Control of Neuronal Synapse Specification by a Highly Dedicated Alternative Splicing program
Ontology highlight
ABSTRACT:
ORGANISM(S): Mus musculus
PROVIDER: GSE79902 | GEO | 2016/05/12
SECONDARY ACCESSION(S): PRJNA317347
REPOSITORIES: GEO
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Project description:The recognition of synaptic partners and specification of synaptic properties are fundamental for the function of neuronal circuits. 'Terminal selector' transcription factors coordinate the expression of terminal gene batteries that specify cell type-specific properties. Moreover, pan-neuronal alternative splicing regulators have been implicated in directing neuronal differentiation. However, the cellular logic of how splicing regulators instruct specific synaptic properties remains poorly understood. Here, we combine genome-wide mapping of mRNA targets and cell type-specific loss-of-function studies to uncover the contribution of the nuclear RNA binding protein SLM2 to hippocampal synapse specification. We find that SLM2 preferentially binds and regulates alternative splicing of transcripts encoding synaptic proteins, thereby generating cell type-specific isoforms. In the absence of SLM2, cell type-specification, differentiation, and viability are unaltered and neuronal populations exhibit normal intrinsic properties. By contrast, cell type-specific loss of SLM2 results in highly selective, non-cell autonomous synaptic phenotypes, altered synaptic transmission, and associated defects in a hippocampus-dependent memory task. Thus, alternative splicing provides a critical layer of gene regulation that instructs specification of neuronal connectivity in a trans-synaptic manner.
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Project description:The paralog RNA binding proteins (RBPs) Sam68 and SLM2 are co-expressed in the cerebral cortex and display very similar splicing activity. However, their relative function(s) in this context is unknown. By performing a time-course analysis, we found that these RBPs exhibit an opposite expression pattern during development. Sam68 expression declines postnatally while SLM2 increases after birth, and this developmental pattern is reinforced by hierarchical control of Sam68 expression by SLM2. Analysis of Sam68:Slm2 double knockout (Sam68:Slm2dko) mice revealed hundreds of exons that are sensitive to concomitant ablation of these proteins. Moreover, parallel analysis of single and double knockout cortices indicated that exons regulated mainly by SLM2 are characterized by a dynamic splicing pattern during development, whereas Sam68-dependent exons are spliced at relatively constant rates. Dynamic splicing of SLM2-sensitive exons is completely suppressed in the Sam68:Slm2dko developing cortex. Sam68:Slm2dko mice die perinatally with defects in neurogenesis and in neuronal differentiation, and the development of a hydrocephalus, consistent with splicing alterations in genes related to these biological processes. Thus, our study reveals that maintenance of the Sam68 and Slm2 paralog genes encoding homologous RBPs enables the orchestration of a dynamic splicing program while ensuring a robust redundant mechanism that supports proper cortical development.
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Project description:Genome-wide mapping of ribosome-associated mRNAs to investigate cell type-specific loss of function of the nuclear RNA binding protein SLM2 in the mouse hippocampus
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Project description:How synapses are assembled and specified in brain is incompletely understood. Latrophilin-3, a postsynaptic adhesion-GPCR, mediates Schaffer-collateral synapse formation in the hippocampus but the mechanisms involved remained unclear. Here we show that Latrophilin-3 organizes synapses by a convergent dual-pathway mechanism by which Latrophilin-3 simultaneously activates GaS/cAMP-signaling and recruits phase-separated postsynaptic protein scaffolds. We found that cell type-specific alternative splicing of Latrophilin-3 controls its G protein coupling mode, resulting in Latrophilin-3 variants that predominantly signal via Gas and cAMP or via Gα12/13. A CRISPR-mediated genetic switch of Latrophilin-3 alternative splicing from a GaS- to a Gα12/13-coupled mode impaired synaptic connectivity similar to the overall deletion of Latrophilin-3, suggesting that GaS/cAMP-signaling by Latrophilin-3 splice variants mediates synapse formation. Moreover, GaS- but not Gα12/13-coupled splice variants of Latrophilin-3 recruit phase-transitioned postsynaptic protein scaffolds that are clustered by binding of presynaptic Latrophilin-3 ligands. Strikingly, neuronal activity promotes alternative splicing of the synaptogenic variant of Latrophilin-3, thereby enhancing synaptic connectivity. Together, these data suggest that activity-dependent alternative splicing of a key synaptic adhesion molecule controls synapse formation by parallel activation of two convergent pathways, GaS/cAMP signaling and the phase separation of postsynaptic protein scaffolds.
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