Dynamic morphometrics reveals contributions of dendritic growth cones and filopodia to dendritogenesis in the intact and awake embryonic brain

Abstract

Using in vivo rapid and long-interval two-photon time-lapse imaging of brain neuronal growth within the intact and unanesthetized Xenopus laevis tadpole, we characterize dynamic dendritic growth behaviors of filopodia, branches, and dendritic growth cones (DGCs), and analyze their contribution to persistent arbor morphology. The maturational progression of dynamic dendritogenesis was captured by short-term, 5 min interval, imaging for 1 h every day for 5 days, and the contribution of short-term growth to persistent structure was captured by imaging at 5 min intervals for 5 h, and at 2 h intervals for 10 h during the height of arbor growth. We find that filopodia and branch stability increases with neuronal maturation, and while the majority of dendritic filopodia rapidly retract, 3% to 7% of interstitial filopodia transition into persistent branches with lifetimes greater than 90 min. Here, we provide the first characterization of DGC dynamics, including morphology and behavior, in the intact and awake developing vertebrate brain. We find that DGCs occur on all growing branches indicating an essential role in branch elongation, and that DGC morphology correlates with dendritic branch growth behavior and varies with maturation. These results demonstrate that dendritogenesis involves a remarkable amount of continuous remodeling, with distinct roles for filopodia and DGCs across neuronal maturation. © 2011 Wiley Periodicals, Inc. Develop Neurobiol 72: 615-627, 2012.