Neuronal circuits are subdivided by differential expression of type-II classic cadherins in postnatal mouse brains

The magnificent compromise: cortical field evolution in mammals

The neocortex of mammals is composed of cortical fields that have a unique organization associated with the animal's ecological niche and lifestyle. Each cortical field has a specific pattern of connections with other cortical fields and brain structures, and together they comprise a neocortical network that generates a variety of behaviors. These networks and the behaviors they generate are variable across mammals, and are particularly complex in some species such as humans. Here I discuss the mechanisms that contribute to neocortical organization in mammals, and how this organization has been altered to generate the variability that exists in different lineages.

Genetic and epigenetic contributions to the cortical phenotype in mammals

One aspect of cortical organization, cortical field size, is variable both within and across species. The observed variability arises from a variety of sources, including genes intrinsic to the neocortex and a number of extrinsic and epigenetic factors. Genes intrinsic to the cortex are directly involved in the development and specification of cortical fields and are regulated from both signaling centers located outside of the neocortex, which secrete diffusible molecules, and the expression of transcription factors within the neocortex. In addition, extrinsic factors such as the type, location and density of sensory receptor arrays and how these receptor arrays are utilized, are also strongly related to cortical field size. Epigenetic factors including the relative activity patterns generated by the different types of physical stimuli in a given environment also contribute to differences in cortical organization, including cortical field size. Since both genetic and epigenetic factors contribute to cortical organization, some aspects of the cortical phenotype evolve, while other aspects of the cortical phenotype persist only if the environment in which an individual develops is relatively stable.

Trio controls the mature organization of neuronal clusters in the hindbrain

During the embryonic development of the hindbrain, movements of neuronal clusters allow the formation of mature "pools", in particular for inferior olivary (ION) and facial motor (fMN) nuclei. The cellular mechanisms of neuron clustering remain uncharacterized. We report that the absence of the Rho-guanine exchange factor Trio, which can activate both RhoG and Rac1 in vivo, prevents the proper formation of ION and fMN subnuclei. Rac1, but not RhoG, appears to be a downstream actor in Trio-induced lamellation. In addition, we report that Cadherin-11 is expressed by a subset of neurons through the overall period of ION and fMN parcellations, and defects observed in trio mutant mice are located specifically in Cadherin-11-expressing regions. Moreover, endogenous Cadherin-11 is found in a complex with Trio when lamellation occurs. Altogether, those results establish a link between Trio activity, the subsequent Rac1 activation, and neuronal clusters organization, as well as a possible recruitment of the Cadherin-11 adhesive receptor to form a complex with Trio.

Differentially expressed genes among motor and prefrontal areas of macaque neocortex

In higher primates, the motor-related areas of the neocortex are highly differentiated into several subareas based on both functional and cytoarchitectural aspects. To assess the molecular basis of this areal specialization, we investigated the gene expression profiles of the primary motor area (M1), premotor area (dorsal and ventral, PMd and PMv, respectively), and prefrontal area (A46) in rhesus monkeys using DNA microarray. We discovered that 476 genes were differentially expressed among these 4 areas. More than half of these genes were most abundantly expressed in M1, and most genes were complementarily expressed between M1 and A46. The expression profiles of PMd and PMv were quite similar to each other and different from those of M1 and A46. The data will provide a fundamental basis for the further analysis of the structure-function relationship of the primate brain.

COUP-TFI regulates the balance of cortical patterning between frontal/motor and sensory areas

We used cortex-specific deletion of the transcription factor gene COUP-TFI (also known as Nr2f1) in mice to demonstrate previously unknown fundamental roles for it in patterning mammalian neocortex into areas. The highest COUP-TFI expression is observed in the cortical progenitors and progeny in parietal and occipital cortex that form sensory areas, and the lowest expression was observed in frontal cortex that includes motor areas. Cortical deletion of COUP-TFI resulted in massive expansion of frontal areas, including motor, to occupy most of neocortex, paralleled by marked compression of sensory areas to caudal occipital cortex. These area patterning changes are preceded and paralleled by corresponding changes in molecular markers of area identity and altered axonal projections to maintain patterned area-specific input and output connections. We conclude that COUP-TFI is required for balancing patterning of neocortex into frontal/motor and sensory areas by acting in its expression domain to repress frontal/motor area identities and to specify sensory area identities.

The mRNA-like noncoding RNA Gomafu constitutes a novel nuclear domain in a subset of neurons

Recent transcriptome analyses have revealed that a large body of noncoding regions of mammalian genomes are actually transcribed into RNAs. Our understanding of the molecular features of these noncoding RNAs is far from complete. We have identified a novel mRNA-like noncoding gene, named Gomafu, which is expressed in a distinct set of neurons in the mouse nervous system. Interestingly, spliced mature Gomafu RNA is localized to the nucleus despite its mRNA-like characteristics, which usually act as potent export signals to the cytoplasm. Within the nucleus, Gomafu RNA is detected as numerous spots that do not colocalize with known nuclear domain markers. Gomafu RNA is extremely insoluble and remains intact after nuclear matrix preparation. Furthermore, heterokaryon assays revealed that Gomafu RNA does not shuttle between the nucleus and cytoplasm, but is retained in the nucleus after its transcription. We propose that Gomafu RNA represents a novel family of mRNA-like noncoding RNA that constitutes a cell-type-specific component of the nuclear matrix.

Spatiotemporal expression pattern of non-clustered protocadherin family members in the developing rat brain

Protocadherins (PCDHs) consist of the largest subgroup of the cadherin superfamily, and most PCDHs are expressed dominantly in the CNS. Because PCDHs are involved in the homophilic cell-cell adhesion, PCDHs in the nervous system have been suggested to play roles in the formation and maintenance of the synaptic connections. Although many PCDHs (>50) are in tandem arranged as a cluster in a specific chromosome locus, there are also considerable numbers of non-clustered PCDH members (approximately 20). In this study, we examined the spatiotemporal distribution of mRNAs for 12 non-clustered PCDHs in rat brain using in situ hybridization. Some of them (PCDH1, PCDH7, PCDH9, PCDH10, PCDH11, PCDH17, and PCDH20) exhibited region-dependent expression pattern in the cerebral cortex during the early postnatal stage (P3), which is a critical period for the establishment of specific synaptic connections: PCDH7 and PCDH20 mRNAs were predominantly expressed in the somatosensory (parietal) and visual (occipital) cortices, whereas PCDH11 and PCDH17 mRNAs were preferentially expressed in the motor (forelimb and hindlimb areas) and auditory (temporal) cortices, and PCDH9 mRNA was highly expressed in the motor and main somatosensory cortices. These PCDHs were also expressed in the specific regions of the connecting thalamic nuclei. These cortical regionalization and thalamic nuclei-specificity appeared to be most distinct in P3 compared with those of embryonic and adult stages. Taken together, these results suggest that PCDHs may play specific roles in the establishment of selective synaptic connections of specific modality of cerebral cortex with other communicating brain regions such as the thalamus.

Novel genes differentially expressed in cortical regions during late neurogenesis

Differential gene expression across the embryonic cerebral cortex is assumed to play a role in the subdivision of the cortex into distinct areas with specific morphology, physiology and function. In a search for genes that may be involved in the cortical regionalization during late neurogenesis in mouse, we performed an extensive in-situ expression analysis at embryonic day (E)16 and E18. The examined candidate genes were selected beforehand by a microarray screen by virtue of their preferential expression in the anlagen of the motor, somatosensory, visual and cingulate cortices or hippocampus. We present new information about graded or regionally enriched expression of 25 genes (nine of which are novel genes) across the mouse embryonic cortex, in progenitor cells as well as in the cortical plate. The established differential expression of most of these genes is persistent at both stages studied, suggesting that their expression is regulated by an intrinsic programme. For some of the genes, the concept of intrinsic regulation is further substantiated by the high similarity of the reported expression patterns at E16 and E18 and published data from earlier stages. Few genes with robust expression in the E16 caudal cortex showed a more restricted pattern at E18, possibly because of their response to extrinsic cues. In addition, several genes appeared to be suitable novel markers for amygdalar and diencephalic nuclei. Taken together, our findings reveal novel molecular partitions of the late mouse cortex that are in accordance with the model of a leading role of intrinsic mechanisms in cortical arealization.

Cadherin expression in the developing mouse olfactory system

Although odor receptors have been implicated in establishing the topography of olfactory sensory neurons (OSNs) in the olfactory bulb (OB), it is likely other molecules are also involved. The cadherins (CDHs) are a large family of cell adhesion molecules that mediate cell:cell interactions elsewhere in the central nervous system. However, their distribution and role in the olfactory system have remained largely unexplored. We previously demonstrated that intracellular binding partners of cadherins, the catenins, have unique spatiotemporal patterns of expression in the developing olfactory system. To further our understanding of cadherin function within the developing olfactory system, we now report on the localization of 11 classical cadherins-CDH1, 2, 3, 4, 5, 6, 8, 10, 11, 13, and 15. We demonstrate the expression of all but CDH5 and CDH15 in neuronal and/or glial cells in primary olfactory structures. CDH1 and CDH2 are expressed by OSNs; CDH2 expression closely parallels that seen for gamma-catenin in OSN axons. CDH3 and CDH11 are expressed by olfactory ensheathing glia, which surround OSN axons in the outer OB. CDH2, CDH4, and CDH6 are expressed within neuropil. CDH2, CDH4, CDH6, CDH8, CDH10, CDH11, and CDH13 are expressed by projection neurons within the main and accessory OBs. We conclude that cadherin proteins in the developing olfactory system are positioned to underlie the formation of the odorant map and local circuits within the OB.

Cadherin-8 is required for the first relay synapses to receive functional inputs from primary sensory afferents for cold sensation

Classic cadherins, comprising multiple subtypes, mediate selective cell-cell adhesion based on their subtype-specific binding nature. Each subtype in the brain is expressed by restricted groups of functionally connected nuclei and laminas. However, whether each subtype has any specific role in neural circuitry remains largely unknown. Here, we show that cadherin-8 (cad8), a type-II classic cadherin, is important for cold sensation, whose circuitry is established by projection of sensory neurons into the spinal cord. Cad8 was expressed by a subset of neurons in the dorsal horn (DH) of the spinal cord, as well as by a small number of neurons in the dorsal root ganglia (DRGs), and the majority of cad8-positive DRG neurons coexpressed cold temperature/menthol receptor (TRPM8). We generated cad8 knock-out mice and analyzed lacZ markers expressed by the targeted cad8 locus using heterozygous mice. LacZ/cad8-expressing sensory neurons and DH neurons were connected together, and cad8 protein was localized around the synaptic junctions formed between them. This relation was, however, not disrupted in cad8-/- mice. We performed whole-cell patch-clamp recordings from DH neurons in spinal cord slices, in combination with menthol stimulation as a tool to excite central terminals of primary afferents expressing TRPM8. LacZ-expressing DH neurons exhibited fast and slow miniature EPSCs. Menthol selectively increased the frequency of the slow mEPSCs in cad8+/- slices, but this effect was abolished in cad8-/- slices. The cad8-/- mice also showed a reduced sensitivity to cold temperature. These results demonstrate that cad8 is essential for establishing the physiological coupling between cold-sensitive sensory neurons and their target DH neurons.

Cortical area size dictates performance at modality-specific behaviors

The mammalian neocortex is organized into unique areas that serve functions such as sensory perception and modality-specific behaviors. The sizes of primary cortical areas vary across species, and also within a species, raising the question of whether area size dictates behavioral performance. We show that adult mice genetically engineered to overexpress the transcription factor EMX2 in embryonic cortical progenitor cells, resulting in reductions in sizes of somatosensory and motor areas, exhibit significant deficiencies at tactile and motor behaviors. Even increasing the size of sensorimotor areas by decreasing cortical EMX2 levels can lead to diminished sensorimotor behaviors. Genetic crosses that retain ectopic Emx2 transgene expression subcortically but restore cortical Emx2 expression to wild-type levels also restore cortical areas to wild-type sizes and in parallel restore tactile and motor behaviors to wild-type performance. These findings show that area size can dictate performance at modality-specific behaviors and suggest that areas have an optimal size, influenced by parameters of its neural system, for maximum behavioral performance. This study underscores the importance of establishing during embryonic development appropriate levels of regulatory proteins that determine area sizes, thereby influencing behavior later in life.

N-cadherin signaling in synapse formation and neuronal physiology

Neural cadherin (N-cadherin) is an adhesion receptor that is localized in abundance at neuronto- neuron synapses. N-cadherin contains an extracellular domain that binds to other cadherins on juxtaposed cell membranes, a single-pass transmembrane region, and a cytoplasmic tail that interacts with various proteins, including catenins, kinases, phosphatases, and presenilin 1. N-cadherin contributes to the structural and functional organization of the synaptic complex by ensuring the adhesion between synaptic membranes and organizing the underlying actin cytoskeleton. Additionally, recent findings have shown that N-cadherin may participate in synaptic physiology by regulating calcium influx through voltage-activated calcium currents. The diverse activities of N-cadherin stem from its ability to operate as both an adhesion molecule that links cytoskeletons across cell membranes and a ligand-activated homophilic receptor capable of initiating intracellular signaling. An important mechanism of cadherin signaling is the regulation of small Rho guanosine triphosphatase activity that affects cytoskeleton dynamics and calcium influx. Because both the regulation of cadherin adhesive activity and cadherin-mediated signaling are affected by the binding of molecules to the intracellular domain, changes in the composition of the N-cadherin complex are central to the regulation of cadherin-mediated functions. This article focuses on the roles that N-cadherin might play at the level of the synapse through its effect on adhesion and signaling in the proximity of the synaptic junction.

Cadherins in development: cell adhesion, sorting, and tissue morphogenesis

Tissue morphogenesis during development is dependent on activities of the cadherin family of cell-cell adhesion proteins that includes classical cadherins, protocadherins, and atypical cadherins (Fat, Dachsous, and Flamingo). The extracellular domain of cadherins contains characteristic repeats that regulate homophilic and heterophilic interactions during adhesion and cell sorting. Although cadherins may have originated to facilitate mechanical cell-cell adhesion, they have evolved to function in many other aspects of morphogenesis. These additional roles rely on cadherin interactions with a wide range of binding partners that modify their expression and adhesion activity by local regulation of the actin cytoskeleton and diverse signaling pathways. Here we examine how different members of the cadherin family act in different developmental contexts, and discuss the mechanisms involved.

Synapses: sites of cell recognition, adhesion, and functional specification

Synapses are specialized adhesive contacts characteristic of many types of cell-cell interactions involving neurons, immune cells, epithelial cells, and even pathogens and host cells. Cell-cell adhesion is mediated by structurally diverse classes of cell-surface glycoproteins, which form homophilic or heterophilic interactions across the intercellular space. Adhesion proteins bind to a cytoplasmic network of scaffolding proteins, regulators of the actin cytoskeleton, and signal transduction pathways that control the structural and functional organization of synapses. The themes of this review are to compare the organization of synapses in different cell types and to understand how different classes of cell adhesion proteins and cytoplasmic protein networks specify the assembly of functionally distinct synapses in different cell contexts.

Sequence analysis and expression mapping of the rat clustered protocadherin gene repertoires

Three closely-linked clusters of protocadherin (Pcdh) genes (alpha, beta, and gamma) encoding more than 50 distinct mRNAs have been identified in humans and mice, and proposed to play important roles in neuronal connectivity in the CNS. The human and mouse Pcdh alpha and gamma clusters each span a region of about 300 kb genomic DNA, and are each organized into a tandem array of more than a dozen highly-similar "variable" exons, and three downstream "constant" exons. Little is known about the expression patterns of the alpha and gamma repertoires in the CNS. Here, we comprehensively analyzed the one megabase rat Pcdh genomic DNA sequences at the nucleotide level using various computational methods. We found that the clustered rat Pcdh genes display strict orthologous relationships with those of mice but not humans. Moreover, each rat Pcdh variable exon is preceded by a distinct promoter. We designed two complete sets of isoform-specific probes and extensively mapped the expression patterns for each member of the alpha and gamma repertoires in the adult rat CNS by non-isotopic in situ hybridization experiments. We found that most alpha and gamma mRNA isoforms are broadly expressed in similar patterns in subsets of cells (with some displaying interesting cortical layer-specific expression) throughout various CNS regions, including the olfactory bulb, cerebral cortex, hippocampus, cerebellum, and spinal cord. The broad expression of most alpha or gamma mRNAs throughout various regions of the CNS is consistent with the hypothesis that these genes may be used for neurons to establish their individuality and also provide the adhesive diversity required for complex synaptic connectivity in the mammalian CNS.

Genetic analysis of anterior posterior expression gradients in the developing mammalian forebrain

Intrinsic regulatory factors play critical roles in early cortical patterning, including the development of the anteroposterior (A-P) axis. To identify genes that are differentially expressed along the A-P axis of the developing cerebral cortex, we analyzed gene expression in presumptive frontal, parietal, and occipital cerebral walls of E12.5 mouse using complementary DNA microarrays. We identified 106 genes, including expressed sequence tags (ESTs), expressed in an A-P gradient in the embryonic brain and screened 88 by in situ hybridization for confirmation. Central nervous system (CNS) expression patterns of many of these genes were previously unknown. Others, such as Sfrp1, CoupTF1, and FABP7, were expressed in a manner consistent with previous studies, providing independent confirmation. Two related transcription factors, previously not implicated in CNS development, Fhl1 and Fhl2, were observed to be enriched in posterior and anterior telencephalon, respectively. We studied patterning gradients in Fhl1 knockout mice but observed no changes in gene expression related to A-P regionalization in the Fhl1 knockout mice. These data provide an important set of new candidates for studies of cortical patterning and maturation.

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.).

The cadherin superfamily in neuronal connections and interactions

Neural development and the organization of complex neuronal circuits involve a number of processes that require cell-cell interaction. During these processes, axons choose specific partners for synapse formation and dendrites elaborate arborizations by interacting with other dendrites. The cadherin superfamily is a group of cell surface receptors that is comprised of more than 100 members. The molecular structures and diversity within this family suggest that these molecules regulate the contacts or signalling between neurons in a variety of ways. In this review I discuss the roles of three subfamilies - classic cadherins, Flamingo/CELSRs and protocadherins - in the regulation of neuronal recognition and connectivity.

Alpha N-catenin deficiency causes defects in axon migration and nuclear organization in restricted regions of the mouse brain

Alpha N-catenin is a cadherin-binding protein, widely expressed in the nervous system; and it plays a crucial role in cadherin-mediated cell-cell adhesion. Here we report the effects of alpha N-catenin gene deficiency on brain morphogenesis. In addition to the previously reported phenotypes, we found that some of the axon tracts did not normally develop, in particular, axons of the anterior commissure failed to cross the midline, migrating, rather, to ectopic places. In restricted nuclei, a population of neurons was missing or their laminar arrangement was distorted. The ventricular structures were also deformed. These results indicate that alpha N-catenin has diverse roles in the organization of the central nervous system, but only in limited portions of the brain.

Distinct expression of Cbln family mRNAs in developing and adult mouse brains

Cbln1 belongs to the C1q and tumour necrosis factor superfamily, and plays crucial roles as a cerebellar granule cell-derived transneuronal regulator for synapse integrity and plasticity in Purkinje cells. Although Cbln2-Cbln4 are also expressed in the brain and could form heteromeric complexes with Cbln1, their precise expressions remain unclear. Here, we investigated gene expression of the Cbln family in developing and adult C57BL mouse brains by reverse transcriptase-polymerase chain reaction (RT-PCR), Northern blot, and high-resolution in situ hybridization (ISH) analyses. In the adult brain, spatial patterns of mRNA expression were highly differential depending on Cbln subtypes. Notably, particularly high levels of Cbln mRNAs were expressed in some nuclei and neurons, whereas their postsynaptic targets often lacked or were low for any Cbln mRNAs, as seen for cerebellar granule cells/Purkinje cells, entorhinal cortex/hippocampus, intralaminar group of thalamic nuclei/caudate-putamen, and dorsal nucleus of the lateral lemniscus/central nucleus of the inferior colliculus. In the developing brain, Cbln1, 2, and 4 mRNAs appeared as early as embryonic day 10-13, and exhibited transient up-regulation during the late embryonic and neonatal periods. For example, Cbln2 mRNA was expressed in the cortical plate of the developing neocortex, displaying a high rostromedial to low caudolateral gradient. In contrast, Cbln3 mRNA was selective to cerebellar granule cells throughout development, and its onset was as late as postnatal day 7-10. These results will provide a molecular-anatomical basis for future studies that characterize roles played by the Cbln family.

The resilient synapse: insights from genetic interference of synaptic cell adhesion molecules

Synaptic cell adhesion molecules (SCAMs) are mostly membrane-anchored molecules with extracellular domains that extend into the synaptic cleft. Prototypical SCAMs interact with homologous or heterologous molecules on the surface of adjacent cells, ensuring the precise apposition of pre- and postsynaptic elements. More recent definitions of SCAMs often include molecules involved in axon pathfinding, cell recognition and synaptic differentiation events, making SCAMs functionally and molecularly a highly diverse group. In this review, we summarize the proposed in vivo functions of a large variety of SCAMs. We mainly focus on results obtained from analyses of genetic model organisms, mostly mouse knockout mutants, lacking expression of the respective candidate genes. In contrast to the substantial effect yielded by some knockouts of molecules involved in synaptic vesicle release, no SCAM mutant has been reported thus far that shows a prominently altered structure of the majority of synapses or even lacks synapses altogether. This surprising resilience of synaptic structure might be explained by a high redundancy between different SCAMs, by the assumption that the crucial molecular players in synapse structure have yet to be discovered or by a grand variability in the mechanisms of synapse formation that underlies the diversity of synapses. Whatever the final answer turns out to be, the genetic dissection of the SCAM superfamilies has led to a much better understanding of the different steps required to form, differentiate and modify a synapse.

Molecular mechanisms of cortical differentiation

During development, several populations of progenitor cells in the dorsal telencephalon generate a large variety of neurons which acquire distinct morphologies and physiological properties and serve distinct functions in the mammalian cortex. This paper reviews recent work that has identified (i) key molecules involved in the specification and differentiation of cortical neurons, (ii) novel genes which distinguish distinct subsets of cortical progenitors and may be involved in the diversification of cortical neurons present in different cortical layers, and (iii) mechanisms involved in the generation of different projection neuronal subtypes in the well-studied model of layer 5 of the rodent cortex.

Neocortical areas, layers, connections, and gene expression

Cortical patterns of gene expression provide a new approach to long standing issues of lamination, and area identity and formation. In this review, we summarize recent findings where molecular biological techniques have revealed a small number of area-specific genes in the nonhuman primate cortex. One of these (occ1) is strongly expressed in primary visual cortex and is associated with thalamocortical connections. Another gene, RBP, is more strongly expressed in association areas. It is not clear whether RBP might be linked with any particular connectional system, but several possibilities are raised. We also discuss possible roles of area-specific genes in postnatal development, and conclude with a brief sketch of future directions.

Fibroblast growth factor 8 regulates neocortical guidance of area-specific thalamic innervation

Thalamic innervation of each neocortical area is vital to cortical function, but the developmental strategies that guide axons to specific areas remain unclear. We took a new approach to determine the contribution of intracortical cues. The cortical patterning molecule fibroblast growth factor 8 (FGF8) was misexpressed in the cortical primordium to rearrange the area map. Thalamic axons faithfully tracked changes in area position and innervated duplicated somatosensory barrel fields induced by an ectopic source of FGF8, indicating that thalamic axons indeed use intracortical positional information. Because cortical layers are generated in temporal order, FGF8 misexpression at different ages could be used to shift regional identity in the subplate and cortical plate either in or out of register. Thalamic axons showed strikingly different responses in the two different conditions, disclosing sources of positional guidance in both subplate and cortical plate. Unexpectedly, axon trajectories indicated that an individual neocortical layer could provide not only laminar but also area-specific guidance. Our findings demonstrate that thalamocortical axons are directed by sequential, positional cues within the cortex and implicate FGF8 as an indirect regulator of thalamocortical innervation.

The mechanisms and molecules that connect photoreceptor axons to their targets in Drosophila

The development of the Drosophila visual system provides a framework for investigating how circuits assemble. A sequence of reciprocal interactions amongst photoreceptors, target neurons and glia creates a precise pattern of connections while reducing the complexity of the targeting process. Both afferent-afferent and afferent-target interactions are required for photoreceptor (R cell) axons to select appropriate synaptic partners. With the identification of some critical cell adhesion and signaling molecules, the logic by which axons make choices amongst alternate synaptic partners is becoming clear. These studies also provide an opportunity to examine the molecular basis of neural circuit evolution.

Prototypical Type I E-cadherin and Type II Cadherin-7 Mediate Very Distinct Adhesiveness through Their Extracellular Domains

Using a dual pipette assay that measures the force required to separate adherent cell doublets, we have quantitatively compared intercellular adhesiveness mediated by Type I (E- or N-cadherin) or Type II (cadherin-7 or -11) cadherins. At similar cadherin expression levels, cells expressing Type I cadherins adhered much more rapidly and strongly than cells expressing Type II cadherins. Using chimeric cadherins, we found that the extracellular domain exerts by far the dominant effect on cell adhesivity, that of E-cadherin conferring high adhesivity, and that of cadherin-7 conferring low adhesivity. Type I cadherins were incorporated to a greater extent into detergent-insoluble cytoskeletal complexes, and their cytoplasmic tails were much more effective in disrupting strong adherent junctions, suggesting that Type II cadherins form less stable complexes with beta-catenin. The present study demonstrates compellingly, for the first time, that cadherins are dramatically different in their ability to promote intercellular adhesiveness, a finding that has profound implications for the regulation of tissue morphogenesis.

Dissociation of corticothalamic and thalamocortical axon targeting by an EphA7-mediated mechanism

Molecular mechanisms generating the topographic organization of corticothalamic (CT) circuits, which comprise more than three-quarters of the synaptic inputs onto sensory relay neurons, and their interdependence with thalamocortical (TC) axon development are unknown. Using in utero electroporation-mediated gene transfer, we show that EphA7-mediated signaling on neocortical axons controls the within-nucleus topography of CT projections in the thalamus. Notably, CT axons that mis-express EphA7 do not shift the relative positioning of their pathway within the subcortical telencephalon (ST), indicating that they do not depend upon EphA7/ephrin-A signaling in the ST for establishing this topography. Moreover, mis-expression of cortical EphA7 results in disrupted topography of CT projections, but unchanged inter- and intra-areal topography of TC projections. Our results support a model in which EphA/ephrin-A signaling controls independently the precision with which CT and TC projections develop, yet is essential for establishing their topographic reciprocity.

Ephrin-as guide the formation of functional maps in the visual cortex

Ephrin-As and their receptors, EphAs, are expressed in the developing cortex where they may act to organize thalamic inputs. Here, we map the visual cortex (V1) in mice deficient for ephrin-A2, -A3, and -A5 functionally, using intrinsic signal optical imaging and microelectrode recording, and structurally, by anatomical tracing of thalamocortical projections. V1 is shifted medially, rotated, and compressed and its internal organization is degraded. Expressing ephrin-A5 ectopically by in utero electroporation in the lateral cortex shifts the map of V1 medially, and expression within V1 disrupts its internal organization. These findings indicate that interactions between gradients of EphA/ephrin-A in the cortex guide map formation, but that factors other than redundant ephrin-As are responsible for the remnant map. Together with earlier work on the retinogeniculate map, the current findings show that the same molecular interactions may operate at successive stages of the visual pathway to organize maps.

Regulation of cadherin-mediated adhesion in morphogenesis

Cadherin cell-adhesion proteins mediate many facets of tissue morphogenesis. The dynamic regulation of cadherins in response to various extracellular signals controls cell sorting, cell rearrangements and cell movements. Cadherins are regulated at the cell surface by an inside-out signalling mechanism that is analogous to the integrins in platelets and leukocytes. Signal-transduction pathways impinge on the catenins (cytoplasmic cadherin-associated proteins), which transduce changes across the membrane to alter the state of the cadherin adhesive bond.

Synaptic contact dynamics controlled by cadherin and catenins

A synapse is the connection between neurons that joins an axon of one neuron to the dendrite of another. One class of synapses is formed at the contact point between an axon and a small protrusion from a dendrite, called a dendritic spine. These spines are motile and deformable, which indicates that synaptic functions are controlled, at least in part, by their morphological changes. Recent studies show that the cadherin cell-adhesion molecules and their cytoplasmic partners, catenins, can modulate axon-spine contacts in a manner that responds to neural activity. These observations indicate that cadherins, which are essential for general cell-cell adhesion, also play a role in the control of synaptic dynamics.

CNR/Pcdhalpha family in subplate neurons, and developing cortical connectivity

The cadherin-related neuronal receptor (CNR)/protocadherin (Pcdh) alpha family is one of the diverse protocadherin families identified as a candidate diversified membrane-associated component regulating the formation of neuronal connectivity. However, its expression during neural circuit formation has not been examined in detail. Here, we used a conserved sequence to study the expression of this protein family during the development of neocortical connectivity, by immunohistochemistry and in situ hybridization. The proteins were detected in developing thalamocortical and corticofugal axons, and in subplate neurons, which pioneer these axon tracts. The expression in subplate neurons was confirmed by birth-date labeling with BrdU, and by examination in homozygous reeler mice. This pattern of CNR/Pcdhalpha expression suggests its involvement in the development of neocortical connectivity.

A novel function for cadherin-11 in the regulation of motor axon elongation and fasciculation

We previously observed that cadherin-11, a type II cadherin, is expressed in growing motor and sensory axons in the mouse embryo. Here, we assessed its functional involvement in the regulation of axon elongation and fasciculation by evaluating the activity of a specific cadherin-11 homophilic ligand, cad11-Fc (cadherin-11 extracellular region fused to Fc fragment of IgG), on the length and organization of motor axons outgrowing from embryonic ventral spinal cord explants. Cad11-Fc substrate enhanced axon growth and prevented interactions occurring between growing axons, providing evidences for a role of cadherin-11 in the control of growth cone progression. Comparison of cadherin-11 with N-cadherin, a type I cadherin concomitantly expressed by motor axons, revealed similarities in their functional properties, including the ability to reorganize the actin cytoskeleton through interactions with catenins, but differences in their axon growth-promoting activity, arguing for subtle differences in their contributions to peripheral nerve elongation.

Temporally distinct demands for classic cadherins in synapse formation and maturation

Classic cadherins are synaptic adhesion proteins that have been implicated in synapse formation and targeting. Brief inactivation of classic cadherin function in young neurons appears to abrogate synapse formation when examined acutely. It remains unknown if such abrogation is unique to young neurons, whether it occurs by stalling neuronal maturation or by directly interfering with the process of synapse assembly, or whether synapse targeting is altered. Here we asked if sustained pan-cadherin blockade would prevent or alter the progression of axonal and dendritic outgrowth, synaptogenesis, or the stereotypic distribution of excitatory and inhibitory synapses on cultured hippocampal neurons. While pre- and postsynaptic cadherins are required for synapse assembly in young neurons, we find that in neurons older than 10 days, classic cadherins are entirely dispensable for joining and aligning presynaptic vesicle clusters with molecular markers of the postsynaptic density. Furthermore, we find that the proportion and relative distributions of excitatory and inhibitory terminals on single neurons are not altered. However, synapses that form on neurons in which cadherin function is blocked are smaller; they exhibit decreased synaptic vesicle recycling and a decreased frequency of spontaneous EPSCs. Moreover, they fail to acquire resistance to F-actin depolymerization, a hallmark of mature, stable contacts. These data provide new evidence that cadherins are required to promote synapse stabilization and structural and functional maturation, but dispensable for the correct subcellular distribution of excitatory and inhibitory synapses.

Drosophila N-cadherin mediates an attractive interaction between photoreceptor axons and their targets

Classical cadherins have been proposed to mediate interactions between pre- and postsynaptic cells that are necessary for synapse formation. We provide the first direct, genetic evidence in favor of this model by examining the role of N-cadherin in controlling the pattern of synaptic connections made by photoreceptor axons in Drosophila. N-cadherin is required in both individual photoreceptors and their target neurons for photoreceptor axon extension. Cell-by-cell reconstruction of wild-type photoreceptor axons extending within mosaic patches of mutant target cells shows that N-cadherin mediates attractive interactions between photoreceptors and their targets. This interaction is not limited to those cells that will become the synaptic partners of photoreceptors. Multiple N-cadherin isoforms are produced, but single isoforms can substitute for endogenous N-cadherin activity. We propose that N-cadherin mediates a homophilic, attractive interaction between photoreceptor growth cones and their targets that precedes synaptic partner choice.

Cadherins and catenins in synapse development

Cadherin-catenin complexes have been well established as key regulators of cell adhesion. Recent work has elucidated a pivotal role for these molecules in synaptic assembly, remodelling and plasticity. Far from being mere adhesive scaffolds, cadherins might directly regulate cell signalling to modulate synaptic connectivity.

Fgf8 regulates the development of intra-neocortical projections

The process of generating functionally distinct neocortical areas requires the formation of an intra-neocortical connectivity map. Here, we explore the early development of murine intra-neocortical projections and find that axons from rostral and caudal neurons remain, respectively, within large rostral and caudal domains of the neonatal neocortex. Despite evidence that thalamic input can regulate neocortical areal properties, we found that the neonatal intra-neocortical projection pattern was not perturbed when thalamic input was absent in Gbx2 mutants. On the contrary, in Fgf8 hypomorphic mutants, the rostral neocortex of which acquires more caudal molecular properties, caudally located neurons ectopically project axons into the rostral cortex. Therefore, neocortical patterning by Fgf8 also contributes to arealization through mediating early development of intra-neocortical connectivity.

Zinc finger gene fez-like functions in the formation of subplate neurons and thalamocortical axons

fez-like (fezl) is a forebrain-expressed zinc finger gene required for the formation of the hypothalamic dopaminergic and serotonergic (monoaminergic) neurons in zebrafish. To reveal its function in mammals, we analyzed the expression of the mouse orthologue of fezl and generated fezl-deficient mice by homologous recombination. Mouse fezl was expressed specifically in the forebrain from embryonic day 8.5. At mid-gestation, fezl expression was detected in subdomains of the forebrain, including the dorsal telencephalon and ventral diencephalon. Unlike the zebrafish fezl mutant too few, the fezl-deficient mice displayed normal development of hypothalamic monoaminergic neurons, but showed abnormal "hyperactive" behavior. In fezl(-/-) mice, the thalamocortical axons (TCA) were reduced in number and aberrantly projected to the cortex. These mutants had a reduced number of subplate neurons, which are involved in guiding the TCA from the dorsal thalamus, although the subplate neurons were born normally. These results suggest that fezl is required for differentiation or survival of the subplate neurons, and reduction of the subplate neurons in fezl-deficient mice leads to abnormal development of the TCA, providing a possible link between the transcriptional regulation of forebrain development and hyperactive behavior.

EMX2 regulates sizes and positioning of the primary sensory and motor areas in neocortex by direct specification of cortical progenitors

Genetic studies of neocortical area patterning are limited, because mice deficient for candidate regulatory genes die before areas emerge and have other complicating issues. To define roles for the homeodomain transcription factor EMX2, we engineered nestin-Emx2 transgenic mice that overexpress Emx2 in cortical progenitors coincident with expression of endogenous Emx2 and survive postnatally. Cortical size, lamination, thalamus, and thalamocortical pathfinding are normal in homozygous nestin-Emx2 mice. However, primary sensory and motor areas are disproportionately altered in size and shift rostrolaterally. Heterozygous transgenics have similar but smaller changes. Opposite changes are found in heterozygous Emx2 knockout mice. Fgf8 expression in the commissural plate of nestin-Emx2 mice is indistinguishable from wild-type, but Pax6 expression is downregulated in rostral cortical progenitors, suggesting that EMX2 repression of PAX6 specification of rostral identities contributes to reduced rostral areas. We conclude that EMX2 levels in cortical progenitors disproportionately specify sizes and positions of primary cortical areas.

Alpha-catenin: at the junction of intercellular adhesion and actin dynamics

Alpha-catenin has often been considered to be a non-regulatory intercellular adhesion protein, in contrast to beta-catenin, which has well-documented dual roles in cell-cell adhesion and signal transduction. Recently, however, alpha-catenin has been found to be important not only in connecting the E-cadherin-beta-catenin complex to the actin cytoskeleton, but also in coordinating actin dynamics and inversely correlating cell adhesion with proliferation. As the number of alpha-catenin-interacting partners increases, intriguing new connections imply even more complex regulatory functions for this protein.

Expression of regulatory genes during differentiation of thalamic nuclei in mouse and monkey

Expression patterns of genes implicated in development of the thalamus were examined in mice and monkeys, using in situ hybridization with RNA probes complementary to Cad6, Dlx1, Dlx2, Dlx5, Gbx2, Id2, and Lef1 cDNAs. Expression patterns were related to the evolving cytoarchitecture in mice at birth (P0) and in adulthood, and in fetal monkeys early and late in the period of gestation when thalamic nuclei are becoming histologically differentiated out of a series of pronuclear masses. At the earlier developmental stage, each gene was expressed in a pattern that appeared to be pronucleus-specific and maintained a nucleus-specific pattern into adulthood, with the possible exception of Gbx2. Each gene displayed a unique expression pattern in the dorsal thalamus, ventral thalamus, and epithalamus, and no gene was expressed throughout all three divisions or in every nucleus of a division. With the exception of Dlx2, whose expression disappeared at the later time point, all continued to be expressed into adulthood at higher levels and with identical patterns. Despite late appearance of gamma-aminobutyric acid (GABA)ergic cells in the dorsal lateral geniculate nucleus of mice, no Dlx genes, which promote formation of a GABAergic phenotype elsewhere, were detected in dorsal thalamus. Each thalamic nucleus was distinguished by expression of a combination of genes, and homologous nuclei in mouse and monkey exhibited the same combination. The presence of a centre médian nucleus and four pulvinar nuclei in monkeys was marked by patterns of expression not found in mice. The centre médian nucleus was marked by high expression of Id2, which was expressed only weakly in very few nuclei of mice.

Distribution of N-cadherin in human cerebral cortex during prenatal development

An important subgroup of adhesion molecules is the superfamily of cadherins, which takes part in cell recognition and differentiation during development. To our knowledge only one study describing N-cadherin expression in developing human brain has been performed so far. Our aim is to identify N-cadherin expression to establish a relationship between its expression and function in human cerebral cortex during prenatal development. In the present study, localization and intensity of N-cadherin was investigated in developing cerebral cortex. Fetuses from spontaneous abortions (n=13) were obtained from first, second, and third trimesters. Western blot analysis revealed three bands and the third trimester samples showed the strongest bands for N-cadherin. Cell processes, axon bundles, and some of the developing neurons revealed immunoreactivity for N-cadherin throughout pregnancy. The immunoreactivity increased in the developing neocortex and expanded from the ventricular layer toward the marginal zone as development progressed. Moreover, the immunoreactivity was strong in vascular endothelium during all three trimesters. We conclude that N-cadherin is dynamically related to the organization of cerebral cortex layers during prenatal development. The dynamic expression pattern implicates N-cadherin as a potential regulator of cell migration, axon extension and fasciculation, the establishment of synaptic contacts, and neurovascular angiogenesis in the developing human cerebral cortex.

Widespread tangential dispersion and extensive cell death during early neurogenesis in the mouse neocortex

The development of the mammalian neocortex requires radial and tangential migration of cells. Radial migration of differentiated neurons from the ventricular zone (VZ) is well established. It is hypothesised that an earlier phase of tangential migration of mitotically active cells lays down a widespread periodically spaced set of progenitors that generate radial arrays of postmitotic neurons. We use a transgenic cell lineage marker to label and observe the behaviour of progenitors before and during the early stages of neurogenesis. Using optical projection tomography (OPT), we show that individual progenitor cells generate many radially arrayed columns of periodically spaced cells. Column positions indicate the paths taken by these progenitor cells as they migrate, often over long distances, through the proliferative zone. Clonally related cells can be distributed in both hemispheres, suggesting progenitor cells cross the midline in the anterior neural plate. We observe a dramatic and rapid decline in the number of labelled clones after E13.5, indicating that there is extensive cell death at this time.

Expression of dominant negative cadherin in the adult mouse brain modifies rearing behavior

The cadherin superfamily of cell-cell adhesion molecules (CAM) are crucial regulators of morphogenesis and axonal guidance during development of the nervous system and have been suggested to play important roles in neural plasticity of the brain. To study the latter, we created a mouse model that expressed a dominant negative classical cadherin in the brain of adult mice. The mice were tested for spontaneous motor activity and exploratory behavior in the open field, anxiety in the plus-maze, and spatial learning and memory in the water-T maze. Mice expressing the dominant negative cadherin displayed reduced rearing behavior, but no change in motor activity, in the open field, indicating deficits in exploratory behavior. In the water maze, animals expressing the mutant cadherin showed normal escape latencies and were indistinguishable from control littermates. Similarly, LTP in hippocampal slices of cadherin mutant and control mice were indistinguishable. These findings demonstrate intact spatial learning in mice expressing a dominant negative cadherin but altered rearing behavior, suggesting the involvement of classical cadherins in mechanisms mediating rearing behavior.

Cadherins guide migrating Purkinje cells to specific parasagittal domains during cerebellar development

Several cadherins are expressed in parasagittal Purkinje cell domains, which can be defined by their afferent and efferent connectivity in the developing and mature cerebellum. By in vivo electroporation in chicken embryos, we demonstrate that Purkinje cell progenitors, which overexpress cadherin-6B or cadherin-7, distribute preferentially to those Purkinje cell domains, which express the respective cadherin endogenously. This differential distribution may be based, at least in part, on the guidance of migrating neurons along neurites that express the same cadherin. Selective induction of apoptosis and cadherin-based cell sorting within cortical domains do not seem to contribute to the differential distribution. These results show that cadherins can tell early neurons where to integrate in functional brain gray matter, possibly by a cadherin-based homotypic adhesive mechanism.

Gene expression analysis of the late embryonic mouse cerebral cortex using DNA microarray: identification of several region- and layer-specific genes

The mammalian neocortex develops layer organizations with regional differences represented by expression of multiple genes at embryonic stages. These genes could play important roles in the formation of areal cyto-architecture, yet, the number of genes identified so far is not sufficient to explain such intricate processes. Here we collected five regions--the medial, dorsal, lateral, rostral and occipital--from the dissected E16.5 mouse cerebral cortex and performed extensive gene expression analysis using the Affymetrix U74Av2 array with probes for 12,500 genes. After relative quantitative analysis, 34, 33 and 15 genes were selected as highly expressed genes in the medial, dorsal and lateral regions, respectively. The combination of GeneChip system, real-time quantitative reverse transcription polymerase chain reaction and in situ hybridization analyses allowed the successful identification of seven genes from the dorsal region (Neuropeptide Y, Wnt7b, TGF-beta RI, Nrf3, Bcl-6, MT4-MMP and Rptp kappa), three genes from the medial region (Hop-pending, HtrA and Crystallin), and three genes from the lateral region (Somatostatin, Ngef and Fxyd7). Particularly, all seven genes identified in the dorsal region demarcated the future somatosensory and auditory areas in the cortical plate with high rostrolateral-low caudomedial gradation. Their expression patterns were not uniform, but delineated either the superficial or the deep layer in the cortical plate. Furthermore, the regional expression pattern of Neuropeptide Y was shifted rostrally and the layer specificity was disorganized in the Pax6-deficient mice. Our results provide new information about a subclass of regionally expressed genes in the cortical plate at the late embryonic stage, which may help understand the molecular mechanisms of neocortical arealization.

Identification of a novel type II classical cadherin: Ratcadherin19 is expressed in the cranial ganglia and Schwann cell precursors during development

To identify a novel type II classical cadherin, we searched the genome database and found rat cadherin19 (cad19) with high similarity to human cadherin19. We also found nucleotide sequences corresponding to rat cad19 in mouse and chicken genomes. In situ hybridization of rat cad19 revealed that rat cad19 mRNA was initially expressed in cephalic neural crest cells, and then in the cranial ganglia, migrating trunk neural crest cells, the nascent dorsal root ganglia, and the sympathetic ganglia. Expression of cad19 overlapped with that of neural crest markers, including Sox10 and AP-2, but cad19 expression was confined to subpopulations of the neural crest-derived cells, those typically observed in the satellite glia at the periphery of the ganglia and Schwann cell precursors along the peripheral nerves. cad19 mRNA was not detected in cells expressing Phox2b, an epibranchial placode-derived neurons, nor in those expressing neuronal markers such as Hu protein. These observations suggest that cad19 is expressed in neural crest-derived, non-neuronal cells. Although the expression of cad19 mRNA persisted in Schwann cell precursors at E14.5, it was no longer detected in maturing Schwann cells at later stages. These results suggest that cad19 is an evolutionarily conserved cadherin and may be involved in the early development of Schwann cells in the peripheral nervous system.

Identification of a nonchordate-type classic cadherin in vertebrates: Chicken Hz-cadherin is expressed in horizontal cells of the neural retina and contains a nonchordate-specific domain complex

Classic cadherins mediate calcium-dependent cell-cell adhesion in a variety of animals, but there are marked differences in their domain structures between chordate and nonchordate animals. The extracellular domain of chordate-type classic cadherins (type I and type II classic cadherins) consists of five tandem repeats of conserved sequences called EC domains, whereas that of nonchordate-type classic cadherins (designated as type III classic cadherin) contains a variable number of EC domains, followed by a characteristic domain complex made of laminin-A globular domains and EGF-like repeats. In the present study, we identified a novel vertebrate type III cadherin showing high sequence similarity to Drosophila N-cadherin, and named this molecule chicken Hz-cadherin (cHz-cadherin), because of the distinct expression in horizontal cells of the neural retina. cHz-cadherin functioned as an adhesion molecule when introduced into cultured cells. Database search revealed one cHz-cadherin homologue in zebrafish and two in puffer fish, but none in other vertebrate species examined. These observations indicate that type III classic cadherins have been conserved in vertebrate species, being expressed by limited cells types, but lost in particular phylogenic groups of the vertebrates.

Presenilin 1 is involved in maturation and trafficking of N-cadherin to the plasma membrane

One pathological characteristic of Alzheimer's disease (AD) is extensive synapse loss. Presenilin 1 (PS1) is linked to the pathogenesis of early onset familial Alzheimer's disease (FAD) and is localized at the synapse, where it binds N-cadherin and modulates its adhesive activity. To elucidate the role of the PS1/N-cadherin interaction in synaptic contact, we established SH-SY5Y cells stably expressing wild-type (wt) PS1 and dominant-negative (D385A) PS1. We show that the formation of cadherin-based cell-cell contact among SH-SY5Y cells stably expressing D385A PS1 was suppressed. Conversely, wt PS1 cells exhibited enhanced cell-cell contact and colony formation. Suppression of cell-cell contact in D385A cells was accompanied by an alteration in N-cadherin subcellular localization; N-cadherin was retained mainly in the endoplasmic reticulum (ER) and cell surface expression was reduced. We conclude that PS1 is essential for efficient trafficking of N-cadherin from the ER to the plasma membrane. PS1-mediated delivery of N-cadherin to the plasma membrane is important for N-cadherin to exert its physiological function, and it may control the state of cell-cell contact.

Differential activities, subcellular distribution and tissue expression patterns of three members of Slingshot family phosphatases that dephosphorylate cofilin

BACKGROUND

Cofilin, a key regulator of actin filament dynamics, is inactivated by phosphorylation at Ser-3 by LIM-kinases and is reactivated by dephosphorylation by a family of protein phosphatases, termed Slingshot (SSH).

RESULTS

We have identified two novel isoforms of SSHs, termed SSH-2L and SSH-3L and characterized them in comparison with SSH-1L that was previously reported. SSH-1L and SSH-2L, but not SSH-3L, tightly bound to and co-localized with actin filaments. When expressed in cultured cells, SSH-1L, SSH-2L and SSH-3L decreased the level of Ser-3-phosphorylated cofilin (P-cofilin) in cells and suppressed LIM-kinase-induced actin reorganization, although SSH-3L was less effective than SSH-1L and SSH-2L. In cell-free assays, SSH-1L and SSH-2L efficiently dephosphorylated P-cofilin, whereas SSH-3L did do so only weakly. Using deleted mutants of SSH-1L and SSH-2L, we found that the N-terminal and C-terminal extracatalytic regions are critical for cofilin-phosphatase and F-actin-binding activities, respectively. In situ hybridization analyses revealed characteristic patterns of expression of each of the mouse Ssh genes in both neuronal and non-neuronal tissues; in particular, expression of Ssh-3 in epithelial tissues is evident.

CONCLUSION

SSH-1L, SSH-2L and SSH-3L have the potential to dephosphorylate P-cofilin, but subcellular distribution, F-actin-binding activity, specific phosphatase activity and expression patterns significantly differ, which suggests that they have related but distinct functions in various cellular and developmental events.