Title: KIF1A dynamically colocalizes with syt-IV and invades dendritic spines along microtubules.
Legend: (a) eGFP-KIF1A colocalizes with mCherry-syt-IV in the dendritic shaft and moves together over time as detected in time-lapse images and in kymographs (scale bar, 5 mm). (b) Kymographs demonstrating that KIF1A (green arrows) does not colocalize with mitochondria (red arrow) in the dendritic shaft. (c) KIF1A colocalizes with syt-IV significantly more (79.4±3.8%) than with mitochondria (19.0±2.4%) in the dendritic shaft (P = 0.0009, n = 8, 7). (d) mCherry-syt-IV (green) invades dendritic spines (outlined in yellow from cyan fluorescent protein (CFP) volume fill) simultaneously with eGFP-KIF1A (magenta) for 30 s before both molecules disappear together (scale bar, 1 mm). (e) tdTomato-KIF1A (magenta) invades a dendritic spine (outlined in yellow) during a MT invasion (eGFP-tubulin, green; scale bar, 1 micron).
Citation: McVicker, D.P., A.M. Awe, K.E. Richters, R.L. Wilson, D.A. Cowdrey, X. Hu, E.R. Chapman and E.W. Dent (2016). Transport of a kinesin-cargo pair along microtubules into dendritic spines undergoing synaptic plasticity. Nature Communications, 7:12741. doi: 10.1038/ncomms12741.
Abstract: Synaptic plasticity often involves changes in the structure and composition of dendritic spines. Vesicular cargos and organelles enter spines either by exocytosing in the dendrite shaft and diffusing into spines or through a kinesin to myosin hand-off at the base of spines. Here we present evidence for microtubule (MT)-based targeting of a specific motor/cargo pair directly into hippocampal dendritic spines. During transient MT polymerization into spines, the kinesin KIF1A and an associated cargo, synaptotagmin-IV (syt-IV), are trafficked in unison along MTs into spines. This trafficking into selected spines is activity-dependent and results in exocytosis of syt-IV-containing vesicles in the spine head. Surprisingly, knockdown of KIF1A causes frequent fusion of syt-IV-containing vesicles throughout the dendritic shaft and diffusion into spines. Taken together, these findings suggest a mechanism for targeting dendritic cargo directly into spines during synaptic plasticity and indicate that MT-bound kinesins prevent unregulated fusion by sequestering vesicular cargo to MTs.
About the Lab: The Dent Lab is interested in understanding how the central nervous system (CNS) develops and functions at the cellular level. Nervous system structure and function is highly dependent on the cytoskeleton. In the CNS, the cytoskeleton is comprised of three polymer systems: actin filaments, microtubules and neurofilaments. The lab’s main focus is understanding how microtubules and actin filaments interact in space and time during important morphological events in neuronal development and adulthood. The lab’s working hypothesis is that many of the same cytoskeletal dynamics that are key for neuritogenesis and axon guidance are recapitulated at later times in development, such as during dendritic spine formation/plasticity. To study these dynamic events, the lab uses several forms of high-resolution, time-lapse microscopy, such as total internal reflection fluorescence microscopy (TIRFM), wide-field microscopy, and confocal imaging. They have recently discovered that microtubules remain dynamic throughout the life of CNS neurons and specifically target small protrusions on dendrites termed spines. These spines are the sites of contact with presynaptic axons and their activity-induced morphological changes are likely to underlie memory formation. Notably, microtubule invasion of spines is regulated by neuronal activity and may be important for spine maintenance and plasticity. They are currently studying cytoskeletal dynamics in both developing and adult mouse CNS tissue, utilizing transfected hippocampal neurons in culture and in hippocampal slices. They are also collaborating with groups in both biomedical engineering and physics to determine how neurons respond to gradients of guidance cues and how micropatterning substrates affect neurite outgrowth.