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Volume 16, Number 19, Issue of October 1, 1996 pp. 6065-6078
Copyright ©1996 Society for Neuroscience

Microtubule Assembly in Growing Dendrites

Received June 3, 1996; revised July 11, 1996; accepted July 15, 1996.

Jun Wang¹, Wenqian Yu², Peter W. Baas², and Mark M. Black¹

¹ Department of Anatomy and Cell Biology, Temple University School of Medicine, Philadelphia, Pennsylvania 19140, and ² Department of Anatomy, University of Wisconsin Medical School, Madison, Wisconsin 53706

Dendritic microtubules (MTs) are nonuniform with respect to polarity orientation, with roughly equal proportions having a plus-end-distal or minus-end-distal orientation. In the present studies, we have microinjected biotin-labeled tubulin (Bt-tub) into cultured sympathetic neurons extending dendrites to explore the contribution of MT assembly to the elaboration and maintenance of the dendritic MT array. Within minutes of injecting Bt-tub, an enormous number of MTs were seen emanating from a point source in the cell body. Over time, this pattern changed such that by 120 min after injection, biotinylated MTs no longer emanated from a discrete site, but were distributed over a broad region that extended from the cell body into the dendrites. The observation that biotinylated MTs emanate from a point source in the soma at relatively short times after injection, but not at longer times, suggests that they undergo a redistribution subsequent to their initial nucleation rather than a simple radial expansion from the somal nucleation site. Bt-tub assembly also occurred in dendrites but, unlike in the cell body, assembly was dispersed throughout the dendrite rather than emanating from a discrete site. Immunoelectron microscopic analyses revealed that assembly in dendrites reflected the addition of Bt-tub onto the ends of both plus-end-distal and minus-end-distal MTs that existed in the cell at the time of injection. The time course of Bt-tub appearance in dendritic MTs suggested an average half-life of ~76 min for these MTs. We discuss these observations in the context of a model for generating the MT array of dendrites that combines both MT transport and MT assembly.

Key words: cultured sympathetic neurons; microtubules; microtubule turnover; dendrites; microinjection; biotin-tubulin

This article has been cited by other articles:

				N. Kobayashi, J. Reiser, W. Kriz, R. Kuriyama, and P. Mundel Nonuniform Microtubular Polarity Established by CHO1/MKLP1 Motor Protein Is Necessary for Process Formation of Podocytes J. Cell Biol., December 28, 1998; 143(7): 1961 - 1970. [Abstract] [Full Text] [PDF]

				T. Slaughter, J. Wang, and M. M. Black Microtubule Transport from the Cell Body into the Axons of Growing Neurons J. Neurosci., August 1, 1997; 17(15): 5807 - 5819. [Abstract] [Full Text] [PDF]

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