The Role of SRGAP2 in Modulating Synaptic Dynamics in Adult Sensory Cortex

Human brain evolution granted us cognitive and behavioral capabilities that are unique amongst animals. SRGAP2 is a gene that was specifically duplicated in the human lineage and plays roles in the regulation of cortical development and synapse dynamics. As paralogs of one of the few known genes that regulates excitatory and inhibitory synapses concurrently, the duplications of SRGAP2 were well-positioned during human evolution to gain novel functions leading to the cognitive and behavioral phenotypes exhibited in humans. SRGAP2C, a human-specific paralog of the ancestral SRGAP2 gene, inhibits every known function of SRGAP2 and induces a phenotype similar to SRGAP2 knockdown. This induces neoteny in the maturation of synapses in mice, allowing us to study a putatively “human-like” phenotype in the mouse brain. While studies have been conducted on the effects of SRGAP2 manipulation in juvenile and young adult mice, its effects on older mice has yet to be determined. In this dissertation, we perform longitudinal imaging experiments to determine the effects of SRGAP2 manipulation in the cortex of adult mice. In Chapter 3, we first examine the effects of SRGAP2 knockdown on the spine dynamics on apical dendrites of layer 5 pyramidal cells in the barrel cortex of adult mice, determining how it regulates spine density, turnover, and survival at baseline and in response to sensory deprivation. In Chapter 4, we study how SRGAP2 knockdown affects the clustered formations of new dendritic spines on the apical dendrites of layer 5 pyramidal cells in the barrel cortex of adult mice. Together, these results represent the first demonstration of SRGAP2 regulating on synapse dynamics in vivo and show that SRGAP2 knockdown can be used to model human brain evolution in adult mice.