1. Mechanisms and principles of branch pattern formation of dendrites
Dendrite morphologies of CNS neurons are highly diverse, depending on cell type and function. The architecture of dendritic arbors critically affects the integration of neuronal inputs and propagation of chemical signals, and hence determines the connectivity of neurons. The question of how neurons acquire their appropriate morphology is a major issue in the study of neuronal development. In spite of the increasing number of molecular signals that have been identified as regulators of dendritic arborization patterns, the precise function of each molecule in the specific steps of branch dynamics largely remains elusive.
Cerebellar Purkinje cells develop intricate dendritic arbors with minimal branch overlap. We developed a method of long-term time-lapse observation of dendritic branch dynamics in growing Purkinje cells in culture. Using a combinatorial approach with quantitative image analyses and computer-aided simulation, we identified the fundamental rules of growth dynamics that govern the construction of the characteristic dendritic patterns in Purkinje cells (Fujishima et al. 2012).
We have successfully visualized the dynamic motility of organelles, including the nucleus, centrosomes, mitochondria and Golgi apparatus, in developing neurons (Wu et al, Fukumitsu et al. 2015). We recently found that developing neurons actively transport mitochondria into growing dendrites to fuel ATP energy necessary for arbor formation. We also found that dendrites sense local ATP levels and tune their growth rates by slowing actin turnover to avoid overconsumption of the ATP necessary for cellular metabolism.
Neuronal dendrites tend to extend radially within the brain to form perpendicular contacts with the afferent axon fibers, which run horizontally. Such organization has been shown to maximize the number of potential anatomical connections, yet the mechanism of how neurons orient dendrites perpendicular to afferent axons is unknown. Using electrospun carbon nanofibers as an artificial scaffold, we cultivated cerebellar neurons and reproduced the perpendicular contact observed between Purkinje cell dendrites and the aligned granule cell axons in culture dishes. Utilizing this system, we seek to identify the molecular and mechanical bases underlying axon-dendrite wiring topology.