Altered cortical synaptic lipid signaling leads to intermediate phenotypes of mental disorders.

Excitation/inhibition (E/I) balance plays important roles in mental disorders. Bioactive phospholipids like lysophosphatidic acid (LPA) are synthesized by the enzyme autotaxin (ATX) at cortical synapses and modulate glutamatergic transmission, and eventually alter E/I balance of cortical networks. Here, we analyzed functional consequences of altered E/I balance in 25 human subjects induced by genetic disruption of the synaptic lipid signaling modifier PRG-1, which were compared to 25 age and sex matched control subjects. Furthermore, we tested therapeutic options targeting ATX in a related mouse line. Using EEG combined with TMS in an instructed fear paradigm, neuropsychological analysis and an fMRI based episodic memory task, we found intermediate phenotypes of mental disorders in human carriers of a loss-of-function single nucleotide polymorphism of PRG-1 (PRG-1R345T/WT). Prg-1R346T/WT animals phenocopied human carriers showing increased anxiety, a depressive phenotype and lower stress resilience. Network analysis revealed that coherence and phase-amplitude coupling were altered by PRG-1 deficiency in memory related circuits in humans and mice alike. Brain oscillation phenotypes were restored by inhibtion of ATX in Prg-1 deficient mice indicating an interventional potential for mental disorders.

Cyclase-associated protein 2 (CAP2) controls MRTF-A localization and SRF activity in mouse embryonic fibroblasts.

Recent studies identified cyclase-associated proteins (CAPs) as important regulators of actin dynamics that control assembly and disassembly of actin filaments (F-actin). While these studies significantly advanced our knowledge of their molecular functions, the physiological relevance of CAPs largely remained elusive. Gene targeting in mice implicated CAP2 in heart physiology and skeletal muscle development. Heart defects in CAP2 mutant mice were associated with altered activity of serum response factor (SRF), a transcription factor involved in multiple biological processes including heart function, but also skeletal muscle development. By exploiting mouse embryonic fibroblasts (MEFs) from CAP2 mutant mice, we aimed at deciphering the CAP2-dependent mechanism relevant for SRF activity. Reporter assays and mRNA quantification by qPCR revealed reduced SRF-dependent gene expression in mutant MEFs. Reduced SRF activity in CAP2 mutant MEFs was associated with altered actin turnover, a shift in the actin equilibrium towards monomeric actin (G-actin) as well as and reduced nuclear levels of myocardin-related transcription factor A (MRTF-A), a transcriptional SRF coactivator that is shuttled out of the nucleus and, hence, inhibited upon G-actin binding. Moreover, pharmacological actin manipulation with jasplakinolide restored MRTF-A distribution in mutant MEFs. Our data are in line with a model in which CAP2 controls the MRTF-SRF pathway in an actin-dependent manner. While MRTF-A localization and SRF activity was impaired under basal conditions, serum stimulation induced nuclear MRTF-A translocation and SRF activity in mutant MEFs similar to controls. In summary, our data revealed that in MEFs CAP2 controls basal MRTF-A localization and SRF activity, while it was dispensable for serum-induced nuclear MRTF-A translocation and SRF stimulation.

CAP2 deficiency delays myofibril actin cytoskeleton differentiation and disturbs skeletal muscle architecture and function.

Actin filaments (F-actin) are key components of sarcomeres, the basic contractile units of skeletal muscle myofibrils. A crucial step during myofibril differentiation is the sequential exchange of α-actin isoforms from smooth muscle (α-SMA) and cardiac (α-CAA) to skeletal muscle α-actin (α-SKA) that, in mice, occurs during early postnatal life. This "α-actin switch" requires the coordinated activity of actin regulators because it is vital that sarcomere structure and function are maintained during differentiation. The molecular machinery that controls the α-actin switch, however, remains enigmatic. Cyclase-associated proteins (CAP) are a family of actin regulators with largely unknown physiological functions. We here report a function for CAP2 in regulating the α-actin exchange during myofibril differentiation. This α-actin switch was delayed in systemic CAP2 mutant mice, and myofibrils remained in an undifferentiated stage at the onset of the often excessive voluntary movements in postnatal mice. The delay in the α-actin switch coincided with the onset of motor function deficits and histopathological changes including a high frequency of type IIB ring fibers. Our data suggest that subtle disturbances of postnatal F-actin remodeling are sufficient for predisposing muscle fibers to form ring fibers. Cofilin2, a putative CAP2 interaction partner, has been recently implicated in myofibril actin cytoskeleton differentiation, and the myopathies in cofilin2 and CAP2 mutant mice showed striking similarities. We therefore propose a model in which CAP2 and cofilin2 cooperate in actin regulation during myofibril differentiation.

The neurodevelopmental effects of serotonin: a behavioural perspective.

Serotonin is well known for its role in psychiatric disorders like depression and autism, but it is less clear how aberrant behaviour associated with these disorders are shaped by serotonergic alterations during prenatal and postnatal development. The use of serotonergic antidepressant agents and other drugs during pregnancy and breastfeeding can change brain development, and the behavioural consequences may depend on the stage of development; prenatal, early and late postnatal. The aim of this review is to provide an overview of the behavioural consequences of changes in serotonin levels during these three critical developmental stages. The studies together demonstrate that risk for mood disorders (including social deficits) is related to serotonergic perturbations during the prenatal and postnatal phases, whereas risk for autism-like features and sexual abnormalities increases when serotonin levels are increased during the postnatal period. This insight may inform timed strategies to reduce risk for psychiatric disorders.