TLS-GFP cannot rescue mRNP formation near spines and spine phenotype in TLS-KO.

RNA-binding protein TLS transports Nd1-L mRNA, which encodes an actin-stabilizing protein, to the neuronal dendrites. TLS-null mouse (TLS-KO) hippocampal neurons display abnormal spine morphology, and thus could be attributed to actin destabilization by the improper supply of Nd1-L mRNA to the dendrites. In this study, we showed that the exogenous expression of TLS in TLS-KO neurons did not rescue the abnormal spine phenotypes. The degree of colocalization between exogenous TLS and Nd1-L mRNA was significantly decreased in both the neuronal dendrites and the spines of TLS-KO neurons. Our results indicate that formation of TLS-Nd1-L mRNA complex clusters, presumable mRNA pools for the local protein synthesis in the spines, was impaired in TLS-deficient neurons.