Project Summary
The “brain-eating amoeba” Naegleria fowleri causes a disease with a 97% fatality rate. Current
treatments are not reliable and risk significant side effects, including brain damage. Because cell proliferation is
essential for disease progression, and the microtubule network in Naegleria has evolutionarily diverged from
that in humans, targeting the mitotic spindle is a promising strategy to develop effective therapeutics with
limited side effects. However, we lack key information about the basic cell biological mechanisms that organize
the Naegleria mitotic spindle, hampering progress towards rational therapies. In particular, dynamic
microtubule turnover is critical in other cells for assembling a bipolar spindle, but it is not known to what extent
the Naegleria spindle relies on microtubule dynamics. A major obstacle is that inhibitors that block microtubule
dynamics in other species are ineffective against Naegleria’s divergent tubulins. Further, while microtubule
motor proteins play key roles in assembling spindles from diverse species, the function or even the identity of
microtubule motors within the Naegleria spindle is completely unknown. Lack of knowledge about the
mechanistic contributions of microtubule turnover and molecular motors to Naegleria spindle organization
constrains identifying key proteins and processes to target for antimicrobial development.
This proposal will address this knowledge gap by testing the hypothesis that microtubule dynamics and
molecular motors both contribute to Naegleria spindle organization. To identify the role of microtubule
dynamics, microtubules will be stabilized with a class of inhibitors that was recently shown to block Naegleria
cell division, and the effect on the organization of the spindle will be measured with super-resolution
microscopy. Comparing untreated and drug-treated spindles at different mitotic stages will reveal which stages
require microtubule turnover. To determine the function of molecular motors in the spindle, motor genes
upregulated during cell division will be identified with RNA sequencing of mitotically synchronized Naegleria
cultures. These motors will be knocked down, and phenotypes scored by microscopy. The proposed project
will provide comprehensive training to prepare the applicant for a career as an independent investigator. With
support from a sponsor, who is a Naegleria expert, and a co-sponsor, who has decades of experience studying
cell division, the applicant will learn: new experimental techniques, such as super-resolution microscopy and
high-throughput sequencing; new conceptual approaches, including the biology of microtubules and mitosis;
and career development skills. This proposal will determine the impact of microtubule stabilization on the
Naegleria spindle and will identify the role of spindle associated molecular motors in spindle organization,
providing new targets for future treatments for the devastating disease caused by Naegleria.