Cloning and expression analysis of cadherin-10 in the CNS of the chicken embryo

Segregated expressions of autism risk genes Cdh11 and Cdh9 in autism-relevant regions of developing cerebellum

Results of recent genome-wide association studies (GWAS) and whole genome sequencing (WGS) highlighted type II cadherins as risk genes for autism spectrum disorders (ASD). To determine whether these cadherins may be linked to the morphogenesis of ASD-relevant brain regions, in situ hybridization (ISH) experiments were carried out to examine the mRNA expression profiles of two ASD-associated cadherins, Cdh9 and Cdh11, in the developing cerebellum. During the first postnatal week, both Cdh9 and Cdh11 were expressed at high levels in segregated sub-populations of Purkinje cells in the cerebellum, and the expression of both genes was declined as development proceeded. Developmental expression of Cdh11 was largely confined to dorsal lobules (lobules VI/VII) of the vermis as well as the lateral hemisphere area equivalent to the Crus I and Crus II areas in human brains, areas known to mediate high order cognitive functions in adults. Moreover, in lobules VI/VII of the vermis, Cdh9 and Cdh11 were expressed in a complementary pattern with the Cdh11-expressing areas flanked by Cdh9-expressing areas. Interestingly, the high level of Cdh11 expression in the central domain of lobules VI/VII was correlated with a low level of expression of the Purkinje cell marker calbindin, coinciding with a delayed maturation of Purkinje cells in the same area. These findings suggest that these two ASD-associated cadherins may exert distinct but coordinated functions to regulate the wiring of ASD-relevant circuits in the cerebellum.

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.

Analysis of Cdh22 expression and function in the developing mouse brain

Classical cadherins are important cell adhesion molecules specifying and separating brain nuclei and developmental compartments. Cadherin-22 (Cdh22) belongs to type II subfamily of classical cadherins, and is expressed at the midbrain-hindbrain boundary during early embryogenesis. In Fgfr1 mutant mouse embryos, which have a disturbed midbrain-hindbrain border, Cdh22 is down-regulated. Here, we studied expression of Cdh22 in developing mouse brain in more detail and compared it to expression of related family members. This revealed both complementary and overlapping patterns of Cdh22, Cdh11, Cdh8, and Cdh6 expression in distinct regions of the forebrain and midbrain. We used a mutated allele of Cdh22 to study its function in brain development. Loss of Cdh22 caused reduced postnatal viability. Despite strong Cdh22 expression in the developing brain, we did not observe defects in compartmentalization or abnormalities in the midbrain and forebrain nuclei in Cdh22 mutants. This may be explained by functional redundancy between type II cadherins.

Expression analysis of cadherins in the songbird brain: relationship to vocal system development

Songbirds learn their songs as juveniles. The brains of songbirds have a series of nuclei and neural circuits called the song system, which is indispensable for vocal learning and production. In the present study we analyzed the expression patterns of cell adhesion molecules, cadherins, in the Bengalese finch (Lonchura striata var. domestica) to investigate their potential involvement in song nuclei and neural circuit formation. We found that cadherin-6B was expressed in many song nuclei of the juvenile and adult brain, while R-cadherin was complementarily expressed in surrounding areas. On the other hand, cadherin-7 was expressed in the robust nucleus of the arcopallium (RA) in the sensory learning stage, and its expression was downregulated during the sensorimotor learning stage. This downregulation of cadherin-7 was sexually dimorphic, suggesting its involvement in song development. Other cadherins, including cadherin-9, -10, and -12, showed different song-nuclei-related expression profiles. These patterns of song nuclei related expression suggest the possibility that cadherins are involved in the formation and maintenance of the song nuclei or neural pathways of the song system.

Expression of classical cadherins in the cerebellar anlage: quantitative and functional aspects

During central nervous system (CNS) development, cell migration precedes and is key to the integration of diverse sets of cells. Mechanistically, CNS histogenesis is realized through a balanced interplay of cell-cell and cell-matrix adhesion molecules. Here, we summarize experiments that probe the developmental expression and potential significance of a set of cadherins, including M-, N- and R-cadherin, for patterning of the cerebellar cortex. We established a transgenic marker that allows cerebellar granule cells to be followed from the neuroblast stage to their final, postmitotic settlement. In conjunction with flow cytometry, this allowed us to derive a quantitative view of cadherin expression in differentiating granule cells and relate it to the expression of the same cadherins in cerebellar inhibitory interneuronal precursors. In vitro reaggregation analysis supports a role for cadherins in cell sorting and migration within the nascent cerebellar cortex that may be rationalized within the context of the differential adhesion hypothesis (Foty, R.A. and Steinberg, M.S., 2005. The differential adhesion hypothesis: a direct evaluation. Dev. Biol. 278, 255-263.).

Cloning and expression analysis of cadherin7 in the central nervous system of the embryonic zebrafish

Cadherin cell adhesion molecules exhibit unique expression patterns during development of the vertebrate central nervous system. In this study, we obtained a full-length cDNA of a novel zebrafish cadherin using reverse transcriptase-polymerase chain reaction (RT-PCR) and 5' and 3' rapid amplification of cDNA ends (RACE). The deduced amino acid sequence of this molecule is most similar to the published amino acid sequences of chicken and mammalian cadherin7 (Cdh7), a member of the type II cadherin subfamily. cadherin7 message (cdh7) expression in embryonic zebrafish was studied using in situ hybridization and RT-PCR methods. cdh7 expression begins at about 12h postfertilization (hpf) in a small patch in the anterior neural keel, and along the midline of the posterior neural keel. By 24 hpf, cdh7 expression in the brain shows a distinct segmental pattern that reflects the neuromeric organization of the brain, while its expression domain in the spinal cord is continuous, but confined to the middle region of the spinal cord. As development proceeds, cdh7 expression is detected in more regions of the brain, including the major visual structures in the fore- and midbrains, while its expression domain in the hindbrain becomes more restricted, and its expression in the spinal cord becomes undetectable. cdh7 expression becomes reduced in 3-day old embryos. Our results show that cdh7 expression in the zebrafish developing central nervous system is both spatially and temporally regulated.

Expression of cadherin10, a type II classic cadherin gene, in the nervous system of the embryonic zebrafish

Cadherins are cell surface adhesion molecules that play important roles in development of tissues and organs. In this study, we analyzed expression pattern of cadherin10, a member of the type II classic cadherin subfamily, in the embryonic zebrafish using in situ hybridization methods. cadherin10 message (cdh10) is first and transiently expressed by the notochord. In the developing nervous system, cdh10 was first detected in a subset of the cranial ganglia, then in restricted brain regions and neural retina. As development proceeds, cdh10 expression domain and/or expression levels increased in the embryonic nervous system. Our results show that cdh10 expression in the zebrafish developing nervous system is both spatially and temporally regulated.

Cadherin-10 is a novel blood-brain barrier adhesion molecule in human and mouse

Maintenance of the specialised environment of the central nervous system requires barriers provided by the endothelium of brain microvessels (the blood-brain barrier (BBB)) or the epithelium lining the ventricles (CSF-brain barrier) or the choroid plexus (blood-CSF barrier). Inter-endothelial junctions are more extensive in the BBB than in other tissues, with elaborate tight junctions. However, few differences in the molecular composition of these junctions have been described. Here, we show, in both human and mouse brain, that the type II classical cadherin, cadherin-10, is expressed in BBB and retinal endothelia, but not in the leaky microvessels of brain circumventricular organs (CVO), or in those of non-CNS tissues. This expression pattern is distinct from, and reciprocal to, VE-cadherin, which is reduced or absent in tight cortical microvessels, but present in leaky CVO vessels. In CVO, the barrier function is switched from the microvasculature to the adjacent ventricular epithelium, which we also find to express cadherin-10. In the vessels of gliobastoma multiforme tumours, where BBB is lost, cadherin-10 is not detected. This demonstration of a distinctive expression pattern of cadherin-10 suggests that it has a pivotal role in the development and maintenance of brain barriers.

Internal structure of the nucleus rotundus revealed by mapping cadherin expression in the embryonic chicken visual system

The nucleus rotundus is the largest nucleus of the avian thalamus. It is an important center of visual information processing and conveys information from the optic tectum to the ectostriatum in the telencephalon. The nucleus rotundus is generally believed to contain internal divisions processing information on color, form, motion, and looming of visual objects. The detailed arrangement of these internal divisions is unclear. Here, we map the expression of four classic cadherins (N-cadherin, R-cadherin, cadherin-6B, and cadherin-7), which are markers for specific functional gray matter divisions and their fiber connections in the vertebrate brain. Results show that each cadherin is expressed by one coherent part of the nucleus rotundus that is connected to other brain structures by fiber tracts expressing the same subtype of cadherin. Overall, the expression of the four cadherins encompasses almost the entire nucleus rotundus. The four cadherin-expressing parts show different degrees of overlap. For example, the cadherin-6B part and the cadherin-7 part overlap extensively, whereas the R-cadherin part and the cadherin-6B part show little overlap and are partially complementary. Regions with shallow gradients of cadherin expression alternate with regions that show relatively abrupt changes in cadherin expression. At some points, changes of cadherin expression are also arranged in a pinwheel-like fashion, alternating between clockwise and counterclockwise orientations. In general, these results are reminiscent of the organization of functional modules in the mammalian visual cortex. It is speculated that each domain of cadherin expression corresponds to a functional domain, which processes a specific stimulus feature.

Spatial organization of the pigeon tectorotundal pathway: an interdigitating topographic arrangement

The retinotectofugal system is the main visual pathway projecting upon the telencephalon in birds and many other nonmammalian vertebrates. The ascending tectal projection arises exclusively from cells located in layer 13 of the optic tectum and is directed bilaterally toward the thalamic nucleus rotundus. Although previous studies provided evidence that different types of tectal layer 13 cells project to different subdivisions in Rt, apparently without maintaining a retinotopic organization, the detailed spatial organization of this projection remains obscure. We reexamined the pigeon tectorotundal projection using conventional tracing techniques plus a new method devised to perform small deep-brain microinjections of crystalline tracers. We found that discrete injections involving restricted zones within one subdivision retrogradely label a small fraction of layer 13 cells that are distributed throughout the layer, covering most of the tectal representation of the contralateral visual field. Double-tracer injections in one subdivision label distinct but intermingled sets of layer 13 neurons. These results, together with the tracing of tectal axonal terminal fields in the rotundus, lead us to propose a novel "interdigitating" topographic arrangement for the tectorotundal projection, in which intermingled sets of layer 13 cells, presumably of the same particular class and distributed in an organized fashion throughout the surface of the tectum, terminate in separate regions within one subdivision. This spatial organization has significant consequences for the understanding of the physiological and functional properties of the tectofugal pathway in birds.

Identification and localization of multiple classic cadherins in developing rat limbic system

Classic cadherins are multifunctional adhesion proteins that play roles in tissue histogenesis, neural differentiation, neurite outgrowth and synapse formation. Several lines of evidence suggest that classic cadherins may establish regional or laminar recognition cues by virtue of their differential expression and tight, and principally homophilic, cell adhesion. As a first step toward investigating the role this family plays in generating limbic system connectivity, we used RT-PCR to amplify type I and type II classic cadherins present in rat hippocampus during the principal period of synaptogenesis. We identified nine different cadherins, one of which, cadherin-9, is novel in hippocampus. Using in situ hybridization, we compared the cellular and regional distribution of five of the cadherins (N, 6, 8, 9 and 10) during the first two postnatal weeks in hippocampus, subiculum, entorhinal cortex, cingulate cortex, anterior thalamus, hypothalamus and amygdala. We find that each cadherin is differentially distributed in distinct, but highly overlapping fields that largely correspond to known anatomical boundaries and are often coordinately expressed in interconnected regions. For example, cadherin-6 expression defines CA1 and its principal target, the subiculum; cadherin-10 is differentially expressed in CA1 and CA3 in a manner correlating with the organization of interconnecting Schaffer collateral axons; and cadherin-9 shows a striking concentration in CA3. Some cadherin mRNAs are highly restricted to particular anatomical fields over the entire time course, while others are more broadly expressed and become concentrated within particular domains coincident with the timing of afferent ingrowth. Our data indicate that classic cadherins are sufficiently diverse and differentially distributed to support a role in cell surface recognition and adhesion during the formation of limbic system connectivity.

Granule cell raphes in the cerebellar cortex of chicken and mouse

The cerebellar cortex of the chicken embryo contains parasagittal segments of Purkinje cells. At intermediate stages of development, cell-dense ribbons of migrating granule cells ("raphes") are found between the segments. The complementary pattern of granule cell raphes and Purkinje cell segments represents a basic scheme of cerebellar organization that coincides with the expression domains of various genes, such as cadherins, gene regulatory proteins, and ephrins and their receptors. We have recently found the raphe/segment pattern also in a mammalian species, the postnatal mouse. Like in the chicken, the parasagittal raphes of granule cells were observed at the boundaries of Purkinje cell segments that differentially express cadherins. The number and arrangement of the raphes in the different cerebellar lobules is roughly similar in both species. The raphe/segment pattern is thus more widely distributed in vertebrates than previously assumed.

Cadherins in the central nervous system

The central nervous system (CNS) is divided into diverse embryological and functional compartments. The early embryonic CNS consists of a series of transverse subdivisions (neuromeres) and longitudinal domains. These embryonic subdivisions represent histogenetic fields in which neurons are born and aggregate in distinct cell groups (brain nuclei and layers). Different subsets of these aggregates become selectively connected by nerve fiber tracts and, finally, by synapses, thus forming the neural circuits of the functional systems in the CNS. Recent work has shown that 30 or more members of the cadherin family of morphoregulatory molecules are differentially expressed in the developing and mature brain at almost all stages of development. In a regionally specific fashion, most cadherins studied to date are expressed by the embryonic subdivisions of the early embryonic brain, by developing brain nuclei, cortical layers and regions, and by fiber tracts, neural circuits and synapses. Each cadherin shows a unique expression pattern that is distinct from that of other cadherins. Experimental evidence suggests that cadherins contribute to CNS regionalization, morphogenesis and fiber tract formation, possibly by conferring preferentially homotypic adhesiveness (or other types of interactions) between the diverse structural elements of the CNS. Cadherin-mediated adhesive specificity may thus provide a molecular code for early embryonic CNS regionalization as well as for the development and maintenance of functional structures in the CNS, from embryonic subdivisions to brain nuclei, cortical layers and neural circuits, down to the level of individual synapses.

Identification of three human type-II classic cadherins and frequent heterophilic interactions between different subclasses of type-II classic cadherins

We identified three novel human type-II classic cadherins, cadherin-7, -9 and -10, by cDNA cloning and sequencing, and confirmed that they interact with catenins and function in cell-cell adhesion as do other classic cadherins. Cell-cell binding activities of the eight human type-II classic cadherins, including the three new molecules, were evaluated by long-term cell-aggregation experiments using mouse L fibroblast clones transfected with the individual cadherins. The experiments indicated that all the type-II cadherins appeared to possess similar binding strength, which was virtually equivalent to that of E-cadherin. We next examined the binding specificities of the type-II cadherins using the mixed cell-aggregation assay. Although all of the type-II cadherins exhibited binding specificities distinct from that of E-cadherin, heterophilic interactions ranging from incomplete to complete were frequently observed among them. The combinations of cadherin-6 and -9, cadherin-7 and -14, cadherin-8 and -11, and cadherin-9 and -10 interacted in a complete manner, and in particular cadherin-7 and -14, and cadherin-8 and -11 showed an indistinguishable binding specificity against other cadherin subclasses, at least in this assay system. Although these data were obtained from an in vitro study, they should be useful for understanding cadherin-mediated mechanisms of development, morphogenesis and cell-cell interactions in vivo.

Morphologic fate of diencephalic prosomeres and their subdivisions revealed by mapping cadherin expression

The expression of four cadherins (cadherin-6B, cadherin-7, R-cadherin, and N-cadherin) was mapped in the diencephalon of chicken embryos at 11 days and 15 days of incubation and was compared with Nissl stains and radial glial topology. Results showed that each cadherin is expressed in a restricted manner by a different set of embryonic divisions, brain nuclei, and their subregions. An analysis of the segmental organization based on the prosomeric model indicated that, in the mature diencephalon, each prosomere persists and forms a coherent domain of gray matter extending across the entire transverse dimension of the neural tube, from the ventricular surface to the pial surface. Moreover, the results suggest the presence of a novel set of secondary subdivisions for the dorsal thalamus (dorsal, intermediate, and ventral tiers and anteroventral subregion). They also confirm the presence of secondary subdivisions in the pretectum (commissural, juxtacommissural, and precommissural). At most of the borders between the prosomeres and their secondary subdivisions, changes in radial glial fiber density were observed. The diencephalic brain nuclei that derive from each of the subdivisions were determined. In addition, a number of previously less well-characterized gray matter regions of the diencephalon were defined in more detail based on the mapping of cadherin expression. The results demonstrate in detail how the divisions of the early embryonic diencephalon persist and transform into mature gray matter architecture during brain morphogenesis, and they support the hypothesis that cadherins play a role in this process by providing a framework of potentially adhesive specificities.

The human cadherin-10 gene: complete coding sequence, predominant expression in the brain, and mapping on chromosome 5p13-14

In a quest for novel cadherin gene family members in the human dbEST database, an interesting EST clone was identified and chosen for subsequent analysis. Using the technique of 5' rapid amplification of cDNA ends, we isolated the complete coding sequence and a large part of the UTRs of a novel gene. The sequence appeared to correspond to the human cadherin-10 gene, whose sequence was only partially known before. The expression pattern of this cadherin was found to be largely brain-specific, with additional expression in both adult and fetal kidney, and with minor expression in prostate and fetal lung. By FISH analysis the genomic location was determined at human chromosome 5p13-14, which is nearby the reported positions of the human cadherin-6, -12, and cadherin-14 (CDH18) genes. Cadherin-10 shows high relationship to the human cadherin-6 gene.

Combinatorial expression of cadherins in the tectum and the sorting of neurites in the tectofugal pathways of the chicken embryo

The expression of four cadherins (N-cadherin, R-cadherin, cadherin-6B and cadherin-7) was mapped in the developing tectal system of the chicken embryo from four to 19 days of incubation. Each of the cadherins is expressed in a restricted fashion in specific tectal layers, with partial overlap between the cadherins. In some layers, subpopulations of neurons differentially express the cadherins, e.g., in the stratum griseum centrale. Double labeling demonstrates that many of the projection neurons in this layer co-express at least two cadherins. Fibers of the efferent (tectofugal) pathways originating in these neurons also differentially express the cadherins, most prominently at around 1 1 days of incubation. While the different subpopulations of cadherin-expressing projection neurons are dispersed and mixed within the tectum, their neurites sort out and fasciculate according to which cadherin they express, as they collect in the major output of the tectum, the brachium colliculi superioris. From here, cadherin-expressing fascicles follow separate paths to their respective target areas, some of which also express the respective cadherins, in a matching fashion. We propose that the preferentially homophilic binding of cadherins provides a potential adhesive basis for the sorting and selective fasciculation of specific subpopulations of neurites, similar to the well-established sorting and aggregation of cells expressing cadherins. The combinatorial expression of cadherins by the tectal projection neurons may contribute to the complexity and specificity of functional connections in this system.

Expression of multiple cadherins and catenins in the chick optic tectum

Cadherins form a large family of homophilic cell adhesion molecules that are involved in numerous aspects of neural development. The best-studied neural cadherin, N-cadherin, is concentrated at synapses made by retinal axons in the chick optic tectum and is required for the arborization of retinal axons in their target (retinorecipient) laminae. By analogy, other cadherins might mediate arborization or synaptogenesis in other tectal laminae. Here we consider which cadherins are expressed in tectum, which cells express them, and how their expression is regulated. First, using N-cadherin as a model, we show that synaptic input regulates both cadherin gene expression and the subcellular distribution of cadherin protein. Second, we demonstrate that N-, R-, and T-cadherin are each expressed in distinct laminar patterns during retinotectal synaptogenesis and that N- and R- are enriched in nonoverlapping synaptic subsets. Third, we show that over 20 cadherin superfamily genes are expressed in the tectum during the time that synapses are forming and that many of them are expressed in restricted groups of cells. Finally, we report that both beta-catenin and gamma-catenin (plakoglobin), cytoplasmic proteins required for cadherin signaling, are enriched at synapses and associated with N-cadherin. However, beta- and gamma-catenins are differentially distributed and regulated, and form mutually exclusive complexes. This result suggests that cadherin-based specificity involves multiple cadherin-dependent signaling pathways as well as multiple cadherins.

Blocking N-cadherin function disrupts the epithelial structure of differentiating neural tissue in the embryonic chicken brain

The cell adhesion molecule N-cadherin is ubiquitously expressed in the early neuroepithelium, with strongest expression in the ependymal lining. We blocked the function of N-cadherin during early chicken brain development by injecting antibodies against N-cadherin into the tectal ventricle of embryos at 4-5 d of incubation [embryonic day 4 (E4)-E5]. N-cadherin blockage results in massive morphological changes in restricted brain regions. At approximately E6, these changes consist of invaginations of pieces of the ependymal lining and the formation of neuroepithelial rosettes. The rosettes are composed of central fragments of ependymal lining, surrounded by an inner ventricular layer and an outer mantle layer. Radial glia processes are radially arranged around the ependymal centers of the rosettes. The normal layering of the neural tissue is thus preserved, but its coherent epithelial structure is disrupted. The observed morphological changes are restricted to specific brain regions such as the tectum and the dorsal thalamus, whereas the ventral thalamus and the pretectum are almost undisturbed. At E10-E11, analysis of late effects of N-cadherin blockage reveals that in the dorsal thalamus, gray matter is fragmented and disorganized; in the tectum, additional layers have formed at the ventricular surface. Together, these results indicate that N-cadherin function is required for the maintenance of a coherent sheet of neuroepithelium in specific brain regions. Disruption of this sheet results in an abnormal morphogenesis of brain gray matter.

Early neuromeric distribution of tyrosine-hydroxylase-immunoreactive neurons in human embryos

A segmental mapping of brain tyrosine-hydroxylase-immunoreactive (TH-IR) neurons in human embryos between 4.5 and 6 weeks of gestation locates with novel precision the dorsoventral and anteroposterior topography of the catecholamine-synthetizing primordia relative to neuromeric units. The data support the following conclusions. (1) All transverse sectors of the brain (prosomeres in the forebrain, midbrain, rhombomeres in the hindbrain, spinal cord) produce TH-IR neuronal populations. (2) Each segment shows peculiarities in its contribution to the catecholamine system, but there are some overall regularities, which reflect that some TH-IR populations develop similarly in different segments. (3) Dorsoventral topology of the TH-IR neurons indicates that at least four separate longitudinal zones (in the floor and basal plates and twice in the alar plate) found across most segments are capable of producing the TH-IR phenotype. (4) Basal plate TH-IR neurons tend to migrate intrasegmentally to a ventrolateral superficial position, although some remain periventricular; those in the brainstem are related to motoneurons of the oculomotor and branchiomotor nuclei. (5) Some alar TH-IR populations migrate superficially within the segmental boundaries. (6) Most catecholaminergic anatomical entities are formed as fusions of smaller segmental components, each of which show similar histogenetic patterns. A nomenclature is proposed that partly adheres to previous terminology but introduces the distinction of embryologically different cell populations and unifies longitudinally analogous entities. Such a model, as presented in the present study, is convenient for resolving problems of homology of the catecholamine system across the diversity of vertebrate forms.

Cadherin-Defined Segments and Parasagittal Cell Ribbons in the Developing Chicken Cerebellum

In the developing chicken cerebellar cortex, three cadherins (Cad6B, Cad7, and R-cadherin) are expressed in distinct parasagittal segments that are separated from each other by ribbons of migrating interneurons and granule cells which express R-cadherin and Cad7, respectively. The segment/ribbon pattern is respected by the expression of other types of molecules, such as engrailed-2 and SC1/BEN/DM-GRASP. The cadherin-defined segments contain young Purkinje cells which are connected to underlying nuclear zones expressing the same cadherin, thereby forming parasagittal cortico-nuclear zones of topographically organized connections. In addition, R-cadherin-positive mossy fiber terminals display a periodic pattern in the internal granular layer. In this layer, Cad7 and R-cadherin are associated with synaptic complexes. These results suggest that cadherins play a pivotal role in the formation of functional cerebellar architecture by providing a three-dimensional scaffold of adhesive information. Copyright 1998 Academic Press.