Roles of Wnt proteins in neural development and maintenance

The primary cilium as a Hedgehog signal transduction machine

The Hedgehog (Hh) signal transduction pathway is essential for the development and patterning of numerous organ systems, and has important roles in a variety of human cancers. Genetic screens for mouse embryonic patterning mutants first showed a connection between mammalian Hh signaling and intraflagellar transport (IFT), a process required for construction of the primary cilium, a small cellular projection found on most vertebrate cells. Additional genetic and cell biological studies have provided very strong evidence that mammalian Hh signaling depends on the primary cilium. Here, we review the evidence that defines the integral roles that IFT proteins and cilia play in the regulation of the Hh signal transduction pathway in vertebrates. We discuss the mechanisms that control localization of Hh pathway proteins to the cilium, focusing on the transmembrane protein Smoothened (Smo), which moves into the cilium in response to Hh ligand. The phenotypes caused by loss of cilia-associated proteins are complex, which suggests that cilia and IFT play active roles in mediating Hh signaling rather than serving simply as a compartment in which pathway components are concentrated. Hh signaling in Drosophila does not depend on cilia, but there appear to be ancient links between cilia and components of the Hh pathway that may reveal how this fundamental difference between the Drosophila and mammalian Hh pathways arose in evolution.

Wnt signalling and cancer stem cells

Intracellular signalling mediated by secreted Wnt proteins is essential for the establishment of cell fates and proper tissue patterning during embryo development and for the regulation of tissue homeostasis and stem cell function in adult tissues. Aberrant activation of Wnt signalling pathways has been directly linked to the genesis of different tumours. Here, the components and molecular mechanisms implicated in the transduction of Wnt signal, along with important results supporting a central role for this signalling pathway in stem cell function regulation and carcinogenesis will be briefl y reviewed.

Ror1-Ror2 complexes modulate synapse formation in hippocampal neurons

Ror1 and Ror2, a small family of tyrosine kinase receptors, have been implicated in multiple aspects of brain development in C. elegans and X. laevis. More recently, we have shown that these receptors modulate the rate of neurite elongation in cultured rat hippocampal neurons. However, no information is available regarding a potential role of these receptors in other developmental milestones in mammalian central neurons. Neither is the identity known of the Ror ligand(s) and/or the signal transduction pathway(s) in which they participate. Here we report that the down regulation of either Ror1 or Ror2 led to a significant decrease in synapse formation in cultured hippocampal neurons. Simultaneous targeting of Ror proteins, however, did not result in an additive phenotype. Our results also indicated that Ror1 and Ror2 physically interact in the mouse brain, suggesting that they might function as heterodimers in central neurons. In addition, these Ror complexes interacted with Wnt-5a mediating its effects on synaptogenesis. Together, these data suggest that Ror proteins play a key role in Wnt-5a-activated signaling pathways leading to synapse formation in the mammalian CNS.

Genetic and protein changes of E-cadherin in meningiomas

PURPOSE

The molecular mechanisms and candidate genes involved in development of meningiomas still needs investigation and elucidation.

METHODS

In the present study 60 meningiomas were analyzed regarding changes of tumor suppressor gene E-cadherin (CDH1), a component of adherens junction and an indirect modulator of the wnt signaling. Gene instability was tested by polymerase chain reaction/loss of heterozygosity (LOH) method. Protein expression was analyzed by immunohistochemistry.

RESULTS

The results of our analysis showed altogether 32% of samples with LOH of the CDH1 gene. Interestingly, another type of genomic instability was detected; replication error-positive samples (RER+). Three out of 28 heterozygous samples were RER+ (11%). The instability is the result of impaired cellular mismatch repair. Fibrous and angiomatous cases showed higher percent of genetic changes, 67 and 75%, respectively. Immunostaining showed that overall 73% of samples had downregulation of E-cadherin expression. Intense downregulation of E-cadherin was noticed in tumors with grades II and III. Five out of nine samples with LOH were accompanied with the downregulation of E-cadherin protein expression (56%). One RER+ sample had lower expression of E-cadherin. We noticed that 36.4% of samples with lower E-cadherin expression had beta-catenin located in the nucleus. Also, 75% of samples with genomic instabilities had beta-catenin in the nucleus. Our findings demonstrated that there is significant association between the genetic changes of CDH1 and the nuclear localization of beta-catenin protein (chi(2) = 5.25, df = 1, P < 0.022). Beta-catenin was progressively upregulated from meningothelial to atypical, while 60% of anaplastic showed upregulation and nuclear localization of the protein.

CONCLUSIONS

Our results suggest that genetic instabilities of the E-cadherin gene have a role in meningioma development and progression. Detected microsatellite instability indicates that mismatch repair may also be targeted in meningioma.

Alpha7 neuronal nicotinic receptors: the missing link to understanding Alzheimer's etiopathology?

Evidence supports the premise that alpha7 nicotinic acetylcholine receptors in the central nervous system, sometimes referred to as neuronal nicotinic receptors (NNRs), play a central role in the development of Alzheimer's disease (AD) pathophysiology. Moreover, these receptors may represent the key to unifying aspects of the cholinergic hypothesis of AD with many of the apparently disparate mechanisms such as beta-amyloid deposition, tau hyperphosphorylation, and ApoE4 abnormalities variously proposed to underlie the progression of the disease. We hypothesize that neuronal degeneration in incipient AD is the result of coincident events involving, at their core, deficits in alpha7 NNR function. The resulting hypocholinergic tone could potentially have serious consequences since alpha7 NNRs are known to modulate fundamental pathways involved in cell survival such as JAK2-STAT3. This hypothesis predicts that any factors that compromise alpha7 function have the potential to negatively impact neuronal viability. For example, such factors could include deficits in the primary neurotransmitter acetylcholine (ACh), underactivity of normal cognitive processes that stimulate alpha7 NNRs (i.e., use-dependency), or the reported binding of beta-amyloid and ApoE4 to alpha7 NNRs, all of which could effectively decouple the receptors from key pro-survival pathways. Since these pathways are known to negatively modulate GSK-3beta, which regulates tau phosphorylation, downstream effects such as tau hyperphosphorylation would be expected to arise. Conversely, the maintenance of normal alpha7 NNR activity by adequate levels of ACh or other NNR agonists would be expected to support normal cholinergic tone, prevent the binding of beta-amyloid and ApoE4 and preserve the integrity of the neurons. We therefore propose that decreased cholinergic tone is at the apex of AD pathophysiology, with factors such as beta-amyloid and ApoE4 playing a contributory role rather that a causal one and hyperphosphorylation of tau representing a detector of concomitant hypocholinergic tone and beta-amyloid deposition. Thus the convergence of beta-amyloid deposition and/or ApoE4 binding and co-localization with alpha7 NNRs, which are favored under conditions of low cholinergic tone, and the downstream cascade of tau hyperphosphorylation through disinhibition of GSK-3beta appear to explain and reconcile many of the discordant findings in this very active area of CNS research.

Frizzled-10 promotes sensory neuron development in Xenopus embryos

Formation of the vertebrate nervous system requires coordinated cell-cell interactions, intracellular signalling events, gene transcription, and morphogenetic cell movements. Wnt signalling has been involved in regulating a wide variety of biological processes such as embryonic patterning, cell proliferation, cell polarity, motility, and the specification of cell fate. Wnt ligands associate with their receptors, members of the frizzled family (Fz). In Xenopus, five members of the frizzled family are expressed in the early nervous system. We have investigated the role of Xenopus frizzled-10 (Fz10) in neural development. We show that Fz10 is expressed in the dorsal neural ectoderm and neural folds in the region where primary sensory neurons develop. Fz10 mediates canonical Wnt signalling and interacts with Wnt1 and Wnt8 but not Wnt3a as shown in synergy assays. We find that Fz10 is required for the late stages of sensory neuron differentiation. Overexpression of Fz10 in Xenopus leads to an increase in the number of sensory neurons. Loss of Fz10 function using morpholinos inhibits the development of sensory neurons in Xenopus at later stages of neurogenesis and this can be rescued by co-injection of modified Fz10B and beta-catenin. In mouse P19 cells induced by retinoic acid to undergo neural differentiation, overexpression of Xenopus Fz10 leads to an increase in the number of neurons generated while siRNA knockdown of endogenous mouse Fz10 inhibits neurogenesis. Thus we propose Fz10 mediates Wnt1 signalling to determine sensory neural differentiation in Xenopus in vivo and in mouse cell culture.

Changes of AXIN-1 and beta-catenin in neuroepithelial brain tumors

In the present study changes of components of Wnt signaling pathway--axin (AXIN1) and beta-catenin (CTNNB1) in a sample of 72 neuroepithelial brain tumors were investigated. AXIN-1 gene was tested by PCR/loss of heterozygosity (LOH). Immunostaining and image analysis revealed the quantity and localization of relevant proteins. Polymorphic marker for AXIN-1, showed LOH in 11.1% of tumors. LOH was distributed to 6.3% of glioblastomas, one was found in neuroepithelial dysembrioplastic tumor and one in medulloblastoma. Down regulation of axin expression and up regulation of beta-catenin were detected in the analyzed tumors. Axin was observed in the cytoplasm in 68.8% of samples, in 28.1% in both the cytoplasm and nucleus and 3.1% had no expression. Beta-catenin was observed mainly in the nucleus and cytoplasm (59.4%). Expression in 34.4% of samples was in the cytoplasm and 6.3% showed no expression. Comparison of mean values of relative increase of axin and beta-catenin showed that they are significantly reversely proportional (P = 0.014). Relative quantity of beta-catenin in patients with gross deletion of AXIN1 was significantly higher in comparison to patients without LOH (P = 0.040). Our results demonstrate that changes of key components of the Wnt signaling play a role in neuroepithelial brain tumors.

Wnt signaling is sufficient to perturb oligodendrocyte maturation

The development of oligodendrocytes, the myelinating cells of the central nervous system, is temporally and spatially controlled by local signaling factors acting as inducers or inhibitors. Dorsal spinal cord tissue has been shown to contain inhibitors of oligodendrogliogenesis, although their identity is not completely known. We have studied the actions of one family of dorsal signaling molecules, the Wnts, on oligodendrocyte development. Using tissue culture models, we have shown that canonical Wnt activity through beta-catenin activation inhibits oligodendrocyte maturation, independently of precursor proliferation, cell death, or diversion to an alternate cell fate. Mice in which Wnt/beta-catenin signaling was constitutively activated in cells of the oligodendrocyte lineage had equal numbers of oligodendrocyte precursors relative to control littermates, but delayed appearance of mature oligodendrocytes, myelin protein, and myelinated axons during development, although these differences largely disappeared by adulthood. These results indicate that activating the Wnt/beta-catenin pathway delays the development of myelinating oligodendrocytes.

GSK3beta in ethanol neurotoxicity

Alcohol consumption during pregnancy is a significant public health problem and may result in a wide range of adverse outcomes for the child. The developing central nervous system (CNS) is particularly susceptible to ethanol toxicity. Children with fetal alcohol spectrum disorders (FASD) have a variety of cognitive, behavioral, and neurological impairments. FASD currently represents the leading cause of mental retardation in North America ahead of Down syndrome and cerebral palsy. Ethanol exposure during development causes multiple abnormalities in the brain such as permanent loss of neurons, ectopic neurons, and alterations in synaptogenesis and myelinogenesis. These alcohol-induced structural alterations in the developing brain underlie many of the behavioral deficits observed in FASD. The cellular and molecular mechanisms of ethanol neurotoxicity, however, remain unclear. Ethanol elicits cellular stresses, including oxidative stress and endoplasmic reticulum stress. Glycogen synthase kinase 3beta (GSK3beta), a multifunctional serine/threonine kinase, responds to various cellular stresses. GSK3beta is particularly abundant in the developing CNS, and regulates diverse developmental events in the immature brain, such as neurogenesis and neuronal differentiation, migration, and survival. Available evidence indicates that the activity of GSK3beta in the CNS is affected by ethanol. GSK3beta inhibition provides protection against ethanol neurotoxicity, whereas high GSK3beta activity/expression sensitizes neuronal cells to ethanol-induced damages. It appears that GSK3beta is a converging signaling point that mediates some of ethanol's neurotoxic effects.

Wnt-5a/JNK signaling promotes the clustering of PSD-95 in hippocampal neurons

During the formation of synapses, specific regions of pre- and postsynaptic cells associate to form a single functional transmission unit. In this process, synaptogenic factors are necessary to modulate pre- and postsynaptic differentiation. In mammals, different Wnt ligands operate through canonical and non-canonical Wnt pathways, and their precise functions to coordinate synapse structure and function in the mature central nervous system are still largely unknown. Here, we studied the effect of different Wnt ligands on postsynaptic organization. We found that Wnt-5a induces short term changes in the clustering of PSD-95, without affecting its total levels. Wnt-5a promotes the recruitment of PSD-95 from a diffuse dendritic cytoplasmic pool to form new PSD-95 clusters in dendritic spines. Moreover, Wnt-5a acting as a non-canonical ligand regulates PSD-95 distribution through a JNK-dependent signaling pathway, as demonstrated by using the TAT-TI-JIP peptide in mature hippocampal neurons. Finally, using adult rat hippocampal slices, we found that Wnt-5a modulates glutamatergic synaptic transmission through a postsynaptic mechanism. Our studies indicate that the Wnt-5a/JNK pathway modulates the postsynaptic region of mammalian synapse directing the clustering and distribution of the physiologically relevant scaffold protein, PSD-95.

NDRG2 gene expression in B16F10 melanoma cells restrains melanogenesis via inhibition of Mitf expression

NDRG2 (N-myc downstream-regulated gene 2) is a candidate tumor suppressor implicated in control of glioblastoma proliferation and dendritic cell differentiation. The microphthalmia-associated transcription factor (Mitf) plays a crucial role in the melanocyte lineage and in melanoma by controlling survival, differentiation, cell cycle entry and exit, and melanoma metastasis. Identifying upstream regulators of Mitf expression, therefore, remains a key issue. In this study, we aimed to assess whether the candidate tumor suppressor NDRG2 can modulate Mitf expression. Here, we show that NDRG2 acts to prevent cAMP and beta-catenin-mediated activation of the Mitf promoter, thereby blocking melanogenesis via the downstream Mitf target genes Tyrosinase, Tyrp1 and Dct. The data suggest that NDRG2 impairs melanogenesis by interfering with both the TCF/beta-catenin and cAMP/CREB pathways that are known to stimulate Mitf expression in melanocytes and have major implications for the role of NDRG2 in pigmentation and melanoma progression. Taken together, the results not only identify NDRG2 as a novel regulator of pigmentation, but also potentially a key factor in regulating melanoma progression via Mitf.

Ventral mesencephalon astrocytes are more efficient than those of other regions in inducing dopaminergic neurons through higher expression level of TGF-beta3

Being supportive cells for neurons in the central nervous system, astrocytes have recently found to be associated with neurogenesis. Ventral mesencephalon (VM) astrocytes were also detected being instructive for VM dopaminergic (DA) neurogenesis, but the underling mechanisms are still unclear. This research is to figure out whether VM astrocytes are more efficient than those from other brain regions in inducing VM DA neurons from their precursors and whether transforming growth factor-betas (TGF-betas) are the underlying molecules. We found that, compared with astrocytes preparations from striatum and hippocampus, VM astrocytes preparations displayed markedly higher efficacy in inducing DA neurogenesis. Besides, they also expressed higher level of TGF-beta3 than those of two other regions. When TGF-beta3 gene expression in astrocytes preparations was inhibited by its antisense oligonucleotide, the induction of DA neurons decreased to a similar level among these three astrocytes preparations. Thus, our experiment indicates that VM astrocytes preparations which contained highly purified astrocytes are more efficient in inducing DA neurogenesis than those from other regions. Furthermore, it also suggests that the regional differences are regulated by different expression levels of TGF-beta3 in those astrocytes preparations from different derivations.

Vascular changes in the cerebellum of Norrin /Ndph knockout mice correlate with high expression of Norrin and Frizzled-4

X-linked Norrie disease, familial exudative vitreoretinopathy (FEVR), Coat's disease and retinopathy of prematurity are severe human eye diseases and can all be caused by mutations in the Norrie disease pseudoglioma gene. They all show vascular defects and characteristic features of retinal hypoxia. Only Norrie disease displays additional neurological symptoms, which are sensorineural hearing loss and mental retardation. In the present study, we analysed transcript levels of the ligand Norrin (Ndph) and its two receptors Frizzled-4 (Fzd4) and LDL-related protein receptor 5 (Lrp5) in six different brain regions (cerebellum, cortex, hippocampus, olfactory bulb, pituitary and brain stem) of 6- to 8-month-old wild-type and Ndph knockout mice by quantitative real-time PCR. No effect of the Ndph knockout allele on Fzd4 or Lrp5 receptor expression was found. Furthermore, no alterations of the transcript levels of three hypoxia-regulated angiogenic factors (Vegfa, Itgrb3 and Tie1) were observed in the absence of Norrin. Interestingly, we identified significant differences in Ndph, Fzd4 and Lrp5 transcript levels in brain regions of wild-type mice and observed highest expression of Norrin and frizzled-4 in cerebellum. Transcript analyses were correlated with morphological data obtained from cerebellum and immunohistochemical studies of blood vessels in different brain regions. Vessel density was reduced in the cerebellum of Ndph knockout mice but the number of Purkinje and granular cells was not altered. This provides the first description of a brain phenotype in Ndph knockout mice, which will help to elucidate the role of Norrin in the brain.

Frizzled-1 is involved in the neuroprotective effect of Wnt3a against Abeta oligomers

The activation of the canonical Wnt signaling pathway protects hippocampal neurons against the toxicity of Alzheimer's amyloid-beta-peptide (Abeta), however, the role played by the Wnt receptors Frizzleds, has not been studied. We report here that Frizzled-1 mediates the activation of the canonical Wnt/beta-catenin pathway by Wnt3a in PC12 cells. In addition, the protective effect of Wnt3a against the toxicity of Abeta oligomers was modulated by Frizzled-1 expression levels in both PC12 cells and hippocampal neurons. Over-expression of Frizzled-1 significantly increased cell survival induced by Wnt3a and diminished caspase-3 activation, while knocking-down Frizzled-1 expression by antisense oligonucleotides decreased the Wnt3a protection. Over-expression of wild-type beta-catenin, but not a transcriptionally inactive mutated version, prevented the toxicity of Abeta suggesting that the transcription of Wnt target genes may be involved in these events. This was confirmed by co-transfecting both Frizzled-1 and the inactive form of beta-catenin, which does not elicited protection levels similar to those showed with endogenous beta-catenin. Our results indicate that Wnt3a protects from Abeta-oligomers toxicity by activating the canonical Wnt signaling pathway through the Frizzled-1 receptor, suggesting a therapeutic potential for this signaling pathway in the treatment of Alzheimer's disease.

Cerebellar granule cells: insights into proliferation, differentiation, and role in medulloblastoma pathogenesis

Cerebellar granule cells originate from precursors located in the dorsal region of rhombomere one within the hindbrain of developing embryos. They undergo proliferation for an extensive period well into postnatal stages of development to form the major cell type of the cerebellum, the most populous structure within the mammalian brain. Granule cell development is highly dependent upon the cerebellar environment and contact with neighbouring cells. In recent years, the molecular basis of these interactions has started to be unravelled. Granule cell precursors and the molecular mechanisms involved in controlling their proliferation have been shown to be involved in the pathogenesis of medulloblastoma, the most common malignant pediatric brain tumour. Here, we review the control of granule cell generation with emphasis on the molecular regulators of cell proliferation and differentiation during normal and malignant development.

GSK-3beta gene expression in human postmortem brain: regional distribution, effects of age and suicide

Glycogen synthase kinase (GSK-3beta) has been implicated in the pathophysiology of mood disorders and schizophrenia. To examine its role in suicide, we determined GSK-3beta messenger RNA (mRNA) in human postmortem brain from suicide and normal control subjects using quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) technique. We found that GSK-3beta mRNA was highly abundant in almost all of the 12 brain areas we studied. We also found a significant age effect on GSK-3beta and that GSK-3beta mRNA level were significantly higher in prefrontal cortex (PFC) and hippocampus of teenage normal controls compared with adult normal controls and was significantly decreased in PFC of teenage suicide but not adult suicide victims compared with respective normal control subjects. The decrease observed in the mRNA levels in teenage suicide but not in adult suicide victims may represent a neurodevelopmentally associated decrease and may be important in the pathophysiology of teenage suicide.

Erythropoietin: elucidating new cellular targets that broaden therapeutic strategies

Given that erythropoietin (EPO) is no longer believed to have exclusive biological activity in the hematopoietic system, EPO is now considered to have applicability in a variety of nervous system disorders that can overlap with vascular disease, metabolic impairments, and immune system function. As a result, EPO may offer efficacy for a broad number of disorders that involve Alzheimer's disease, cardiac insufficiency, stroke, trauma, and diabetic complications. During a number of clinical conditions, EPO is robust and can prevent metabolic compromise, neuronal and vascular degeneration, and inflammatory cell activation. Yet, use of EPO is not without its considerations especially in light of frequent concerns that may compromise clinical care. Recent work has elucidated a number of novel cellular pathways governed by EPO that can open new avenues to avert deleterious effects of this agent and offer previously unrecognized perspectives for therapeutic strategies. Obtaining greater insight into the role of EPO in the nervous system and elucidating its unique cellular pathways may provide greater cellular viability not only in the nervous system but also throughout the body.

Amyloid-beta binds to the extracellular cysteine-rich domain of Frizzled and inhibits Wnt/beta-catenin signaling

The amyloid-beta peptide (Abeta) plays a major role in neuronal dysfunction and neurotoxicity in Alzheimer disease. However, the signal transduction mechanisms involved in Abeta-induced neuronal dysfunction remain to be fully elucidated. A major current unknown is the identity of the protein receptor(s) involved in neuronal Abeta binding. Using phage display of peptide libraries, we have identified a number of peptides that bind Abeta and are homologous to neuronal receptors putatively involved in Abeta interactions. We report here on a cysteine-linked cyclic heptapeptide (denominated cSP5) that binds Abeta with high affinity and is homologous to the extracellular cysteine-rich domain of several members of the Frizzled (Fz) family of Wnt receptors. Based on this homology, we investigated the interaction between Abeta and Fz. The results show that Abeta binds to the Fz cysteine-rich domain at or in close proximity to the Wnt-binding site and inhibits the canonical Wnt signaling pathway. Interestingly, the cSP5 peptide completely blocks Abeta binding to Fz and prevents inhibition of Wnt signaling. These results indicate that the Abeta-binding site in Fz is homologous to cSP5 and that this is a relevant target for Abeta-instigated neurotoxicity. Furthermore, they suggest that blocking the interaction of Abeta with Fz might lead to novel therapeutic approaches to prevent neuronal dysfunction in Alzheimer disease.

Triple play: promoting neurovascular longevity with nicotinamide, WNT, and erythropoietin in diabetes mellitus

Oxidative stress is a principal pathway for the dysfunction and ultimate destruction of cells in the neuronal and vascular systems for several disease entities, not promoting the ravages of oxidative stress to any less of a degree than diabetes mellitus. Diabetes mellitus is increasing in incidence as a result of changes in human behavior that relate to diet and daily exercise and is predicted to affect almost 400 million individuals worldwide in another two decades. Furthermore, both type 1 and type 2 diabetes mellitus can lead to significant disability in the nervous and cardiovascular systems, such as cognitive loss and cardiac insufficiency. As a result, innovative strategies that directly target oxidative stress to preserve neuronal and vascular longevity could offer viable therapeutic options to diabetic patients in addition to more conventional treatments that are designed to control serum glucose levels. Here we discuss the novel application of nicotinamide, Wnt signaling, and erythropoietin that modulate cellular oxidative stress and offer significant promise for the prevention of diabetic complications in the nervous and vascular systems. Essential to this process is the precise focus upon diverse as well as common cellular pathways governed by nicotinamide, Wnt signaling, and erythropoietin to outline not only the potential benefits, but also the challenges and possible detriments of these therapies. In this way, new avenues of investigation can hopefully bypass toxic complications, or at the very least, avoid contraindications that may limit care and offer both safe and robust clinical treatment for patients.

No significant association between the genetic polymorphisms in the GSK-3 beta gene and schizophrenia in the Chinese population

The GSK-3 beta gene encodes a protein kinase which is abundant in the brain, and its product is involved in signal transduction cascades of neuronal cell development, energy metabolism and body pattern formation. Previous studies have suggested that GSK-3 beta might act as a potential candidate locus for schizophrenia susceptibility. We genotyped six SNPs within the gene and conducted a case-control study involving 329 schizophrenic patients and 288 healthy subjects in the Chinese population. We examined allele and genotype frequencies and haplotype distributions in the subtype of paranoid schizophrenic patients as well as schizophrenic subjects in general. Our results fail to replicate the association of the GSK-3 beta gene with susceptibility to schizophrenia in the Chinese population.

The Wnt signaling pathway: aging gracefully as a protectionist?

No longer considered to be exclusive to cellular developmental pathways, the Wnt family of secreted cysteine-rich glycosylated proteins has emerged as versatile targets for a variety of conditions that involve cardiovascular disease, aging, cancer, diabetes, neurodegeneration, and inflammation. In particular, modulation of Wnt signaling may fill a critical void for the treatment of disorders that impact upon both cellular survival and cellular longevity. Yet, in some scenarios, Wnt signaling can become the catalyst for disease development or promote cell senescence that can compromise clinical utility. This double edge sword in regards to the role of Wnt and its signaling pathways highlights the critical need to further elucidate the cellular mechanisms governed by Wnt in conjunction with the development of robust pharmacological ligands that may open new avenues for disease treatment. Here we discuss the influence of the Wnt pathway during cell survival, metabolism, and aging in order for one to gain a greater insight for the novel role of Wnt signaling as well as exemplify its unique cellular pathways that influence both normal physiology and disease.

Genetic alterations of E-cadherin and beta-catenin in germinoma and teratoma: report of two central nervous system cases

The genetic basis as well as mechanisms of development of germ cell tumors of the CNS are still unexplained. In the present article changes of Ecadherin (CDH1) and beta-catenin (CTNNB1) genes in two CNS germ cell tumors are reported. Both gene products are components of adherens junctions, but are also involved in the Wnt signaling pathway. A case of germinoma of the central nervous system and a case of spinal channel teratoma were tested for loss of heterozygosity (LOH) of E-cadherin gene by PCR amplification of tetranucleotide polymorphism (D16S752). Changes of beta-catenin were tested by heteroduplex method. Both germ cell tumors analyzed demonstrated LOH of the CDH1 gene. Analysis of exon 3 of the CTNNB1 gene showed additional band in the germinoma, suggesting that this sample harbors mutation in the beta-catenin gene. Immunostaining showed that LOHs in our samples were accompanied with the absence of E-cadherin protein. We also investigated E-cadherin expression in four other germinomas, of which three were negative and one was mildly positive. Our findings may contribute to better understanding of the genetic profile of germ cell tumors.

Wnt-7a modulates the synaptic vesicle cycle and synaptic transmission in hippocampal neurons

Wnt signaling is essential for neuronal development and the maintenance of the developing nervous system. Recent studies indicated that Wnt signaling modulates long term potentiation in adult hippocampal slices. We report here that different Wnt ligands are present in hippocampal neurons of rat embryo and adult rat, including Wnt-4, -5a, -7a, and -11. Wnt-7a acts as a canonical Wnt ligand in rat hippocampal neurons, stimulates clustering of presynaptic proteins, and induces recycling and exocytosis of synaptic vesicles as studied by FM dyes. Wnt-3a has a moderate effect on recycling of synaptic vesicles, and no effect of Wnt-1 and Wnt-5a was detected. Electrophysiological analysis on adult rat hippocampal slices indicates that Wnt-7a, but not Wnt-5a, increases neurotransmitter release in CA3-CA1 synapses by decreasing paired pulse facilitation and increasing the miniature excitatory post-synaptic currents frequency. These results indicate that the presynaptic function of rat hippocampal neurons is modulated by the canonical Wnt signaling.

Meningiomas exhibit loss of heterozygosity of the APC gene

The molecular mechanisms and candidate genes involved in development of meningiomas still need investigation and elucidation. In the present study 33 meningiomas were analyzed regarding genetic changes of tumor suppressor gene Adenomatous polyposis coli (APC), a component of the wnt signaling. Gene instability was tested by polymerase chain reaction/loss of heterozygosity (LOH) using Restriction Fragment Length Polymorphism (RFLP) method. RFLP was performed by two genetic markers, Rsa I in APC's exon 11 and Msp I in its exon 15. The results of our analysis showed altogether 15 samples with LOH of the APC gene out of 32 heterozygous patients (47%). Seven patients had LOHs at both exons, while four LOHs were exclusive for exon 11 and four for exon 15. The changes were distributed according to pathohistological grade as follows: 46% of meningothelial meningioma showed LOH; 33% of fibrous; 75% of mixed (transitional); 75% of angiomatous, and one LOH was found in a single case of psammomatous meningioma. None of the LOHs were found in atypical and anaplastic cases. Immunostaining showed that samples with LOHs were accompanied with the absence of APC protein expression or presence of mutant APC proteins (chi(2 )= 13.81, df = 2, P < 0.001). We also showed that nuclear localization of beta-catenin correlates to APC genetic changes (chi(2 )= 21.96, df = 2, P < 0.0001). The results of this investigation suggest that genetic changes of APC gene play a role in meningioma formation.

Multilineage potential of stable human mesenchymal stem cell line derived from fetal marrow

Human bone marrow contains two major cell types, hematopoietic stem cells (HSCs) and mesenchymal stem cells (MSCs). MSCs possess self-renewal capacity and pluripotency defined by their ability to differentiate into osteoblasts, chondrocytes, adipocytes and muscle cells. MSCs are also known to differentiate into neurons and glial cells in vitro, and in vivo following transplantation into the brain of animal models of neurological disorders including ischemia and intracerebral hemorrhage (ICH) stroke. In order to obtain sufficient number and homogeneous population of human MSCs, we have clonally isolated permanent and stable human MSC lines by transfecting primary cell cultures of fetal human bone marrow MSCs with a retroviral vector encoding v-myc gene. One of the cell lines, HM3.B10 (B10), was found to differentiate into neural cell types including neural stem cells, neurons, astrocytes and oligodendrocytes in vitro as shown by expression of genetic markers for neural stem cells (nestin and Musashi1), neurons (neurofilament protein, synapsin and MAP2), astrocytes (glial fibrillary acidic protein, GFAP) and oligodendrocytes (myelin basic protein, MBP) as determined by RT-PCR assay. In addition, B10 cells were found to differentiate into neural cell types as shown by immunocytochical demonstration of nestin (for neural stem cells), neurofilament protein and β-tubulin III (neurons) GFAP (astrocytes), and galactocerebroside (oligodendrocytes). Following brain transplantation in mouse ICH stroke model, B10 human MSCs integrate into host brain, survive, differentiate into neurons and astrocytes and induce behavioral improvement in the ICH animals. B10 human MSC cell line is not only a useful tool for the studies of organogenesis and specifically for the neurogenesis, but also provides a valuable source of cells for cell therapy studies in animal models of stroke and other neurological disorders.

The nerve growth factor and its receptors in airway inflammatory diseases

The nerve growth factor (NGF) belongs to the neurotrophin family and induces its effects through activation of 2 distinct receptor types: the tropomyosin-related kinase A (TrkA) receptor, carrying an intrinsic tyrosine kinase activity in its intracellular domain, and the receptor p75 for neurotrophins (p75NTR), belonging to the death receptor family. Through activation of its TrkA receptor, NGF activates signalling pathways, including phospholipase Cgamma (PLCgamma), phosphatidyl-inositol 3-kinase (PI3K), the small G protein Ras, and mitogen-activated protein kinases (MAPK). Through its p75NTR receptor, NGF activates proapoptotic signalling pathways including the MAPK c-Jun N-terminal kinase (JNK), ceramides, and the small G protein Rac, but also activates pathways promoting cell survival through the transcription factor nuclear factor-kappaB (NF-kappaB). NGF was first described by Rita Levi-Montalcini and collaborators as an important factor involved in nerve differentiation and survival. Another role for NGF has since been established in inflammation, in particular of the airways, with increased NGF levels in chronic inflammatory diseases. In this review, we will first describe NGF structure and synthesis and NGF receptors and their signalling pathways. We will then provide information about NGF in the airways, describing its expression and regulation, as well as pointing out its potential role in inflammation, hyperresponsiveness, and remodelling process observed in airway inflammatory diseases, in particular in asthma.

Beta-catenin signaling promotes proliferation of progenitor cells in the adult mouse subventricular zone

The subventricular zone (SVZ) is the largest germinal zone in the mature rodent brain, and it continuously produces young neurons that migrate to the olfactory bulb. Neural stem cells in this region generate migratory neuroblasts via highly proliferative transit-amplifying cells. The Wnt/beta-catenin signaling pathway partially regulates the proliferation and neuronal differentiation of neural progenitor cells in the embryonic brain. Here, we studied the role of beta-catenin signaling in the adult mouse SVZ. beta-Catenin-dependent expression of a destabilized form of green fluorescent protein was detected in progenitor cells in the adult SVZ of Axin2-d2EGFP reporter mice. Retrovirus-mediated expression of a stabilized beta-catenin promoted the proliferation of Mash1+ cells and inhibited their differentiation into neuroblasts. Conversely, the expression of Dkk1, an inhibitor of Wnt signaling, reduced the proliferation of Mash1+ cells. In addition, an inhibitor of GSK3 beta promoted the proliferation of Mash1+ cells and increased the number of new neurons in the olfactory bulb 14 days later. These results suggest that beta-catenin signaling plays a role in the proliferation of progenitor cells in the SVZ of the adult mouse brain.

Wnt-7a induces presynaptic colocalization of alpha 7-nicotinic acetylcholine receptors and adenomatous polyposis coli in hippocampal neurons

Nicotinic acetylcholine receptors (nAChRs) contribute significantly to hippocampal function. Alpha7-nAChRs are present in presynaptic sites in hippocampal neurons and may influence transmitter release, but the factors that determine their presynaptic localization are unknown. We report here that Wnt-7a, a ligand active in the canonical Wnt signaling pathway, induces dissociation of the adenomatous polyposis coli (APC) protein from the beta-catenin cytoplasmic complex and the interaction of APC with alpha7-nAChRs in hippocampal neurons. Interestingly, Wnt-7a induces the relocalization of APC to membranes, clustering of APC in neurites, and coclustering of APC with different, presynaptic protein markers. Wnt-7a also increases the number and size of coclusters of alpha7-nAChRs and APC in presynaptic terminals. These short-term changes in alpha7-nAChRs occur in the few minutes after ligand exposure and involve translocation to the plasma membrane without affecting total receptor levels. Longer-term exposure to Wnt-7a increases nAChR alpha7 subunit levels in an APC-independent manner and increases clusters of alpha7-nAChRs in neurites via an APC-dependent process. Together, these results demonstrate that stimulation through the canonical Wnt pathway regulates the presynaptic localization of APC and alpha7-nAChRs with APC serving as an intermediary in the alpha7-nAChR relocalization process. Modulation by Wnt signaling may be essential for alpha7-nAChR expression and function in synapses.

Patterning the zebrafish diencephalon by the conserved zinc-finger protein Fezl

The forebrain constitutes the most anterior part of the central nervous system, and is functionally crucial and structurally conserved in all vertebrates. It includes the dorsally positioned telencephalon and eyes, the ventrally positioned hypothalamus, and the more caudally located diencephalon [from rostral to caudal: the prethalamus, the zona limitans intrathalamica (ZLI), the thalamus and the pretectum]. Although antagonizing Wnt proteins are known to establish the identity of the telencephalon and eyes, it is unclear how various subdivisions are established within the diencephalon--a complex integration center and relay station of the vertebrate brain. The conserved forebrain-specific zinc-finger-containing protein Fezl plays a crucial role in regulating neuronal differentiation in the vertebrate forebrain. Here, we report a new and essential role of zebrafish Fezl in establishing regional subdivisions within the diencephalon. First, reduced activity of fezl results in a deficit of the prethalamus and a corresponding expansion of the ZLI. Second, Gal4-UAS-mediated fezl overexpression in late gastrula is capable of expanding the prethalamus telencephalon and hypothalamus at the expense of the ZLI and other fore- and/or mid-brain regions. Such altered brain regionalization is preceded by the early downregulation of wnt expression in the prospective diencephalon. Finally, fezl overexpression is able to restore the anterior forebrain and downregulate wnt expression in Headless- and/or Tcf3 (also known as Tcf7l1a)-deficient embryos. Our findings reveal that Fezl is crucial for establishing regional subdivisions within the diencephalon and may also play a role in the development of the telencephalon and hypothalamus.

Nucleus- and cell-specific gene expression in monkey thalamus

Nuclei of the mammalian thalamus are aggregations of neurons with unique architectures and input-output connections, yet the molecular determinants of their organizational specificity remain unknown. By comparing expression profiles of thalamus and cerebral cortex in adult rhesus monkeys, we identified transcripts that are unique to dorsal thalamus or to individual nuclei within it. Real-time quantitative PCR and in situ hybridization analyses confirmed the findings. Expression profiling of individual nuclei microdissected from the dorsal thalamus revealed additional subsets of nucleus-specific genes. Functional annotation using Gene Ontology (GO) vocabulary and Ingenuity Pathways Analysis revealed overrepresentation of GO categories related to development, morphogenesis, cell-cell interactions, and extracellular matrix within the thalamus- and nucleus-specific genes, many involved in the Wnt signaling pathway. Examples included the transcription factor TCF7L2, localized exclusively to excitatory neurons; a calmodulin-binding protein PCP4; the bone extracellular matrix molecules SPP1 and SPARC; and other genes involved in axon outgrowth and cell matrix interactions. Other nucleus-specific genes such as CBLN1 are involved in synaptogenesis. The genes identified likely underlie nuclear specification, cell phenotype, and connectivity during development and their maintenance in the adult thalamus.

Wnt-5a induces Dishevelled phosphorylation and dopaminergic differentiation via a CK1-dependent mechanism

Previously, we have shown that Wnt-5a strongly regulates dopaminergic neuron differentiation by inducing phosphorylation of Dishevelled (Dvl). Here, we identify additional components of the Wnt-5a-Dvl pathway in dopaminergic cells. Using in vitro gain-of-function and loss-of-function approaches, we reveal that casein kinase 1 (CK1) delta and CK1epsilon are crucial for Dvl phosphorylation by non-canonical Wnts. We show that in response to Wnt-5a, CK1epsilon binds Dvl and is subsequently phosphorylated. Moreover, in response to Wnt-5a or CK1epsilon, the distribution of Dvl changed from punctate to an even appearance within the cytoplasm. The opposite effect was induced by a CK1epsilon kinase-dead mutant or by CK1 inhibitors. As expected, Wnt-5a blocked the Wnt-3a-induced activation of beta-catenin. However, both Wnt-3a and Wnt-5a activated Dvl2 by a CK1-dependent mechanism in a cooperative manner. Finally, we show that CK1 kinase activity is necessary for Wnt-5a-induced differentiation of primary dopaminergic precursors. Thus, our data identify CK1 as a component of Wnt-5a-induced signalling machinery that regulates dopaminergic differentiation, and suggest that CK1delta/epsilon-mediated phosphorylation of Dvl is a common step in both canonical and non-canonical Wnt signalling.

A signaling network for patterning of neuronal connectivity in the Drosophila brain

The precise number and pattern of axonal connections generated during brain development regulates animal behavior. Therefore, understanding how developmental signals interact to regulate axonal extension and retraction to achieve precise neuronal connectivity is a fundamental goal of neurobiology. We investigated this question in the developing adult brain of Drosophila and find that it is regulated by crosstalk between Wnt, fibroblast growth factor (FGF) receptor, and Jun N-terminal kinase (JNK) signaling, but independent of neuronal activity. The Rac1 GTPase integrates a Wnt-Frizzled-Disheveled axon-stabilizing signal and a Branchless (FGF)-Breathless (FGF receptor) axon-retracting signal to modulate JNK activity. JNK activity is necessary and sufficient for axon extension, whereas the antagonistic Wnt and FGF signals act to balance the extension and retraction required for the generation of the precise wiring pattern.

Mechanistic insights into diabetes mellitus and oxidative stress

Diabetes mellitus (DM) is a significant healthcare concern worldwide that affects more than 165 million individuals leading to cardiovascular disease, nephropathy, retinopathy, and widespread disease of both the peripheral and central nervous systems. The incidence of undiagnosed diabetes, impaired glucose tolerance, and impaired fasting glucose levels raises future concerns in regards to the financial and patient care resources that will be necessary to care for patients with DM. Interestingly, disease of the nervous system can become one of the most debilitating complications and affect sensitive cognitive regions of the brain, such as the hippocampus that modulates memory function, resulting in significant functional impairment and dementia. Oxidative stress forms the foundation for the induction of multiple cellular pathways that can ultimately lead to both the onset and subsequent complications of DM. In particular, novel pathways that involve metabotropic receptor signaling, protein-tyrosine phosphatases, Wnt proteins, Akt, GSK-3beta, and forkhead transcription factors may be responsible for the onset and progression of complications form DM. Further knowledge acquired in understanding the complexity of DM and its ability to impair cellular systems throughout the body will foster new strategies for the treatment of DM and its complications.

Wnt7a overexpression delays beta-tubulin III expression in transgenic mouse embryos

Wnt7a and HA-tagged Wnt7a have previously been shown to promote or delay neuronal differentiation respectively. In this study, we show that embryonic days 9.5 and 10.5 transgenic mouse embryos overexpressing Wnt7a specifically in nestin-positive neural stem/progenitor cells displayed a delay in neuronal differentiation, assayed by beta-tubulin III expression. Our results corroborate previous studies using HA-Wnt7a, and suggest a critical role for Wnt7a in control of neuronal progenitor maturation.

'Suicide' of crickets harbouring hairworms: a proteomics investigation

Despite increasing evidence of host phenotypic manipulation by parasites, the underlying mechanisms causing infected hosts to act in ways that benefit the parasite remain enigmatic in most cases. Here, we used proteomics tools to identify the biochemical alterations that occur in the head of the cricket Nemobius sylvestris when it is driven to water by the hairworm Paragordius tricuspidatus. We characterized host and parasite proteomes during the expression of the water-seeking behaviour. We found that the parasite produces molecules from the Wnt family that may act directly on the development of the central nervous system (CNS). In the head of manipulated cricket, we found differential expression of proteins specifically linked to neurogenesis, circadian rhythm and neurotransmitter activities. We also detected proteins for which the function(s) are still unknown. This proteomics study on the biochemical pathways altered by hairworms has also allowed us to tackle questions of physiological and molecular convergence in the mechanism(s) causing the alteration of orthoptera behaviour. The two hairworm species produce effective molecules acting directly on the CNS of their orthoptera hosts.

Wnt-3a utilizes a novel low dose and rapid pathway that does not require casein kinase 1-mediated phosphorylation of Dvl to activate beta-catenin

The current view of canonical Wnt signalling is that following Wnt binding to its receptors (Frizzled-Lrp5/6), dishevelled (Dvl) becomes hyperphosphorylated, and the signal is transduced to the APC-GSK3beta-axin-beta-catenin multiprotein complex, which subsequently dissociates. As a result beta-catenin is not phosphorylated, escapes proteosomal degradation and activates its target genes after translocation to the nucleus. Here, we analyzed the importance of the Wnt-3a-induced phosphorylation and shift in electrophoretic migration of Dvl (PS-Dvl) for the activation of beta-catenin. Analysis of Wnt-3a time- and dose-responses in a dopaminergic cell line showed that beta-catenin is activated rapidly (within minutes) and at a low dose of Wnt-3a (1 ng/ml). Surprisingly, PS-Dvl appeared only after 30 min and at greater doses (> or =20 ng/ml) of Wnt-3a. Moreover, we found that a casein kinase 1 inhibitor (D4476) or siRNA for casein kinase 1 delta/epsilon (CK1delta/epsilon) blocked the Wnt-3a-induced PS-Dvl. Interestingly, CK1 inhibition or siRNA for CK1delta/epsilon did not ablate the activation of beta-catenin by Wnt-3a, indicating that there is a PS-Dvl-independent path to activate beta-catenin. The increase in beta-catenin activation by Wnt-3a (PS-Dvl-dependent or -independent) were blocked by Dickkopf1 (Dkk1), suggesting that the effect of Wnt-3a is in both cases mediated by Lrp5/6 receptors. Thus, our results show that Wnt-3a rapidly induce a partial activation of beta-catenin in the absence of PS-Dvl at low doses, while at high doses induce a full activation of beta-catenin in a PS-Dvl-dependent manner.

Identification of potential target genes for RFX4_v3, a transcription factor critical for brain development

Regulatory factor X4 variant transcript 3 (Rfx4_v3) gene disruption in mice demonstrated that interruption of a single allele (heterozygous, +/-) prevented formation of the subcommissural organ, resulting in congenital hydrocephalus, while interruption of two alleles (homozygous, -/-) caused fatal failure of dorsal midline brain structure formation. To identify potential target genes for RFX4_v3, we used microarray analysis to identify differentially expressed genes in Rfx4_v3-deficient mouse brains at embryonic day 10.5, before gross structural changes were apparent. Of 109 differentially expressed transcripts, 24 were chosen for validation and 22 were confirmed by real-time PCR. Many validated genes encoded critical proteins involved in brain morphogenesis, such as the signaling components in the Wnt, bone morphogenetic protein (BMP) and retinoic acid (RA) pathways. Cx3cl1, a CX3C-type chemokine gene that is highly expressed in brain, was down-regulated in the Rfx4_v3-null mice. Both human and mouse Cx3cl1 proximal promoters contained highly conserved X-boxes, known cis-acting elements for RFX protein binding. Using the Cx3cl1 promoter as an example of a target gene, we demonstrated direct binding of RFX4_v3 to the Cx3cl1 promoter, and trans-acting activity of RFX4_v3 protein to stimulate gene expression. These data suggest that RFX4_v3 may act upstream of critical signaling pathways in the process of brain development.

The roles of specific genes implicated as circulating factors involved in normal and disordered phosphate homeostasis: frizzled related protein-4, matrix extracellular phosphoglycoprotein, and fibroblast growth factor 23

Normal serum phosphate (Pi) concentrations are relatively tightly controlled by endocrine mediators of Pi balance. Recent data involving several disorders of Pi homeostasis have shed new light on the regulation of serum Pi balance. It has been hypothesized that circulating phosphaturic factors, or phosphatonins, exist that, when present at high serum concentrations, directly act on the kidney to induce renal Pi wasting. This review will focus upon recently discovered factors that are overexpressed in tumors associated with tumor-induced osteomalacia and have reported activity consistent with effecting Pi balance in vivo. Currently, the best-characterized group of phosphatonin-like polypeptides includes secreted frizzled related protein-4, matrix extracellular phosphoglycoprotein, and fibroblast growth factor-23. Our understanding of these factors will, in the short term, aid us in understanding normal Pi balance and, in the future, help to design novel therapeutic strategies for disorders of Pi handling.

Increase in proliferation and differentiation of neural progenitor cells isolated from postnatal and adult mice brain by Wnt-3a and Wnt-5a

Wnt signaling is implicated in the control of cell growth and differentiation during CNS development. These findings are based on studies of mouse and chick models. However, the action of Wnt signaling, at the cellular level, is poorly understood. In this study, we investigated the roles of Wnt-3a and Wnt-5a on differentiation and proliferation of postnatal neural progenitor cells (NPCs) in mice.NPCs were isolated from the subventricular zone (SVZ) of PN-1 and adult ICR mice. Plasmids containing active Wnt-3a or Wnt-5a were transfected to NPCs; their effects on the formation of neurospheres and differentiation into neuronal cells were then determined. Transfection of Wnt-3a and Wnt-5a plasmids promoted regeneration of neurospheres and differentiation into Map2-positive cells, and decreased differentiation into GFAP-positive cells. The conditioned media obtained from Wnt-3a or Wnt-5a transfected NPCs showed similar effects on differentiation of NPCs with cDNA transfection, although the magnitude of stimulatory effect was less than that by plasmid transfection. Wnt-3a and Wnt-5a transfection did not affect Brdu incorporation of neuronal or glial progenitors in differentiation media. Wnt-3a and Wnt-5a plasmid transfection and the treatment of Wnt-3a and Wnt-5a conditioned media increased beta-catenin levels in NPCs. Wnt-3a had a greater effect on beta-catenin levels than Wnt-5a. The PKC inhibitor completely blocked the Wnt-5a effect on neuronal differentiation in NPCs. These findings suggest that Wnt-3a and Wnt-5a each have distinct effects on the proliferation and differentiation of NPCs in postnatal mice.

SSEA-1 marks regionally restricted immature subpopulations of embryonic retinal progenitor cells that are regulated by the Wnt signaling pathway

Identification and expansion of retinal progenitor cells are critical issues from both scientific and clinical aspects. Here, we identified SSEA-1 (CD15) as a novel surface antigen that can be used to define immature retinal progenitor cells. SSEA-1-expressing retinal cells were found in the peripheral region of the early embryonic mouse retina, and then their number dramatically disappeared along with retinal development. FACS analysis showed that the cells strongly positive for SSEA-1 co-expressed Ki67 proliferation antigen in all the developmental stages examined. The SSEA-1-expressing cells formed larger colonies than the non-expressing ones in retinal re-aggregation cultures. Moreover, late onset of rhodopsin expression was observed in SSEA-1-positive progenitor cells, supporting the idea that these cells have an intrinsically immature character. Differential expression of Wnt signal-related genes between SSEA-1-positive and -negative subpopulations of retina cells was revealed, and the expression of constitutively active forms of Wnt signaling molecules resulted in a greater number of SSEA-1-positive cells. In light of all of the data taken together, we propose SSEA-1 to be a surface marker to define a regionally restricted immature subset of progenitor cells of mouse neural retina, with SSEA-1 expression by them positively regulated by Wnt signals.

Migratory routes and fates of cells transcribing the Wnt-1 gene in the murine hindbrain

To investigate the origins, migrations, and fates of Wnt-1-expressing cells in the murine hindbrain, mice carrying a Wnt-1 enhancer/lacZ transgene were observed from embryonic day (E) 8 through postnatal day 18. The transgene-stained ventricular layer waxed and waned prior to and following migrations from it. Stained cells migrated first external to the hindbrain as neural crest and then within it to form typical populations of the rhombic lip, as well as others not recognized as lip derivatives. Migrations originated in a temporally defined sequence, many from discrete rhombomeres. All moved first radially, then rostrally and/or ventrally, ipsi-, or contralaterally, in the mantle or marginal layers. These movements ultimately formed elements of several nuclei, aligned in four longitudinal bands: dorsal (including the gracile, cuneate, cochlear, and vestibular nuclei, plus cerebellar granular cells), dorsal intermediate (including trigeminal sensory, parvicellular reticular, and deep cerebellar nuclei), ventral intermediate (including lateral and intermediate reticular nuclei), and ventral (including the raphe obscurus and pontine nuclei). Transgene staining often persisted long enough to identify stained cells in their definitive, adult nuclei. However, staining was transient. The strength of the staining, however, was in its ability to reveal origins and migrations in both whole-mounts and sections, in single cell detail. The present results will permit analyses of the effects of genetic manipulations on Wnt-1 lineage cells.

Expression of mouse Coiled-coil-DIX1 (Ccd1), a positive regulator of Wnt signaling, during embryonic development

Wnt signaling plays an important role in cell growth, differentiation, polarity formation, and neural development. We have recently identified the Coiled-coil-DIX1 (Ccd1) gene encoding a third type of a DIX domain-containing protein. Ccd1 forms homomeric and heteromeric complexes with Dishevelled and Axin, and positively regulates the Wnt/beta-catenin pathway. Here, we examined the spatiotemporal expression pattern of Ccd1 mRNA in mouse embryos from embryonic day 6.5 (E6.5) to E17.5 by in situ hybridization. Ccd1 expression was detected in the node region in gastrula embryos, in the cephalic mesenchyme and tail bud at E8.5, and in the branchial arch and forelimb bud at E9.5. In the central nervous system, Ccd1 expression began and persisted in the regions where the neurons differentiated, so that it was observed throughout the brain and spinal cord at E17.5. Ccd1 expression was also strong in the peripheral nervous system, including sensory cranial ganglia (trigeminal, facial, and vestibulocochlear ganglia), dorsal root ganglia, and autonomic ganglia (sympathetic ganglia, celiac ganglion, and hypogastric plexus). Ccd1 was detected in the sensory organs, such as the inner nuclear layer of the neural retina, saccule and cochlea of the inner ear, and nasal epithelium. Outside the nervous system, Ccd1 mRNA was observed in the cartilage, tongue, lung bud, stomach, and gonad at E12.5-E14.5, and in the tooth bud, bronchial epithelium, and kidney at E17.5. Taken together, these findings demonstrate that Ccd1 expression is observed in all the neurons in the nervous system, closely associated with neural crest-derived tissues, and largely overlapping with the regions where several Wnt genes are reported to play a role.

Ventral midbrain glia express region-specific transcription factors and regulate dopaminergic neurogenesis through Wnt-5a secretion

Glial cells have been classically described as supporting cells for neurons. Recently, additional roles during neural development have begun to emerge. Here, we report that ventral midbrain glia, including astrocytes and radial glia, are the source of signals required by neural precursors to acquire a dopaminergic phenotype. We found that ventral midbrain glia, but not cortical glia, secrete high levels of the glycolipoprotein Wnt-5a, express region-specific transcription factors such as Pax-2, En-1 and Otx-2 and increase the differentiation of cortical or ventral midbrain Nurr1 precursors into tyrosine hydroxylase-positive neurons. Moreover, blocking experiments using a Wnt-5a blocking antibody indicated that the effects of ventral midbrain glia on Nurr1-positive neural precursors are partially mediated by Wnt-5a. Thus, our results identify Wnt-5a as an important component of the dopaminergic inductive activity of the ventral midbrain glia.

Similarities and differences between the Wnt and reelin pathways in the forming brain

One of the key features in development is the reutilization of successful signaling pathways. Here, we emphasize the involvement of the Wnt pathway, one of the five kinds of signal transduction pathway predominating early embryonic development of all animals, in regulating the formation of brain structure. We discuss the interrelationships between the Wnt and reelin pathways in the regulation of cortical layering. We summarize data emphasizing key molecules, which, when mutated, result in abnormal brain development. This integrated view, which is based on conservation of pathways, reveals the relative position of participants in the pathway, points to control mechanisms, and allows raising testable working hypotheses. Nevertheless, although signaling pathways are highly conserved from flies to humans, the overall morphology is not. We propose that future studies directed at understanding of diversification will provide fruitful insights on mammalian brain formation.