Expression of planar cell polarity genes during development of the mouse CNS

Knockdown of the Non-canonical Wnt Gene Prickle2 Leads to Cerebellar Purkinje Cell Abnormalities While Cerebellar-Mediated Behaviors Remain Intact

Autism spectrum disorders (ASD) involve brain wide abnormalities that contribute to a constellation of symptoms including behavioral inflexibility, cognitive dysfunction, learning impairments, altered social interactions, and perceptive time difficulties. Although a single genetic variation does not cause ASD, genetic variations such as one involving a non-canonical Wnt signaling gene, Prickle2, has been found in individuals with ASD. Previous work looking into phenotypes of Prickle2 knock-out (Prickle2-/-) and heterozygous mice (Prickle2-/+) suggest patterns of behavior similar to individuals with ASD including altered social interaction and behavioral inflexibility. Growing evidence implicates the cerebellum in ASD. As Prickle2 is expressed in the cerebellum, this animal model presents a unique opportunity to investigate the cerebellar contribution to autism-like phenotypes. Here, we explore cerebellar structural and physiological abnormalities in animals with Prickle2 knockdown using immunohistochemistry, whole-cell patch clamp electrophysiology, and several cerebellar-associated motor and timing tasks, including interval timing and eyeblink conditioning. Histologically, Prickle2-/- mice have significantly more empty spaces or gaps between Purkinje cells in the posterior lobules and a decreased propensity for Purkinje cells to fire action potentials. These structural cerebellar abnormalities did not impair cerebellar-associated behaviors as eyeblink conditioning and interval timing remained intact. Therefore, although Prickle-/- mice show classic phenotypes of ASD, they do not recapitulate the involvement of the adult cerebellum and may not represent the pathophysiological heterogeneity of the disorder.

A 4D transcriptomic map for the evolution of multiple sclerosis-like lesions in the marmoset brain

Single-time-point histopathological studies on postmortem multiple sclerosis (MS) tissue fail to capture lesion evolution dynamics, posing challenges for therapy development targeting development and repair of focal inflammatory demyelination. To close this gap, we studied experimental autoimmune encephalitis (EAE) in the common marmoset, the most faithful animal model of these processes. Using MRI-informed RNA profiling, we analyzed ~600,000 single-nucleus and ~55,000 spatial transcriptomes, comparing them against EAE inoculation status, longitudinal radiological signals, and histopathological features. We categorized 5 groups of microenvironments pertinent to neural function, immune and glial responses, tissue destruction and repair, and regulatory network at brain borders. Exploring perilesional microenvironment diversity, we uncovered central roles of EAE-associated astrocytes, oligodendrocyte precursor cells, and ependyma in lesion formation and resolution. We pinpointed imaging and molecular features capturing the pathological trajectory of WM, offering potential for assessing treatment outcomes using marmoset as a platform.

Celsr2 Knockout Alleviates Inhibitory Synaptic Stripping and Benefits Motoneuron Survival and Axon Regeneration After Branchial Plexus Avulsion

Axotomy-induced synaptic stripping modulates survival and axon regeneration of injured motoneurons. Celsr2 is supposed to mediate homophilic interactions of neighboring cells during development, and its role in synaptic stripping remains unknow. In a model of brachial plexus avulsion, Celsr2 knockout improved functional recovery, motoneuron survival, and axon regeneration. Celsr2 was indicated to express in spinal motoneurons, excitatory and inhibitory interneurons, astrocytes, and a subset of oligodendrocytes using Celsr2^LacZ mice. Double immunostaining showed that the coverage of inhibitory and excitatory vesicles on injured motoneurons were remarkably reduced after injury, whereas more inhibitory vesicles were maintained in Celsr2^-/- mutants than control mice. In the ultrastructure, the density of inhibitory F-boutons on injured motoneurons was higher in Celsr2^-/- mutants than controls. Conditional knockout of Celsr2 in astrocytes or oligodendrocytes showed the similar axotomy-induced synaptic withdrawal to the control. RNAseq of injured spinal samples identified 12 MHC I molecules with significant changes between Celsr2^-/- and control mice. After injury, expression of MHC I surrounding injured motoneurons was increased, particularly high in Celsr2^-/- mutants. In conclusion, Celsr2 knockout enhances MHC I signaling, alleviates inhibitory synaptic stripping cell-autonomously, and contributes to motoneuron survival and regeneration, and Celsr2 is a potential target for neural repair.

Functional interaction between Vangl2 and N-cadherin regulates planar cell polarization of the developing neural tube and cochlear sensory epithelium

Although the core constituents of the Wnt/planar cell polarity (PCP) signaling have been extensively studied, their downstream molecules and protein-protein interactions have not yet been fully elucidated. Here, we show genetic and molecular evidence that the PCP factor, Vangl2, functionally interacts with the cell-cell adhesion molecule, N-cadherin (also known as Cdh2), for typical PCP-dependent neural development. Vangl2 and N-cadherin physically interact in the neural plates undergoing convergent extension. Unlike monogenic heterozygotes, digenic heterozygous mice with Vangl2 and Cdh2 mutants exhibited defects in neural tube closure and cochlear hair cell orientation. Despite this genetic interaction, neuroepithelial cells derived from the digenic heterozygotes did not show additive changes from the monogenic heterozygotes of Vangl2 in the RhoA-ROCK-Mypt1 and c-Jun N-terminal kinase (JNK)-Jun pathways of Wnt/PCP signaling. Thus, cooperation between Vangl2 and N-cadherin is at least partly via direct molecular interaction; it is essential for the planar polarized development of neural tissues but not significantly associated with RhoA or JNK pathways.

G protein-coupled receptors in cochlea: Potential therapeutic targets for hearing loss

The prevalence of hearing loss-related diseases caused by different factors is increasing worldwide year by year. Currently, however, the patient’s hearing loss has not been effectively improved. Therefore, there is an urgent need to adopt new treatment measures and treatment techniques to help improve the therapeutic effect of hearing loss. G protein-coupled receptors (GPCRs), as crucial cell surface receptors, can widely participate in different physiological and pathological processes, particularly play an essential role in many disease occurrences and be served as promising therapeutic targets. However, no specific drugs on the market have been found to target the GPCRs of the cochlea. Interestingly, many recent studies have demonstrated that GPCRs can participate in various pathogenic process related to hearing loss in the cochlea including heredity, noise, ototoxic drugs, cochlear structure, and so on. In this review, we comprehensively summarize the functions of 53 GPCRs known in the cochlea and their relationships with hearing loss, and highlight the recent advances of new techniques used in cochlear study including cryo-EM, AI, GPCR drug screening, gene therapy vectors, and CRISPR editing technology, as well as discuss in depth the future direction of novel GPCR-based drug development and gene therapy for cochlear hearing loss. Collectively, this review is to facilitate basic and (pre-) clinical research in this area, and provide beneficial help for emerging GPCR-based cochlear therapies.

WNT signaling at the intersection between neurogenesis and brain tumorigenesis

Neurogenesis and tumorigenesis share signaling molecules/pathways involved in cell proliferation, differentiation, migration, and death. Self-renewal of neural stem cells is a tightly regulated process that secures the accuracy of cell division and eliminates cells that undergo mitotic errors. Abnormalities in the molecular mechanisms controlling this process can trigger aneuploidy and genome instability, leading to neoplastic transformation. Mutations that affect cell adhesion, polarity, or migration enhance the invasive potential and favor the progression of tumors. Here, we review recent evidence of the WNT pathway’s involvement in both neurogenesis and tumorigenesis and discuss the experimental progress on therapeutic opportunities targeting components of this pathway.

Inactivating Celsr2 promotes motor axon fasciculation and regeneration in mouse and human

Understanding new modulators of axon regeneration is central to neural repair. Our previous work demonstrated critical roles of atypical cadherin Celsr2 during neural development, including cilia organization, neuron migration and axon navigation. Here, we address its role in axon regeneration.

We show that Celsr2 is highly expressed in both mouse and human spinal motor neurons. Celsr2 knockout promotes axon regeneration and fasciculation in mouse cultured spinal explants. Similarly, cultured Celsr2 mutant motor neurons extend longer neurites and larger growth cones, with increased expression of end-binding protein 3 and higher potassium-induced calcium influx. Mice with Celsr2 conditional knockout in spinal motor neurons do not exhibit any behavioural deficits; however, after branchial plexus injury, axon regeneration and functional forelimb locomotor recovery are significantly improved. Similarly, knockdown of CELSR2 using shRNA interference in cultured human spinal motor explants and motor neurons increases axonal fasciculation and growth. In mouse adult spinal cord after root avulsion, in mouse embryonic spinal cords, and in cultured human motor neurons, Celsr2 downregulation is accompanied by increased levels of GTP-bound Rac1 and Cdc42, and of JNK and c-Jun.

In conclusion, Celsr2 negatively regulates motor axon regeneration and is a potential target to improve neural repair.

Planar cell polarity protein Vangl2 and its interacting protein Ap2m1 regulate dendritic branching in cortical neurons

Van Gogh-like 2 (Vangl2) is a mammalian homolog of Drosophila core planar cell polarity (PCP) protein Vang/Strabismus, which organizes asymmetric cell axes for developmental proliferation, fate determination, and polarized movements in multiple tissues, including neurons. Although the PCP pathway has an essential role for dendrite and dendritic spine formation, the molecular mechanism remains to be clarified. To investigate the mechanism of Vangl2-related neuronal development, we screened for proteins that interact with the Vangl2 cytosolic N-terminus from postnatal day 9 mouse brains using a yeast two-hybrid system. From 61 genes, we identified adaptor-related protein complex 2, mu 1 subunit (Ap2m1) as the Vangl2 N-terminal binding protein. Intriguingly, however, the pull-down assay demonstrated that Vangl2 interacted with Ap2m1 not only at its N-terminus but also at the C-terminal Prickle binding domain. Furthermore, we verified that the downregulation of Ap2m1 in the developing cortical neurons reduced the dendritic branching similar to what occurs in a knockdown of Vangl2. From these results, we suggest that the membrane internalization regulated by the PCP pathway is required for the developmental morphological change in neurons.

The Celsr3-Kif2a axis directs neuronal migration in the postnatal brain

The tangential migration of immature neurons in the postnatal brain involves consecutive migration cycles and depends on constant remodeling of the cell cytoskeleton, particularly in the leading process (LP). Despite the identification of several proteins with permissive and empowering functions, the mechanisms that specify the direction of migration remain largely unknown. Here, we report that planar cell polarity protein Celsr3 orients neuroblasts migration from the subventricular zone (SVZ) to olfactory bulb (OB). In Celsr3-forebrain conditional knockout mice, neuroblasts loose directionality and few can reach the OB. Celsr3-deficient neuroblasts exhibit aberrant branching of LP, de novo LP formation, and decreased growth rate of microtubules (MT). Mechanistically, we show that Celsr3 interacts physically with Kif2a, a MT depolymerizing protein and that conditional inactivation of Kif2a in the forebrain recapitulates the Celsr3 knockout phenotype. Our findings provide evidence that Celsr3 and Kif2a cooperatively specify the directionality of neuroblasts tangential migration in the postnatal brain.

Celsr3 is required for Purkinje cell maturation and regulates cerebellar postsynaptic plasticity

Atypical cadherin Celsr3 is critical for brain embryonic development, and its role in the postnatal cerebellum remains unknown. Using Celsr3-GFP mice, Celsr3 shows high expression in postnatal Purkinje cells (PCs). Mice with conditional knockout (cKO) of Celsr3 in postnatal PCs exhibit deficit in motor coordination and learning, atrophic PC dendrites, and decreased synapses. Whole-PC recording in cerebellar slices discloses a reduction frequency of mEPSC and defective postsynaptic plasticity (LTP and LTD) in Celsr3 cKO mutants. Wnt5a perfusion enhances LTP formation, which could be occluded by cAMP agonist and diminished by cAMP antagonist in control, but not in Celsr3 cKO or Fzd3 cKO cerebellar slices. Celsr3 cKO resulted in the failure of mGluR1 agonist-induced LTD and paired stimulation-induced PKCα overexpression in PC dendrites, and downregulation of mGluR1 expression compvared to controls. In conclusion, Celsr3 is required for PCs maturation and regulates postsynaptic LTP and LTD through Wnt5a/cAMP and mGluR1/PKCα signaling respectively.

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Celsr3 cKO in postnatal PCs impairs mouse motor coordination and learning

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Celsr3 inactivation affects the maturation of PC dendrites and synapses

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Celsr3 is required for the cerebellar LTP induction via the Wnt5a/cAMP signaling

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Celsr3 regulates the cerebellar LTD induction through the mGluR1/PKCα pathway

Distribution of planar cell polarity proteins in the developing avian retina

Planar cell polarity (PCP) is evolutionary conserved and play a critical role in proper tissue development and function. During central nervous system development, PCP proteins exhibit specific patterns of distribution and are indispensable for axonal growth, dendritogenesis, neuronal migration, and neuronal differentiation. The retina constitutes an excellent model in which to study molecular mechanisms involved in neural development. The analysis of the spatiotemporal expression of PCP proteins in this model constitutes an useful histological approach in order to identify possible roles of these proteins in retinogenesis. Immunohistochemical techniques revealed that Frz6, Celsr1, Vangl1, Pk1, Pk3, and Fat1 were present in emerging axons from recently differentiated ganglion cells in the chicken retina. Except for Vangl1, they were also asymmetrically distributed in differentiated amacrine cells. Pk1 and Pk3 were restricted in the outer nuclear layer to the outer segment of photoreceptors. Vangl1 was also located in the cell somata of Müller glia. Given these findings together, the distribution of PCP proteins in the developing chicken retina suggest essential roles in axonal guidance during early retinogenesis and a possible involvement in the establishment of cell asymmetry and maintenance of retinal cell phenotypes.

MicroRNA targeting of the non-canonical planar cell polarity pathway in the developing neural tube

MicroRNAs (miRNAs) provide context-dependent transcriptional regulation of genes comprising signalling networks throughout the developing organism including morphogenesis of the embryonic neural tube (NT). Using a high-sensitivity, high-coverage microarray analysis platform, miRNA expression in the murine embryonic NT during the critical stages of its formation was examined. Analysis of a number of differentially expressed (DE) miRNAs enabled identification of several gene targets associated with cellular processes essential for normal NT development. Using computational pathway analysis, interactive biologic networks and functional relationships connecting DE miRNAs with their targeted messenger RNAs (mRNAs) were identified. Potential mRNA targets and a key signal transduction pathway governing critical cellular processes indispensable for normal mammalian neurulation were also identified. RNA preparations were also used to hybridize both miRNA arrays and mRNA arrays allowing miRNA-mRNA target analysis using data of DE miRNAs and DE mRNAs - co-expressed in the same developing NT tissue samples. Identification of these miRNA targets provides key insight into the epigenetic regulation of NT development as well as into potential mechanistic underpinning of NT defects. SIGNIFICANCE OF THE STUDY: This study underscores the premise that microRNAs are potential coordinators of normal neural tube (NT) formation, via regulation of the crucial, planar cell polarity pathway. Any alteration in their expression during neurulation would result in abnormal NT development.

Vangl2 acts at the interface between actin and N-cadherin to modulate mammalian neuronal outgrowth

Dynamic mechanical interactions between adhesion complexes and the cytoskeleton are essential for axon outgrowth and guidance. Whether planar cell polarity (PCP) proteins, which regulate cytoskeleton dynamics and appear necessary for some axon guidance, also mediate interactions with membrane adhesion is still unclear. Here we show that Vangl2 controls growth cone velocity by regulating the internal retrograde actin flow in an N-cadherin-dependent fashion. Single molecule tracking experiments show that the loss of Vangl2 decreased fast-diffusing N-cadherin membrane molecules and increased confined N-cadherin trajectories. Using optically manipulated N-cadherin-coated microspheres, we correlated this behavior to a stronger mechanical coupling of N-cadherin with the actin cytoskeleton. Lastly, we show that the spatial distribution of Vangl2 within the growth cone is selectively affected by an N-cadherin-coated substrate. Altogether, our data show that Vangl2 acts as a negative regulator of axonal outgrowth by regulating the strength of the molecular clutch between N-cadherin and the actin cytoskeleton.

Linking Cell Polarity to Cortical Development and Malformations

Cell polarity refers to the asymmetric distribution of signaling molecules, cellular organelles, and cytoskeleton in a cell. Neural progenitors and neurons are highly polarized cells in which the cell membrane and cytoplasmic components are compartmentalized into distinct functional domains in response to internal and external cues that coordinate polarity and behavior during development and disease. In neural progenitor cells, polarity has a prominent impact on cell shape and coordinate several processes such as adhesion, division, and fate determination. Polarity also accompanies a neuron from the beginning until the end of its life. It is essential for development and later functionality of neuronal circuitries. During development, polarity governs transitions between multipolar and bipolar during migration of postmitotic neurons, and directs the specification and directional growth of axons. Once reaching final positions in cortical layers, neurons form dendrites which become compartmentalized to ensure proper establishment of neuronal connections and signaling. Changes in neuronal polarity induce signaling cascades that regulate cytoskeletal changes, as well as mRNA, protein, and vesicle trafficking, required for synapses to form and function. Hence, defects in establishing and maintaining cell polarity are associated with several neural disorders such as microcephaly, lissencephaly, schizophrenia, autism, and epilepsy. In this review we summarize the role of polarity genes in cortical development and emphasize the relationship between polarity dysfunctions and cortical malformations.

Vangl2 interaction plays a role in the proteasomal degradation of Prickle2

The PET and LIM domain-containing protein, Prickle, plays a key role in planar cell polarity (PCP) in Drosophila. It has been reported that mutations in the PRICKLE2 gene, which encodes one of the human orthologues of Prickle, are associated with human diseases such as epilepsy and autism spectrum disorder. To develop preventive and therapeutic strategies for these intractable diseases, we studied the regulation of Prickle2 protein levels in transfected HEK293T cells. Prickle2 levels were negatively regulated by a physical interaction with another PCP protein, Van Gogh-like 2 (Vangl2). The Vangl2-mediated reduction in Prickle2 levels was, at least in part, relieved by proteasome inhibitors or by functional inhibition of the Cullin-1 E3 ubiquitin ligase. Furthermore, the expression of Vangl2 enhanced the polyubiquitination of Prickle2. This ubiquitination was partially blocked by co-expression of a ubiquitin mutant, which cannot be polymerised through their Lys48 residue to induce target proteins toward proteasomal degradation. Together, these results suggest that Prickle2 is polyubiquitinated by the Vangl2 interaction in a Cullin-1-dependent manner to limit its expression levels. This regulation may play a role in the local and temporal fine-tuning of Prickle protein levels during PCP signal-dependent cellular behaviours.

A non-autonomous function of the core PCP protein VANGL2 directs peripheral axon turning in the developing cochlea

The cochlea is innervated by neurons that relay sound information from hair cells to central auditory targets. A subset of these are the type II spiral ganglion neurons, which have nociceptive features and contribute to feedback circuits providing neuroprotection in extreme noise. Type II neurons make a distinctive 90° turn towards the cochlear base to synapse with 10-15 outer hair cells. We demonstrate that this axon turning event requires planar cell polarity (PCP) signaling and is disrupted in Vangl2 and Celsr1 knockout mice, and that VANGL2 acts non-autonomously from the cochlea to direct turning. Moreover, VANGL2 is asymmetrically distributed at intercellular junctions between cochlear supporting cells, and in a pattern that could allow it to act directly as an axon guidance cue. Together, these data reveal a non-autonomous function for PCP signaling during axon guidance occurring in the tissue that is innervated, rather than the navigating growth cone.

Dishevelled has a YAP nuclear export function in a tumor suppressor context-dependent manner

Phosphorylation-dependent YAP translocation is a well-known intracellular mechanism of the Hippo pathway; however, the molecular effectors governing YAP cytoplasmic translocation remains undefined. Recent findings indicate that oncogenic YAP paradoxically suppresses Wnt activity. Here, we show that Wnt scaffolding protein Dishevelled (DVL) is responsible for cytosolic translocation of phosphorylated YAP. Mutational inactivation of the nuclear export signal embedded in DVL leads to nuclear YAP retention, with an increase in TEAD transcriptional activity. DVL is also required for YAP subcellular localization induced by E-cadherin, α-catenin, or AMPK activation. Importantly, the nuclear-cytoplasmic trafficking is dependent on the p53-Lats2 or LKB1-AMPK tumor suppressor axes, which determine YAP phosphorylation status. In vivo and clinical data support that the loss of p53 or LKB1 relieves DVL-linked reciprocal inhibition between the Wnt and nuclear YAP activity. Our observations provide mechanistic insights into controlled proliferation coupled with epithelial polarity during development and human cancer.

Hippo and Wnt pathways are important for cancer development, and they can cross talk; however, the mechanisms behind this connection are unknown. Here the authors show that DVL (a scaffold protein in the Wnt pathway) regulates the shuttling of YAP (a key component of the Hippo pathway) between cytoplasm and nucleus in specific tumor suppressor contexts.

Molecular guidance cues in the development of visual pathway

70%–80% of our sensory input comes from vision. Light hit the retina at the back of our eyes and the visual information is relayed into the dorsal lateral geniculate nuclei (dLGN) and primary visual cortex (V1) thereafter, constituting the image-forming visual circuit. Molecular cues are one of the key factors to guide the wiring and refinement of the image-forming visual circuit during pre- and post-embryonic stages. Distinct molecular cues are involved in different developmental stages and nucleus, suggesting diverse guidance mechanisms. In this review, we summarize molecular guidance cues throughout the image-forming visual circuit, including chiasm determination, eye-specific segregation and refinement in the dLGN, and at last the reciprocal connections between the dLGN and V1.

Seven pass Cadherins CELSR1-3

Cadherin EGF LAG seven-pass G-type receptors 1, 2 and 3 (CELSR1-3) form a family of three atypical cadherins with multiple functions in epithelia and in the nervous system. During the past decade, evidence has accumulated for a key role of CELSR1 in epithelial planar cell polarity (PCP), and for CELSR2 and CELSR3 in ciliogenesis and neural development, especially neuron migration and axon guidance in the central, peripheral and enteric nervous systems. Phenotypes in mutant mice indicate that CELSR proteins work in concert with FZD3 and FZD6, but several questions remain. Apart from PCP signaling pathways implicating CELSR1 that begin to be unraveled, little is known about other signals generated by CELSR2 and CELSR3. A crucial question concerns the putative ligands that trigger signaling, in particular what is the role of WNT factors. Another critical issue is the identification of novel intracellular pathways and effectors that relay and transmit signals in receptive cells? Answers to those questions should further our understanding of the role of those important molecules not only in development but also in regeneration and disease.

Expression of planar cell polarity genes during mouse tooth development

OBJECTIVE

Planar cell polarity (PCP) refers to the cell polarity across the tissue plane and controls various cell behaviors and structures. Although the expression of several PCP signaling components has been detected in tooth germs, knowledge of the gene expression patterns of these PCP components during tooth development remains incomplete. The aim of this study is to characterize the temporal and spatial changes in PCP gene expression during tooth development.

DESIGN

Expression of Celsr1 and 2, Fzd3 and 6, Vangl1 and 2, and Dvl1-3 genes was analyzed in mouse molar germs from the bud to the bell stage using in situ hybridization.

RESULTS

At the bud stage, all target genes were expressed in all areas of the tooth bud. In the enamel organ at the cap stage, expression of Fzd3 was suppressed in the enamel knot, whereas Fzd6 was strongly expressed there. Expression of Vangl2 was strongly expressed in the inner dental epithelium from the cap stage onwards. In the inner dental epithelium, strong expression of Fzd3, Dvl2 and Vangl2 was noted at the early bell stage, and of Celsr1, Fzd3, Fzd6, Vangl2 and Dvl2 at the bell stage. Furthermore, differentiated odontoblasts strongly expressed Celsr1, Vangl2, and Dvl2.

CONCLUSION

The gene expression patterns delineated in this study improve our understanding of the role(s) of PCP components during tooth development.

Celsr1 coordinates the planar polarity of vestibular hair cells during inner ear development

Vestibular hair cells of the inner ear are specialized receptors that detect mechanical stimuli from gravity and motion via the deflection of a polarized bundle of stereocilia located on their apical cell surfaces. The orientation of stereociliary bundles is coordinated between neighboring cells by core PCP proteins including the large adhesive G-protein coupled receptor Celsr1. We show that mice lacking Celsr1 have vestibular behavioral phenotypes including circling. In addition, we show that Celsr1 is asymmetrically distributed at cell boundaries between hair cells and neighboring supporting cells in the developing vestibular and auditory sensory epithelia. In the absence of Celsr1 the stereociliary bundles of vestibular hair cells are misoriented relative to their neighbors, a phenotype that is greatest in the cristae of the semicircular canals. Since horizontal semi-circular canal defects lead to circling in other mutant mouse lines, we propose that this PCP phenotype is the cellular basis of the circling behavior in Celsr1 mutants.

Altered tooth morphogenesis after silencing the planar cell polarity core component, Vangl2

Vangl2, one of the core components of the planar cell polarity (PCP) pathway, has an important role in the regulation of morphogenesis in several tissues. Although the expression of Vangl2 has been detected in the developing tooth, its role in tooth morphogenesis is not known. In this study, we show that Vangl2 is expressed in the inner dental epithelium (IDE) and in the secondary enamel knots (SEKs) of bell stage tooth germs. Inhibition of Vangl2 expression by siRNA treatment in in vitro-cultured tooth germs resulted in retarded tooth germ growth with deregulated cell proliferation and apoptosis. After kidney transplantation of Vangl2 siRNA-treated tooth germs, teeth were observed to be small and malformed. We also show that Vangl2 is required to maintain the proper pattern of cell alignment in SEKs, which maybe important for the function of SEKs as signaling centers. These results suggest that Vangl2 plays an important role in the morphogenesis of teeth.

The atypical cadherin Celsr1 functions non-cell autonomously to block rostral migration of facial branchiomotor neurons in mice

The caudal migration of facial branchiomotor (FBM) neurons from rhombomere (r) 4 to r6 in the hindbrain is an excellent model to study neuronal migration mechanisms. Although several Wnt/Planar Cell Polarity (PCP) components are required for FBM neuron migration, only Celsr1, an atypical cadherin, regulates the direction of migration in mice. In Celsr1 mutants, a subset of FBM neurons migrates rostrally instead of caudally. Interestingly, Celsr1 is not expressed in the migrating FBM neurons, but rather in the adjacent floor plate and adjoining ventricular zone. To evaluate the contribution of different expression domains to neuronal migration, we conditionally inactivated Celsr1 in specific cell types. Intriguingly, inactivation of Celsr1 in the ventricular zone of r3-r5, but not in the floor plate, leads to rostral migration of FBM neurons, greatly resembling the migration defect of Celsr1 mutants. Dye fill experiments indicate that the rostrally-migrated FBM neurons in Celsr1 mutants originate from the anterior margin of r4. These data suggest strongly that Celsr1 ensures that FBM neurons migrate caudally by suppressing molecular cues in the rostral hindbrain that can attract FBM neurons.

Prickle1 promotes focal adhesion disassembly in cooperation with the CLASP-LL5β complex in migrating cells

Prickle is known to be involved in planar cell polarity, including convergent extension and cell migration; however, the detailed mechanism by which Prickle regulates cellular functions is not well understood. Here, we show that Prickle1 regulates front-rear polarization and migration of gastric cancer MKN1 cells. Prickle1 preferentially accumulated at the cell retraction site in close proximity to paxillin at focal adhesions. Prickle1 dynamics correlated with those of paxillin during focal adhesion disassembly. Furthermore, Prickle1 was required for focal adhesion disassembly. CLASPs (of which there are two isoforms, CLASP1 and CLASP2, in mammals) and LL5β (also known as PHLDB2) have been reported to form a complex at cell edges and to control microtubule-dependent focal adhesion disassembly. Prickle1 was associated with CLASPs and LL5β, and was required for the LL5β-dependent accumulation of CLASPs at the cell edge. Knockdown of CLASPs and LL5β suppressed Prickle1-dependent cell polarization and migration. Prickle1 localized to the membrane through its farnesyl moiety, and the membrane localization was necessary for Prickle1 to regulate migration, to bind to CLASPs and LL5β, and to promote microtubule targeting of focal adhesions. Taken together, these results suggest that Prickle1 promotes focal adhesion disassembly during the retraction processes of cell polarization and migration.

Feedback regulation of apical progenitor fate by immature neurons through Wnt7-Celsr3-Fzd3 signalling

Sequential generation of neurons and glial cells during development is critical for the wiring and function of the cerebral cortex. This process requires accurate coordination of neural progenitor cell (NPC) fate decisions, by NPC-autonomous mechanisms as well as by negative feedback from neurons. Here, we show that neurogenesis is protracted and gliogenesis decreased in mice with mutations of genes Celsr3 and Fzd3. This phenotype is not due to gene inactivation in progenitors, but rather in immature cortical neurons. Mutant neurons are unable to upregulate expression of Jag1 in response to cortical Wnt7, resulting in blunted activation of Notch signalling in NPC. Thus, Celsr3 and Fzd3 enable immature neurons to respond to Wnt7, upregulate Jag1 and thereby facilitate feedback signals that tune the timing of NPC fate decisions via Notch activation.

The role of G protein-coupled receptors in the early evolution of neurotransmission and the nervous system

The origin and evolution of the nervous system is one of the most intriguing and enigmatic events in biology. The recent sequencing of complete genomes from early metazoan organisms provides a new platform to study the origins of neuronal gene families. This review explores the early metazoan expansion of the largest integral transmembrane protein family, the G protein-coupled receptors (GPCRs), which serve as molecular targets for a large subset of neurotransmitters and neuropeptides in higher animals. GPCR repertories from four pre-bilaterian metazoan genomes were compared. This includes the cnidarian Nematostella vectensis and the ctenophore Mnemiopsis leidyi, which have primitive nervous systems (nerve nets), the demosponge Amphimedon queenslandica and the placozoan Trichoplax adhaerens, which lack nerve and muscle cells. Comparative genomics demonstrate that the rhodopsin and glutamate receptor families, known to be involved in neurotransmission in higher animals are also widely found in pre-bilaterian metazoans and possess substantial expansions of rhodopsin-family-like GPCRs. Furthermore, the emerging knowledge on the functions of adhesion GPCRs in the vertebrate nervous system provides a platform to examine possible analogous roles of their closest homologues in pre-bilaterians. Intriguingly, the presence of molecular components required for GPCR-mediated neurotransmission in pre-bilaterians reveals that they exist in both primitive nervous systems and nerve-cell-free environments, providing essential comparative models to better understand the origins of the nervous system and neurotransmission.

The Wnt adaptor protein ATP6AP2 regulates multiple stages of adult hippocampal neurogenesis

In the mammalian hippocampus, canonical Wnt signals provided by the microenvironment regulate the differentiation of adult neural stem cells (NSCs) toward the neuronal lineage. Wnts are part of a complex and diverse set of signaling pathways and the role of Wnt/Planar cell polarity (PCP) signaling in adult neurogenesis remains unknown. Using in vitro assays on differentiating adult NSCs, we identified a transition of Wnt signaling responsiveness from Wnt/β-catenin to Wnt/PCP signaling. In mice, retroviral knockdown strategies against ATP6AP2, a recently discovered core protein involved in both signaling pathways, revealed that its dual role is critical for granule cell fate and morphogenesis. We were able to confirm its dual role in neurogenic Wnt signaling in vitro for both canonical Wnt signaling in proliferating adult NSCs and non-canonical Wnt signaling in differentiating neuroblasts. Although LRP6 appeared to be critical for granule cell fate determination, in vivo knockdown of PCP core proteins FZD3 and CELSR1-3 revealed severe maturational defects without changing the identity of newborn granule cells. Furthermore, we found that CELSR1-3 control distinctive aspects of PCP-mediated granule cell morphogenesis with CELSR1 regulating the direction of dendrite initiation sites and CELSR2/3 controlling radial migration and dendritic patterning. The data presented here characterize distinctive roles for Wnt/β-catenin signaling in granule cell fate determination and for Wnt/PCP signaling in controlling the morphological maturation of differentiating neuroblasts.

Partial interchangeability of Fz3 and Fz6 in tissue polarity signaling for epithelial orientation and axon growth and guidance

In mammals, a set of anatomically diverse polarity processes - including axon growth and guidance, hair follicle orientation, and stereociliary bundle orientation in inner ear sensory hair cells - appear to be mechanistically related, as judged by their dependence on vertebrate homologues of core tissue polarity/planar cell polarity (PCP) genes in Drosophila. To explore more deeply the mechanistic similarities between different polarity processes, we have determined the extent to which frizzled 3 (Fz3) can rescue the hair follicle and Merkel cell polarity defects in frizzled 6-null (Fz6(-/-)) mice, and, reciprocally, the extent to which Fz6 can rescue the axon growth and guidance defects in Fz3(-/-) mice. These experiments reveal full rescue of the Fz6(-/-) phenotype by Fz3 and partial rescue of the Fz3(-/-) phenotype by Fz6, implying that these two proteins are likely to act in a conserved manner in these two contexts. Stimulated by these observations, we searched for additional anatomical structures that exhibit macroscopic polarity and that might plausibly use Fz3 and/or Fz6 signaling. This search has revealed a hitherto unappreciated pattern of papillae on the dorsal surface of the tongue that depends, at least in part, on redundant signaling by Fz3 and Fz6. Taken together, these experiments provide compelling evidence for a close mechanistic relationship between multiple anatomically diverse polarity processes.

The planar cell polarity protein Vangl2 bidirectionally regulates dendritic branching in cultured hippocampal neurons

Background

Van Gogh-like (Vangl) 2 is a planar cell polarity (PCP) protein that regulates the induction of polarized cellular and tissue morphology during animal development. In the nervous system, the core PCP signaling proteins have been identified to regulate neuronal maturation. In axonal growth cones, the antagonistic interaction of PCP components makes the tips of filopodia sensitive to guidance cues. However, the molecular mechanism by which the PCP signaling regulates spine and dendritic development remains obscure.

Findings

Here we explored the finding that a loss of function of Vangl2 results in a significant reduction in spine density and complexity of dendritic branching. In spite of a previous report, in which the Vangl2 C-terminal TSV motif was shown to be required for the interaction with PSD-95 and the C-terminal intracellular domain was shown to associate with N-cadherin, overexpression of deletion mutants (Vangl2-∆TSV and Vangl2-∆C) had little effect on spine density. However, when an N-terminal region deletion mutant was overexpressed, spine density was slightly down-regulated. Intriguingly, the deletion mutants had a more potent effect on dendritic branching, such that the deletion of the N-terminal region reduced dendritic branching, whereas deletion of the C-terminal region increased it.

Conclusions

Based on these results, Vangl2, a core PCP signaling pathway component, appears to have a functional role in neural complex formation. Especially in the case of dendritic branching, Vangl2 serves as a molecular hub to regulate neural morphology in opposite directions.

Understanding cadherin EGF LAG seven-pass G-type receptors

The cadherin epidermal growth factor (EGF) laminin G (LAG) seven-pass G-type receptors (CELSRs) are a special subgroup of adhesion G protein-coupled receptors, which are pivotal regulators of many biologic processes such as neuronal/endocrine cell differentiation, vessel valve formation, and the control of planar cell polarity during embryonic development. All three members of the CELSR family (CELSR1-3) have large ecto-domains that form homophilic interactions and encompass more than 2000 amino acids. Mutations in the ecto-domain or other gene locations of CELSRs are associated with neural tube defects and other diseases in humans. Celsr knockout (KO) animals have many developmental defects. Therefore, specific agonists or antagonists of CELSR members may have therapeutic potential. Although significant progress has been made regarding the functions and biochemical properties of CELSRs, our knowledge of these receptors is still lacking, especially considering that they are broadly distributed but have few characterized functions in a limited number of tissues. The dynamic activation and inactivation of CELSRs and the presence of endogenous ligands beyond homophilic interactions remain elusive, as do the regulatory mechanisms and downstream signaling of these receptors. Given this motivation, future studies with more advanced cell biology or biochemical tools, such as conditional KO mice, may provide further insights into the mechanisms underlying CELSR function, laying the foundation for the design of new CELSR-targeted therapeutic reagents. The cadherin EGF LAG seven-pass G-type receptors (CELSRs) are a special subgroup of adhesion G protein-coupled receptors (GPCRs), which have large ecto-domains that form homophilic interactions and encompass more than 2000 amino acids. Recent studies have revealed that CELSRs are pivotal regulators of many biological processes, such as neuronal/endocrine cell differentiation, vessel valve formation and the control of planar cell polarity during embryonic development.

Insm1 promotes endocrine cell differentiation by modulating the expression of a network of genes that includes Neurog3 and Ripply3

Insulinoma associated 1 (Insm1) plays an important role in regulating the development of cells in the central and peripheral nervous systems, olfactory epithelium and endocrine pancreas. To better define the role of Insm1 in pancreatic endocrine cell development we generated mice with an Insm1^GFPCre reporter allele and used them to study Insm1-expressing and null populations. Endocrine progenitor cells lacking Insm1 were less differentiated and exhibited broad defects in hormone production, cell proliferation and cell migration. Embryos lacking Insm1 contained greater amounts of a non-coding Neurog3 mRNA splice variant and had fewer Neurog3/Insm1 co-expressing progenitor cells, suggesting that Insm1 positively regulates Neurog3. Moreover, endocrine progenitor cells that express either high or low levels of Pdx1, and thus may be biased towards the formation of specific cell lineages, exhibited cell type-specific differences in the genes regulated by Insm1. Analysis of the function of Ripply3, an Insm1-regulated gene enriched in the Pdx1-high cell population, revealed that it negatively regulates the proliferation of early endocrine cells. Taken together, these findings indicate that in developing pancreatic endocrine cells Insm1 promotes the transition from a ductal progenitor to a committed endocrine cell by repressing a progenitor cell program and activating genes essential for RNA splicing, cell migration, controlled cellular proliferation, vasculogenesis, extracellular matrix and hormone secretion.

A dual role for planar cell polarity genes in ciliated cells

In the nervous system, cilia dysfunction perturbs the circulation of the cerebrospinal fluid, thus affecting neurogenesis and brain homeostasis. A role for planar cell polarity (PCP) signaling in the orientation of cilia (rotational polarity) and ciliogenesis is established. However, whether and how PCP regulates cilia positioning in the apical domain (translational polarity) in radial progenitors and ependymal cells remain unclear. By analysis of a large panel of mutant mice, we show that two PCP signals are operating in ciliated cells. The first signal, controlled by cadherin, EGF-like, laminin G-like, seven-pass, G-type receptor (Celsr) 2, Celsr3, Frizzled3 (Fzd3) and Van Gogh like2 (Vangl2) organizes multicilia in individual cells (single-cell polarity), whereas the second signal, governed by Celsr1, Fzd3, and Vangl2, coordinates polarity between cells in both radial progenitors and ependymal cells (tissue polarity). Loss of either of these signals is associated with specific defects in the cytoskeleton. Our data reveal unreported functions of PCP and provide an integrated view of planar polarization of the brain ciliated cells.

Planar cell polarity genes, Celsr1-3, in neural development

flamingo is among the 'core' planar cell-polarity genes, protein of which belongs to a unique cadherin subfamily. In contrast to the classic cadherins, composed of several extracellular cadherin repeats, one transmembrane domain and one cytoplasmic segment linked to catenin binding, Drosophila Flamingo has seven transmembrane segments and a cytoplasmic tail with no catenin-binding sequence. In Drosophila, Flamingo has pleotropic roles in controlling epithelial polarity and neuronal morphogenesis. Three mammalian orthologs of flamingo, Celsr1-3, are widely expressed in the nervous system. Recent work has shown that Celsr1-3 play important roles in neural development, such as in axon guidance, neuronal migration, and cilium polarity. Celsr1-3 single-gene knockout mice exhibit different phenotypes, but there are cooperative interactions among these genes.

Comparative expression study of the endo-G protein coupled receptor (GPCR) repertoire in human glioblastoma cancer stem-like cells, U87-MG cells and non malignant cells of neural origin unveils new potential therapeutic targets

Glioblastomas (GBMs) are highly aggressive, invasive brain tumors with bad prognosis and unmet medical need. These tumors are heterogeneous being constituted by a variety of cells in different states of differentiation. Among these, cells endowed with stem properties, tumor initiating/propagating properties and particularly resistant to chemo- and radiotherapies are designed as the real culprits for tumor maintenance and relapse after treatment. These cells, termed cancer stem-like cells, have been designed as prominent targets for new and more efficient cancer therapies. G-protein coupled receptors (GPCRs), a family of membrane receptors, play a prominent role in cell signaling, cell communication and crosstalk with the microenvironment. Their role in cancer has been highlighted but remains largely unexplored. Here, we report a descriptive study of the differential expression of the endo-GPCR repertoire in human glioblastoma cancer stem-like cells (GSCs), U-87 MG cells, human astrocytes and fetal neural stem cells (f-NSCs). The endo-GPCR transcriptome has been studied using Taqman Low Density Arrays. Of the 356 GPCRs investigated, 138 were retained for comparative studies between the different cell types. At the transcriptomic level, eight GPCRs were specifically expressed/overexpressed in GSCs. Seventeen GPCRs appeared specifically expressed in cells with stem properties (GSCs and f-NSCs). Results of GPCR expression at the protein level using mass spectrometry and proteomic analysis are also presented. The comparative GPCR expression study presented here gives clues for new pathways specifically used by GSCs and unveils novel potential therapeutic targets.

Facial motor neuron migration advances

During development, the migration of specific neuronal subtypes is required for the correct establishment of neural circuits. In mice and zebrafish, facial branchiomotor (FBM) neurons undergo a tangential migration from rhombomere 4 caudally through the hindbrain. Recent advances in the field have capitalized on genetic studies in zebrafish and mouse, and high-resolution time-lapse imaging in zebrafish. Planar cell polarity signaling has emerged as a critical conserved factor in FBM neuron migration, functioning both within the neurons and their environment. In zebrafish, migration depends on specialized 'pioneer' neurons to lead follower FBM neurons through the hindbrain, and on interactions with structural components including pre-laid axon tracts and the basement membrane. Despite fundamental conservation, species-specific differences in migration mechanisms are being uncovered.

Wnt signaling is required for long-term memory formation

Wnt signaling regulates synaptic plasticity and neurogenesis in the adult nervous system, suggesting a potential role in behavioral processes. Here, we probed the requirement for Wnt signaling during olfactory memory formation in Drosophila using an inducible RNAi approach. Interfering with β-catenin expression in adult mushroom body neurons specifically impaired long-term memory (LTM) without altering short-term memory. The impairment was reversible, being rescued by expression of a wild-type β-catenin transgene, and correlated with disruption of a cellular LTM trace. Inhibition of wingless, a Wnt ligand, and arrow, a Wnt coreceptor, also impaired LTM. Wingless expression in wild-type flies was transiently elevated in the brain after LTM conditioning. Thus, inhibiting three key components of the Wnt signaling pathway in adult mushroom bodies impairs LTM, indicating that this pathway mechanistically underlies this specific form of memory.

Prickle1 stunts limb growth through alteration of cell polarity and gene expression

BACKGROUND

Wnt/PCP signaling plays a critical role in multiple developmental processes, including limb development. Wnt5a, a ligand of the PCP pathway, signals through the Ror2/Vangl2 or the Vangl2/Ryk complex to regulate limb development along the proximal-distal axis in mice. Based on the interaction between Van Gogh and Prickle in Drosophila, we hypothesized the vertebrate Prickle1 has a similar function as Vangl2 in limb development.

RESULTS

We show Prickle1 is expressed in the skeletal condensates that will differentiate into chondrocytes and later form bones. Disrupted Prickle1 function in Prickle1(C251X/C251X) mouse mutants alters expression of genes such as Bmp4, Fgf8, Vangl2, and Wnt5a. These expression changes correlate with shorter and wider bones in the limbs and loss of one phalangeal segment in digits 2-5 of Prickle1C251X mutants. These growth defects along the proximal-distal axis are also associated with increased cell death in the growing digit tip, reduced cell death in the interdigital membrane, and disrupted chondrocyte polarity.

CONCLUSIONS

We suggest Prickle1 is part of the Wnt5a/PCP signaling, regulating cell polarity and affecting expression of multiple factors to stunt limb growth through altered patterns of gene expression, including the PCP genes Wnt5a and Vangl2.

The PCP protein Vangl2 regulates migration of hindbrain motor neurons by acting in floor plate cells, and independently of cilia function

Vangl2, a core component of the Planar Cell Polarity pathway, is necessary for the caudal migration of Facial Branchiomotor (FBM) neurons in the vertebrate hindbrain. Studies in zebrafish suggest that vangl2 functions largely non-cell autonomously to regulate FBM neuron migration out of rhombomere 4 (r4), but the cell-type within which it acts is not known. Here, we demonstrate that vangl2 functions largely in floor plate cells to regulate caudal neuronal migration. Furthermore, FBM neurons fail to migrate caudally in the mouse Gli2 mutant that lacks the floor plate, suggesting an evolutionarily conserved role for this cell type in neuronal migration. Although hindbrain floor plate cilia are disorganized in vangl2 mutant embryos, cilia appear to be dispensable for neuronal migration. Notably, Vangl2 is enriched in the basolateral, but not apical, membranes of floor plate cells. Taken together, our data suggest strongly that Vangl2 regulates FBM neuron migration by acting in floor plate cells, independently of cilia function.

Shaping the nervous system: role of the core planar cell polarity genes

Planar cell polarity (PCP) is complementary to the intrinsic polarization of single cells and refers to the global coordination of cell behaviour in the plane of a tissue and, by extension, to the signalling pathways that control it. PCP is most evident in cell sheets, and research into PCP was for years confined to studies in Drosophila melanogaster. However, PCP has more recently emerged as an important phenomenon in vertebrates, in which it regulates various developmental processes and is associated with multiple disorders. In particular, core PCP genes are crucial for the development and function of the nervous system. They are involved in neural tube closure, ependymal polarity, neuronal migration, dendritic growth and axon guidance.

Vangl2, the planar cell polarity protein, is complexed with postsynaptic density protein PSD-95 [corrected]

Vangl is a component of the non-canonical Wnt/planar cell polarity pathway, which is implicated in various cell polarity functions. However, little is known about its synaptic localization in neurons. Here, we show that Vangl1 and Vangl2 are expressed in adult rat neurons, where they are tightly associated with the postsynaptic density (PSD) fraction. Vangl2 forms a complex with PSD-95 through direct binding. Furthermore, the C-terminal PDZ-binding motif of Vangl2 is required for localization to dendritic spines. These results suggest that Vangl2 is a new component of the PSD that forms a complex with PSD-95 in the adult brain.

Planar cell polarity genes control the connectivity of enteric neurons

A highly complex network of intrinsic enteric neurons is required for the digestive and homeostatic functions of the gut. Nevertheless, the genetic and molecular mechanisms that regulate their assembly into functional neuronal circuits are currently unknown. Here we report that the planar cell polarity (PCP) genes Celsr3 and Fzd3 are required during murine embryogenesis to specifically control the guidance and growth of enteric neuronal projections relative to the longitudinal and radial gut axes. Ablation of these genes disrupts the normal organization of nascent neuronal projections, leading to subtle changes of axonal tract configuration in the mature enteric nervous system (ENS), but profound abnormalities in gastrointestinal motility. Our data argue that PCP-dependent modules of connectivity established at early stages of enteric neurogenesis control gastrointestinal function in adult animals and provide the first evidence that developmental deficits in ENS wiring may contribute to the pathogenesis of idiopathic bowel disorders.

Dishevelled proteins are associated with olfactory sensory neuron presynaptic terminals

Olfactory sensory neurons (OSNs) project their axons from the olfactory epithelium toward the olfactory bulb (OB) in a heterogeneous and unsorted arrangement. However, as the axons approach the glomerular layer of the OB, axons from OSNs expressing the same odorant receptor (OR) sort and converge to form molecularly homogeneous glomeruli. Axon guidance cues, cell adhesion molecules, and OR induced activity have been implicated in the final targeting of OSN axons to specific glomeruli. Less understood, and often controversial, are the mechanisms used by OSN axons to initially navigate from the OE toward the OB. We previously demonstrated a role for Wnt and Frizzled (Fz) molecules in OSN axon extension and organization within the olfactory nerve. Building on that we now turned our attention to the downstream signaling cascades from Wnt-Fz interactions. Dishevelled (Dvl) is a key molecule downstream of Fz receptors. Three isoforms of Dvl with specific as well as overlapping functions are found in mammals. Here, we show that Dvl-1 expression is restricted to OSNs in the dorsal recess of the nasal cavity, and labels a unique subpopulation of glomeruli. Dvl-2 and Dvl-3 have a widespread distribution in both the OE and OB. Both Dvl-1 and Dvl-2 are associated with intra-glomerular pre-synaptic OSN terminals, suggesting a role in synapse formation/stabilization. Moreover, because Dvl proteins were observed in all OSN axons, we hypothesize that they are important determinants of OSN cell differentiation and axon extension.

Prickle1 is expressed in distinct cell populations of the central nervous system and contributes to neuronal morphogenesis

Development of axons and dendrites constitutes a critical event in neuronal maturation and seems to require signaling through the planar cell polarity (PCP) pathway. Mutations in components of the PCP pathway lead to a spectrum of neurological phenotypes and disorders. For example, a missense mutation in Prickle 1 (Pk1) is associated with progressive myoclonus epilepsy (PME) in humans, and its reduced gene dosage increases sensitivity to induced seizure in mice. In an effort to unravel the role of the PCP pathway in mammalian neuronal development, we examined the expression of Pk1 in the central nervous system (CNS) using in situ hybridization (ISH) in combination with a genetic knock-in approach. We show that Pk1 transcripts are detected in the postmitotic cells of the subplate and cortical plate during mid- and late stages of cortical neurogenesis. In adult brain, Pk1 is expressed in distinct neuronal and glial cell populations, with dynamic formation of dendrites and glial processes during development. Of all the cell types in the mature retina, the highest expression of Pk1 is detected in cholinergic amacrine neurons. Knockdown of Pk1 by shRNA or dominant-negative constructs causes reduced axonal and dendritic extension in hippocampal neurons. Similarly, Pk1 knockdown in neonatal retina leads to defects in inner and outer segments and axon terminals of photoreceptors. Our studies implicate Pk1 function in axonal-dendritic development associated with the maturation of CNS neurons.

A role for atypical cadherin Celsr3 in hippocampal maturation and connectivity

Atypical cadherin Celsr3, a regulator of planar cell polarity, is critical for the development of the axonal blueprint. We previously showed that expression of Celsr3 is necessary to establish forebrain connections such as the anterior commissure and thalamocortical and corticospinal tracts. The requirement for Celsr3 during hippocampal wiring and its action in the hippocampus remain largely unexplored. Here, we compared the connectivity and maturation of the hippocampal formation in Celsr3|Foxg1 and Celsr3|Dlx mice. Celsr3 is inactivated in the whole telencephalon, including the hippocampal primordium, in Celsr3|Foxg1 mice, and in the early basal telencephalon, including ganglionic eminences and ventral diencephalon, in Celsr3|Dlx mice. Behavioral tests showed that both mutants were hyperactive and had impaired learning and memory. Abnormal cytoarchitecture of CA1, CA3, and dentate gyrus was found in the Celsr3|Foxg1 mutant, in which afferent and efferent hippocampal pathways, as well as intrinsic connections, were dramatically disrupted. In Celsr3|Dlx mutant mice, hippocampal cytoarchitecture was mildly affected and extrinsic and intrinsic connectivity moderately disturbed. In both mutants, pyramidal neurons in CA1 harbored atrophic dendritic trees, with decreased synapse density and increased proportion of symmetric versus asymmetric synapses, and long-term potentiation was altered. In contrast, mutant hippocampal neurons extended neurites that were normal, even longer than those of control neurons, indicating that anomalies in vivo are secondary to defective connections. Postnatal neurogenesis was preserved and mutant interneurons were able to migrate to the hippocampus. Thus, like in neocortex, Celsr3 is required for hippocampal development, connectivity and function, and for pyramidal cell maturation.

Wnt signaling in eye organogenesis

The vertebrate eye consists of multiple tissues with distinct embryonic origins. To ensure formation of the eye as a functional organ, development of ocular tissues must be precisely coordinated. Besides intrinsic regulators, several extracellular pathways have been shown to participate in controlling critical steps during eye development. Many components of Wnt/Frizzled signaling pathways are expressed in developing ocular tissues, and substantial progress has been made in the past few years in understanding their function during vertebrate eye development. Here, I summarize recent work using functional experiments to elucidate the roles of Wnt/Frizzled pathways during development of ocular tissues in different vertebrates.