Unspecific binding of cRNA probe to plaques in two mouse models for Alzheimer's disease.

BACKGROUND: Alzheimer's disease (AD) is characterized by the pathological deposition of amyloid-ß (Aß) protein-containing plaques. Microglia and astrocytes are commonly attracted to the plaques by an unknown mechanism that may involve cell adhesion. One cell adhesion family of proteins, the cadherins, are widely expressed in the central nervous system. Therefore, our study was designed to map the expression of cadherins in AD mouse brains. A particular focus was on plaques because diverse mRNA-species were found in plaques and their surrounding area in brains of AD patients. METHODS: In this study, we used in situ hybridization to visualize cadherin expression in brains of two mouse models for AD (APP/PS1 and APP23). RESULTS: A variable number of plaques was detected in transgenic brain sections, depending on the probe used. Our first impression was that the cadherin probes visualized specific mRNA expression in plaques and that endogenous staining was unaffected. However, control experiments revealed unspecific binding with sense probes. Further experiments with variations in probe length, probe sequence, molecular tag and experimental procedure lead us to conclude that cRNA probes bind generally and in an unspecific manner to plaques. CONCLUSIONS: We demonstrate unspecific binding of cRNA probes to plaques in two mouse models for AD. The widespread and general staining of the plaques prevented us from studying endogenous expression of cadherins in transgenic brain by in situ hybridization.

Inhibition of TFG function causes hereditary axon degeneration by impairing endoplasmic reticulum structure.

Hereditary spastic paraplegias are a clinically and genetically heterogeneous group of gait disorders. Their pathological hallmark is a length-dependent distal axonopathy of nerve fibers in the corticospinal tract. Involvement of other neurons can cause additional neurological symptoms, which define a diverse set of complex hereditary spastic paraplegias. We present two siblings who have the unusual combination of early-onset spastic paraplegia, optic atrophy, and neuropathy. Genome-wide SNP-typing, linkage analysis, and exome sequencing revealed a homozygous c.316C>T (p.R106C) variant in the Trk-fused gene (TFG) as the only plausible mutation. Biochemical characterization of the mutant protein demonstrated a defect in its ability to self-assemble into an oligomeric complex, which is critical for normal TFG function. In cell lines, TFG inhibition slows protein secretion from the endoplasmic reticulum (ER) and alters ER morphology, disrupting organization of peripheral ER tubules and causing collapse of the ER network onto the underlying microtubule cytoskeleton. The present study provides a unique link between altered ER architecture and neurodegeneration.

Exome sequencing identifies a REEP1 mutation involved in distal hereditary motor neuropathy type V.

The distal hereditary motor neuropathies (dHMNs) are a heterogeneous group of neurodegenerative disorders affecting the lower motoneuron. In a family with both autosomal-dominant dHMN and dHMN type V (dHMN/dHMN-V) present in three generations, we excluded mutations in all genes known to be associated with a dHMN phenotype through Sanger sequencing and defined three potential loci through linkage analysis. Whole-exome sequencing of two affected individuals revealed a single candidate variant within the linking regions, i.e., a splice-site alteration in REEP1 (c.304-2A>G). A minigene assay confirmed complete loss of splice-acceptor functionality and skipping of the in-frame exon 5. The resulting mRNA is predicted to be expressed at normal levels and to encode an internally shortened protein (p.102_139del). Loss-of-function REEP1 mutations have previously been identified in dominant hereditary spastic paraplegia (HSP), a disease associated with upper-motoneuron pathology. Consistent with our clinical-genetic data, we show that REEP1 is strongly expressed in the lower motoneurons as well. Upon exogeneous overexpression in cell lines we observe a subcellular localization defect for p.102_139del that differs from that observed for the known HSP-associated missense mutation c.59C>A (p.Ala20Glu). Moreover, we show that p.102_139del, but not p.Ala20Glu, recruits atlastin-1, i.e., one of the REEP1 binding partners, to the altered sites of localization. These data corroborate the loss-of-function nature of REEP1 mutations in HSP and suggest that a different mechanism applies in REEP1-associated dHMN.

Absence of layer-specific cadherin expression profiles in the neocortex of the reeler mutant mouse.

Cadherins are a superfamily of Ca(2+)-dependent cell surface glycoproteins that play a morphogenetic role in a wide variety of developmental processes. They provide a code of potentially adhesive cues for layer formation in mammalian cerebral cortex. One of the animal models used for studying corticogenesis is the reeler mouse. Previous investigations showed that radial neuronal migration is impaired in this mutant, possibly resulting in an inversion of cortical layers. However, the extent of this "outside-in" cortical layering remains unclear. In the present study, we investigated the mRNA expression of cadherins (Cdh4, Cdh6, Cdh7, Cdh8, Pcdh8, Pcdh9, Pcdh11, Pcdh17, and Pcdh19) in the cerebral cortex of wild-type (wt) mice and reeler mutants. All cadherins show a layer-specific expression profile in wt mice, but, in reeler cortex, cadherin-expressing cells are distributed widely across the radial dimension. The altered layering in reeler mutants completely disrupts the radial expression of cadherins, which is more patchy, rather than laminar. Regionalized gradient-like expression of cadherins is preserved. Our findings are compatible with a model, in which the ubiquitous dispersion of cadherin-expressing cells results from a dysgenesis of radial glial cells and a misrouting of migrating neuroblasts.

Expression profile of N-cadherin and protocadherin-19 in postnatal mouse limbic structures.

Cadherins are a superfamily of calcium-dependent cell adhesion molecules that are involved in brain development and organization. Previous genetic studies revealed that mutations in protocadherin-19 (Pcdh19) lead to an epilepsy syndrome with a variable degree of cognitive disability. Seizure origins are located in the frontotemporal and limbic structures. Expression studies of Pcdh19 in mouse confirmed a widespread presence during brain development while the function and the pathogenesis of Pcdh19 are still unknown in mammals. The neuronal cadherin (N-cadherin; Ncdh) is known for its important role in neurulation, brain development and regulation of synaptic function. Studies in zebrafish revealed that both cadherins can interact with each other in cell adhesion. We investigated the expression pattern of Pcdh19 and Ncdh in limbic structures at four postnatal stages of C57BL/6J mice by using double-label in situ hybridization. Results confirm a strong expression of both, Ncdh and Pcdh19, in structures of the limbic system with overlapping expression patterns particularly within regions of the amygdala, the hippocampus and the ventral hypothalamus. A detailed analysis of the limbic system highlight clear expression boundaries between several nuclei and reveal the fine regulation of Pcdh19 and Ncdh expression during the first postnatal week. Most expression patterns of both cadherins remain constant with a few exceptions particularly between P2 and P5.

A Multivariate Granger Causality Concept towards Full Brain Functional Connectivity.

Detecting changes of spatially high-resolution functional connectivity patterns in the brain is crucial for improving the fundamental understanding of brain function in both health and disease, yet still poses one of the biggest challenges in computational neuroscience. Currently, classical multivariate Granger Causality analyses of directed interactions between single process components in coupled systems are commonly restricted to spatially low- dimensional data, which requires a pre-selection or aggregation of time series as a preprocessing step. In this paper we propose a new fully multivariate Granger Causality approach with embedded dimension reduction that makes it possible to obtain a representation of functional connectivity for spatially high-dimensional data. The resulting functional connectivity networks may consist of several thousand vertices and thus contain more detailed information compared to connectivity networks obtained from approaches based on particular regions of interest. Our large scale Granger Causality approach is applied to synthetic and resting state fMRI data with a focus on how well network community structure, which represents a functional segmentation of the network, is preserved. It is demonstrated that a number of different community detection algorithms, which utilize a variety of algorithmic strategies and exploit topological features differently, reveal meaningful information on the underlying network module structure.

Identification of whole-brain network modules based on a large scale Granger Causality approach.

Spatially high resolved neurophysiological data commonly pose a computational and analytical problem for the identification of functional networks in the human brain. We introduce a multivariate linear Granger Causality approach with an embedded dimension reduction that enables the computation of brain networks at the large scale. In order to grasp the information about connectivity patterns contained in the resulting high-dimensional directed networks, we furthermore propose the inclusion of module detection methods from network theory that can help to identify functionally associated brain areas. As a proof of concept, the methodology is verified by means of synthetic data with known ground truth module properties. Resting state fMRI data are used to demonstrate the applicability and benefit in the case of clinical data.

Inversion of layer-specific cadherin expression profiles and maintenance of cytoarchitectonic areas in the allocortex of the reeler mutant mouse.

Cadherins are calcium-depending cell adhesion proteins that play critical roles in brain morphogenesis and wiring. They provide an adhesive code for the development of cortical layers, due to their homophilic interactions and their restricted spatiotemporal expression patterns. In the adult organism, cadherins are involved in the maintenance and plasticity of neuronal circuits that play a role in learning. A well-known model for studying corticogenesis is the reeler mouse model. Numerous investigations of neocortical development suggest that, in the reeler mutant mouse, the lack of the protein Reelin results in cell-type and region-dependent changes of the neocortical layers. To investigate in detail how layer formation and regionalization is perturbed in the phylogenetically older archicortex of the adult reeler mutant mouse, we studied the expression of 11 different cadherins (Cdh4, Cdh7, Cdh8, Cdh11, Pcdh1, Pcdh7, Pcdh8, Pcdh9, Pcdh10, Pcdh17, and Pcdh19) and of the transcription factors ER81 and Cux2 by in situ hybridization in the (peri-)archicortex. All cadherins studied show a layer-specific expression in the (peri-)archicortex of the wildtype brain. In the archicortex of the reeler mutant, the cadherin-expressing cell layers are dispersed in the radial dimension, whereas in the periarchicortex the superficial and deep layers are inverted, both in the adult and during development. Possibly, this inversion relates to the histoarchitectural division of the reeler entorhinal cortex into an external and an internal zone. The regionalized, gradient-like expression of the cadherins is preserved in the reeler mutant mouse.

A spastic paraplegia mouse model reveals REEP1-dependent ER shaping.

Axonopathies are a group of clinically diverse disorders characterized by the progressive degeneration of the axons of specific neurons. In hereditary spastic paraplegia (HSP), the axons of cortical motor neurons degenerate and cause a spastic movement disorder. HSP is linked to mutations in several loci known collectively as the spastic paraplegia genes (SPGs). We identified a heterozygous receptor accessory protein 1 (REEP1) exon 2 deletion in a patient suffering from the autosomal dominantly inherited HSP variant SPG31. We generated the corresponding mouse model to study the underlying cellular pathology. Mice with heterozygous deletion of exon 2 in Reep1 displayed a gait disorder closely resembling SPG31 in humans. Homozygous exon 2 deletion resulted in the complete loss of REEP1 and a more severe phenotype with earlier onset. At the molecular level, we demonstrated that REEP1 is a neuron-specific, membrane-binding, and membrane curvature-inducing protein that resides in the ER. We further show that Reep1 expression was prominent in cortical motor neurons. In REEP1-deficient mice, these neurons showed reduced complexity of the peripheral ER upon ultrastructural analysis. Our study connects proper neuronal ER architecture to long-term axon survival.

Cadherin expression delineates the divisions of the postnatal and adult mouse amygdala.

The amygdaloid complex represents a group of telencephalic nuclei and cortical areas that control emotional and social behavior. Amygdalar development is poorly understood. It is generally accepted that the structures of the amygdala originate from the neuroepithelium at both sides of the pallial-subpallial boundary. In the present study, we mapped the expression of 13 members of the cadherin superfamily of cell adhesion molecules, which provide an adhesive code for the development and maintenance of functional structures in the central nervous system (CNS). Five classic cadherins (Cdh4, Cdh6, Cdh7, Cdh8, Cdh11) and eight delta-protocadherins (Pcdh1, Pcdh7, Pcdh8, Pcdh9, Pcdh10, Pcdh11, PCdh17, PCdh19) were studied by in situ hybridization in the postnatal (P5) and adult mouse amygdala. In the different parts of the amygdala, each of these (proto-) cadherins shows a distinct and spatially restricted expression pattern that is highly similar at postnatal and adult stages. The combinatorial expression of (proto-) cadherins allows the distinction of multiple molecular subdivisions within the amygdala that partially coincide with previously described morphological divisions. Beyond these expected results, a number of novel molecular subdivisions and subpopulations of cells were identified; for example, additional molecular subdomains, patches, or cell aggregates with distinct (proto-) cadherin expression in several nuclei/areas of the amygdala. We also show that several cadherins are molecular markers for particular functional subsystems within the amygdala, such as in the olfactory projections. In summary, (proto-) cadherins provide a code of potentially adhesive cues that can aid the understanding of functional organization in the amygdala.

Cadherins and neuropsychiatric disorders.

Cadherins mediate cell-cell adhesion but are also involved in intracellular signaling pathways associated with neuropsychiatric disease. Most of the ∼100 cadherins that are expressed in the brain exhibit characteristic spatiotemporal expression profiles. Cadherins have been shown to regulate neural tube regionalization, neuronal migration, gray matter differentiation, neural circuit formation, spine morphology, synapse formation and synaptic remodeling. The dysfunction of the cadherin-based adhesive system may alter functional connectivity and coherent information processing in the human brain in neuropsychiatric disease. Several neuropsychiatric disorders, such as epilepsy/mental retardation, autism, bipolar disease and schizophrenia, have been associated with cadherins, mostly by genome-wide association studies. For example, CDH15 and PCDH19 are associated with cognitive impairment; CDH5, CDH8, CDH9, CDH10, CDH13, CDH15, PCDH10, PCDH19 and PCDHb4 with autism; CDH7, CDH12, CDH18, PCDH12 and FAT with bipolar disease and schizophrenia; and CDH11, CDH12 and CDH13 with methamphetamine and alcohol dependency. To date, disease-causing mutations are established for PCDH19 in patients with epilepsy, cognitive impairment and/or autistic features. In conclusion, genes encoding members of the cadherin superfamily are of special interest in the pathogenesis of neuropsychiatric disease because cadherins play a pivotal role in the development of the neural circuitry as well as in mature synaptic function.

A cadherin-based code for the divisions of the mouse basal ganglia.

The expression of 12 different classic cadherins and delta-protocadherins was mapped in consecutive series of sections through the basal ganglia of the postnatal and adult mouse by in situ hybridization. A particular focus was the caudoputamen, which consists of patches (striosomes) and a surrounding matrix that is histologically uniform. The different areas within the caudoputamen are connected specifically to other parts of the basal ganglia and to other brain regions, for example, the substantia nigra. The molecules regulating the morphogenesis and functional connectivity of the basal ganglia are largely unknown. Previous studies suggested that cadherins, a large family of adhesion molecules, are involved in basal ganglia development. In the present work, we study the expression of 12 cadherins and show that the patch and matrix compartments of the caudoputamen express the cadherins differentially, although partial overlap is observed. Moreover, the cadherins are expressed in multiple and diverse gradients within the caudoputamen and other parts of the basal ganglia. The persistence of the expression patterns in the adult basal ganglia suggests the possibility that cadherins also play a role at adult stages. Our results suggest that cadherins provide a code of potentially adhesive cues that specify not only patch and matrix compartments but also multiple molecular gradients within the basal ganglia. This code may relate to patterns of connectivity.