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

Adhesion-Based Self-Organization in Tissue Patterning

Since the proposal of the differential adhesion hypothesis, scientists have been fascinated by how cell adhesion mediates cellular self-organization to form spatial patterns during development. The search for molecular tool kits with homophilic binding specificity resulted in a diverse repertoire of adhesion molecules. Recent understanding of the dominant role of cortical tension over adhesion binding redirects the focus of differential adhesion studies to the signaling function of adhesion proteins to regulate actomyosin contractility. The broader framework of differential interfacial tension encompasses both adhesion and nonadhesion molecules, sharing the common function of modulating interfacial tension during cell sorting to generate diverse tissue patterns. Robust adhesion-based patterning requires close coordination between morphogen signaling, cell fate decisions, and changes in adhesion. Current advances in bridging theoretical and experimental approaches present exciting opportunities to understand molecular, cellular, and tissue dynamics during adhesion-based tissue patterning across multiple time and length scales.

Long-Term Enhancement of NMDA Receptor Function in Inhibitory Neurons Preferentially Modulates Potassium Channels and Cell Adhesion Molecules

Effectively enhancing the activity of inhibitory neurons has great therapeutic potentials since their reduced function/activity has significant contributions to pathology in various brain diseases. We showed previously that NMDAR positive allosteric modulator GNE-8324 and M-8324 selectively increase NMDAR activity on the inhibitory neurons and elevates their activity in vitro and in vivo. Here we examined the impact of long-term administering M-8324 on the functions and transcriptional profiling of parvalbumin-containing neurons in two representative brain regions, primary auditory cortex (Au1) and prelimbic prefrontal cortex (PrL-PFC). We found small changes in key electrophysiological parameters and RNA levels of neurotransmitter receptors, Na⁺ and Ca²⁺ channels. In contrast, large differences in cell adhesion molecules and K⁺ channels were found between Au1 and PrL-PFC in drug-naïve mice, and differences in cell adhesion molecules became much smaller after M-8324 treatment. There was also minor impact of M-8324 on cell cycle and apoptosis, suggesting a fine safety profile.

Protocadherin-7 Regulates Osteoclast Differentiation through Intracellular SET-Binding Domain-Mediated RhoA and Rac1 Activation

Protocadherin-7 (Pcdh7) is a member of the non-clustered protocadherin δ1 subgroup of the cadherin superfamily. Although the cell-intrinsic role of Pcdh7 in osteoclast differentiation has been demonstrated, the molecular mechanisms of Pcdh7 regulating osteoclast differentiation remain to be determined. Here, we demonstrate that Pcdh7 contributes to osteoclast differentiation by regulating small GTPases, RhoA and Rac1, through its SET oncoprotein binding domain. Pcdh7 is associated with SET along with RhoA and Rac1 during osteoclast differentiation. Pcdh7-deficient (Pcdh7-/-) cells showed abolished RANKL-induced RhoA and Rac1 activation, and impaired osteoclast differentiation. Impaired osteoclast differentiation in Pcdh7-/- cells was restored by retroviral transduction of full-length Pcdh7 but not by a Pcdh7 mutant that lacks SET binding domain. The direct crosslink of the Pcdh7 intracellular region induced the activation of RhoA and Rac1, which was not observed when Pcdh7 lacks the SET binding domain. Additionally, retroviral transduction of the constitutively active form of RhoA and Rac1 completely restored the impaired osteoclast differentiation in Pcdh7-/- cells. Collectively, these results demonstrate that Pcdh7 controls osteoclast differentiation by regulating RhoA and Rac1 activation through the SET binding domain.

The distribution of Cdh20 mRNA demarcates somatotopic subregions and subpopulations of spiny projection neurons in the rat dorsolateral striatum

The dorsolateral striatum (DLS) of rodents is functionally subdivided into somatotopic subregions that represent each body part along both the dorsoventral and anteroposterior (A-P) axes and play crucial roles in sensorimotor functions via corticostriatal pathways. However, little is known about the spatial gene expression patterns and heterogeneity of spiny projection neurons (SPNs) within somatotopic subregions. Here, we show that the cell adhesion molecule gene Cdh20, which encodes a Type II cadherin, is expressed in discrete subregions covering the inner orofacial area and part of the forelimb area in the ventral domain of the DLS (v-DLS) in rats. Cdh20-expressing cells were localized in the v-DLS at the intermediate level of the striatum along the A-P axis and could be classified as direct-pathway SPNs or indirect-pathway SPNs. Unexpectedly, comprehensive analysis revealed that Cdh20 is expressed in SPNs in the rat DLS but not in the mouse DLS or the ferret putamen (Pu). Our observations reveal that Cdh20 expression demarcates somatotopic subregions and subpopulations of SPNs specifically in the rat DLS and suggest divergent regulation of genes differentially expressed in the v-DLS and Pu among mammals.

Differential Spatiotemporal Expression of Type I and Type II Cadherins Associated With the Segmentation of the Central Nervous System and Formation of Brain Nuclei in the Developing Mouse

Type I and type II classical cadherins comprise a family of cell adhesion molecules that regulate cell sorting and tissue separation by forming specific homo and heterophilic bonds. Factors that affect cadherin-mediated cell-cell adhesion include cadherin binding affinity and expression level. This study examines the expression pattern of type I cadherins (Cdh1, Cdh2, Cdh3, and Cdh4), type II cadherins (Cdh6, Cdh7, Cdh8, Cdh9, Cdh10, Cdh11, Cdh12, Cdh18, Cdh20, and Cdh24), and the atypical cadherin 13 (Cdh13) during distinct morphogenetic events in the developing mouse central nervous system from embryonic day 11.5 to postnatal day 56. Cadherin mRNA expression levels obtained from in situ hybridization experiments carried out at the Allen Institute for Brain Science (https://alleninstitute.org/) were retrieved from the Allen Developing Mouse Brain Atlas. Cdh2 is the most abundantly expressed type I cadherin throughout development, while Cdh1, Cdh3, and Cdh4 are expressed at low levels. Type II cadherins show a dynamic pattern of expression that varies between neuroanatomical structures and developmental ages. Atypical Cdh13 expression pattern correlates with Cdh2 in abundancy and localization. Analyses of cadherin-mediated relative adhesion estimated from their expression level and binding affinity show substantial differences in adhesive properties between regions of the neural tube associated with the segmentation along the anterior–posterior axis. Differences in relative adhesion were also observed between brain nuclei in the developing subpallium (basal ganglia), suggesting that differential cell adhesion contributes to the segregation of neuronal pools. In the adult cerebral cortex, type II cadherins Cdh6, Cdh8, Cdh10, and Cdh12 are abundant in intermediate layers, while Cdh11 shows a gradated expression from the deeper layer 6 to the superficial layer 1, and Cdh9, Cdh18, and Cdh24 are more abundant in the deeper layers. Person’s correlation analyses of cadherins mRNA expression patterns between areas and layers of the cerebral cortex and the nuclei of the subpallium show significant correlations between certain cortical areas and the basal ganglia. The study shows that differential cadherin expression and cadherin-mediated adhesion are associated with a wide range of morphogenetic events in the developing central nervous system including the organization of neurons into layers, the segregation of neurons into nuclei, and the formation of neuronal circuits.

Right Place at the Right Time: How Changes in Protocadherins Affect Synaptic Connections Contributing to the Etiology of Neurodevelopmental Disorders

During brain development, neurons need to form the correct connections with one another in order to give rise to a functional neuronal circuitry. Mistakes during this process, leading to the formation of improper neuronal connectivity, can result in a number of brain abnormalities and impairments collectively referred to as neurodevelopmental disorders. Cell adhesion molecules (CAMs), present on the cell surface, take part in the neurodevelopmental process regulating migration and recognition of specific cells to form functional neuronal assemblies. Among CAMs, the members of the protocadherin (PCDH) group stand out because they are involved in cell adhesion, neurite initiation and outgrowth, axon pathfinding and fasciculation, and synapse formation and stabilization. Given the critical role of these macromolecules in the major neurodevelopmental processes, it is not surprising that clinical and basic research in the past two decades has identified several PCDH genes as responsible for a large fraction of neurodevelopmental disorders. In the present article, we review these findings with a focus on the non-clustered PCDH sub-group, discussing the proteins implicated in the main neurodevelopmental disorders.

Cognitive Stimulation Induces Differential Gene Expression in Octopus vulgaris: The Key Role of Protocadherins

Octopuses are unique invertebrates, with sophisticated and flexible behaviors controlled by a high degree of brain plasticity, learning, and memory. Moreover, in Octopus vulgaris, it has been demonstrated that animals housed in an enriched environment show adult neurogenesis in specific brain areas. Firstly, we evaluated the optimal acclimatization period needed for an O. vulgaris before starting a cognitive stimulation experiment. Subsequently, we analyzed differential gene expression in specific brain areas in adult animals kept in tested (enriched environment), wild (naturally enriched environment), and control conditions (unenriched environment). We selected and sequenced three protocadherin genes (PCDHs) involved in the development and maintenance of the nervous system; three Pax genes that control cell specification and tissue differentiation; the Elav gene, an earliest marker for neural cells; and the Zic1 gene, involved in early neural formation in the brain. In this paper, we evaluated gene expression levels in O. vulgaris under different cognitive stimulations. Our data shows that Oct-PCDHs genes are upregulated in the learning and lower motor centers in the brain of both tested and wild animals (higher in the latter). Combining these results with our previous studies on O. vulgaris neurogenesis, we proposed that PCDH genes may be involved in adult neurogenesis processes, and related with their cognitive abilities.

In silico Identification and Expression of Protocadherin Gene Family in Octopus vulgaris

Connecting millions of neurons to create a functional neural circuit is a daunting challenge. Vertebrates developed a molecular system at the cell membrane to allow neurons to recognize each other by distinguishing self from non-self through homophilic protocadherin interactions. In mammals, the protocadherin gene family counts about 50 different genes. By hetero-multimerization, protocadherins are capable of generating an impressive number of molecular interfaces. Surprisingly, in the California two-spot octopus, Octopus bimaculoides, an invertebrate belonging to the Phylum Mollusca, over 160 protocadherins (PCDHs) have been identified. Here we briefly discuss the role of PCDHs in neural wiring and conduct a comparative study of the protocadherin gene family in two closely related octopus species, Octopus vulgaris and O. bimaculoides. A first glance at the expression patterns of protocadherins in O. vulgaris is also provided. Finally, we comment on PCDH evolution in the light of invertebrate nervous system plasticity.

Regulation of neural circuit formation by protocadherins

The protocadherins (Pcdhs), which make up the most diverse group within the cadherin superfamily, were first discovered in the early 1990s. Data implicating the Pcdhs, including ~60 proteins encoded by the tandem Pcdha, Pcdhb, and Pcdhg gene clusters and another ~10 non-clustered Pcdhs, in the regulation of neural development have continually accumulated, with a significant expansion of the field over the past decade. Here, we review the many roles played by clustered and non-clustered Pcdhs in multiple steps important for the formation and function of neural circuits, including dendrite arborization, axon outgrowth and targeting, synaptogenesis, and synapse elimination. We further discuss studies implicating mutation or epigenetic dysregulation of Pcdh genes in a variety of human neurodevelopmental and neurological disorders. With recent structural modeling of Pcdh proteins, the prospects for uncovering molecular mechanisms of Pcdh extracellular and intracellular interactions, and their role in normal and disrupted neural circuit formation, are bright.

Cadherins mediate cocaine-induced synaptic plasticity and behavioral conditioning

Drugs of abuse alter synaptic connections in the ‘reward circuit’ of the brain, which leads to long-lasting behavioral changes that underlie addiction. Here we show that cadherin adhesion molecules play a critical role in mediating synaptic plasticity and behavioral changes driven by cocaine. We demonstrate that cadherin is essential for long-term potentiation (LTP) in the ventral tegmental area (VTA), and is recruited to the synaptic membrane of excitatory inputs onto dopaminergic neurons following cocaine-mediated behavioral conditioning. Furthermore, we show that stabilization of cadherin at the membrane of these synapses blocks cocaine-induced synaptic plasticity, leading to a significant reduction in conditioned place preference induced by cocaine. Our findings identify cadherins and associated molecules as targets of interest for understanding pathological plasticity associated with addiction.

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-β (Aβ) 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.

Electronic supplementary material

The online version of this article (doi:10.1186/s12952-016-0065-9) contains supplementary material, which is available to authorized users.

Specification of synaptic connectivity by cell surface interactions

The molecular diversification of cell surface molecules has long been postulated to impart specific surface identities on neuronal cell types. The existence of unique cell surface identities would allow neurons to distinguish one another and connect with their appropriate target cells. Although progress has been made in identifying cell type-specific surface molecule repertoires and in characterizing their extracellular interactions, determining how this molecular diversity contributes to the precise wiring of neural circuitry has proven challenging. Here, we review the role of the cadherin, neurexin, immunoglobulin and leucine-rich repeat protein superfamilies in the specification of connectivity. The emerging evidence suggests that the concerted actions of these proteins may critically contribute to the assembly of neural circuits.

Protocadherins and hypothalamic development: do they play an unappreciated role?

Normal brain development requires coordinated cell movements at precise times. It has long been established that cell-cell adhesion proteins of the cadherin superfamily are involved in the adhesion and sorting of cells during tissue morphogenesis. In the present review, we focus on protocadherins, which form the largest subfamily of the cadherin superfamily and mediate homophilic cell-cell adhesion in the developing brain. These molecules are highly expressed during neural development and the exact roles that they play are still emerging. Although, historically, protocadherins were considered to provide mechanical and chemical connections between adjacent cells, recent research suggests that they may also serve as molecular identity markers of neurones to help guide cell recognition and sorting, cell migration, outgrowth of neuronal processes, and synapse formation. This phenomenon of single cell diversity stems, in part, from the vast variation in protein structure, genomic organisation and molecular function of the protocadherins. Although expression profiles and genetic manipulations have provided evidence for the role of protocadherins in the developing brain, we have only begun to construct a complete understanding of protocadherin function. We examine our current understanding of how protocadherins influence brain development and discuss the possible roles for this large superfamily within the hypothalamus. We conclude that further research into these underappreciated but vitally important genes will shed insight into hypothalamic development and perhaps the underlying aetiology of neuroendocrine disorders.

Differential expression of protocadherin-19, protocadherin-17, and cadherin-6 in adult zebrafish brain

Cell adhesion molecule cadherins play important roles in both development and maintenance of adult structures. Most studies on cadherin expression have been carried out in developing organisms, but information on cadherin distribution in adult vertebrate brains is limited. In this study we used in situ hybridization to examine mRNA expression of three cadherins, protocadherin-19, protocadherin-17, and cadherin-6 in adult zebrafish brain. Each cadherin exhibits a distinct expression pattern in the fish brain, with protocadherin-19 and protocadherin-17 showing much wider and stronger expression than that of cadherin-6. Both protocadherin-19 and protocadherin-17-expressing cells occur throughout the brain, with strong expression in the ventromedial telencephalon, periventricular regions of the thalamus and anterior hypothalamus, stratum periventriculare of the optic tectum, dorsal tegmental nucleus, granular regions of the cerebellar body and valvula, and superficial layers of the facial and vagal lobes. Numerous sensory structures (e.g., auditory, gustatory, lateral line, olfactory, and visual nuclei) and motor nuclei (e.g., oculomotor, trochlear, trigeminal motor, abducens, and vagal motor nuclei) contain protocadherin-19 and/or protocadherin-17-expressing cell. Expression of these two protocadherins is similar in the ventromedial telencephalon, thalamus, hypothalamus, facial, and vagal lobes, but substantially different in the dorsolateral telencephalon, intermediate layers of the optic tectum, and cerebellar valvula. In contrast to the two protocadherins, cadherin-6 expression is much weaker and limited in the adult fish brain.

Cadherins mediate sequential roles through a hierarchy of mechanisms in the developing mammillary body

Expression of intricate combinations of cadherins (a family of adhesive membrane proteins) is common in the developing central nervous system. On this basis, a combinatorial cadherin code has long been proposed to underlie neuronal sorting and to be ultimately responsible for the layers, columns and nuclei of the brain. However, experimental proof of this particular function of cadherins has proven difficult to obtain and the question is still not clear. Alternatively, non-specific, non-combinatorial, purely quantitative adhesive differentials have been proposed to explain neuronal sorting in the brain. Do cadherin combinations underlie brain cytoarchitecture? We approached this question using as model a well-defined forebrain nucleus, the mammillary body (MBO), which shows strong, homogeneous expression of one single cadherin (Cdh11) and patterned, combinatorial expression of Cdh6, −8 and −10. We found that, besides the known combinatorial Cdh pattern, MBO cells are organized into a second, non-overlapping pattern grouping neurons with the same date of neurogenesis. We report that, in the Foxb1 mouse mutant, Cdh11 expression fails to be maintained during MBO development. This disrupted the combination-based as well as the birthdate-based sorting in the mutant MBO. In utero RNA interference (RNAi) experiments knocking down Cdh11 in MBO-fated migrating neurons at one specific age showed that Cdh11 expression is required for chronological entrance in the MBO. Our results suggest that neuronal sorting in the developing MBO is caused by adhesion-based, non-combinatorial mechanisms that keep neurons sorted according to birthdate information (possibly matching them to target neurons chronologically sorted in the same manner). Non-specific adhesion mechanisms would also prevent cadherin combinations from altering the birthdate-based sorting. Cadherin combinations would presumably act later to support specific synaptogenesis through specific axonal fasciculation and final target recognition.

Emerging roles of protocadherins: from self-avoidance to enhancement of motility

Protocadherins are a group of transmembrane proteins belonging to the cadherin superfamily that are subgrouped into 'clustered' and 'non-clustered' protocadherins. Although cadherin superfamily members are known to regulate various forms of cell-cell interactions, including cell-cell adhesion, the functions of protocadherins have long been elusive. Recent studies are, however, uncovering their unique roles. The clustered protocadherins regulate neuronal survival, as well as dendrite self-avoidance. Combinatorial expression of clustered protocadherin isoforms creates a great diversity of adhesive specificity for cells, and this process is likely to underlie the dendritic self-avoidance. Non-clustered protocadherins promote cell motility rather than the stabilization of cell adhesion, unlike the classic cadherins, and mediate dynamic cellular processes, such as growth cone migration. Protocadherin dysfunction in humans is implicated in neurological disorders, such as epilepsy and mental retardation. This Commentary provides an overview of recent findings regarding protocadherin functions, as well as a discussion of the molecular basis underlying these functions.

Cadherin-8 expression, synaptic localization, and molecular control of neuronal form in prefrontal corticostriatal circuits

Neocortical interactions with the dorsal striatum support many motor and executive functions, and such underlying functional networks are particularly vulnerable to a variety of developmental, neurological, and psychiatric brain disorders, including autism spectrum disorders, Parkinson's disease, and Huntington's disease. Relatively little is known about the development of functional corticostriatal interactions, and in particular, virtually nothing is known of the molecular mechanisms that control generation of prefrontal cortex-striatal circuits. Here, we used regional and cellular in situ hybridization techniques coupled with neuronal tract tracing to show that Cadherin-8 (Cdh8), a homophilic adhesion protein encoded by a gene associated with autism spectrum disorders and learning disability susceptibility, is enriched within striatal projection neurons in the medial prefrontal cortex and in striatal medium spiny neurons forming the direct or indirect pathways. Developmental analysis of quantitative real-time polymerase chain reaction and western blot data show that Cdh8 expression peaks in the prefrontal cortex and striatum at P10, when cortical projections start to form synapses in the striatum. High-resolution immunoelectron microscopy shows that Cdh8 is concentrated at excitatory synapses in the dorsal striatum, and Cdh8 knockdown in cortical neurons impairs dendritic arborization and dendrite self-avoidance. Taken together, our findings indicate that Cdh8 delineates developing corticostriatal circuits where it is a strong candidate for regulating the generation of normal cortical projections, neuronal morphology, and corticostriatal synapses.

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.

Protocadherin 11 x regulates differentiation and proliferation of neural stem cell in vitro and in vivo

Protocadherin 11 X-linked (Pcdh11x) protein is a member of the cadherin superfamily with established roles in cell adhesion. Previous studies have shown the molecular biology and possible relevance of Pcdh11x with neurological disease in humans. However, little is known about the neurophysiological function of Pcdh11x in neural development. Here, we verified that Pcdh11x is primarily expressed in various brain areas including the cortex, hippocampus, and ventricular/subventricular zone (VZ/SVZ) at different embryonic stages. Furthermore, both in vitro and in vivo experiments showed that Pcdh11x decreased neural differentiation but increased the neural proliferation. These observations demonstrate a crucial function for Pcdh11x during the development of central nervous system.

An MRI atlas of the mouse basal ganglia

The basal ganglia are a group of subpallial nuclei that play an important role in motor, emotional, and cognitive functions. Morphological changes and disrupted afferent/efferent connections in the basal ganglia have been associated with a variety of neurological disorders including psychiatric and movement disorders. While high-resolution magnetic resonance imaging has been used to characterize changes in brain structure in mouse models of these disorders, no systematic method for segmentation of the C57BL/6 J mouse basal ganglia exists. In this study we have used high-resolution MR images of ex vivo C57BL/6 J mouse brain to create a detailed protocol for segmenting the basal ganglia. We created a three-dimensional minimum deformation atlas, which includes the segmentation of 35 striatal, pallidal, and basal ganglia-related structures. In addition, we provide mean volumes, mean T2 contrast intensities and mean FA and ADC values for each structure. This MR atlas is available for download, and enables researchers to perform automated segmentation in genetic models of basal ganglia disorders.

Protocadherin 17 regulates presynaptic assembly in topographic corticobasal Ganglia circuits

Highly topographic organization of neural circuits exists for the regulation of various brain functions in corticobasal ganglia circuits. Although neural circuit-specific refinement during synapse development is essential for the execution of particular neural functions, the molecular and cellular mechanisms for synapse refinement are largely unknown. Here, we show that protocadherin 17 (PCDH17), one of the nonclustered δ2-protocadherin family members, is enriched along corticobasal ganglia synapses in a zone-specific manner during synaptogenesis and regulates presynaptic assembly in these synapses. PCDH17 deficiency in mice causes facilitated presynaptic vesicle accumulation and enhanced synaptic transmission efficacy in corticobasal ganglia circuits. Furthermore, PCDH17(-/-) mice exhibit antidepressant-like phenotypes that are known to be regulated by corticobasal ganglia circuits. Our findings demonstrate a critical role for PCDH17 in the synaptic development of specific corticobasal ganglia circuits and suggest the involvement of PCDH17 in such circuits in depressive behaviors.

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.

Comparative analysis of protocadherin-11 X-linked expression among postnatal rodents, non-human primates, and songbirds suggests its possible involvement in brain evolution

Background

Protocadherin-11 is a cell adhesion molecule of the cadherin superfamily. Since, only in humans, its paralog is found on the Y chromosome, it is expected that protocadherin-11X/Y plays some role in human brain evolution or sex differences. Recently, a genetic mutation of protocadherin-11X/Y was reported to be associated with a language development disorder. Here, we compared the expression of protocadherin-11 X-linked in developing postnatal brains of mouse (rodent) and common marmoset (non-human primate) to explore its possible involvement in mammalian brain evolution. We also investigated its expression in the Bengalese finch (songbird) to explore a possible function in animal vocalization and human language faculties.

Methodology/Principal Findings

Protocadherin-11 X-linked was strongly expressed in the cerebral cortex, hippocampus, amygdala and brainstem. Comparative analysis between mice and marmosets revealed that in certain areas of marmoset brain, the expression was clearly enriched. In Bengalese finches, protocadherin-11 X-linked was expressed not only in nuclei of regions of the vocal production pathway and the tracheosyringeal hypoglossal nucleus, but also in areas homologous to the mammalian amygdala and hippocampus. In both marmosets and Bengalese finches, its expression in pallial vocal control areas was developmentally regulated, and no clear expression was seen in the dorsal striatum, indicating a similarity between songbirds and non-human primates.

Conclusions/Significance

Our results suggest that the enriched expression of protocadherin-11 X-linked is involved in primate brain evolution and that some similarity exists between songbirds and primates regarding the neural basis for vocalization.

Distribution of protocadherin 9 protein in the developing mouse nervous system

Protocadherin 9 (Pcdh9) is a member of the protocadherin family, which includes many members involved in various phenomena, such as cell-cell adhesion, neural projection, and synapse formation. Here, we identified Pcdh9 protein in the mouse brain and examined its distribution during neural development. Pcdh9, with a molecular weight of approximately 180 kDa, was localized at cell-cell contact sites in COS-1 cells transfected with Pcdh9 cDNA. In cultured neurons, it was detected at the growth cone and at adhesion sites along neurites. In the E13.5 brain, prominent Pcdh9 immunoreactivity was detected in the dorsal thalamus along with other regions including the vestibulocochlear nerve. As development proceeded (E15.5-P1), Pcdh9 immunoreactivity became observable in various brain regions but was restricted to certain fiber tracts and brain nuclei. Interestingly, many Pcdh9-positive brain nuclei and fascicles belonged to the vestibular (e.g. vestibulocochlear nerve, vestibular nuclei, and the vestibulocerebellum) and oculomotor systems (medial longitudinal fascicles, oculomotor nucleus, trochlear nucleus, and interstitial nucleus of Cajal). In addition, we examined the distribution of Pcdh9 protein in the olfactory bulb, retina, spinal cord, and dorsal root ganglion. In these regions, Pcdh9 and OL-protocadherin proteins were differentially distributed, with the difference highlighted in the olfactory bulb, where they were enriched in different subsets of glomeruli. In the mature retina, Pcdh9 immunoreactivity was detected in distinct sublaminae of the inner and outer plexiform layers. In the dorsal root ganglion, only certain subsets of neurons showed Pcdh9 immunoreactivity. These results suggest that Pcdh9 might be involved in formation of specific neural circuits during neural development.

Expression of delta-protocadherins in the spinal cord of the chicken embryo

Protocadherins constitute the largest subfamily of cadherin genes and are widely expressed in the nervous system. In the present study, we cloned eight members of the delta-protocadherin subfamily of cadherins (Pcdh1, Pcdh7, Pcdh8, Pcdh9, Pcdh10, Pcdh17, Pcdh18, and Pcdh19) from the chicken, and investigated their expression in the developing chicken spinal cord by in situ hybridization. Our results showed that each of the investigated delta-protocadherins exhibits a spatially restricted and temporally regulated pattern of expression. Pcdh1, Pcdh8, Pcdh18, and Pcdh19 are expressed in restricted dorsoventral domains of the neuroepithelial layer at early developmental stages (E2.5–E4). In the differentiating mantle layer, specific expression profiles are observed for all eight delta-protocadherins along the dorsoventral, mediolateral, and rostrocaudal dimensions at intermediate stages of development (E6–E10). Expression profiles are especially diverse in the motor column, where different pools of motor neurons exhibit signal for subsets of delta-protocadherins. In the dorsal root ganglion, subpopulations of cells express combinations of Pcdh1, Pcdh7, Pcdh8, Pcdh9, Pcdh10, and Pcdh17. The ventral boundary cap cells are positive for Pcdh7, Pcdh9, and Pcdh10. Signals for Pcdh8, Pcdh18, and Pcdh19 are found in the meninges. Surrounding tissues, such as the notochord, dermomyotome, and sclerotome also exhibit differential expression patterns. The highly regulated spatiotemporal expression patterns of delta-protocadherins suggest that they have multiple and diverse functions during development of the spinal cord and its surrounding tissues.

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.

Protocadherin 11X/Y a human-specific gene pair: an immunohistochemical survey of fetal and adult brains

Protocadherins 11X and 11Y are cell adhesion molecules of the δ1-protocadherin family. Pcdh11X is present throughout the mammalian radiation; however, 6 million years ago (MYA), a reduplicative translocation of the Xq21.3 block onto what is now human Yp11 created the Homo sapiens-specific PCDH11Y. Therefore, modern human females express PCDH11X whereas males express both PCDH11X and PCDH11Y. PCDH11X/Y has been subject to accelerated evolution resulting in human-specific changes to both proteins, most notably 2 cysteine substitutions in the PCDH11X ectodomain that may alter binding characteristics. The PCDH11X/Y gene pair is postulated to be critical to aspects of human brain evolution related to the neural correlates of language. Therefore, we raised antibodies to investigate the temporal and spatial expression of PCDH11X/Y in cortical and sub-cortical areas of the human fetal brain between 12 and 34 postconceptional weeks. We then used the antibodies to determine if this expression was consistent in a series of adult brains. PCDH11X/Y immunoreactivity was detectable at all developmental stages. Strong expression was detected in the fetal neocortex, ganglionic eminences, cerebellum, and inferior olive. In the adult brain, the cerebral cortex, hippocampal formation, and cerebellum were strongly immunoreactive, with expression also detectable in the brainstem.

Cadherin-6 mediates axon-target matching in a non-image-forming visual circuit

Neural circuits consist of highly precise connections among specific types of neurons that serve a common functional goal. How neurons distinguish among different synaptic targets to form functionally precise circuits remains largely unknown. Here, we show that during development, the adhesion molecule cadherin-6 (Cdh6) is expressed by a subset of retinal ganglion cells (RGCs) and also by their targets in the brain. All of the Cdh6-expressing retinorecipient nuclei mediate non-image-forming visual functions. A screen of mice expressing GFP in specific subsets of RGCs revealed that Cdh3-RGCs which also express Cdh6 selectively innervate Cdh6-expressing retinorecipient targets. Moreover, in Cdh6-deficient mice, the axons of Cdh3-RGCs fail to properly innervate their targets and instead project to other visual nuclei. These findings provide functional evidence that classical cadherins promote mammalian CNS circuit development by ensuring that axons of specific cell types connect to their appropriate synaptic targets.

Non-clustered protocadherin

The cadherin family is classified into classical cadherins, desmosomal cadherins and protocadherins (PCDHs). Genomic structures distinguish between PCDHs and other cadherins, and between clustered and non-clustered PCDHs. The phylogenetic analysis with full sequences of non-clustered PCDHs enabled them to be further classified into three subgroups: δ1 (PCDH1, PCDH7, PCDH9, PCDH11 and PCDH20), δ2 (PCDH8, PCDH10, PCDH12, PCDH17, PCDH18 and PCDH19) and ε (PCDH15, PCDH16, PCDH21 and MUCDHL). ε-PCDH members except PCDH21 have either higher or lower numbers of cadherin repeats than those of other PCDHs. Non-clustered PCDHs are expressed predominantly in the nervous system and have spatiotemporally diverse expression patterns. Especially, the region-specific expressions of non-clustered PCDHs have been observed in cortical area of early postnatal stage and in caudate putaman and/or hippocampal formation of mature brains, suggesting that non-clustered PCDHs play roles in the circuit formation and maintenance. The non-clustered PCDHs appear to have homophilic/heterophilc cell-cell adhesion properties, and each member has diverse cell signaling partnership distinct from those of other members (PCDH7/TAF1; PCDH8/TAO2β; PCDH10/Nap1; PCDH11/β-catenin; PCDH18/mDab1). Furthermore, each PCDH has several isoforms with differential cytoplasmic sequences, suggesting that one PCDH isoform could activate intracellular signaling differential from other isoforms. These facts suggest that non-clustered PCDHs play roles as a mediator of a regulator of other molecules as well as cell-cell adhesion. Furthermore, some non-clustered PCDHs have been considered to be involved in neuronal diseases such as autism-spectrum disorders, schizophrenia, and female-limited epilepsy and cognitive impairment, suggesting that they play multiple, tightly regulated roles in normal brain function. In addition, some non-clustered PCDHs have been suggested as candidate tumor suppressor genes in several tissues. Although molecular adhesive and regulatory properties of some PCDHs began to be unveiled, the endeavor to understand the molecular mechanism of non-clustered PCDH is still in its infancy and requires future study.

Cadherin expression in the somatosensory cortex: evidence for a combinatorial molecular code at the single-cell level

Cadherin superfamily genes play a role in a wide variety of developmental processes and mature functions of the vertebrate brain. In the present study, we mapped in situ the expression pattern of five classic cadherins (Cdh4, Cdh6, Cdh7, Cdh8, Cdh11) and eight δ-protocadherins (Pcdh1, Pcdh7, Pcdh8, Pcdh9, Pcdh10, Pcdh11, Pcdh17 and Pcdh19) in the primary somatosensory cortex of the adult mouse. All of these cadherins show layer-specific expression profiles in primary somatosensory cortex. Some cadherins (for example, Cdh4, Cdh7, Pcdh8) mark subsets of cells within a given lamina, while other cadherins (Cdh11 and Pcdh10) are expressed more widely in multiple layers. Results from tyramide-based double-fluorescence in situ hybridization (FISH) provide evidence that most single neurons express more than one cadherin in a combinatorial fashion in all layers of cerebral cortex. This combinatorial code is rather comprehensive because pairwise expression of cadherins can assume any type of combination (complementarity, partial or complete overlap, subset-specific expression, cell-size specific expression, etc.). We propose that the combinatorial expression of multiple cadherin genes contributes to the molecular specification of the vast complexity of neurons in cerebral cortex.

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.

The expression of non-clustered protocadherins in adult rat hippocampal formation and the connecting brain regions

Non-clustered protocadherins (PCDHs) are calcium-dependent adhesion molecules which have attracted attention for their possible roles in the neuronal circuit formation during development and their implications in the neurological disorders such as autism and mental retardation. Previously, we found that a subset of the non-clustered PCDHs exhibited circuit-dependent expression patterns in thalamo-cortical connections in early postnatal rat brain, but such patterns disappeared in adulthood. In this study, we identified that the non-clustered PCDHs showed differential expression patterns along the septotemporal axis in the subregions of adult hippocampus and dentate gyrus with topographical preferences. The expressions of PCDH1, PCDH9, PCDH10 and PCDH20 showed septal preferences, whereas the expressions of PCDH8, PCDH11, PCDH17 and PCDH19 showed temporal preferences, suggesting that they play roles in the formation/maintenance of intrahippocampal circuits. PCDHs also exhibited the region-specific expression patterns in the areas connected to hippocampal formation such as entorhinal cortex, lateral septum, and basolateral amygdaloid complex. Furthermore, the expression levels of three PCDHs (PCDH8, PCDH19 and PCDH20) were regulated by the electroconvulsive shock stimulation of the brain in the adult hippocampus and dentate gyrus. These results suggest that non-clustered PCDHs are involved in the maintenance and plasticity of adult hippocampal circuitry.

Adhesion properties and retinofugal expression of chicken protocadherin-19

Protocadherin-19 has been implicated in some neurological diseases, but even the basic properties of this protocadherin have not yet been characterized well. Hence, various basic properties of chicken protocadherin-19 were examined to elucidate its biological role. The protocadherin-19 expressed in L cells was localized at the intercellular contact sites and showed Ca(2+)-dependent homophilic cell aggregation activity that was relatively weak but showed stringent specificity. The results of a pull-down assay using fusion proteins of the cytoplasmic domain and glutathione S-transferase yielded specifically bound proteins. In the bound fractions, liquid chromatography-mass spectrometry identified Nck-associated protein 1 and cytoplasmic FMP1 interacting protein 2, which have been reported to bind to glutathione S-transferase fused with the cytoplasmic domain of OL-protocadherin, suggesting that these proteins generally have affinity for delta protocadherins. Protocadherin-19 was mainly expressed in the central nervous system. In the chicken retina, protocadherin-19 was expressed as early as embryonic day 5 and was localized in the ganglion cell layer, inner plexiform layer, and optic nerve layer. Chicken protocadherin-19 was co-localized with syntaxin 1 in inner plexiform layer and was also expressed in the optic nerve and in specific layers of optic tectum. These results suggest that protocadherin-19 plays a role as an adhesion protein in optic nerve fiber bundling, optic nerve targeting, and/or synapse formation.

Expression of cadherin superfamily genes in brain vascular development

Cadherins are Ca2+-dependent cell adhesion molecules that are important in vertebrate nervous system development. We identified seven members of the cadherin superfamily (cadherin-4, cadherin-5, cadherin-6, cadherin-6, cadherin-11, protocadherin-1, and protocadherin-17) and an intracellular binding partner of delta-protocadherins, protein phosphatase 1alpha, as novel markers for developing blood vessels in the ferret brain. Some of the cadherin molecules are restricted to specific brain regions or a subset of blood vessels. The expression levels show a peak during perinatal vascular development. Our results suggest that multiple cadherins, which are also involved in neurogenesis, are regulators of angiogenesis in developing vertebrate brain.

Expression of protocadherin-1 (Pcdh1) during mouse development

Protocadherin-1 (Pcdh1) is a member of the delta-protocadherin subgroup of non-clustered protocadherins. We studied the expression of Pcdh1 from the early embryonic to the adult stage of mouse development by semi-quantitative RT-PCR and in situ hybridization. Pcdh1 can be detected as early as embryonic day 9.5. In early embryogenesis, expression is especially prominent in blood vessels. During later development and in the adult mouse, organs derived from the embryonic gut, such as the esophagus, intestines, liver, lung, and submandibular gland, contain epithelia and other types of tissues that are Pcdh1-positive. Other positive organs include the brain, spinal cord, retina, peripheral ganglia, the inner ear, hair follicles, kidney, vagina, uterus, placenta, testis, prostate, and the seminal gland. The tight spatial and temporal regulation of Pcdh1 expression suggests that this protocadherin plays multiple roles not only during development but also in mature tissues and organs in the mouse.

Layer-specific expression of multiple cadherins in the developing visual cortex (V1) of the ferret

Cadherins are superfamily of Ca2+-dependent transmembrane glycoproteins with more than 100 members. They play a role in a wide variety of developmental mechanisms, including cell proliferation, cell differentiation, cell-cell recognition, neurite outgrowth and synaptogenesis. We cloned 16 novel members of the classic cadherin and delta-protocadherin subgroups from ferret brain. Their expression patterns were investigated by in situ hybridization in the developing primary visual cortex (V1) of the ferret. Fifteen out of the 16 cadherins are expressed in a spatiotemporally restricted fashion throughout development. Each layer of V1 can be characterized by the combinatorial expression of a subset of cadherins at any given developmental stage. A few cadherins are expressed by subsets of neurons in specific layers or by neurons dispersed throughout all cortical layers. Generally, the expression of protocadherins is more widespread, whereas that of classic cadherins is more restricted to specific layers. At the V1/V2 boundary, changes in layer-specific cadherin expression are observed. In conclusion, our results suggest that cadherins provide a code of potentially adhesive cues for layer formation in ferret V1. The persistence of expression in the adult suggests a functional role also in the mature cortex.