[Identification of novel PSD proteins and their possible functions]

There are a number of mRNA species localizing to dendrites of neuronal cells, and a postsynaptic local translation system may allow local and rapid synthesis of key postsynaptic proteins required for expression of synaptic plasticity. Most mRNAs localizing in the postsynaptic region may be translated into postsynaptic proteins, localizing in the postsynaptic subcompartments, such as PSD, the synaptic plasma membrane (SPM), or the cytoplasmic region of the spines or dendrites. However, there appears to be a number of dendritic mRNAs (Dems) and postsynaptic proteins still to be found. Recently, we developed a method to identify a large number of mRNA species associated with PSD fraction (Tian et al (1999) Mol Brain Res, 72: 147-157). During the identification process of these mRNAs, we cloned several full-length cDNAs, such as a synaptic short form LDL receptor-related protein (ssLRP) (Tian et al (2002) Soc Neurosci Abst, 28: 405), synaptic ubiquitin-specific protease (synUSP), TANC (a protein containing tetratricopeptide repeat [TPR], ankyrin repeat, and coiled-coil domain) (Suzuki et al (2003) Soc Neurosci Abst, 29), and so forth. In situ hybridization and immunochemical studies confirmed dendritic localization of mRNAs for these proteins in dendrites, and the localization of these proteins in postsynaptic regions, respectively. Some proteins contained signals for targeting the PSD and interacted with various PSD proteins. We present properties and possible physiological functions of these proteins and report the recent progress in our project to identify a large number of postsynaptic proteins based on the identification of dendritically localizing mRNAs.