Dissecting the Signaling and Cellular Mechanisms of Notochord Patterning In Zebrafish

ABSTRACT The vertebral column or spine is a segmented support structure composed of alternating vertebrae and intervertebral domains. In zebrafish, the notochord sheath segments into cartilage-like (col9a2+) and mineralizing (entpd5a+) domains in a Notch dependent process. Osteoblasts are then specifically recruited to the mineralized domains, producing highly regular and symmetrical vertebrae. Notochord segmentation occurs sequentially along the anterior-posterior (AP) axis, much like somite formation, which takes place alongside the notochord several days earlier in development. However, unlike somitogenesis, notochord segmentation is not associated with oscillations in Notch signaling, suggesting that different signaling mechanisms control notochord and somite segmentation. The goal of this proposal is to integrate genetics, cell biology, and quantitative imaging methods to investigate the signaling processes that drive notochord segmentation. Specifically, we will elucidate both the clock mechanism that times the addition of new mineralizing segments at a rate of about 2-3 segments per day and the mechanisms that ensure that segments form in the correct spatial location. Finally, we will investigate how after segments are formed their boundaries are sharpened via self-organizing cellular and mechanical interactions. The mechanisms elucidated by our studies will build a new paradigm of periodic pattern formation. Our studies will also help understand the formation and organization of gene expression domains within biological tubes, which may underlie the regionalization and specialization of functional domains within organs.