Date of Degree
PhD (Doctor of Philosophy)
Yuriy M. Usachev
Ca2+-dependent transcription is a fundamental process by which neurons translate activation experience into cellular level adaptations. The nuclear factor of activated T-cells (NFAT) family of proteins comprise four Ca2+/CaN-dependent transcription factors that are widely expressed throughout virtually all tissues. Within neurons, NFAT dependent signaling is critical for axonal development, regulation of synapse number and efficacy, and survival. Furthermore, NFAT is implicated in activity dependent regulation of genes involved in synaptic transmission, learning and memory, mood, and pain sensation. NFAT is activated upon elevations in intracellular Ca2+, which results in CaN -dependent dephosphorylation of multiple serine residues within an N-terminal regulatory region. NFAT dephosphorylation permits NFAT translocation to the nucleus, where it can regulate gene expression, frequently co-operatively with other transcription factors, including AP-1 and MEF2. NFAT activation is opposed or terminated by several kinases, including CK1 and GSK3. Despite the importance of NFAT proteins as regulators of Ca2+-dependent transcription, little is known about the regulation and function of specific NFAT isoforms within neurons.
In Aim 1 of this thesis I characterized the differential activation of NFATc3 and NFATc4 in DRG neurons. While NFATc3 rapidly translocates the nucleus upon Ca2+-influx through voltage-gated calcium channels, NFATc4 remained remarkably intransient. Modular substitution of NFATc3 regulatory elements increased the rate or retention of NFATc4, whereas converse substitutions of NFATc4 regulatory elements into NFATc3 decreased NFATc3 nuclear translocation. The activation of NFATc4 appears to be inhibited by preferential phosphorylation by kinases, such as GSK3, which counteract CaN-dependent dephosphorylation. In Aim 2 I investigated the role of NFATc3 in hippocampal neurons. While the majority of NFAT reports in neurons have focused on NFATc4, my data suggest that NFATc3 is the predominantly expressed isoform in hippocampal neurons and is critical for depolarization-induced NFAT target gene expression. I further characterized NFATc3 KO mice in a battery of behavioral assays to test whether loss of NFATc3 expression would affect the baseline anxiety/depression state of the animal, or if NFATc3 was critical for learning and memory. Taken together, my data suggest that NFATc3 is important for NFAT-dependent gene expression in central and peripheral neurons and that distinct regulation of NFAT isoforms within neurons may underlie isoform-specific effects on gene expression.
Calcium, Neuron, NFAT, Transcription
2, xv, 90 pages
Includes bibliographical references (pages 81-90).
Copyright 2011 Jason D. Ulrich