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Cognition, learning, memory, and behavior are highly dynamic phenomena that stem from cellular connections in the brain. Synaptic connections between neurons exhibit strong plasticity, and are considered one of the primary cellular components of higher neurological function. A comprehension of the cellular mechanisms behind neuronal plasticity is critical to fully understanding systemic activity. The focus of my laboratory is to study signaling mechanisms involved in synaptic plasticity, with the goal of understanding how synapses are formed and changed. My experiments utilize cultured neurons from the rat hippocampus, a region of the brain shown to be critical for learning and memory. Techniques used include generation and transfection of DNA constructs, RNA interference, immunofluorescence, and live-cell fluorescence microscopy.
My specific research interests involve the protein CaMKII, calcium/calmodulin-dependent protein kinase II. CaMKII is a serine/threonine kinase that comprises 1-2% of all protein in the hippocampus, making it one of the abundant signaling proteins in the brain. CaMKII has many neuronal substrates and binding partners, including receptors, scaffolding proteins, cytoskeletal proteins, motor proteins, and signaling proteins. CaMKII has been demonstrated to play an important role in plasticity and learning, as demonstrated using knockout mice and pharmacological inhibitors. CaMKIIa has been shown to transiently translocate to post-synaptic densities (PSDs) following stimulation, targeting the protein to where it can have the most impact on synaptic plasticity. My research identified an isoform-specific role CaMKIIb plays in promoting filopodia formation, motility, and synaptogenesis. This work sheds light on how CaMKII isoforms can modulate synaptogenesis in neurons. When levels of CaMKIIb are high, filopodia initiation, motility, and synaptogenesis are promoted, as would be observed in early neuronal development. CaMKIIa has an opposing affect of stabilizing, or even reducing, dendritic arborization.
There are many questions remaining, which remain active areas of research in the lab. Some of these include:
What is the signaling pathway for CaMKIIb regulation of filopodia and synapses? The specific substrate for CaMKIIb remains unknown, as well as other upstream and downstream members of this signaling network.
What roles do other isoforms of CaMK play in neurons? There are two other isoforms (d and g) of CaMKII, with more than 30 splice variants, and multiple isoforms of CaMKI present in neurons. However, to this point only CaMKII remains well studied.
How is translocation of CaMKII to the PSD regulated? There are more than 80 constituents of the PSD. Which of these play roles in CaMKII dynamics? Also, the specifics of the stimuli that result in CaMKII translocation remain to be investigated.
What role do phosphatases play in neuronal plasticity? Also representing the opposite side of the coin to kinases, much less is known about their role in neuronal signaling networks. PP1, PP2A, and PP2B are the primary neuronal phosphatases, with multiple isoforms for each. Much remains to be discovered about the details of their role balancing kinase activity in neurons.
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