The Development of Microtubule Polarity and Organelle Localization in the Dendrites of Drosophila Neurons
Open Access
- Author:
- Hill, Sarah Elizabeth
- Area of Honors:
- Biochemistry and Molecular Biology
- Degree:
- Bachelor of Science
- Document Type:
- Thesis
- Thesis Supervisors:
- Melissa Rolls, Thesis Supervisor
Joseph C. Reese, Thesis Honors Advisor
Dr. Wendy Hanna-Rose, Faculty Reader - Keywords:
- Drosophila
microtubules
polarity
dendrites
ribosomes
mitochondria
Apc2
neuron - Abstract:
- Microtubule polarity is highly organized in neurons, with different orientations in the axon and dendrites. Differences in polarity effect neuronal function, because polarized microtubules transport a variety of cargo throughout the neuron. Dendrites are of particular interest, because while axons have plus-end-out microtubule orientation conserved across species, dendritic microtubule orientation is more varied. While mature Drosophila dendrites have uniform microtubule polarity with minus ends distal to the cell body, young embryos resemble mammalian cells with mixed polarity in dendrites. We seek to understand when this change to uniform polarity occurs in Drosophila and if uniform minus-end-out microtubule polarity is necessary for characteristic localizations of organelles to dendrites. This investigation was done using confocal microscopy to visualize embryos and larvae expressing EB1-GFP, which is a plus-end microtubule binding protein. By tracking EB1-GFP binding to dynamically growing microtubule ends, we were able to assay microtubule polarity. The results showed that change in polarity occurs gradually. While young embryos had mixed polarity, older embryos and young larvae had ~70% minus-end-out microtubule polarity. It was not until the larvae were several days old, however, that mature uniform minus-end-out polarity was observed. Next, mitochondrial, ribosomal, and Apc2 localizations were traced in developing dendrites in order to establish whether or not mature localizations could occur in dendrites with mixed microtubule polarity. This was also done using fluorescently tagged constructs. The percentage of branch points occupied was quantitated. We expected to see a difference between the young embryos and the mature larvae, since microtubule polarity changes over time and microtubules are used to transport organelles throughout the dendrites. In general, we saw localization to branch points occurring early on in development, before minus-end-out microtubule polarity emerged. This indicates that mature microtubule polarity is not necessary for characteristic localization of dendritic organelles.