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Abstract
Dendritic spines are heterogeneous and exist with various morphologies. Altered spine morphology might underlie the cognitive deficits in neurodevelopmental disorders such as autism, but how different subtypes of dendritic spines are selectively maintained along development is still poorly understood. Spine maturation requires spontaneous activity of N-methyl-d-aspartate (NMDA) receptor and local dendritic protein synthesis. STRN4 (also called zinedin) belongs to the striatin family of scaffold proteins, and some of the potential striatin-interacting proteins are encoded by autism risk genes. Although previous studies have demonstrated their localization in dendritic spines, the function of various striatin family members in the neuron remains unknown. Here, we demonstrate that Strn4 mRNA is present in neuronal dendrites, and the local expression of STRN4 protein depends on NMDA receptor activation. Notably, STRN4 is preferentially expressed in mushroom spines, and STRN4 specifically maintains mushroom spines but not thin spines and filopodia through interaction with the phosphatase PP2A. Our findings have therefore unraveled the local expression of STRN4 as a novel mechanism for the control of dendritic spine morphology.
Highlights
Dendritic spines are heterogeneous and exist with various morphologies
STRN4 is preferentially expressed in mushroom spines, and STRN4 maintains mushroom spines but not thin spines and filopodia through interaction with the phosphatase PP2A
As a first step to understand the function of STRN4 in synapse development, we examine the expression of Strn4 mRNA and protein in the neuron as well as their regulation by synaptic activity
Summary
Spontaneous NMDA receptor activity locally regulates the expression of STRN4 in dendritic spine. Relatively few (24.4 Ϯ 5.6%; 46 puncta from two dendrites) of the non-spine-associated STRN4 puncta in the dendritic shaft were co-localized with the inhibitory postsynaptic scaffold protein gephyrin (Fig. 1D) These findings indicate that STRN4 is mostly expressed at excitatory synapses. Double immunofluorescence staining with PSD-95 antibody verified the reduction of synaptic STRN4 expression after APV treatment (Fig. 2F) Taken together, these findings indicate that the expression of STRN4 is regulated locally at excitatory synapses by spontaneous activation of the NMDA receptor. We found that the loss of mushroom spines and PSD-95 clusters upon knockdown of STRN4 could be reversed by co-expression of the RNAi-resistant STRN4, indicating that STRN4 is required for maintaining proper spine morphology (Fig. 7, A–D, and supplemental Fig. S5). Our findings collectively indicate that the tight regulation of PP2A by STRN4 in the STRIPAK complex is critical to govern dendritic spine morphology
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