The mammalian cortex and hippocampus consist of roughly 80-90% glutamatergic excitatory neurons and 10-20% GABAergic inhibitory interneurons. From electrophysiological experiments it is known that glutamatergic synapses in different neuronal populations have different properties and "rules" for plasticity. However, the molecular basis supporting these differences is poorly understood. Our lab is particularly interested in the composition, and regulation, of glutamatergic synapses located within GABAergic inhibitory interneurons. We seek to identify and evaluate proteins that are enriched at glutamatergic synapses in inhibitory interneurons. One such protein is Btbd11, which is specifically enriched at the post synaptic density of glutamatergic synapses in inhibitory interneurons (Figure 1).
(A) We have used a combination of genetic tools, biochemistry, and mass spectrometry to identify glutamatergic synaptic complexes originating from excitatory (CaMKII) or inhibitory interneurons (vGAT). (B) Btbd11 was found to be selectively expressed in inhibitory interneurons, as observed with immunohistochemistry in mouse hippocampus. Btbd11 is shown in green. Lhx6 was used as a marker for a subpopulation of inhibitory interneurons (shown in magenta). (C) We used CRISPR/Cas9 to knock-in a GFP tag to endogenous Btbd11 in primary cultured neurons. Using immunofluorescence, we observed that Btbd11 was colocalized with Psd95, but not gephyrin. This showed that Btbd11 localization was restricted to glutamatergic but not GABAergic synapses.
We utilize broad methods in the lab to evaluate glutamatergic synapse function including: