Identifying the function of kinesin-13 family members and how they contribute to neuronal development.
Open Access
- Author:
- Long, Melissa Katherine
- Graduate Program:
- Cell and Developmental Biology
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- August 06, 2014
- Committee Members:
- Melissa Rolls, Thesis Advisor/Co-Advisor
Wendy Hanna Rose, Thesis Advisor/Co-Advisor
William O Hancock, Thesis Advisor/Co-Advisor - Keywords:
- kinesin-13
Klp59C
Klp10A
neuronal development
microtubules
cell polarity - Abstract:
- Neurons are highly specialized cells that transmit information over long distances by way of polarized processes known as axons and dendrites. One of the major cell biological differences between axons and dendrites is the arrangement of microtubules. In Drosophila dendritic arborization (da) neurons, which are multipolar neurons with a single axon and many dendrites, dendritic microtubules are minus-end-out and axonal microtubules are plus-end-out (Stone 2008). While microtubule polarity is likely to play a key role in maintaining neuronal polarity, it is not known how a single cell can establish two compartments with completely different arrangements of microtubules. In a screen to identify regulators of microtubule polarity in da neurons, we identified kinesin-13s, which are known to be important for spindle organization in mitosis, as regulators of neuronal microtubules. Kinesin-13s are a family of non-canonical microtubule-based motors that are known to be microtubule depolymerases in mitotic and interphase cells (Mennella 2005); however, there have been very few studies of their roles in neurons. In Drosophila, there are three kinesin-13s. We found that two of these, Klp59C and Klp10A, play important roles in da neurons. Reduction of Klp59C caused severe mixing of microtubule polarity in dendrites as well as dendrite branching defects. No non-microtubule functions were observed. Reduction of Klp10A had a comparably mild effect in dendrites, and instead showed the greatest phenotype in axons, changing both microtubule orientation and overall number of polymerizing microtubule plus ends. We therefore conclude that Klp59C and Klp10A act differentially on dendritic and axonal microtubules; Klp59C is a major regulator of dendritic microtubules and Klp10A is a major regulator of axonal microtubules. Their localized function may be one mechanism that allows neurons to establish different arrangements of microtubules within axons and dendrites. Interestingly, neurons were observed to be especially sensitive to early developmental loss of Klp59C. With genomic deletion of the kinesin-13, microtubule polarity is restored but the number of dynamic plus ends are disrupted. We suggest that, upon loss of Klp59C, neurons use a kinesin-13 independent “bypass pathway” to maintain normal polarized microtubule growth. JNK signaling may play a key role in this bypass pathway. Additional factors, such as microtubule minus end regulators, may also play a role. In the future, we seek to elucidate the molecular players that help to control microtubule polarity in the kinesin-13 bypass pathway.