Date of Completion
Dendrite, Spine, Kalirin, Cocaine, NMDA, Morphology, Addiction, Phosphorylation
Field of Study
Kalirin-7 (Kal7) is a Rho-guanine nucleotide exchange factor localized to the post-synaptic density (PSD) of neurons in the forebrain. For several years, Kal7 has been known to be an important regulator of dendritic spine formation and stabilization in cultured neurons. However, the functional consequences of these morphological changes remained largely unexplored. A transgenic mouse with a constitutive genetic deletion of Kal7 (Kal7KO) was developed and characterized. Initial studies on this mouse showed that Kal7 was essential for normal dendritic spine formation in the hippocampus and hippocampal long-term potentiation. Additionally, Kal7KO mice displayed decreased anxiety-like behavior and fear conditioning, while exhibiting normal behavior in other hippocampal-dependent learning tasks. Biochemical characterization of these mice showed that Kal7KO caused a compensatory increase in other splice variants of Kalirin, and decreased PSD levels of the NR2B subunit of the NMDA receptor. Following this initial characterization, Kal7KO mice were examined in models of cocaine addiction. Kal7KO mice exhibited increased locomotor sensitivity to cocaine, but showed decreased preference for cocaine in a conditioned place preference assay. While wild-type mice exhibited an increase in dendritic spine density in the nucleus accumbens following cocaine treatments, Kal7KO mice did not. Hence, we looked more closely at the decrease in NR2B levels in Kal7KO mice. We saw specific decreases in NR2B currents and cell surface localization in the Kal7KO. Biochemical studies revealed a direct interaction between Kal7 and NR2B. Inhibition of NR2B currents prior to fear or cocaine conditioning caused wild-type mice to phenocopy Kal7KO mice, while leaving the Kal7KO unaffected. This suggests that decreases in NR2B mediated currents account for behavioral abnormalities seen in Kal7KO mice. Finally, we used mass spectrometry to identify >30 sites of phosphorylation in Kal7 isolated from mouse brain and transfected cells. Phosphorylation sites for a number of kinases known to be crucial for normal synaptic plasticity were identified. These studies identify Kal7 as a critical component of morphological response and NMDA receptor function in dendritic spines, consistent with its essential role in normal behavioral adaptations.
Kiraly, Drew D., "Characterization of the Rho-GEF Kalirin-7 in the Mouse Brain: Evidence for a Role in Learning and Addictive-Like Behaviors, as Well as Neuronal Morphology and NMDA Receptor Signaling." (2013). Doctoral Dissertations. 43.