CRC 629 B12 - Chemotactic gradient formation in zebrafish

Basic data for this project

Description

Cell migration is essential during embryogenesis (e.g. for organ development and tissue organization) and in adult life (e.g. for tissue repair and fighting infections). Cell migration is often guided by secreted molecules that form a gradient within the tissue. Such gradients provide the cells with directional information, thereby dictating the migration path. To study the molecular mechanisms controlling cell migration in the context of the live embryo, we are exploring the process of germ cell migration in zebrafish. The translucent zebrafish embryo and specific labeling of the migrating cells with fluorescent proteins allow relatively easy analysis of the process. We have identified the molecule that serves as the guidance cue for the migrating cells as well as its receptor that is expressed by the germ cells (the chemokine SDF-1 and its 7-transmembrane receptor CXCR4 respectively). In embryos lacking the function of either one of these molecules, the germ cells are migrating non-directionally and fail to reach their target. Interestingly, we have identified another SDF-1 receptor termed CXCR7, whose function is excreted in the surrounding tissue rather than in the germ cells themselves. We found that CXCR7 is a non-signaling receptor whose function is important for removing SDF-1 from the environment by internalizing it and directing it to degradation. This function, which eliminates excess of SDF-1 is essential for proper generation of the chemotactic gradient. Indeed, in embryos lacking CXCR7 function the germ cells do not migrate due to abnormally high SDF-1 levels in the tissue. Specific objectives: The project is aimed at determining the molecular basis for the difference between CXCR4 and CXCR7 with respect to their ability to bind SDF-1 at a very high affinity and target it to lysosomes (for CXCR7), or induce directional cell migration (for CXCR4). To this end we will examine the function of chimeras of the two receptors thereby pinpointing the amino acids responsible for each of these features. We will then examine the mechanisms by which these protein domains perform their task by identifying other proteins that bind those sequences and study their function in the cell.