Tackling nervous movements: Migration of Q neuroblasts and their descendents in Caenorhabditis elegans

Abstract

Cell migration is a crucial process in animal development and defective cell migration can lead to developmental abnormalities and disease. C.elegans has been widely used as a model organism to study the control of cellular movements in vivo. Particularly, the migration of two neuronal stem cells, the left and right Q neuroblasts, and their descendents has been proven to be an excellent model system to study the developmental control of cell migration. At hatching, the left (QL) and right (QR) Q neuroblasts are located in the lateral row of hypodermal seam cells. In the first larval stage both Q neuroblasts delineate from the row of seam cells, migrate a short distance and then undergo cell division. Q daughter cells continue to migrate along the anteroposterior axis of the animal. At hatching both Q neuroblasts are similar in shape and morphology. Interestingly, the QR neuroblast and its descendents migrate anteriorly while QL and its descendents migrate posteriorly. Extensive genetic analysis revealed many insights into the genetic control of this asymmetric process. A highly conserved canonical Wnt/ß-catenin pathway regulates the posterior migration of QL descendent cells while a non-canonical Wnt signaling pathway controls anterior migration of QR daughter cells. Furthermore, it was shown that Homeobox genes were also involved in the control of Q cell migration. For example, the Antennapedia-like gene mab-5 is both necessary and sufficient for posterior migration of QL daughter cells. It is widely accepted that cell migration requires dramatic reorganizations of the actin cytoskeleton. Indeed, many genes that were shown to be involved in regulating actin reorganizations were also implicated in the control of Q cell migration. Finally, in determining the direction of migration, the initial short-range migration of Q neuroblasts was shown to be critical since mutations affecting this process were also shown to result in aberrant migration of Q neuroblast descendents. Here, I will give an overview of the various control mechanisms known to date that are involved in the regulation of Q cell migration.