| Abstract No.: | A-A1018 |
| Country: | Canada |
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| Title: | DENDRITIC GROWTH CONES IMAGED LIVE IN THEIR NATIVE ENVIRONMENT |
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| Authors/Affiliations: | 1 Sharmin Hossain*; 1 Kurt Haas;
1 University of British Columbia, Vancouver, BC, Canada
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| Content: | Objective: Connecting appropriate pre- and postsynaptic components to achieve proper circuit formation in the developing brain is critical to normal brain function. Because axons must travel long distances to reach postsynaptic targets, specialized organelles called growth cones are employed to sense directional molecular cues present in the extracellular environment. Like axons, dendrites require mechanisms for guided growth, for they must also extend into appropriate regions, or distinct lamina, to localize with their postsynaptic counterparts. The predominant theory underlying dendritic arborization is synaptic stabilization of interstitial filopodia and the filopodia’s subsequent elongation. This is in contrast to net extension of branches guided by terminal dendritic growth cones. Although axonal growth cones have been studied extensively, in vivo examination and characterization of dendritic growth cones have remained elusive due to technical challenges in staining embryonic tissue and imaging in the developing brain. Here, we have developed in vivo time-lapse imaging techniques specifically designed to capture and characterize dendritic growth cones of individual newly differentiated neurons and their impact on dendritic arbour growth within the unanesthetized and intact developing brain.
Materials and Methods: We used single-cell electroporation to transfect and label individual neurons within the optic tectum of the transparent albino Xenopus laevis tadpole , and subsequent in vivo two-photon time-lapse imaging to visualize dendritic growth cones in the unanesthetized brain.
Result: In vivo time-lapse imaging of growing tectal neurons revealed a high incidence of dendritic growth cones, whose growth greatly contributed to arbour elaboration. Each primary dendritic branch is tipped by a dendritic growth cone with filopodia and lamellipodia. Dendritic growth cone-mediated branch growth was highly dynamic, involving periods of rapid extension and retraction. Furthermore, we find that new interstitial filopodia can develop growth cones, and that expression of growth cones on interstitial filopodia increases their lifetimes.
Conclusion: Our findings indicate that dendritic growth cones are common in developing neurons during dendritic arbour elaboration. Dendritic growth cones occur both at tips of primary branches as well as at the tips of maturing and extending interstitial filopodia. These findings indicate that dendritic growth cone-mediated growth is a major component and mechanism of dendritic arbour elaboration.
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