Kctd12 and Ulk2 partner to regulate habenular dendritogenesis and behavior / spinophilin regulates dendritic spine formation and F-actin dynamics in hippocampal neurons

Abstract

Appropriate neuronal morphogenesis is essential for forming the distinct functional domains of each of the hundreds of types of neurons in the brain. Generating the correct size and shape of dendrites is essential for a neuron to satisfactorily sample and process the signals that converge on its dendritic field. Understanding the control of neuronal circuit development is key to understanding normal and abnormal brain function and behavior. The habenular nuclei of the limbic system regulate responses, such as anxiety, to aversive stimuli in the environment. The habenulae receive inputs from the telencephalon via elaborate dendrites that form in the center of the nuclei. The kinase Ulk2 positively regulates dendritogenesis on habenular neurons, and in turn is negatively regulated by the cytoplasmic protein Kctd12. Given that the habenulae are a nexus in the aversive response circuit, we suspected that incomplete habenular dendritogenesis would have profound implications for behavior. We find that Ulk2, which interacts with Kctd12 proteins via a small proline-serine rich domain, promotes branching and elaboration of dendrites. Loss of Kctd12 results in increased branching/elaboration and decreased anxiety. We conclude that fine-tuning of habenular dendritogenesis during development is essential for appropriate behavioral responses to negative stimuli. In addition to dendritic shaft development, dendritic spine development is a key event in synapse formation. Dendritic spines are protrusions emanating from the dendritic shaft that interact with axons to form excitatory synapses. Here we show that spinophilin/neurabin II, a scaffolding protein that is highly expressed in dendritic spines, has an important role in dendritic spine and synapse formation in hippocampal neurons. Knockdown of endogenous spinophilin with a short hairpin RNA (shRNA) causes a significant decrease in synapse and spine density, as shown by immunostaining for the presynaptic marker synaptic vesicle protein 2 and the postsynaptic marker postsynaptic density protein 95. On the other hand, expression of mCherry-spinophilin results in an increase in spine density. These results suggest that spinophilin is critical for dendritic spine and synapse formation. We hypothesized that spinophilin was promoting dendritic spine and synapse formation by regulating F-actin accumulation. Indeed, expression of GFP-spinophilin led to an increase in the amount of F-actin in spine heads. Collectively our data demonstrate an important function for spinophilin in modulating the formation of dendritic spines and synapses.