|M.Sc Student||Klarina Shertser|
|Subject||The role of Dlgap2 (SAPAP2) in PSD zone: Possible|
Implication to Synapse Formation
|Department||Department of Medicine||Supervisor||Full Professor Ben-Shachar Dorit|
|Full Thesis text|
The postsynaptic density (PSD) zone is an electron-dense structure that contains hundreds of proteins, creating a complicated signaling system. In the glutamatergic synapse, the brain’s main excitatory neurotransmitter, the PSD region contains receptors such as the ionotropic NMDA receptor and signaling proteins such as CaMKII organized through sequential protein-protein interactions around the scaffolding protein PSD-95. This central protein plays a role in plasticity of spines and synapses and in long-term potentiation (LTP), both implicated in learning and memory. PSD zone is thus regarded as the main structure underlying synaptic plasticity, the synapses ability to change their strength based on their recent history. Dlgap variants are enriched in the PSD zone of glutamatergic synapses and are proposed to function as adaptor proteins linking PSD-95 to sub-synaptic cytoskeleton proteins or to downstream signaling molecules through Shank. In addition, it was suggested that Dlgap members may play a role in the PSD-95. Interestingly, recent studies have tied Dlgap family abnormal expression to many psychiatric disorders, which are thought to develop due to impaired synaptic plasticity.
In our present study, we identified a physiological role for Dlgap that may affect synaptic plasticity. We characterized time dependent changes in Dlgap2 mRNA levels in the hippocampal primary culture, which paralleled those of PSD-95 and the PSD-95 anchored proteins NMDA-R, NLG's and CaMKII, suggesting a role for Dlgap2 in PSD zone organization. Next, in order to unravel the role of Dlgap2 in PSD zone, we silenced Dlgap2 mRNA and protein levels using lentiviral infection, resulting in significant decrease in synaptic contacts between the presynaptic marker Synapsin1 and the post-synaptic marker PSD-95, indicating that Dlgap2 plays a role in the formation of neural synapses. Interestingly, this study revealed a novel role for Dlgap2 in the modulation of PSD-95 mRNA expression levels as well as mRNA of CaMKII and an NMDA-R subunit. We hypothesize that this action of Dlgap2 is mediated through an interaction with mRNA binding fragile mental retardation protein (FMRP), which regulates mRNAs stability. It was reported that FMRP phosphorylation which regulates its function corresponds with Dlgap3 expression. Altogether, the data of the present study may provide a possible explanation for Dlgap2 implication in neuropsychiatric disorders involving cognitive abnormalities. The present data are in favor of further studies to unravel the mechanism by which Dlgap2 affects PSD zone organization and mRNA expression of its members, important factors in synaptic functioning.