Evaluating a cell type-specific mechanism of glutamatergic synapse function and organization

Project Summary/Abstract
Impaired inhibitory signaling underlies the development of various neuropsychiatric disorders including
anxiety, epilepsy, autism, and schizophrenia. Inhibition is mediated by interneurons (INs), a small but diverse
population of cells that coordinates network activity of principal neuron underlying cognition. Glutamatergic
excitation of INs determines subsequent firing and control of downstream circuits, and glutamatergic synapses
received by INs have unique basal transmission properties and exhibit distinct synaptic plasticity compared to
excitatory neurons. These differences in functionality are likely due to cell-type specific differences in
postsynaptic density (PSD) composition and maintenance mechanisms. For example, recently identified
postsynaptic proteins such as Btbd11 which are expressed exclusively in glutamatergic IN-PSD could underly
the unique synaptic properties seen in INs. Growing evidence supports the idea that the PSD is organized
through liquid-liquid phase separation (LLPS), the process of maintaining protein-dense, membrane-less
organelles. Btbd11 has been shown to i) regulate synaptic function in INs and ii) undergo LLPS with key
glutamatergic scaffolding proteins. However, whether Btbd11’s regulation of glutamatergic synapses requires
LLPS is not yet known, and the extent to which Btbd11 mediates synaptic composition has not been explored.
To investigate how the protein composition of glutamatergic IN-PSD contributes to the unique function of
INs and subsequent role in pathophysiology, this application will utilize molecular biology, proteomic
analysis, live cellular imaging and electrophysiology to address the novel hypothesis that Btbd11
promotes glutamatergic IN-PSD function through stabilizing interactions with Psd-95 and associated
protein complexes via LLPS. In Aim 1, we will examine how Btbd11 ablation alters the IN-PSD proteome and
levels of glutamatergic signaling molecules to determine a role in synaptic organization. In Aim 2, we will
investigate how Btbd11’s phase separation properties and phospho-regulation are crucial for synaptic function
and PSD protein stability through Btbd11 knockout and rescue experiments. Together, successful completion of
the proposed project will provide insight into a cell-type specific mechanism of stability and function of an
essential but understudied synapse, while further revealing the role of phase separation at the synapse.
Through this proposal, I will be thoroughly trained in molecular biology, electrophysiology, live cellular
imaging, and bioinformatics. In addition, mentorship from Dr. Bygrave and co-sponsor Dr. Maguire will provide
an environment with exceptional guidance and rigorous training, access to all necessary equipment, and
opportunities for networking, mentorship, and career development activities. Collectively, this proposal will
provide me with the scientific training and growth necessary for establishing the foundations for a future
successful career as an independent neuroscience researcher.

Grant Number: 5F31MH140553-02
NIH Institute/Center: NIH
Principal Investigator: Molly Boyer