’s vesicle. We find that interfering with the deposition of components of the extracellular matrix, or with the intracellular anchors of the cells to the matrix, impairs the polarisation of the DFC’s and leads to subsequent defects in lumen formation. In addition, we have developed a method to culture the DFCs ex vivo, allowing us to precisely manipulate the extracellular environment. The possibility of combining the genetic study of Kupffer’s vesicle formation in the live embryo with cell biological techniques in organ culture make this system uniquely relevant for studying the role of the ECM in polarisation during organogenesis.