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Parkinson's disease (PD) represents the most common neurodegenerative movement disorder. We recently identified 16 novel genes associated with PD. In this study, we focused the attention on the common and rare variants identified in the lysosomal K + channel TMEM175. The study includes a detailed clinical and genetic analysis of 400 cases and 300 controls. Molecular studies were performed on patient-derived fibroblasts. The functional properties of the mutant channels were assessed by patch-clamp technique and co-immunoprecipitation. We have found that TMEM175 was highly expressed in dopaminergic neurons of the substantia nigra pars compacta and in microglia of the cerebral cortex of the human brain. Four common variants were associated with PD, including two novel variants rs2290402 (c.-10C > T) and rs80114247 (c.T1022C, p.M341T), located in the Kozak consensus sequence and TM3II domain, respectively. We also disclosed 13 novel highly penetrant detrimental mutations in the TMEM175 gene associated with PD. At least nine of these mutations (p.R35C, p. R183X, p.A270T, p.P308L, p.S348L, p. L405V, p.R414W, p.P427fs, p.R481W) may be sufficient to cause the disease, and the presence of mutations of other genes correlated with an earlier disease onset. In vitro functional analysis of the ion channel encoded by the mutated TMEM175 gene revealed a loss of the K + conductance and a reduced channel affinity for Akt. Moreover, we observed an impaired autophagic/lysosomal proteolytic flux and an increase expression of unfolded protein response markers in patient-derived fibroblasts. These data suggest that mutations in TMEM175 gene may contribute to the pathophysiology of PD., (© 2023. The Author(s).)

Background: Parkinson's disease (PD) is a neurodegenerative movement disorder affecting 1-5% of the general population for which neither effective cure nor early diagnostic tools are available that could tackle the pathology in the early phase. Here we report a multi-stage procedure to identify candidate genes likely involved in the etiopathogenesis of PD., Methods: The study includes a discovery stage based on the analysis of whole exome data from 26 dominant late onset PD families, a validation analysis performed on 1542 independent PD patients and 706 controls from different cohorts and the assessment of polygenic variants load in the Italian cohort (394 unrelated patients and 203 controls)., Results: Family-based approach identified 28 disrupting variants in 26 candidate genes for PD including PARK2, PINK1, DJ-1(PARK7), LRRK2, HTRA2, FBXO7, EIF4G1, DNAJC6, DNAJC13, SNCAIP, AIMP2, CHMP1A, GIPC1, HMOX2, HSPA8, IMMT, KIF21B, KIF24, MAN2C1, RHOT2, SLC25A39, SPTBN1, TMEM175, TOMM22, TVP23A and ZSCAN21. Sixteen of them have not been associated to PD before, were expressed in mesencephalon and were involved in pathways potentially deregulated in PD. Mutation analysis in independent cohorts disclosed a significant excess of highly deleterious variants in cases (p = 0.0001), supporting their role in PD. Moreover, we demonstrated that the co-inheritance of multiple rare variants (≥ 2) in the 26 genes may predict PD occurrence in about 20% of patients, both familial and sporadic cases, with high specificity (> 93%; p = 4.4 × 10 - 5 ). Moreover, our data highlight the fact that the genetic landmarks of late onset PD does not systematically differ between sporadic and familial forms, especially in the case of small nuclear families and underline the importance of rare variants in the genetics of sporadic PD. Furthermore, patients carrying multiple rare variants showed higher risk of manifesting dyskinesia induced by levodopa treatment., Conclusions: Besides confirming the extreme genetic heterogeneity of PD, these data provide novel insights into the genetic of the disease and may be relevant for its prediction, diagnosis and treatment.

In mammals, the pre-gastrula proximal epiblast gives rise to primordial germ cells (PGCs) or somatic precursors in response to BMP4 and WNT signaling. Entry into the germline requires activation of a naïve-like pluripotency gene regulatory network (GRN). Recent work has shown that suppression of OTX2 expression in the epiblast by BMP4 allows cells to develop a PGC fate in a precise temporal window. However, the mechanisms by which OTX2 suppresses PGC fate are unknown. Here, we show that, in mice, OTX2 prevents epiblast cells from activating the pluripotency GRN by direct repression of Oct4 and Nanog. Loss of this control during PGC differentiation in vitro causes widespread activation of the pluripotency GRN and a deregulated response to LIF, BMP4 and WNT signaling. These abnormalities, in specific cell culture conditions, result in massive germline entry at the expense of somatic mesoderm differentiation. Increased generation of PGCs also occurs in mutant embryos. We propose that the OTX2-mediated repressive control of Oct4 and Nanog is the basis of the mechanism that determines epiblast contribution to germline and somatic lineage., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2021. Published by The Company of Biologists Ltd.)

Parkinson Disease (PD) is a complex neurodegenerative disorder characterized by large genetic heterogeneity and missing heritability. Since the genetic background of PD can partly vary among ethnicities and neurological scales have been scarcely investigated in a PD setting, we performed an exploratory Whole Exome Sequencing (WES) analysis of 123 PD patients from mainland Italy, investigating scales assessing motor (UPDRS), cognitive (MoCA), and other non-motor symptoms (NMS). We performed variant prioritization, followed by targeted association testing of prioritized variants in 446 PD cases and 211 controls. Then we ran Exome-Wide Association Scans (EWAS) within sequenced PD cases ( N = 113), testing both motor and non-motor PD endophenotypes, as well as their associations with Polygenic Risk Scores (PRS) influencing brain subcortical volumes. We identified a variant associated with PD, rs201330591 in GTF2H2 (5q13; alternative T allele: OR [CI] = 8.16[1.08; 61.52], FDR = 0.048), which was not replicated in an independent cohort of European ancestry (1,148 PD cases, 503 controls). In the EWAS, polygenic analyses revealed statistically significant multivariable associations of amygdala- [β(SE) = -0.039(0.013); FDR = 0.039] and caudate-PRS [0.043(0.013); 0.028] with motor symptoms. All subcortical PRSs in a multivariable model notably increased the variance explained in motor (adjusted-R 2 = 38.6%), cognitive (32.2%) and other non-motor symptoms (28.9%), compared to baseline models (~20%). Although, the small sample size warrants further replications, these findings suggest shared genetic architecture between PD symptoms and subcortical structures, and provide interesting clues on PD genetic and neuroimaging features., (Copyright © 2020 Gialluisi, Reccia, Tirozzi, Nutile, Lombardi, De Sanctis, International Parkinson's Disease Genomic Consortium (IPDGC), Varanese, Pietracupa, Modugno, Simeone, Ciullo and Esposito.)

Polymorphic variants of the gene encoding for metabotropic glutamate receptor 3 (mGlu3) are linked to schizophrenia. Because abnormalities of cortical GABAergic interneurons lie at the core of the pathophysiology of schizophrenia, we examined whether mGlu3 receptors influence the developmental trajectory of cortical GABAergic transmission in the postnatal life. mGlu3 -/- mice showed robust changes in the expression of interneuron-related genes in the prefrontal cortex (PFC), including large reductions in the expression of parvalbumin (PV) and the GluN1 subunit of NMDA receptors. The number of cortical cells enwrapped by perineuronal nets was increased in mGlu3 -/- mice, suggesting that mGlu3 receptors shape the temporal window of plasticity of PV + interneurons. Electrophysiological measurements of GABA A receptor-mediated responses revealed a more depolarized reversal potential of GABA currents in the somata of PFC pyramidal neurons in mGlu3 -/- mice at postnatal d 9 associated with a reduced expression of the K + /Cl - symporter. Finally, adult mGlu3 -/- mice showed lower power in electroencephalographic rhythms at 1-45 Hz in quiet wakefulness as compared with their wild-type counterparts. These findings suggest that mGlu3 receptors have a strong impact on the development of cortical GABAergic transmission and cortical neural synchronization mechanisms corroborating the concept that genetic variants of mGlu3 receptors may predispose to psychiatric disorders.-Imbriglio, T., Verhaeghe, R., Martinello, K., Pascarelli, M. T., Chece, G., Bucci, D., Notartomaso, S., Quattromani, M., Mascio, G., Scalabrì, F., Simeone, A., Maccari, S., Del Percio, C., Wieloch, T., Fucile, S., Babiloni, C., Battaglia, G., Limatola, C., Nicoletti, F., Cannella, M. Developmental abnormalities in cortical GABAergic system in mice lacking mGlu3 metabotropic glutamate receptors.

The successful segregation of germ cells from somatic lineages is vital for sexual reproduction and species survival. In the mouse, primordial germ cells (PGCs), precursors of all germ cells, are induced from the post-implantation epiblast 1 . Induction requires BMP4 signalling to prospective PGCs 2 and the intrinsic action of PGC transcription factors 3-6 . However, the molecular mechanisms that connect BMP4 to induction of the PGC transcription factors that are responsible for segregating PGCs from somatic lineages are unknown. Here we show that the transcription factor OTX2 is a key regulator of these processes. Downregulation of Otx2 precedes the initiation of the PGC programme both in vitro and in vivo. Deletion of Otx2 in vitro markedly increases the efficiency of PGC-like cell differentiation and prolongs the period of PGC competence. In the absence of Otx2 activity, differentiation of PGC-like cells becomes independent of the otherwise essential cytokine signals, with germline entry initiating even in the absence of the PGC transcription factor BLIMP1. Deletion of Otx2 in vivo increases PGC numbers. These data demonstrate that OTX2 functions repressively upstream of PGC transcription factors, acting as a roadblock to limit entry of epiblast cells to the germline to a small window in space and time, thereby ensuring correct numerical segregation of germline cells from the soma.

Establishing specific cell lineages from human induced pluripotent stem cells (hiPSCs) is vital for cell therapy approaches in regenerative medicine, particularly for neurodegenerative disorders. While neural precursors have been induced from hiPSCs, the establishment of hiPSC-derived human neural stem cells (hiNSCs), with characteristics that match foetal hNSCs and abide by cGMP standards, thus allowing clinical applications, has not been described. We generated hiNSCs by a virus-free technique, whose properties recapitulate those of the clinical-grade hNSCs successfully used in an Amyotrophic Lateral Sclerosis (ALS) phase I clinical trial. Ex vivo, hiNSCs critically depend on exogenous mitogens for stable self-renewal and amplification and spontaneously differentiate into astrocytes, oligodendrocytes and neurons upon their removal. In the brain of immunodeficient mice, hiNSCs engraft and differentiate into neurons and glia, without tumour formation. These findings now warrant the establishment of clinical-grade, autologous and continuous hiNSC lines for clinical trials in neurological diseases such as Huntington's, Parkinson's and Alzheimer's, among others.

Embryonic stem cells (ESCs) cultured in leukemia inhibitory factor (LIF) plus fetal bovine serum (FBS) exhibit heterogeneity in the expression of naive and primed transcription factors. This heterogeneity reflects the dynamic condition of ESCs and their versatility to promptly respond to signaling effectors promoting naive or primed pluripotency. Here, we report that ESCs lacking Nanog or overexpressing Otx2 exhibit an early primed identity in LIF + FBS and fail to convert into 2i-induced naive state. Conversely, Otx2-null ESCs possess naive identity features in LIF + FBS similar to Nanog-overexpressing ESCs and convert poorly into FGF-induced early primed state. When both Nanog and Otx2 are inactivated, ESCs cultured in LIF + FBS exhibit primed identity and weakened ability to convert into naive state. These data suggest that, through mutual antagonism, NANOG and OTX2 specify the heterogeneous identity of ESCs cultured in LIF + FBS and individually predispose them for optimal response to naive or primed inducing factors., (Copyright © 2017 The Authors. Published by Elsevier Inc. All rights reserved.)

Mouse embryonic stem cells (ESCs) and the inner cell mass (ICM)-derived epiblast exhibit naive pluripotency. ESC-derived epiblast stem cells (EpiSCs) and the postimplantation epiblast exhibit primed pluripotency. Although core pluripotency factors are well-characterized, additional regulators, including Otx2, recently have been shown to function during the transition from naive to primed pluripotency. Here we uncover a role for Otx2 in the control of the naive pluripotent state. We analyzed Otx2-binding activity in ESCs and EpiSCs and identified Nanog, Oct4, and Sox2 as direct targets. To unravel the Otx2 transcriptional network, we targeted the strongest Otx2-binding site in the Nanog promoter, finding that this site modulates the size of specific ESC-subtype compartments in cultured cells and promotes Nanog expression in vivo, predisposing ICM differentiation to epiblast. Otx2-mediated Nanog regulation thus contributes to the integrity of the ESC state and cell lineage specification in preimplantation development., (Copyright © 2016 The Author(s). Published by Elsevier Inc. All rights reserved.)

OTX2 (orthodenticle homeobox 2) haplodeficiency causes diverse defects in mammalian visual systems ranging from retinal dysfunction to anophthalmia. We find that the retinal dystrophy of Otx2(+/GFP) heterozygous knockin mice is mainly due to the loss of bipolar cells and consequent deficits in retinal activity. Among bipolar cell types, OFF-cone bipolar subsets, which lack autonomous Otx2 gene expression but receive Otx2 proteins from photoreceptors, degenerate most rapidly in Otx2(+/GFP) mouse retinas, suggesting a neuroprotective effect of the imported Otx2 protein. In support of this hypothesis, retinal dystrophy in Otx2(+/GFP) mice is prevented by intraocular injection of Otx2 protein, which localizes to the mitochondria of bipolar cells and facilitates ATP synthesis as a part of mitochondrial ATP synthase complex. Taken together, our findings demonstrate a mitochondrial function for Otx2 and suggest a potential therapeutic application of OTX2 protein delivery in human retinal dystrophy., (Copyright © 2015 The Authors. Published by Elsevier Inc. All rights reserved.)

The protracted and age-dependent degeneration of dopamine (DA)-producing neurons of the Substantia nigra pars compacta (SNc) and ventral tegmental area (VTA) in the mammalian midbrain is a hallmark of human Parkinson's Disease (PD) and of certain genetic mouse models of PD, such as mice heterozygous for the homeodomain transcription factor Engrailed 1 (En1(+/-) mice). Neurotoxin-based animal models of PD, in contrast, are characterized by the fast and partly reversible degeneration of the SNc and VTA DA neurons. The secreted protein WNT1 was previously shown to be strongly induced in the neurotoxin-injured adult ventral midbrain (VM), and to protect the SNc and VTA DA neurons from cell death in this context. We demonstrate here that the sustained and ectopic expression of Wnt1 in the SNc and VTA DA neurons of En1(+/Wnt1) mice also protected these genetically affected En1 heterozygote (En1(+/-)) neurons from their premature degeneration in the adult mouse VM. We identified a developmental gene cascade that is up-regulated in the adult En1(+/Wnt1) VM, including the direct WNT1/β-catenin signaling targets Lef1, Lmx1a, Fgf20 and Dkk3, as well as the indirect targets Pitx3 (activated by LMX1A) and Bdnf (activated by PITX3). We also show that the secreted neurotrophin BDNF and the secreted WNT modulator DKK3, but not the secreted growth factor FGF20, increased the survival of En1 mutant dopaminergic neurons in vitro. The WNT1-mediated signaling pathway and its downstream targets BDNF and DKK3 might thus provide a useful means to treat certain genetic and environmental (neurotoxic) forms of human PD., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Wingless-related MMTV integration site 1 (WNT1)/β-catenin signaling plays a crucial role in the generation of mesodiencephalic dopaminergic (mdDA) neurons, including the substantia nigra pars compacta (SNc) subpopulation that preferentially degenerates in Parkinson's disease (PD). However, the precise functions of WNT1/β-catenin signaling in this context remain unknown. Stem cell-based regenerative (transplantation) therapies for PD have not been implemented widely in the clinical context, among other reasons because of the heterogeneity and incomplete differentiation of the transplanted cells. This might result in tumor formation and poor integration of the transplanted cells into the dopaminergic circuitry of the brain. Dickkopf 3 (DKK3) is a secreted glycoprotein implicated in the modulation of WNT/β-catenin signaling. Using mutant mice, primary ventral midbrain cells, and pluripotent stem cells, we show that DKK3 is necessary and sufficient for the correct differentiation of a rostrolateral mdDA neuron subset. Dkk3 transcription in the murine ventral midbrain coincides with the onset of mdDA neurogenesis and is required for the activation and/or maintenance of LMX1A (LIM homeobox transcription factor 1α) and PITX3 (paired-like homeodomain transcription factor 3) expression in the corresponding mdDA precursor subset, without affecting the proliferation or specification of their progenitors. Notably, the treatment of differentiating pluripotent stem cells with recombinant DKK3 and WNT1 proteins also increases the proportion of mdDA neurons with molecular SNc DA cell characteristics in these cultures. The specific effects of DKK3 on the differentiation of rostrolateral mdDA neurons in the murine ventral midbrain, together with its known prosurvival and anti-tumorigenic properties, make it a good candidate for the improvement of regenerative and neuroprotective strategies in the treatment of PD. Significance statement: We show here that Dickkopf 3 (DKK3), a secreted modulator of WNT (Wingless-related MMTV integration site)/β-catenin signaling, is both necessary and sufficient for the proper differentiation and survival of a rostrolateral (parabrachial pigmented nucleus and dorsomedial substantia nigra pars compacta) mesodiencephalic dopaminergic neuron subset, using Dkk3 mutant mice and murine primary ventral midbrain and pluripotent stem cells. The progressive loss of these dopamine-producing mesodiencephalic neurons is a hallmark of human Parkinson's disease, which can up to now not be halted by clinical treatments of this disease. Thus, the soluble DKK3 protein might be a promising new agent for the improvement of current protocols for the directed differentiation of pluripotent and multipotent stem cells into mesodiencephalic dopaminergic neurons and for the promotion of their survival in situ., (Copyright © 2015 the authors 0270-6474/15/3513386-17$15.00/0.)

Distinct midbrain dopamine (mDA) neuron subtypes are found in the substantia nigra pars compacta (SNc) and the ventral tegmental area (VTA), but it is mainly SNc neurons that degenerate in Parkinson's disease. Interest in how mDA neurons develop has been stimulated by the potential use of stem cells in therapy or disease modeling. However, very little is known about how specific dopaminergic subtypes are generated. Here, we show that the expression profiles of the transcription factors Sox6, Otx2, and Nolz1 define subpopulations of mDA neurons already at the neural progenitor cell stage. After cell-cycle exit, Sox6 selectively localizes to SNc neurons, while Otx2 and Nolz1 are expressed in a subset of VTA neurons. Importantly, Sox6 ablation leads to decreased expression of SNc markers and a corresponding increase in VTA markers, while Otx2 ablation has the opposite effect. Moreover, deletion of Sox6 affects striatal innervation and dopamine levels. We also find reduced Sox6 levels in Parkinson's disease patients. These findings identify Sox6 as a determinant of SNc neuron development and should facilitate the engineering of relevant mDA neurons for cell therapy and disease modeling., (Copyright © 2014 The Authors. Published by Elsevier Inc. All rights reserved.)

Plasticity in the visual cerebral cortex is regulated by the internalization of Otx2 homeoprotein into parvalbumin neurons in cortical layers II/III and IV. However the Otx2 locus is not active in these neurons and the protein is imported from external sources, including the choroid plexus. Because Otx1 and Otx2 may have redundant functions, we wanted to verify if part of the staining in parvalbumin neurons corresponds to Otx1 transported from cortical layer V neurons. It is demonstrated here that Otx staining in layer IV cells is maintained in Otx1-null mice. The immunoprecipitation of extracts from finely dissected granular and supragranular cortex (layers I-IV) gave immunoblots with a band corresponding to Otx2 and not Otx1. Moreover, high-resolution mass spectrometry analysis after immunoprecipitation identifies two peptides within the Otx2 homeodomain. One of these peptides is specific for Otx2 and is not found in Otx1. These results unambiguously establish that the staining in parvalbumin neurons revealed with the anti-Otx2 antibodies used in our previous studies identifies non-cell autonomous Otx2.

The normal cellular organization and layering of the vertebrate cerebellum is established during embryonic and early postnatal development by the interplay of a complex array of genetic and signaling pathways. Disruption of these processes and of the proper layering of the cerebellum usually leads to ataxic behaviors. Here, we analyzed the relative contribution of Fibroblast growth factor receptor 2 (FGFR2)-mediated signaling to cerebellar development in conditional Fgfr2 single mutant mice. We show that during embryonic mouse development, Fgfr2 expression is higher in the anterior cerebellar primordium and excluded from the proliferative ventricular neuroepithelium. Consistent with this finding, conditional Fgfr2 single mutant mice display the most prominent defects in the anterior lobules of the adult cerebellum. In this context, FGFR2-mediated signaling is required for the proper generation of Bergmann glia cells and the correct positioning of these cells within the Purkinje cell layer, and for cell survival in the developing cerebellar primordium. Using cerebellar microexplant cultures treated with an FGFR agonist (FGF9) or antagonist (SU5402), we also show that FGF9/FGFR-mediated signaling inhibits the outward migration of radial glia and Bergmann glia precursors and cells, and might thus act as a positioning cue for these cells. Altogether, our findings reveal the specific functions of the FGFR2-mediated signaling pathway in the generation and positioning of Bergmann glia cells during cerebellar development in the mouse.

Naive and primed pluripotency is characterized by distinct signaling requirements, transcriptomes, and developmental properties, but both cellular states share key transcriptional regulators: Oct4, Sox2, and Nanog. Here, we demonstrate that transition between these two pluripotent states is associated with widespread Oct4 relocalization, mirrored by global rearrangement of enhancer chromatin landscapes. Our genomic and biochemical analyses identified candidate mediators of primed state-specific Oct4 binding, including Otx2 and Zic2/3. Even when differentiation cues are blocked, premature Otx2 overexpression is sufficient to exit the naive state, induce transcription of a substantial subset of primed pluripotency-associated genes, and redirect Oct4 to previously inaccessible enhancer sites. However, the ability of Otx2 to engage new enhancer regions is determined by its levels, cis-encoded properties of the sites, and the signaling environment. Our results illuminate regulatory mechanisms underlying pluripotency and suggest that the capacity of transcription factors such as Otx2 and Oct4 to pioneer new enhancer sites is highly context dependent., (Copyright © 2014 Elsevier Inc. All rights reserved.)

In the human, mutations of OTX2 (Orthodenticle homeobox 2 transcription factor) translate into eye malformations of variable expressivity (even between the two eyes of the same individual) and incomplete penetrance, suggesting the existence of subtle thresholds in OTX2 activity. We have addressed this issue by analyzing retinal structure and function in six mutant mice with graded Otx2 activity: Otx2(+/+), Otx2(+/AA), Otx2(+/GFP), Otx2(AA/AA), Otx2(AA/GFP) and Otx2(GFP/GFP). Null mice (Otx2(GFP/GFP)) fail to develop the head and are embryonic lethal, and compound heterozygous Otx2(AA/GFP) mice show a truncated head and die at birth. All other genotypes develop until adulthood. We analyzed eye structure and visual physiology in the genotypes that develop until adulthood and report that phenotype severity parallels Otx2 activity. Otx2(+/AA) are only mildly affected whereas Otx2(+/GFP) are more affected than Otx2(+/AA) but less than Otx2(AA/AA) mice. Otx2(AA/AA) mice later manifest the most severe defects, with variable expressivity. Electrophysiological and histological analyses of the mouse retina revealed progressive death of bipolar cells and cone photoreceptors that is both Otx2 activity- and age-dependent with the same ranking of phenotypic severity. This study demonstrates the importance of gene dosage in the development of age-dependent pathologies and underscores the fact that small gene dosage differences can cause significant pathological states.

During embryonic development, the rostral neuroectoderm is regionalized into broad areas that are subsequently subdivided into progenitor compartments with specialized identity and fate. These events are controlled by signals emitted by organizing centers and interpreted by target progenitors, which activate superimposing waves of intrinsic factors restricting their identity and fate. The transcription factor Otx2 plays a crucial role in mesencephalic development by positioning the midbrain-hindbrain boundary (MHB) and its organizing activity. Here, we investigated whether Otx2 is cell-autonomously required to control identity and fate of dorsal mesencephalic progenitors. With this aim, we have inactivated Otx2 in the Pax7(+) dorsal mesencephalic domain, previously named m1, without affecting MHB integrity. We found that the Pax7(+) m1 domain can be further subdivided into a dorsal Zic1(+) m1a and a ventral Zic1(-) m1b sub-domain. Loss of Otx2 in the m1a (Pax7(+) Zic1(+)) sub-domain impairs the identity and fate of progenitors, which undergo a full switch into a coordinated cerebellum differentiation program. By contrast, in the m1b sub-domain (Pax7(+) Zic1(-)) Otx2 is prevalently required for post-mitotic transition of mesencephalic GABAergic precursors. Moreover, genetic cell fate, BrdU cell labeling and Otx2 conditional inactivation experiments indicate that in Otx2 mutants all ectopic cerebellar cell types, including external granule cell layer (EGL) precursors, originate from the m1a progenitor sub-domain and that reprogramming of mesencephalic precursors into EGL or cerebellar GABAergic progenitors depends on temporal sensitivity to Otx2 ablation. Together, these findings indicate that Otx2 intrinsically controls different aspects of dorsal mesencephalic neurogenesis. In this context, Otx2 is cell-autonomously required in the m1a sub-domain to suppress cerebellar fate and promote mesencephalic differentiation independently of the MHB organizing activity.

Dorsal horn neurons in the spinal cord integrate and relay sensory information to higher brain centers. These neurons are organized in specific laminae and different transcription factors are involved in their specification. The murine homeodomain Gbx1 protein is expressed in the mantle zone of the spinal cord at E12.5-13.5, correlating with the appearance of a discernable dorsal horn around E14 and eventually defining a narrow layer in the dorsal horn around perinatal stages. At postnatal stages, Gbx1 identifies a specific subpopulation of GABAergic neurons in the dorsal spinal cord. We have generated a loss of function mutation for Gbx1 and analyzed its consequences during spinal cord development. Gbx1 (-/-) mice are viable and can reproduce as homozygous null mutants. However, the adult mutant mice display an altered gait during forward movement that specifically affects the hindlimbs. This abnormal gait was evaluated by a series of behavioral tests, indicating that locomotion is impaired, but not muscle strength or motor coordination. Molecular analysis showed that the development of the dorsal horn is not profoundly affected in Gbx1 (-/-) mutant mice. However, analysis of terminal neuronal differentiation revealed that the proportion of GABAergic inhibitory interneurons in the superficial dorsal horn is diminished. Our study unveiled a role for Gbx1 in specifying a subset of GABAergic neurons in the dorsal horn of the spinal cord involved in the control of posterior limb movement.

PATZ1 is an emerging cancer-related gene coding for a POZ/AT-hook/kruppel Zinc finger transcription factor, which is lost or misexpressed in human neoplasias. Here, we investigated its role in development exploring wild-type and Patz1-knockout mice during embryogenesis. We report that the Patz1 gene is ubiquitously expressed at early stages of development and becomes more restricted at later stages, with high levels of expression in actively proliferating neuroblasts belonging to the ventricular zones of the central nervous system (CNS). The analysis of embryos in which Patz1 was disrupted revealed the presence of severe defects in the CNS and in the cardiac outflow tract, which eventually lead to a pre-mature in utero death during late gestation or soon after birth. Moreover, the Patz1-null mice showed a general growth retardation, which was consistent with the slower growth rate and the increased susceptibility to senescence of Patz1(-/-) mouse embryonic fibroblasts (MEFs) compared to wild-type controls. Therefore, these results indicate a critical role of PATZ1 in the control of cell growth and embryonic development., (Copyright © 2012 Wiley Periodicals, Inc.)

The choroid plexuses (ChPs) are the main regulators of cerebrospinal fluid (CSF) composition and thereby also control the composition of a principal source of signaling molecules that is in direct contact with neural stem cells in the developing brain. The regulators of ChP development mediating the acquisition of a fate that differs from the neighboring neuroepithelial cells are poorly understood. Here, we demonstrate in mice a crucial role for the transcription factor Otx2 in the development and maintenance of ChP cells. Deletion of Otx2 by the Otx2-CreERT2 driver line at E9 resulted in a lack of all ChPs, whereas deletion by the Gdf7-Cre driver line affected predominately the hindbrain ChP, which was reduced in size, primarily owing to an increase in apoptosis upon Otx2 deletion. Strikingly, Otx2 was still required for the maintenance of hindbrain ChP cells at later stages when Otx2 deletion was induced at E15, demonstrating a central role of Otx2 in ChP development and maintenance. Moreover, the predominant defects in the hindbrain ChP mediated by Gdf7-Cre deletion of Otx2 revealed its key role in regulating early CSF composition, which was altered in protein content, including the levels of Wnt4 and the Wnt modulator Tgm2. Accordingly, proliferation and Wnt signaling levels were increased in the distant cerebral cortex, suggesting a role of the hindbrain ChP in regulating CSF composition, including key signaling molecules. Thus, Otx2 acts as a master regulator of ChP development, thereby influencing one of the principal sources of signaling in the developing brain, the CSF.

Mouse embryonic stem cells (ESCs) represent the naïve ground state of the preimplantation epiblast and epiblast stem cells (EpiSCs) represent the primed state of the postimplantation epiblast. Studies have revealed that the ESC state is maintained by a dynamic mechanism characterized by cell-to-cell spontaneous and reversible differences in sensitivity to self-renewal and susceptibility to differentiation. This metastable condition ensures indefinite self-renewal and, at the same time, predisposes ESCs for differentiation to EpiSCs. Despite considerable advances, the molecular mechanism controlling the ESC state and pluripotency transition from ESCs to EpiSCs have not been fully elucidated. Here we show that Otx2, a transcription factor essential for brain development, plays a crucial role in ESCs and EpiSCs. Otx2 is required to maintain the ESC metastable state by antagonizing ground state pluripotency and promoting commitment to differentiation. Furthermore, Otx2 is required for ESC transition into EpiSCs and, subsequently, to stabilize the EpiSC state by suppressing, in pluripotent cells, the mesendoderm-to-neural fate switch in cooperation with BMP4 and Fgf2. However, according to its central role in neural development and differentiation, Otx2 is crucially required for the specification of ESC-derived neural precursors fated to generate telencephalic and mesencephalic neurons. We propose that Otx2 is a novel intrinsic determinant controlling the functional integrity of ESCs and EpiSCs.

Understanding the molecular basis underlying the neurogenesis of mesencephalic-diencephalic Dopaminergic (mdDA) neurons is a major task fueled by their relevance in controlling locomotor activity and emotion and their involvement in neurodegenerative and psychiatric diseases. Increasing evidence suggests that mdDA neurons of the substantia nigra pars compacta (SNpc) and ventral tegmental area (VTA) represent two main distinct neuronal populations, which, in turn, include specific neuronal subsets. Relevant studies provided important results on mdDA neurogenesis, but, nevertheless, have not yet clarified how the identity of mdDA neuronal subtypes is established and, in particular, whether neurogenic factors may direct progenitors towards the differentiation of specific mdDA neuronal subclasses. The transcription factor Otx2 is required for the neurogenesis of mesencephalic DA (mesDA) neurons and to control neuron subtype identity and sensitivity to the MPTP neurotoxin in the adult VTA. Here we studied whether Otx2 is required in mdDA progenitors for the generation of specific mdDA neuronal subtypes. We found that although expressed in virtually all mdDA progenitors, Otx2 is required selectively for the differentiation of VTA neuronal subtypes expressing Ahd2 and/or Calb but not for those co-expressing Girk2 and glyco-Dat. Moreover, mild over-expression of Otx2 in SNpc progenitors and neurons is sufficient to rescue En1 haploinsufficiency-dependent defects, such as progressive loss and increased MPTP sensitivity of SNpc neurons. Collectively, these data suggest that mdDA progenitors exhibit differential sensitivity to Otx2, which selectively influences the generation of a large and specific subset of VTA neurons. In addition, these data suggest that Otx2 and En1 may share similar properties and control survival and vulnerability to MPTP neurotoxin respectively in VTA and SNpc., (Copyright © 2012 Elsevier Inc. All rights reserved.)

JMJD3 (KDM6B) antagonizes Polycomb silencing by demethylating lysine 27 on histone H3. The interplay of methyltransferases and demethylases at this residue is thought to underlie critical cell fate transitions, and the dynamics of H3K27me3 during neurogenesis posited for JMJD3 a critical role in the acquisition of neural fate. Despite evidence of its involvement in early neural commitment, however, its role in the emergence and maturation of the mammalian CNS remains unknown. Here, we inactivated Jmjd3 in the mouse and found that its loss causes perinatal lethality with the complete and selective disruption of the pre-Bötzinger complex (PBC), the pacemaker of the respiratory rhythm generator. Through genetic and electrophysiological approaches, we show that the enzymatic activity of JMJD3 is selectively required for the maintenance of the PBC and controls critical regulators of PBC activity, uncovering an unanticipated role of this enzyme in the late structuring and function of neuronal networks., (Copyright © 2012 The Authors. Published by Elsevier Inc. All rights reserved.)

The Shc family of adaptor proteins are crucial mediators of a plethora of receptors such as the tyrosine kinase receptors, cytokine receptors, and integrins that drive signaling pathways governing proliferation, differentiation, and migration. Here, we report the role of the newly identified family member, ShcD/RaLP, whose expression in vitro and in vivo suggests a function in embryonic stem cell (ESC) to epiblast stem cells (EpiSCs) transition. The transition from the naïve (ESC) to the primed (EpiSC) pluripotent state is the initial important step for ESCs to commit to differentiation and the mechanisms underlying this process are still largely unknown. Using a novel approach to simultaneously assess pluripotency, apoptosis, and proliferation by multiparameter flow cytometry, we show that ESC to EpiSC transition is a process involving a tight coordination between the modulation of the Oct4 expression, cell cycle progression, and cell death. We also describe, by high-content immunofluorescence analysis and time-lapse microscopy, the emergence of cells expressing caudal-related homeobox 2 (Cdx2) transcription factor during ESC to EpiSC transition. The use of the ShcD knockout ESCs allowed the unmasking of this process as they presented deregulated Oct4 modulation and an enrichment in Oct4-negative Cdx2-positive cells with increased MAPK/extracellular-regulated kinases 1/2 activation, within the differentiating population. Collectively, our data reveal ShcD as an important modulator in the switch of key pathway(s) involved in determining EpiSC identity., (Copyright © 2012 AlphaMed Press.)

Mesencephalic-diencephalic dopaminergic (mdDA) neurons play a relevant role in the control of movement, behavior, and cognition. Indeed loss and/or abnormal functioning of mdDA neurons are responsible for Parkinson's disease as well as for addictive and psychiatric disorders. In the last years a wealth of information has been provided on gene functions controlling identity, fate, and proliferation of mdDA progenitors. This review will focus on the role exerted by Otx genes in early decisions regulating sequential steps required for the neurogenesis of mesencephalic dopaminergic (mesDA) neurons. In this context, the regulatory network involving Otx functional interactions with signaling molecules and transcription factors required to promote or prevent the development of mesDA neurons will be analyzed in detail., (Copyright © 2011 Wiley Periodicals, Inc.)

Mesencephalic and diencephalic dopaminergic (mdDA) progenitors generate two major groups of neurons corresponding to the A9 neurons of the substantia nigra pars compacta (SNpc) and the A10 neurons of the ventral tegmental area (VTA). MdDA neurons control motor, sensorimotor and motivated behaviour and their degeneration or abnormal functioning is associated to Parkinson's disease and psychiatric disorders. Although relevant advances have been made, the molecular basis controlling identity, survival and vulnerability to neurodegeneration of SNpc and VTA neurons remains poorly understood. Here, we will review recent findings on the role exerted by the transcription factor Otx2 in adult mdDA neurons. Otx2 expression is restricted to a relevant fraction of VTA neurons and absent in the SNpc. In particular, Otx2 is prevalently excluded from neurons of the dorsal-lateral VTA, which expressed Girk2 and high level of the dopamine transporter (Dat). Loss and gain of function mouse models revealed that Otx2 controls neuron subtype identity by antagonizing molecular and functional features of the dorsal-lateral VTA such as Girk2 and Dat expression as well as vulnerability to the parkinsonian MPTP toxin. Furthermore, when ectopically expressed in the SNpc, Otx2 suppresses Dat expression and confers efficient neuroprotection to MPTP toxicity by suppressing efficient DA uptake.

The balanced proliferation and cell cycle exit of neural progenitors, by generating the appropriate amount of postmitotic progeny at the correct time and in the proper location, is required for the establishment of the highly ordered structure of the adult brain. Little is known about the extrinsic signals regulating these processes, particularly in the midbrain. Fibroblast growth factor (Fgf) 15, the mouse ortholog of FGF19 and member of an atypical Fgf subfamily, is prominently expressed in the dorsolateral midbrain of the midgestational mouse embryo. In the absence of Fgf15, dorsal midbrain neural progenitors fail to exit the cell cycle and to generate the proper amount of postmitotic neurons. We show here that this is due to the altered expression of inhibitory/neurogenic and proneural/neuronal differentiation helix-loop-helix transcription factor (TF) genes. The expression of Id1, Id3, and Hes5 was strongly increased and ectopically expanded, whereas the expression of Ascl1 (Mash1), Neurog1 (Ngn1) and Neurog2 (Ngn2) was strongly decreased and transcription of Neurod1 (NeuroD) was completely abolished in the dorsolateral midbrain of Fgf15(-/-) mice. These abnormalities were not caused by the mis-expression of cell cycle regulatory proteins such as cyclin-dependent kinase inhibitors or retinoblastoma proteins. Furthermore, human FGF19 promotes cell cycle exit of murine dorsal neural progenitors in vitro. Therefore, our data suggest that Fgf15 is a crucial signaling molecule regulating the postmitotic transition of dorsal neural progenitors and thus the initiation and proper progression of dorsal midbrain neurogenesis in the mouse, by controlling the expression of neurogenic and proneural TFs., (Copyright © 2010 Elsevier Inc. All rights reserved.)

Mesencephalic-diencephalic dopaminergic neurons control locomotor activity and emotion and are affected in neurodegenerative and psychiatric diseases. The homeoprotein Otx2 is restricted to ventral tegmental area (VTA) neurons that are prevalently complementary to those expressing Girk2 and glycosylated active form of the dopamine transporter (Dat). High levels of glycosylated Dat mark neurons with efficient dopamine uptake and pronounced vulnerability to Parkinsonian degeneration. We found that Otx2 controls neuron subtype identity by antagonizing molecular and functional features of dorsal-lateral VTA, such as Girk2 and Dat expression. Otx2 limited the number of VTA neurons with efficient dopamine uptake and conferred resistance to the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-HCl (MPTP) neurotoxin. Ectopic Otx2 expression also provided neurons of the substantia nigra with efficient neuroprotection to MPTP. These findings indicate that Otx2 is required to specify neuron subtype identity in VTA and may antagonize vulnerability to the Parkinsonian toxin MPTP.

The locus coeruleus (LC) which is the major noradrenergic nucleus in the brain develops under the influence of Bmps secreted by the roof plate and Fgf8 emitted from the mid-hindbrain organizer. We studied the development of the LC in different Bmp mouse mutants and report the absence of this nucleus in Bmp5(-/-);Bmp7(-/-) double knockouts. Notably, genes marking organizers and neuronal populations adjacent to the LC precursor field are unperturbed in Bmp5(-/-);Bmp7(-/-) animals. In addition, we found that in En1(+/Otx2) mutants in which the caudal Otx2 expression domain and thereby the mid-hindbrain organizer are shifted caudally, LC neurons are concomitantly reduced along with Bmp5/7. Complementing these results, Otx1(-/-);Otx2(+/-) mutants, in which the mid-hinbrain organizer is shifted rostrally, show a rostrally extended Bmp5 expression area and an increase in LC neurons. Taken together, our data indicate that LC development requires either Bmp5 or Bmp7, and one is able to compensate for the loss of the other. In addition, we conclude that the position of the mid-hindbrain organizer determines the size of the LC and propose that Bmp5/7 play an important role in mediating this organizer function., (Copyright 2010 Elsevier Inc. All rights reserved.)

Two adjacent groups of midbrain dopaminergic neurons, A9 (substantia nigra pars compacta) and A10 (ventral tegmental area), have distinct projections and exhibit differential vulnerability in Parkinson's disease. Little is known about transcription factors that influence midbrain dopaminergic subgroup phenotypes or their potential role in disease. Here, we demonstrate elevated expression of the transcription factor orthodenticle homeobox 2 in A10 dopaminergic neurons of embryonic and adult mouse, primate and human midbrain. Overexpression of orthodenticle homeobox 2 using lentivirus increased levels of known A10 elevated genes, including neuropilin 1, neuropilin 2, slit2 and adenylyl cyclase-activating peptide in both MN9D cells and ventral mesencephalic cultures, whereas knockdown of endogenous orthodenticle homeobox 2 levels via short hairpin RNA reduced expression of these genes in ventral mesencephalic cultures. Lack of orthodenticle homeobox 2 in the ventral mesencephalon of orthodenticle homeobox 2 conditional knockout mice caused a reduction of midbrain dopaminergic neurons and selective loss of A10 dopaminergic projections. Orthodenticle homeobox 2 overexpression protected dopaminergic neurons in ventral mesencephalic cultures from Parkinson's disease-relevant toxin, 1-methyl-4-phenylpyridinium, whereas downregulation of orthodenticle homeobox 2 using short hairpin RNA increased their susceptibility. These results show that orthodenticle homeobox 2 is important for establishing subgroup phenotypes of post-mitotic midbrain dopaminergic neurons and may alter neuronal vulnerability.

Neurons usually migrate and differentiate in one particular encephalic vesicle. We identified a murine population of diencephalic neurons that colonized the telencephalic amygdaloid complex, migrating along a tangential route that crosses a boundary between developing brain vesicles. The diencephalic transcription factor OTP was necessary for this migratory behavior.

Mesencephalic-diencephalic dopaminergic (mdDA) neurons control motor, sensorimotor and motivated behaviour and their degeneration or abnormal functioning is associated with important pathologies, such as Parkinsons disease and psychiatric disorders. Despite great efforts, the molecular basis and the genetic factors differentially controlling identity, survival and vulnerability to neurodegeneration of mdDA neurons of the substantia nigra (SN) and ventral tegmental area (VTA) are poorly understood. We have previously shown that the transcription factor Otx2 is required for identity, fate and proliferation of mesencephalic DA (mesDA) progenitors. By using mouse models and immunohistochemistry, we have investigated whether Otx2 is expressed also in post-mitotic mdDA neurons. Our data reveal that Otx2 is expressed in post-mitotic mesDA neurons during mid-late gestation and in the adult brain. Remarkably, Otx2 expression is sharply excluded from mdDA neurons of the SN and is restricted to a relevant fraction of VTA neurons. Otx2+-TH+ neurons are concentrated to the ventral part of the VTA. Combined expression with other regionalized VTA markers shows that Otx2+-TH+ neurons are prevalently Girk2- and Calb+ and among these, those located in the medial and ventralmost portion of the VTA are also Ahd2+. These findings indicate that Otx2 represents the first transcription factor with a proven role in mdDA neurogenesis whose expression discriminates between SN and a relevant proportion of VTA neurons. This supports the possibility that Otx2 may act as a post-mitotic selector controlling functional features (e.g. identity and/or survival) of a relevant fraction of VTA neurons in the adult.

The roles in brain development. Previous studies have shown the association between OTX2 and OTX1 with anaplastic and desmoplastic medulloblastomas, respectively. Here, we investigated OTX1 and OTX2 expression in Non-Hodgkin Lymphoma (NHL) and multiple myeloma. A combination of semiquantitative RT-PCR, Western blot, and immunohistochemical analyses was used to measure OTX1 and OTX2 levels in normal lymphoid tissues and in 184 tumor specimens representative of various forms of NHL and multiple myeloma. OTX1 expression was activated in 94% of diffuse large B-cell lymphomas, in all Burkitt lymphomas, and in 90% of high-grade follicular lymphomas. OTX1 was undetectable in precursor-B lymphoblastic lymphoma, chronic lymphocytic leukemia, and in most marginal zone and mantle cell lymphomas and multiple myeloma. OTX2 was undetectable in all analyzed malignancies. Analysis of OTX1 expression in normal lymphoid tissues identified a subset of resting germinal center (GC) B cells lacking PAX5 and BCL6 and expressing cytoplasmic IgG and syndecan. About 50% of OTX1(+) GC B cells co-expressed CD10 and CD20. This study identifies OTX1 as a molecular marker for high-grade GC-derived NHL and suggests an involvement of this transcription factor in B-cell lymphomagenesis. Furthermore, OTX1 expression in a subset of normal GC B cells carrying plasma cell markers suggests its possible contribution to terminal B-cell differentiation.

The vestibular portion of the inner ear, the three semicircular canals and their sensory cristae, is responsible for detecting angular head movements. It was proposed that sensory cristae induce formation of their non-sensory components, the semicircular canals. Here, we analyzed the inner ears of Foxg1(-/-) mouse mutants, which display vestibular defects that are in conflict with the above model. In Foxg1(-/-) ears, the lateral canal is present without the lateral ampulla, which houses the lateral crista. Our gene expression analyses indicate that at the time when canal specification is thought to occur, the prospective lateral crista is present, which could have induced lateral canal formation prior to its demise. Our genetic fate-mapping analyses indicate an improper separation between anterior and lateral cristae in Foxg1(-/-) mutants. Our data further suggest that a function of Foxg1 in the inner ear is to restrict sensory fate., (Copyright 2009 Wiley-Liss, Inc.)

Genetic and embryological experiments demonstrated that the visceral endoderm (VE) is essential for positioning the primitive streak at one pole of the embryo and head morphogenesis through antagonism of the Wnt and Nodal signaling pathways. The transcription factor Otx2 is required for VE anteriorization and specification of rostral neuroectoderm at least in part by controlling the expression of Dkk1 and Lefty1. Here, we investigated the relevance of the Otx2 transcriptional control in these processes. Otx2 protein is encoded by different mRNAs variants, which, on the basis of their transcription start site, may be distinguished in distal and proximal. Distal isoforms are prevalently expressed in the epiblast and neuroectoderm, while proximal isoforms prevalently in the VE. Selective inactivation of Otx2 variants reveals that distal isoforms are not required for gastrulation, but essential for maintenance of forebrain and midbrain identities; conversely, proximal isoforms control VE anteriorization and, indirectly, primitive streak positioning through the activation of Dkk1 and Lefty1. Moreover, in these mutants the expression of proximal isoforms is not affected by the lack of distal mRNAs and vice versa. Taken together these findings indicate that proximal and distal isoforms, whose expression is independently regulated in the VE and epiblast-derived neuroectoderm, functionally cooperate to provide these tissues with the sufficient level of Otx2 necessary to promote a normal development. Furthermore, we discovered that in the VE the expression of Otx2 isoforms is tightly controlled at single cell level, and we hypothesize that this molecular diversity may potentially confer specific functional properties to different subsets of VE cells.

Little is known about the cues controlling the generation of motoneuron populations in the mammalian ventral midbrain. We show that Otx2 provides the crucial anterior-posterior positional information for the generation of red nucleus neurons in the murine midbrain. Moreover, the homeodomain transcription factor Nkx6-1 controls the proper development of the red nucleus and of the oculomotor and trochlear nucleus neurons. Nkx6-1 is expressed in ventral midbrain progenitors and acts as a fate determinant of the Brn3a(+) (also known as Pou4f1) red nucleus neurons. These progenitors are partially dorsalized in the absence of Nkx6-1, and a fraction of their postmitotic offspring adopts an alternative cell fate, as revealed by the activation of Dbx1 and Otx2 in these cells. Nkx6-1 is also expressed in postmitotic Isl1(+) oculomotor and trochlear neurons. Similar to hindbrain visceral (branchio-) motoneurons, Nkx6-1 controls the proper migration and axon outgrowth of these neurons by regulating the expression of at least three axon guidance/neuronal migration molecules. Based on these findings, we provide additional evidence that the developmental mechanism of the oculomotor and trochlear neurons exhibits more similarity with that of special visceral motoneurons than with that controlling the generation of somatic motoneurons located in the murine caudal hindbrain and spinal cord.

The mesencephalic dopaminergic (mesDA) neurons play a relevant role in the control of movement, behaviour and cognition. Indeed loss and/or abnormal development of mesDA neurons is responsible for Parkinson's disease as well as for addictive and psychiatric disorders. A wealth of information has been provided on gene functions involved in the molecular mechanism controlling identity, fate and survival of mesDA neurons. Collectively, these studies are contributing to a growing knowledge of the genetic networks required for proper mesDA development, thus disclosing new perspectives for therapeutic approaches of mesDA disorders. Here we will focus on the control exerted by Otx genes in early decisions regulating the differentiation of progenitors located in the ventral midbrain. In this context, the regulatory network involving Otx functional interactions with signalling molecules and transcription factors required to promote or prevent the development of mesDA neurons will be analyzed in detail.

Meso-diencephalic dopaminergic (mdDA) neurons control voluntary movement, cognition and the reward response, and their degeneration is associated with Parkinson's disease (PD). Prospective cell transplantation therapies for PD require full knowledge of the developmental pathways that control mdDA neurogenesis. We have previously shown that Otx2 is required for the establishment of the mesencephalic field and molecular code of the entire ventral mesencephalon (VM). Here, we investigate whether Otx2 is a specific determinant of mesencephalic dopaminergic (mesDA) neurogenesis by studying mouse mutants that conditionally overexpress or lack Otx2. Our data show that Otx2 overexpression in the VM causes a dose-dependent and selective increase in both mesDA progenitors and neurons, which correlates with a remarkable and specific enhancement in the proliferating activity of mesDA progenitors. Consistently, lack of Otx2 in the VM specifically affects the proliferation of Sox2+ mesDA progenitors and causes their premature post-mitotic transition. Analysis of the developmental pathway that controls the differentiation of mesDA neurons shows that, in the absence of Otx2, the expression of Lmx1a and Msx1, and the proneural genes Ngn2 and Mash1 is not activated in Sox2+ mesDA progenitors, which largely fail to differentiate into Nurr1+ mesDA precursors. Furthermore, proliferation and differentiation abnormalities exhibit increasing severity along the anterior-posterior (AP) axis of the VM. These findings demonstrate that Otx2, through an AP graded effect, is intrinsically required to control proliferation and differentiation of mesDA progenitors. Thus, our data provide new insights into the mechanism of mesDA neuron specification and suggest Otx2 as a potential target for cell replacement-based therapeutic approaches in PD.

The homeobox-containing transcription factor Otx2 is crucially involved in fate determination of midbrain neurons. Mutant mice, in which Otx2 was conditionally inactivated by a Cre recombinase expressed under the transcriptional control of the Engrailed1 (En1) gene (En1(cre/+); Otx2(flox/flox)), show a reduced number of dopaminergic neurons and an increased number of serotonergic neurons in the ventral midbrain. Despite these developmental anatomical alterations, En1(cre/+); Otx2(flox/flox) adult mice display normal motor function. Here, we further investigated the neurological consequences of Otx2 inactivation in adult En1(cre/+); Otx2(flox/flox) mice. Adult En1(cre/+); Otx2(flox/flox) mice showed increased serotonin (5-HT) levels in the pons, ventral midbrain, hippocampus (CA3 subfield), and cerebral cortex, as indicated by HPLC and immunohistochemistry. Conversely, SERT (5-HT transporter) levels were decreased in conditional mutant brains. As a consequence of this increased 5-HT hyperinnervation, En1(cre/+); Otx2(flox/flox) mice were resistant to generalized seizures induced by the glutamate agonist kainic acid (KA). Indeed, prolonged pretreatment of En1(cre/+); Otx2(flox/flox) mice with the 5-HT synthesis inhibitor para-chlorophenylalanine (pCPA) restored brain 5-HT content to control levels, fully reestablishing KA seizure susceptibility. Accordingly, c-fos mRNA induction after KA was restricted to the hippocampus in En1(cre/+); Otx2(flox/flox) mice, whereas a widespread c-fos mRNA labeling was observed throughout the brain of En1(cre/+); Otx2(flox/flox) mice pretreated with pCPA. These results clearly show that increased brain 5-HT levels are responsible for seizure resistance in En1(cre/+); Otx2(flox/flox) mice and confirm the important role of 5-HT in the control of seizure spread.

Neurons that produce dopamine as a neurotransmitter constitute a heterogeneous group involved in the control of various behaviors and physiology. In mammals, dopaminergic neurons are found in distinct clusters mainly located in the ventral midbrain and the caudal forebrain [1]. Although much is known about midbrain dopaminergic neurons, development of diencephalic dopaminergic neurons is poorly understood. Here we demonstrate that Orthopedia (Otp) homeodomain protein is essential for the development of specific subsets of diencephalic dopaminergic neurons. Zebrafish embryos lacking Otp activity are devoid of dopaminergic neurons in the hypothalamus and the posterior tuberculum. Similarly, Otp-/- mouse [2, 3] embryos lack diencephalic dopaminergic neurons of the A11 group, which constitutes the diencephalospinal dopaminergic system. In both systems, Otp is expressed in the affected dopaminergic neurons as well as in potential precursor populations, and it might contribute to dopaminergic cell specification and differentiation. In fish, overexpression of Otp can induce ectopic tyrosine hydroxylase and dopamine transporter expression, indicating that Otp can specify aspects of dopaminergic identity. Thus, Otp is one of the few known transcription factors that can determine aspects of the dopaminergic phenotype and the first known factor to control the development of the diencephalospinal dopaminergic system.

One of the earliest organizational decisions in the development of the vertebrate brain is the division of the neural plate into Otx2-positive anterior and Gbx2-positive posterior territories. At the junction of these two expression domains, a local signaling center is formed, known as the midbrain-hindbrain boundary (MHB). This tissue coordinates or "organizes" the development of neighboring brain structures, such as the midbrain and cerebellum. Correct positioning of the MHB is thought to depend on mutual repression involving these two homeobox genes. Using a cell culture colocalization assay and coimmunoprecipitation experiments, we show that engrailed homology region 1 (eh1)-like motifs of both transcription factors physically interact with the WD40 domain of Groucho/Tle corepressor proteins. In addition, heat shock-induced expression of wild-type and mutant Otx2 and Gbx2 in medaka embryos demonstrates that Groucho is required for the repression of Otx2 by Gbx2. On the other hand, the repressive functions of Otx2 on Gbx2 do not appear to be dependent on corepressor interaction. Interestingly, the association of Groucho with Otx2 is also required for the repression of Fgf8 in the MHB. Therefore Groucho/Tle family members appear to regulate key aspects in the MHB development of the vertebrate brain.

GABAergic and glutamatergic neurons modulate inhibitory and excitatory networks in the CNS, and their impairment may cause neurological and psychiatric disorders. Thus, understanding the molecular mechanisms that control neurotransmitter phenotype and identity of excitatory and inhibitory progenitors has considerable relevance. Here we investigated the consequence of Otx2 (orthodenticle homolog) ablation in glutamatergic progenitors of the dorsal thalamus (referred to as thalamus). We report that Otx2 is cell-autonomously required in these progenitors to repress GABAergic differentiation. Our data indicate that Otx2 may prevent GABAergic fate switch by repressing the basic helix-loop-helix gene Mash1 (mammalian achaete-schute homolog) in progenitors expressing Ngn2 (neurogenin homolog). The lack of Otx2 also resulted in the activation of Pax3 (paired box gene), Pax7, and Lim1 (Lin-11/Isl-1/Mec-3), three genes normally coexpressed with Mash1 and GABAergic markers in the pretectum, thus suggesting that thalamic progenitors lacking Otx2 exhibit marker similarities with those of the pretectum. Furthermore, Otx2 ablation gave rise to a marked increase in proliferating activity of thalamic progenitors and the formation of hyperplastic cell masses. Thus, this study provides evidence for a novel and crucial role of Otx2 in the molecular mechanism by which identity and fate of glutamatergic precursors are established in the thalamus. Our data also support the concept that proper assignment of identity and fate of neuronal precursors occurs through the suppression of alternative differentiation programs.

Although the secreted molecule Fgf8 is a key player of the isthmic organiser function, the mechanisms by which it acts remain unclear. Here, we present evidence indicating that Fgf8 is not instructive in establishing zebrafish cerebellar cell identities, although it is required for proliferation and morphogenesis of this territory. We first show that, as in mouse, lack of Otx function in zebrafish leads to transformation of the presumptive mesencephalon into an extended rhombomere 1 (r1). Expanded Fgf8 expression was proposed to be the cause of this fate transformation. However, this report demonstrates that zebrafish embryos lacking both Otx and fgf8 functions retain an extended r1 and display differentiation of at least two cerebellar cell fates. We show that this is not caused by presence of other Fgfs, which implies that in absence of Otx, Fgf function is not necessary for the differentiation of cerebellar cell types. Otx proteins are therefore potent repressors of cerebellar fates, kept out of r1 progeny by Fgf8. Because Otx transcripts are not present in presumptive r1 territory prior to fgf8 expression, Fgf8 is required to maintain, rather than induce, the posterior boundary of Otx expression. This maintenance is enough to allow cerebellar differentiation.

The specification of neuronal cell types in the developing neural tube is orchestrated by signaling centers. However, how patterned territories of the central nervous system (CNS) are organized into structures with appropriate size and shape is still unclear. We report that in the absence of the mouse transcription factor mBtd/Sp8, a posterior shift of the isthmic organizer (IsO) occurs, suggesting a crucial role for Sp8 in this process. In addition, large patches of cells ectopically expressing Fgf8, Otx2 and/or Wnt1 in the rostral hindbrain are detected in Sp8 mutant embryos. In this context, midbrain dopaminergic neurons are found posterior to the IsO. Furthermore, we provide evidence that cell proliferation in the mid- and hindbrain is tightly controlled by Sp8 activity. Our observations are consistent with a role for Sp8 in restricting Fgf8 expression at the IsO.

Here, we have investigated the neurological consequences of restricted inactivation of Otx2 in adult En1(cre/+); Otx2(flox/flox) mice. In agreement with the crucial role of Otx2 in midbrain patterning, the mutants had a substantial reduction in tyrosine hydroxylase containing neurons. Although the reduction in the number of DAergic neurons was comparable between the SNc and the VTA, we found an unexpected selectivity in the deinnervation of the terminal fields affecting preferentially the ventral striatum and the olfactory tubercle. Interestingly, the mutants showed no abnormalities in exploratory activity or motor coordination. However, the absence of normal DA tone generated significant alterations in DA D1-receptor signalling as indicated by increased mutant striatal levels of phosphorylated DARPP-32 and by an altered motor response to amphetamine. Therefore, we suggest that the En1(cre/+); Otx2(flox/flox) mutant mouse model represents a genetic tool for investigating molecular and behavioural consequences of developmental neuronal dysfunction in the DAergic system.

Midbrain neurons synthesizing the neurotransmitter dopamine play a central role in the modulation of different brain functions and are associated with major neurological and psychiatric disorders. Despite the importance of these cells, the molecular mechanisms controlling their development are still poorly understood. The secreted glycoprotein Wnt1 is expressed in close vicinity to developing midbrain dopaminergic neurons. Here, we show that Wnt1 regulates the genetic network, including Otx2 and Nkx2-2, that is required for the establishment of the midbrain dopaminergic progenitor domain during embryonic development. In addition, Wnt1 is required for the terminal differentiation of midbrain dopaminergic neurons at later stages of embryogenesis. These results identify Wnt1 as a key molecule in the development of midbrain dopaminergic neurons in vivo. They also suggest the Wnt1-controlled signaling pathway as a promising target for new therapeutic strategies in the treatment of Parkinson's disease.

Only until a decade ago, animal phylogeny was traditionally based on the assumption that evolution of bilaterians went from simple to complex through gradual steps in which the extant species would represent grades of intermediate complexity that reflect the organizational levels of their ancestors. The advent of more sophisticated molecular biology techniques combined to an increasing variety of functional experiments has provided new tools, which lead us to consider evolutionary studies under a brand new light. An ancestral versus derived low-complexity of a given organism has now to be carefully re-assessed and also the molecular data so far accumulated needs to be re-evaluated. Conserved gene families expressed in the nervous system of all the species have been extensively used to reconstruct evolutionary steps, which may lead to identify the morphological as well as molecular features of the last common ancestor of bilaterians (Urbilateria). The Otx gene family is among these and will be here reviewed.

The transcription factor Otx2 is required to determine mesencephalic versus metencephalic (cerebellum/pons) territory during embryogenesis. This function of Otx2 primarily involves positioning and maintaining the mid-hindbrain organizer at the border between midbrain and anterior hindbrain. Otx2 expression is maintained long after this organizer is established. We therefore generated conditional mutants of Otx2 using the Cre/loxP system to study later roles during rostral brain development. For inactivation of Otx2 in neuronal progenitor cells, we crossed Otx2(flox/flox) animals with Nestin-Cre transgenic animals. In Nestin-Cre/+; Otx2(flox/flox) embryos, Otx2 activity was lost from the ventral midbrain starting at embryonic day 10.5 (E10.5). In these mutant embryos, the mid-hindbrain organizer was properly positioned at E12.5, although Otx2 is absent from the midbrain. Hence, the Nestin-Cre/+; Otx2(flox/flox) animals represent a novel mouse model for studying the role of Otx2 in the midbrain, independently of abnormal development of the mid-hindbrain organizer. Our data demonstrate that Otx2 controls the development of several neuronal populations in the midbrain by regulating progenitor identity and neurogenesis. Dorsal midbrain progenitors ectopically expressed Math1 and generate an ectopic cerebellar-like structure. Similarly, Nkx2.2 ectopic expression ventrally into tegmentum progenitors is responsible for the formation of serotonergic neurons and hypoplasia of the red nucleus in the midbrain. In addition, we discovered a novel role for Otx2 in regulating neurogenesis of dopaminergic neurons. Altogether, these results demonstrate that Otx2 is required from E10.5 onward to regulate neuronal subtype identity and neurogenesis in the midbrain.

The mesencephalic dopaminergic (mesDA) system controls movement and emotional behaviour, and its degeneration causes Parkinson's disease and other psychiatric disorders. Recent findings are leading to better understanding of the genetic control of generation and functioning of the mesDA system. This advancement could disclose new perspectives for therapeutic approaches of mesDA-related disorders.