The spatio-temporal expression of ProSAP/shank family members and their interaction partner LAPSER1 during Xenopus laevis development

Members of the ProSAP/Shank family are important scaffolding proteins of the postsynaptic density (PSD). We investigated for the first time the expression of the three family members named Shank1, ProSAP1/Shank2, and ProSAP2/Shank3 during Xenopus laevis development. Shank1 is expressed in the neural tube, the retina, and the cranial ganglions. In contrast, ProSAP1/Shank2 transcripts could be visualized in the otic vesicle, the pronephros, the liver, the neural tube, and the retina. ProSAP2/Shank3 could be detected in the cardiovascular network, the neural tube, the pronephros, and the retina. Furthermore, we showed that LAPSER1 interacts with all three ProSAP/Shank family members in Xenopus embryos and co-localizes with ProSAP/Shank in a cell-based assay. In Xenopus, LAPSER1 is expressed in somites, brain, proctodeum, pronephros, and in some cranial ganglions. Thus, we suggest that members of the ProSAP/Shank family and LAPSER1 not only play a role in PSD formation and plasticity, but also during embryonic development.

An SK3 channel/nWASP/Abi-1 complex is involved in early neurogenesis

Background

The stabilization or regulated reorganization of the actin cytoskeleton is essential for cellular structure and function. Recently, we could show that the activation of the SK3-channel that represents the predominant SK-channel in neural stem cells, leads to a rapid local outgrowth of long filopodial processes. This observation indicates that the rearrangement of the actin based cytoskeleton via membrane bound SK3-channels might selectively be controlled in defined micro compartments of the cell.

Principal Findings

We found two important proteins for cytoskeletal rearrangement, the Abelson interacting protein 1, Abi-1 and the neural Wiskott Aldrich Syndrome Protein, nWASP, to be in complex with SK3- channels in neural stem cells (NSCs). Moreover, this interaction is also found in spines and postsynaptic compartments of developing primary hippocampal neurons and regulates neurite outgrowth during early phases of differentiation. Overexpression of the proteins or pharmacological activation of SK3 channels induces obvious structural changes in NSCs and hippocampal neurons. In both neuronal cell systems SK3 channels and nWASP act synergistic by strongly inducing filopodial outgrowth while Abi-1 behaves antagonistic to its interaction partners.

Conclusions

Our results give good evidence for a functional interplay of a trimeric complex that transforms incoming signals via SK3-channel activation into the local rearrangement of the cytoskeleton in early steps of neuronal differentiation involving nWASP and Abi-1 actin binding proteins.

Synaptic cross-talk between N-methyl-D-aspartate receptors and LAPSER1-beta-catenin at excitatory synapses

Memory formation in the brain is thought to be depending upon long lasting plastic changes of synaptic contacts that require alterations on the transcriptional level. Here, we characterize LAPSER1, a putative cytokinetic tumor suppressor that binds directly to ProSAP2/Shank3 and the synaptic Rap-Gap protein SPAR1 as a novel postsynaptic density component. Postsynaptic LAPSER1 is in complex with all important members of the canonical Wnt pathway including beta-catenin. Upon N-methyl-D-aspartate receptor-dependent activation, LAPSER1 and beta-catenin comigrate from the postsynaptic density to the nucleus and induce the transcription and translation of known beta-catenin target genes, including Tcfe2a and c-Myc. The nuclear export and cytoplasmic redistribution of beta-catenin is tightly regulated by LAPSER1. We postulate a postsynaptic cross-talk between N-methyl-D-aspartate receptors and a LAPSER1-beta-catenin complex that results in a self-regulated, synaptic activity-dependent expression of beta-catenin target genes. This calls for a novel role of Tcfe2a and c-Myc in plastic changes of neural tissue.