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Title

Identification of FGF14 as an Essential Regulatory Subunit of Voltage-Gated Sodium Channels

Date of Award

Spring 5-15-2015

Author's School

Graduate School of Arts and Sciences

Author's Department

Biology & Biomedical Sciences (Neurosciences)

Degree Name

Doctor of Philosophy (PhD)

Degree Type

Dissertation

Abstract

Fibroblast growth factor 14 (FGF14) is an intracellular protein that interacts with voltage-gated sodium (Nav) channels and regulates their voltage-dependent properties. Mutation or loss of FGF14 in mice and humans results in ataxia, a neurological disorder characterized by loss of movement control, and attenuates the excitability of cerebellar Purkinje and granule neurons. However, the mechanism(s) underlying FGF14 control of neuronal excitability and motor coordination are not fully understood.

FGF14 is highly expressed in the developing and adult nervous systems. To differentiate between developmental and homeostatic functions of FGF14, a viral system to knockdown or restore FGF14 levels in mature neurons in vivo was developed. Electrophysiological methods were used to assess the firing properties of virally transduced cells. Knockdown of FGF14 in mature Purkinje neurons resulted in silencing of spontaneous repetitive action potential firing and impaired motor coordination in mice, suggesting that neuronal excitability and motor behavior requires the presence of FGF14 in mature neurons. Additionally, following membrane hyperpolarization, repetitive firing could be restored to Purkinje neurons with acute knockdown of FGF14 and neurons from FGF14 knockout mice. These results are consistent with FGF14 regulation of the voltage-dependence of Nav channel inactivation and suggest that FGF14 is an essential determinant of neuronal excitability and motor coordination in adult mice.

In living cells, proteins commonly interact with multiple binding partners. However, the only known binding partners for FGF14 are Nav -subunits. To determine if FGF14 interacts with proteins other than Nav -subunits in cerebellum, a proteomic approach was used. Interestingly, the vast majority of proteins identified in this assay were Nav -subunits or proteins that were previously known to interact with Nav -subunits. The ability of FGF14 to interact with Nav -subunits, the cell-autonomous regulation of Nav activity in mature neurons in vivo, and the ability to modulate the biophysical properties of Nav channels, suggests that FGF14 is a functional regulatory subunit of voltage-gated sodium channels.

Language

English (en)

Chair and Committee

David M Ornitz

Committee Members

Jeanne M Nerbonne, Kelvin Yamada, Andreas Burkhalter, Valeria Cavalli, Philip Stahl

Comments

Permanent URL: https://doi.org/10.7936/K7DV1H22

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