Epithelial-mesenchymal transition-like phenotypic changes of retinal pigment epithelium induced by TGF-ß are prevented by PPAR-γ agonists.

PURPOSE: Proliferative eye diseases, such as proliferative vitreoretinopathy and proliferative diabetic retinopathy, are caused partly by fibrotic change of retinal pigment epithelial cells (RPECs). The purpose of our study was to examine the effect of the peroxisome proliferator-activated receptor-γ (PPAR-γ) agonist on the fibrotic change of primate RPECs. METHODS: Monkey RPECs (MRPECs) isolated from a cynomolgus monkey eye were subcultured. To induce fibrotic change, MRPECs were cultured with TGF-ß2 (3 ng/mL), and also cultured in the coexistence of TGF-ß2 and the PPAR-γ agonist pioglitazone (30 µM). The phenotype of the cultured MRPECs was evaluated by phase contrast microscopy and immunocytochemical analysis. The phosphorylation of Smad2/Smad3 proteins was examined by Western blot analysis. RESULTS: Primary MRPECs were cultured as a monolayer with a hexagonal cell shape, and positive expression of ZO-1, Na(+)/K(+)-ATPase, and RPE65 was confirmed. Cell morphology and the expression of these markers were maintained in the presence of pioglitazone, whereas the cells were elongated and the expression of these markers was reduced in its absence. Conversely, the expression of phalloidin, α-smooth muscle actin, and fibronectin was reduced in the presence of pioglitazone, whereas it was increased in the absence. Western blot assay demonstrated that phosphorylation of Smad2/Smad3 proteins was suppressed by pioglitazone. CONCLUSIONS: The PPAR-γ agonist pioglitazone inhibited the fibrotic change of primary MRPECs through the suppression of TGF-ß signaling. Pioglitazone might prove to be a clinically applicable and effective pharmaceutic treatment for proliferative eye diseases.

Ontogeny-recapitulating generation and tissue integration of ES cell-derived Purkinje cells.

Purkinje cells are the sole output neurons of the cerebellar cortex and their dysfunction causes severe ataxia. We found that Purkinje cells could be robustly generated from mouse embryonic stem (ES) cells by recapitulating the self-inductive signaling microenvironments of the isthmic organizer. The cell-surface marker Neph3 enabled us to carry out timed prospective selection of Purkinje cell progenitors, which generated morphologically characteristic neurons with highly arborized dendrites that expressed mature Purkinje cell-specific markers such as the glutamate receptor subunit GluRδ2. Similar to mature Purkinje cells, these neurons also showed characteristic spontaneous and repeated action potentials and their postsynaptic excitatory potentials were generated exclusively through nonNMDA glutamate receptors. Fetal transplantation of precursors isolated by fluorescence-activated cell sorting showed orthotopic integration of the grafted neurons into the Purkinje cell layer with their axons extending to the deep cerebellar nuclei and dendrites receiving climbing and parallel fibers. This selective preparation of bona fide Purkinje cells should aid future investigation of this important neuron.

Lmx1a and Lmx1b cooperate with Foxa2 to coordinate the specification of dopaminergic neurons and control of floor plate cell differentiation in the developing mesencephalon.

Mesencephalic dopaminergic (mesDA) neurons control movement and behavior, and their loss causes severe neurological disorders, such as Parkinson's disease. Recent studies have revealed that mesDA neurons originate from mesencephalic floor plate (FP) cells, which had been thought of as non-neurogenic organizer cells regulating regional patterning and axonal projections. Otx2 and its FP-specific downstream factor Lmx1a have been shown to be sufficient to confer neurogenic activity on FP cells and determine a mesDA fate. However, the mechanism underlying how these factors control mesDA development and how FP cells and mesDA neurons are coordinately specified are still largely unknown. In the present study, we obtained evidence that Lmx1a and Lmx1b cooperate with Foxa2 to specify mesDA neuron identity by gain-of-function approaches using transgenic mice. Lmx1a/b appeared to select a mesDA fate by suppressing red nucleus fate in the context of Foxa2-positive progenitors, at least in part, through repressing the Sim1-Lhx1 and Ngn1 pathways that inhibit proper mesDA differentiation. We also found that, in the mesencephalon, FP cell fate is primarily determined by Foxa2 with a supportive action of Lmx1a/b through repressing Nkx6.1, which inhibits FP cell differentiation. Thus, FP and mesDA identities are determined by distinct specification pathways, both of which are controlled by the same combination of transcription factors, Lmx1a/b and Foxa2, and, as a consequence, mesDA neurons are generated from mesencephalic FP cells.

Purkinje cells originate from cerebellar ventricular zone progenitors positive for Neph3 and E-cadherin.

GABAergic Purkinje cells (PCs) provide the primary output from the cerebellar cortex, which controls movement and posture. Although the mechanisms of PC differentiation have been well studied, the precise origin and initial specification mechanism of PCs remain to be clarified. Here, we identified a cerebellar and spinal cord GABAergic progenitor-selective cell surface marker, Neph3, which is a direct downstream target gene of Ptf1a, an essential regulator of GABAergic neuron development. Using FACS, Neph3(+) GABAergic progenitors were sorted from the embryonic cerebellum, and the cell fate of this population was mapped by culturing in vitro. We found that most of the Neph3(+) populations sorted from the mouse E12.5 cerebellum were fated to differentiate into PCs while the remaining small fraction of Neph3(+) cells were progenitors for Pax2(+) interneurons, which are likely to be deep cerebellar nuclei GABAergic neurons. These results were confirmed by short-term in vivo lineage-tracing experiments using transgenic mice expressing Neph3 promoter-driven GFP. In addition, we identified E-cadherin as a marker selectively expressed by a dorsally localized subset of cerebellar Neph3(+) cells. Sorting experiments revealed that the Neph3(+) E-cadherin(high) population in the embryonic cerebellum defined PC progenitors while progenitors for Pax2(+) interneurons were enriched in the Neph3(+) E-cadherin(low) population. Taken together, our results identify two spatially demarcated subregions that generate distinct cerebellar GABAergic subtypes and reveal the origin of PCs in the ventricular zone of the cerebellar primordium.

Identification of a novel transcriptional corepressor, Corl2, as a cerebellar Purkinje cell-selective marker.

The developmental origin of cerebellar Purkinje cells (PCs) has not been precisely mapped and the genetic program of the specification of this neuronal subtype is largely unknown. Here, we report the isolation of a novel mouse gene encoding a transcriptional corepressor, Corl2, and its expression pattern. Corl2 expression was restricted to the central nervous system in both adult and embryonic stages. In situ hybridization and immunohistochemistry using a polyclonal antibody against Corl2 revealed that Corl2 is selectively expressed at high levels in the developing cerebellum, ventral metencephalon and myelencephalon at E12.5. In these brain regions, neural progenitors did not express Corl2 during the proliferative state but started to express it shortly after exit from the cell cycle. In the cerebellum, Corl2 was specifically expressed in PCs at the adult stage, and consistently, most Corl2(+) cells expressed PC markers, such as RORalpha and calbindin, at the late embryonic stage. At E12.5, when PCs are emerging, GABAergic neurons generated from the dorsal part of the Ptf1a(+) progenitor domain selectively expressed Corl2. Importantly, Corl2(+) cells in the cerebellum did not express the GABAergic interneuron marker Pax2 at any of the developmental stages. Collectively, these results strongly suggest that Corl2 is a specific marker for PCs in the cerebellum from their emergence until the adult stage. Furthermore, this marker was useful for unmasking the precise origin of PCs and delineating the domain map within the ventricular zone that generates cerebellar GABAergic neurons.

Differences in neurogenic potential in floor plate cells along an anteroposterior location: midbrain dopaminergic neurons originate from mesencephalic floor plate cells.

Directed differentiation and purification of mesencephalic dopaminergic (mesDA) neurons from stem cells are crucial issues for realizing safe and efficient cell transplantation therapies for Parkinson's disease. Although recent studies have identified the factors that regulate mesDA neuron development, the mechanisms underlying mesDA neuron specification are not fully understood. Recently, it has been suggested that mesencephalic floor plate (FP) cells acquire neural progenitor characteristics to generate mesDA neurons. Here, we directly examined this in a fate mapping experiment using fluorescence-activated cell sorting (FACS) with an FP cell-specific surface marker, and demonstrate that mesencephalic FP cells have neurogenic activity and generate mesDA neurons in vitro. By contrast, sorted caudal FP cells have no neurogenic potential, as previously thought. Analysis of dreher mutant mice carrying a mutation in the Lmx1a locus and transgenic mice ectopically expressing Otx2 in caudal FP cells demonstrated that Otx2 determines anterior identity that confers neurogenic activity to FP cells and specifies a mesDA fate, at least in part through the induction of Lmx1a. We further show that FACS can isolate mesDA progenitors, a suitable transplantation material, from embryonic stem cell-derived neural cells. Our data provide insights into the mechanisms of specification and generation of mesDA neurons, and illustrate a useful cell replacement approach for Parkinson's disease.

Migrating postmitotic neural precursor cells in the ventricular zone extend apical processes and form adherens junctions near the ventricle in the developing spinal cord.

Postmitotic neural precursors are generated in the ventricular zone (VZ) of the developing neural tube and immediately migrate to the mantle layer (ML) where they differentiate into mature neurons. Although the regulation of neuronal differentiation and migration has extensively been studied, the behavior of the early postmitotic precursors migrating toward the ML is largely unknown. In this study, we have identified Neph3 as a specific marker for early postmitotic neural precursors in the VZ of the developing spinal cord. Analysis of Neph3 localization by immunofluorescence and immunoelectron microscopy revealed that early neural precursors in the VZ possessed not only pia-connected processes but also ones that reached the ventricle. This apical extension of processes was confirmed by analyzing another early postmitotic marker, Dll1 mRNA, which was actively transported toward the ventricle and accumulated at the termini of the processes. Furthermore, adherens junctions (AJs) were formed around the apical end of processes extending from Neph3- and Dll1 mRNA-positive postmitotic precursors. Taken together, these observations suggest that migrating early postmitotic neural precursors in the VZ of the developing spinal cord form a neuroepithelial cell-like bipolar morphology and communicate with their neighboring cells through AJs.

MAGI1 recruits Dll1 to cadherin-based adherens junctions and stabilizes it on the cell surface.

Delta-Notch signaling plays an essential role in cell fate determination in many tissue types, including the central nervous system. Although the signaling mechanism of Notch has been extensively studied, the behaviors of its ligands are not well understood. In the present study, we found that, in the developing neural tube, Dll1(Delta-like 1) was mainly localized on the processes extending from nascent neurons toward both the pia and the ventricle and accumulated at apical termini, where adherens junctions (AJs) were formed. To understand the mechanism of Dll1 localization, we searched for binding proteins for Dll1 and identified a scaffolding molecule, MAGI1. In the developing spinal cord, MAGI1 mRNA was highly expressed in the ventricular zone, where Dll1 mRNA was expressed. MAGI1 protein accumulated at the AJs formed around the termini of apically extending processes and was partially colocalized with Dll1. MAGI1 bound not only to Dll1 but also to N-cadherin-beta-catenin complexes. In cultured AJ-forming fibroblasts, MAGI1 was localized at AJs, and Dll1 was recruited to these AJs through binding to MAGI1. In addition, Dll1 was stabilized on the cell surface by MAGI1. Taken together, these results suggest that Dll1 is presented on the surface of AJs formed at the apical termini of processes through interaction with MAGI1 to activate Notch on neighboring cells in the developing central nervous system.

Corl1, a novel neuronal lineage-specific transcriptional corepressor for the homeodomain transcription factor Lbx1.

During development, neuronal identity is determined by a combination of numerous transcription factors. However, the mechanisms of synergistic action of these factors in transcriptional regulation and subsequent cell fate specification are largely unknown. In this study, we identified a novel gene, Corl1, encoding a nuclear protein with homology to the Ski oncoprotein. Corl1 was highly selectively expressed in the central nervous system (CNS). In the embryonic CNS, Corl1 was expressed in a certain subset of postmitotic neurons generated posterior to the midbrain-hindbrain border. In the developing spinal cord, Corl1 was selectively expressed in the dorsal horn interneurons where a homeodomain transcription factor, Lbx1, is required for proper specification. Corl1 was localized in a nuclear dot-like structure and interacted with general transcriptional corepressors. In addition, Corl1 showed transcriptional repression activity in the GAL4-fusion system, indicating its involvement in the regulation of transcriptional repression. Furthermore, Corl1 interacted with Lbx1 and cooperatively repressed transcription, suggesting that it acts as a transcriptional corepressor for Lbx1 in regulating cell fate determination in the dorsal spinal cord. Corl1 corepressor activity did not depend on Gro/TLE activity, and Gro/TLE also functioned as a corepressor for Lbx1. Thus, Lbx1 can select two independent partners, Corl1 and Gro/TLE, as corepressors. Identification of a novel transcriptional corepressor with neuronal subtype-restricted expression might provide insights into the mechanisms of cell fate determination in neurons.

Helt, a novel basic-helix-loop-helix transcriptional repressor expressed in the developing central nervous system.

Neuronal differentiation is regulated by many basic-helix-loop-helix (bHLH) family transcriptional activators and repressors, and the balance of activity between these factors is important for the differentiation process. Here, we report the identification of a novel transcriptional repressor, designated Helt. Helt encoded a Hey-related bHLH protein containing the bHLH and Orange domains. Helt could homodimerize, and heterodimerize with Hes5 or Hey2. Both the bHLH and Orange domains were involved in the homodimerization. In contrast, only the bHLH domain was required for the heterodimerization with Hey2, whereas only the Orange domain mediated the interaction between Helt and Hes5. Thus, Helt has two dimerization domains, and these domains independently select a partner. Identification of preferred recognition sequences by CASTing experiments revealed that Helt bound to the E box, which was distinct from the Hes1 optimal sequence around the E box core. Not only the core sequence but also sequences flanking the E box were essential for the recognition by Helt and Hes1. Furthermore, Helt repressed transcription from an artificial promoter through binding to the optimal E box elements, as well as transcription from its own promoter. Using in situ hybridization and immunohistochemistry, Helt expression in embryos was investigated. Helt was mainly expressed in undifferentiated neural progenitors in some of the developing brain regions, including the mesencephalon and diencephalon, at the neurogenesis stage. These results suggest that Helt acts as a transcriptional repressor to regulate neuronal differentiation and/or identity.