Modulation of cognition and neuronal plasticity in gain- and loss-of-function mouse models of the schizophrenia risk gene Tcf4.

The transcription factor TCF4 was confirmed in several large genome-wide association studies as one of the most significant schizophrenia (SZ) susceptibility genes. Transgenic mice moderately overexpressing Tcf4 in forebrain (Tcf4tg) display deficits in fear memory and sensorimotor gating. As second hit, we exposed Tcf4tg animals to isolation rearing (IR), chronic social defeat (SD), enriched environment (EE), or handling control (HC) conditions and examined mice with heterozygous deletion of the exon 4 (Tcf4Ex4δ+/-) to unravel gene-dosage effects. We applied multivariate statistics for behavioral profiling and demonstrate that IR and SD cause strong cognitive deficits of Tcf4tg mice, whereas EE masked the genetic vulnerability. We observed enhanced long-term depression in Tcf4tg mice and enhanced long-term potentiation in Tcf4Ex4δ+/- mice indicating specific gene-dosage effects. Tcf4tg mice showed higher density of immature spines during development as assessed by STED nanoscopy and proteomic analyses of synaptosomes revealed concurrently increased levels of proteins involved in synaptic function and metabolic pathways. We conclude that environmental stress and Tcf4 misexpression precipitate cognitive deficits in 2-hit mouse models of relevance for schizophrenia.

Nanoscale organization of nicotinic acetylcholine receptors revealed by stimulated emission depletion microscopy.

Acetylcholine receptor (AChR) supramolecular aggregates that have hitherto only been accessible to examination by electron microscopy were imaged with stimulated emission depletion (STED) fluorescence microscopy, providing resolution beyond limits of diffraction of classical wide-field or confocal microscopes. We examined a Chinese hamster ovary cell liner CHO-K1/A5, that stably expresses adult murine AChR. Whereas confocal microscopy displays AChR clusters as diffraction-limited dots of approximately 200 nm diameter, STED microscopy yields nanoclusters with a peak size distribution of approximately 55 nm. Utilizing this resolution, we show that cholesterol depletion by acute (30 min, 37 degrees C) exposure to methyl-beta-cyclodextrin alters the short and long range organization of AChR nanoclusters on the cell surface. In the short range, AChRs form larger nanoclusters, possibly related to the alteration of cholesterol-dependent protein-protein associations. Ripley's K-test on STED images reveals changes in nanocluster distribution on larger scales (0.5-3.5 microm), which possibly are related to the abolition of cytoskeletal physical barriers preventing the lateral diffusion of AChR nanoclusters.