Control of neuronal excitation-inhibition balance by BMP-SMAD1 signalling.

Throughout life, neuronal networks in the mammalian neocortex maintain a balance of excitation and inhibition, which is essential for neuronal computation. Deviations from a balanced state have been linked to neurodevelopmental disorders, and severe disruptions result in epilepsy. To maintain balance, neuronal microcircuits composed of excitatory and inhibitory neurons sense alterations in neural activity and adjust neuronal connectivity and function.

A cell-type-specific alternative splicing regulator shapes synapse properties in a trans-synaptic manner.

The specification of synaptic properties is fundamental for the function of neuronal circuits. "Terminal selector" transcription factors coordinate terminal gene batteries that specify cell-type-specific properties. Moreover, pan-neuronal splicing regulators have been implicated in directing neuronal differentiation.

Quantitative Detection of Protein Splice Variants by Selected Reaction Monitoring (SRM) Mass Spectrometry.

Molecular diversification of the cellular proteome through alternative splicing has emerged as an important biological principle. However, the lack of tools to specifically detect and quantify proteoforms (Smith et al., Nat Methods 10:186-187, 2013) is a major impediment to functional studies.

Targeted proteoform mapping uncovers specific Neurexin-3 variants required for dendritic inhibition.

The diversification of cell adhesion molecules by alternative splicing is proposed to underlie molecular codes for neuronal wiring. Transcriptomic approaches mapped detailed cell-type-specific mRNA splicing programs. However, it has been hard to probe the synapse-specific localization and function of the resulting protein splice isoforms, or "proteoforms," in vivo.

Specification of CNS macrophage subsets occurs postnatally in defined niches.

All tissue-resident macrophages of the central nervous system (CNS)-including parenchymal microglia, as well as CNS-associated macrophages (CAMs) such as meningeal and perivascular macrophages-are part of the CNS endogenous innate immune system that acts as the first line of defence during infections or trauma. It has been suggested that microglia and all subsets of CAMs are derived from prenatal cellular sources in the yolk sac that were defined as early erythromyeloid progenitors. However, the precise ontogenetic relationships, the underlying transcriptional programs and the molecular signals that drive the development of distinct CAM subsets in situ are poorly understood.

MyD88 signaling by neurons induces chemokines that recruit protective leukocytes to the virus-infected CNS.

Viral encephalitis initiates a series of immunological events in the brain that can lead to brain damage and death. Astrocytes express IFN-β in response to neurotropic infection, whereas activated microglia produce proinflammatory cytokines and accumulate at sites of infection. Here, we observed that neurotropic vesicular stomatitis virus (VSV) infection causes recruitment of leukocytes into the central nervous system (CNS), which requires MyD88, an adaptor of Toll-like receptor and interleukin-1 receptor signaling.

Rescue of oxytocin response and social behaviour in a mouse model of autism.

A fundamental challenge in developing treatments for autism spectrum disorders is the heterogeneity of the condition. More than one hundred genetic mutations confer high risk for autism, with each individual mutation accounting for only a small fraction of cases. Subsets of risk genes can be grouped into functionally related pathways, most prominently those involving synaptic proteins, translational regulation, and chromatin modifications.

AAV2/DJ-mediated alpha-synuclein overexpression in the rat substantia nigra as early stage model of Parkinson's disease.

Parkinson's disease (PD) is pathologically characterized by the progressive loss of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc) and alpha-synucleinopathy. We mimic the disease pathology with overexpression of either the human α-syn wildtype (α-syn-WT) or E46K mutant form (α-syn-E46K) in DA neurons of the SNpc in adult rats using AAV2/DJ as a viral vector for the first time. Transduction efficiency was compared to an equal virus titer expressing the green fluorescent protein (GFP).

A Sam68-dependent alternative splicing program shapes postsynaptic protein complexes.

Alternative splicing is one of the key mechanisms to increase the diversity of cellular transcriptomes, thereby expanding the coding capacity of the genome. This diversity is of particular importance in the nervous system with its elaborated cellular networks. Sam68, a member of the Signal Transduction Associated RNA-binding (STAR) family of RNA-binding proteins, is expressed in the developing and mature nervous system but its neuronal functions are poorly understood.

Deficiency of fibroblast growth factor 2 (FGF-2) leads to abnormal spermatogenesis and altered sperm physiology.

In previous studies, we described the presence of fibroblast growth factor 2 (FGF-2) and its receptors (FGFRs) in human testis and sperm, which are involved in spermatogenesis and in motility regulation. The aim of the present study was to analyze the role of FGF-2 in the maintenance of sperm physiology using FGF-2 knockout (KO) mice. Our results showed that in wild-type (WT) animals, FGF-2 is expressed in germ cells of the seminiferous epithelium, in epithelial cells of the epididymis, and in the flagellum and acrosomal region of epididymal sperm.

γ-Protocadherins Interact with Neuroligin-1 and Negatively Regulate Dendritic Spine Morphogenesis.

The 22 γ-Protocadherin (γ-Pcdh) cell adhesion molecules are critical for the elaboration of complex dendritic arbors in the cerebral cortex. Here, we provide evidence that the γ-Pcdhs negatively regulate synapse development by inhibiting the postsynaptic cell adhesion molecule, neuroligin-1 (Nlg1). Mice lacking all γ-Pcdhs in the forebrain exhibit significantly increased dendritic spine density in vivo, while spine density is significantly decreased in mice overexpressing one of the 22 γ-Pcdh isoforms.

Synapse biology in the 'circuit-age'-paths toward molecular connectomics.

The neural connectome is a critical determinant of brain function. Circuits of precisely wired neurons, and the features of transmission at the synapses connecting them, are thought to dictate information processing in the brain. While recent technological advances now allow to define the anatomical and functional neural connectome at unprecedented resolution, the elucidation of the molecular mechanisms that establish the precise patterns of connectivity and the functional characteristics of synapses has remained challenging.

An alternative splicing switch shapes neurexin repertoires in principal neurons versus interneurons in the mouse hippocampus.

The unique anatomical and functional features of principal and interneuron populations are critical for the appropriate function of neuronal circuits. Cell type-specific properties are encoded by selective gene expression programs that shape molecular repertoires and synaptic protein complexes. However, the nature of such programs, particularly for post-transcriptional regulation at the level of alternative splicing is only beginning to emerge.

Presynaptic spinophilin tunes neurexin signalling to control active zone architecture and function.

Assembly and maturation of synapses at the Drosophila neuromuscular junction (NMJ) depend on trans-synaptic neurexin/neuroligin signalling, which is promoted by the scaffolding protein Syd-1 binding to neurexin. Here we report that the scaffold protein spinophilin binds to the C-terminal portion of neurexin and is needed to limit neurexin/neuroligin signalling by acting antagonistic to Syd-1. Loss of presynaptic spinophilin results in the formation of excess, but atypically small active zones.

Protein Kinase C Phosphorylation of a γ-Protocadherin C-terminal Lipid Binding Domain Regulates Focal Adhesion Kinase Inhibition and Dendrite Arborization.

The γ-protocadherins (γ-Pcdhs) are a family of 22 adhesion molecules with multiple critical developmental functions, including the proper formation of dendritic arbors by forebrain neurons. The γ-Pcdhs bind to and inhibit focal adhesion kinase (FAK) via a constant C-terminal cytoplasmic domain shared by all 22 proteins. In cortical neurons lacking the γ-Pcdhs, aberrantly high activity of FAK and of PKC disrupts dendrite arborization.

Quantitative isoform-profiling of highly diversified recognition molecules.

Complex biological systems rely on cell surface cues that govern cellular self-recognition and selective interactions with appropriate partners. Molecular diversification of cell surface recognition molecules through DNA recombination and complex alternative splicing has emerged as an important principle for encoding such interactions. However, the lack of tools to specifically detect and quantify receptor protein isoforms is a major impediment to functional studies.

Targeted combinatorial alternative splicing generates brain region-specific repertoires of neurexins.

Molecular diversity of surface receptors has been hypothesized to provide a mechanism for selective synaptic connectivity. Neurexins are highly diversified receptors that drive the morphological and functional differentiation of synapses. Using a single cDNA sequencing approach, we detected 1,364 unique neurexin-α and 37 neurexin-β mRNAs produced by alternative splicing of neurexin pre-mRNAs.

Polymorphic receptors: neuronal functions and molecular mechanisms of diversification.

The formation of neuronal circuits is driven by complex developmental programs. A key feature of such programs is the precise spatiotemporal control of cell surface recognition molecules in genetically defined cells. Moreover, epigenetic modifications and alternative splicing processes have emerged that are not genetically predetermined but stochastic in nature.

γ-protocadherins control cortical dendrite arborization by regulating the activity of a FAK/PKC/MARCKS signaling pathway.

The 22 γ-protocadherins (γ-Pcdhs) potentially specify thousands of distinct homophilic adhesive interactions in the brain. Neonatal lethality of mice lacking the Pcdh-γ gene cluster has, however, precluded analysis of many brain regions. Here, we use a conditional Pcdh-γ allele to restrict mutation to the cerebral cortex and find that, in contrast to other central nervous system phenotypes, loss of γ-Pcdhs in cortical neurons does not affect their survival or result in reduced synaptic density.

Molecular heterogeneity in the choroid plexus epithelium: the 22-member γ-protocadherin family is differentially expressed, apically localized, and implicated in CSF regulation.

The choroid plexus (CP) epithelium develops from the ependyma that lines the ventricular system, and plays a critical role in the development and function of the brain. In addition to being the primary site of CSF production, the CP maintains the blood-CSF barrier via apical tight junctions between epithelial cells. Here we show that the 22-member γ-protocadherin (γ-Pcdh) family of cell adhesion molecules, which we have implicated previously in synaptogenesis and neuronal survival, is highly expressed by both CP epithelial and ependymal cells, in which γ-Pcdh protein localization is, surprisingly, tightly restricted to the apical membrane.

Combinatorial homophilic interaction between gamma-protocadherin multimers greatly expands the molecular diversity of cell adhesion.

The specificity of interactions between neurons is believed to be mediated by diverse cell adhesion molecules, including members of the cadherin superfamily. Whereas mechanisms of classical cadherin adhesion have been studied extensively, much less is known about the related protocadherins (Pcdhs), which together make up the majority of the superfamily. Here we use quantitative cell aggregation assays and biochemical analyses to characterize cis and trans interactions among the 22-member gamma-Pcdh family, which have been shown to be critical for the control of synaptogenesis and neuronal survival.

Cell and molecular biology of the novel protein tyrosine-phosphatase-interacting protein 51.

This chapter examines the current state of knowledge about the expression profile, as well as biochemical properties and biological functions of the evolutionarily conserved protein PTPIP51. PTPIP51 is apparently expressed in splice variants and shows a particularly high expression in epithelia, skeletal muscle, placenta, and germ cells, as well as during mammalian development and in cancer. PTPIP51 is an in vitro substrate of Src- and protein kinase A, the PTP1B/TCPTP protein tyrosine phosphatases and interacts with 14-3-3 proteins, the Nuf2 kinetochore protein, the ninein-interacting CGI-99 protein, diacylglycerol kinase alpha, and also with itself forming dimers and trimers.

Expression of PTPIP51 during mouse eye development.

The expression pattern of the novel tyrosine phosphatase interacting protein 51 (PTPIP51) was studied during the organogenesis of mouse eye on a transcriptional (RT-PCR and in situ hybridization) and translational level (immunohistochemistry and immunoblotting). Timed developmental stages from day E12 to day E18 were analyzed regarding the distribution of PTPIP51 and compared to the expression patterns observed during postnatal developmental stages and adult eye. PTPIP51 was found to be expressed in all investigated developmental stages in derivatives of mesoderm and ectoderm, such as developing cornea, lens, neuroretina and extraocular muscles.