OTX2 Research Articles

CBIO-14. EXPLORING THE OTX2 REGULATORY NETWORK: TARGETING THE “GROW AND GO” ARMS OF THE MOST AGGRESSIVE MEDULLOBLASTOMAS

Medulloblastoma (MB) is a highly heterogeneous primary malignant pediatric brain cancer. Despite improved 5-year survival rates, MB is frequently accompanied by metastatic dissemination and poor long-term prognosis. The most aggressive tumors are refractory to conventional chemotherapy and radiation. Our goal is to identify new signaling pathways that regulate the treatment-resistant MB cellular phenotypes, namely the stem cells and metastatic or highly motile cells. To this end, we have discovered that the OTX2 gene, which is amplified or overexpressed in the majority of aggressive MBs, is a central regulator of both stem cell function or self-renewal and cell migration in these tumors. However, the molecular mechanisms by which OTX2 regulates these functions are still unknown. Here, we employed complementary bioinformatics approaches to characterize the OTX2 regulatory network and have discovered a novel relationship between OTX2 and neurodevelopmental genes associated with axon guidance signaling in Group 3 and Group 4 MB stem/progenitor cells. Following OTX2 knockdown, transcripts associated with semaphorin, netrin, ephrin and slit signaling were mostly upregulated. ChIP-sequencing identified putative OTX2 DNA binding sites and revealed statistically significant associations between OTX2 and these axon guidance pathway genes, with the presence of 1 or more OTX2 binding peaks within the transcription start site. Further, Group 3 and 4 MB patient samples were evaluated for correlations between expression of axon guidance pathway genes, OTX2 and survival. Semaphorin signaling was the most overrepresented pathway across all datasets with expression of all pathway genes being upregulated following OTX2 KD. Moreover, one semaphorin gene was identified as a novel prognostic biomarker. We anticipate that delineation of the OTX2 network will identify molecular regulators of both self-renewal and motility, and that these genes will serve as better targets for development of novel therapeutics to effectively eradicate both the “grow and go” arms of the most aggressive MB.

Accuracy analysis of identifying molecular subtypes of children and adolescents with medulloblastoma using real-time fluorescence quantitative PCR

Objective To investigate the reliability of diagnosing the molecular subtypes of children and adolescents with medulloblastoma (MB) using real-time fluorescence quantitative PCR (RT-qPCR). Methods Thirty patients with MB diagnosed by pathology and admitted to the Department of Neurosurgery, Beijing Tiantan Hospital, Capital Medical University from January 2011 to December 2015 were enrolled retrospectively. RT-qPCR was used to detect the frozen samples of MB. Eleven subgroup-specific protein-coding genes (OTX2, FOXG1B, MYC, DKK1, WIF1, DKK2, MYCN, SFRP1, HHIP, OTX1, and NPR3) were selected. Unsupervised hierarchical cluster analysis and prediction analysis of microarray were conducted according to the differences of gene expression levels, and the heat map and gravity map were drawn. The result of subgroup was validated by immunohistochemical method and expression profile. One-way ANOVA was used analyze the differences of the marker gene expression value among the molecular subtypes. The differences of the clinical factor distribution of the molecular subtypes were analyzed. Results Thirty patients with MB were divided into 4 molecular subtypes by using RT-qPCR, including SHH subtype (n=17), WNT subtype (n=4), Group 3 subytype (n=4), and Group 4 subtype (n=5). The results of grouping, immunohistochemical staining and unsupervised clustering analysis were completely consistent. There were significant differences in 11 subgroup-specific protein-coding genes expression among the subgroups (P<0.01 or P<0.05). Among them, SFRP1, MYCN, NPR3, and MYC were the key genes for distinguishing subtypes. There were significant differences in the sex distribution (male: female, 4.7 ∶1.0 and 1 ∶3 respectively) and age at diagnosis (≤3 year: 3-16, 1.0 ∶4.7 and 3 ∶1 respectively) between the SHH subtype and the WNT subtype (all P=0.022). Conclusion RT-qPCR may accurately identify the 4 molecular subtypes in children and adolescents with MB. Key words: Medulloblastoma; Molecular subtype; Child; Adolescent; Polymerase chain reaction; Immunochemistry

Activated monocytes resist elimination by retinal pigment epithelium and downregulate their OTX2 expression via TNF-α.

SummaryOrthodenticle homeobox 2 (OTX2) controls essential, homeostatic retinal pigment epithelial (RPE) genes in the adult. Using cocultures of human CD14+ blood monocytes (Mos) and primary porcine RPE cells and a fully humanized system using human‐induced pluripotent stem cell‐derived RPE cells, we show that activated Mos markedly inhibit RPE OTX2 expression and resist elimination in contact with the immunosuppressive RPE. Mechanistically, we demonstrate that TNF‐α, secreted from activated Mos, mediates the downregulation of OTX2 and essential RPE genes of the visual cycle among others. Our data show how subretinal, chronic inflammation and in particular TNF‐α can affect RPE function, which might contribute to the visual dysfunctions in diseases such as age‐related macular degeneration (AMD) where subretinal macrophages are observed. Our findings provide important mechanistic insights into the regulation of OTX2 under inflammatory conditions. Therapeutic restoration of OTX2 expression might help revive RPE and visual function in retinal diseases such as AMD.

Retinal Pigment Epithelium Responses to Selective Retina Therapy in Mouse Eyes.

To investigate the characteristics of retinal pigment epithelium (RPE) and retinal damage induced by selective retina therapy (SRT) in mice, and to elucidate longitudinal changes in RPE cells. C57BL/6J mice received SRT and continuous-wave laser photocoagulation (cwPC). The cell death pattern was evaluated using TUNEL assay, and proliferative potential of the RPE cells was evaluated using 5-ethynyl-2'-dexoyuridine (EdU) assay. To investigate the cell-cell integrity of RPE cells, β-catenin staining was performed. The number and hexagonality of RPE cells in the SRT-treated area were estimated using a Voronoi diagram with time periods of 3 hours to 14 days. Antibodies to microphthalmia-associated transcription factor (MiTF) and orthodenticle homeobox 2 (Otx2) were used to confirm the specific characteristics of RPE cells in the SRT-treated area. The number of TUNEL-positive cells located in the neural retina was significantly lower in lesions treated with SRT compared to those treated with cwPC. EdU-positive RPE cells were first detected 3 to 12 hours after SRT, and increased until 3 to 7 days after SRT. β-catenin staining showed that hexagonality was compromised and subsequently, RPE cells expanded in size within the targeted location. The number of RPE cells in SRT lesions decreased gradually until 12 hours after SRT and recovered by 14 days. Upregulated expression of MiTF and Otx2 was observed for 2 weeks in the SRT lesions. Selective retina therapy seems to induce selective RPE damage without collateral thermal injury in the neural retina. Furthermore, SRT-treated lesions recovered by proliferation of RPE cells that were present in the treated lesions and by expansion of adjacent RPE cells.

Abstract B12: March E3 ubiquitin ligase is required for head formation by mediating Dishevelled degradation during Xenopus development

Abstract Wnt signaling controls numerous biological events including vertebrate development, adult tissue homeostasis and organogenesis. In addition, dysregulation of Wnt itself or its downstream signaling components causes human birth defects and cancer. Dishevelled (Dvl) is a crucial scaffolding protein that exerts activation of Wnt signaling pathway. Recently, several Dvl-interacting proteins have been suggested to mediate the stability of Dvl. However, the molecular mechanisms by which Dvl undergoes degradation remain to be elucidated. Here we identify March, a RING domain-containing ubiquitin ligase, targeting Dvl protein and show that it regulates canonical Wnt signaling in Xenopus. During Xenopus embryogenesis, March transcripts were ubiquitously expressed. We intriguingly found that March depletion by microinjection of morpholino oligonucleotide caused defects in the anterior head formation, including loss of the forebrain, cement gland and eye structures. We also found that these defective phenotypes were caused by the Wnt antagonistic function of March in the head organizer region. Knockdown of March suppressed expression of head organizer genes Gsc, Chd and Otx2 at the dorsal marginal region of the gastrula embryo. Wnt reporter assay, western blot analysis measuring phosphorylation of LRP6 and activation of β-catenin, RT-PCR and axis duplication assay in Xenopus revealed that March inhibits canonical Wnt signaling pathway. Furthermore, we identified that March protein associates with Dvl and mediates its poly-ubiquitination for lysosomal degradation in Xenopus embryos. Taken together, these results suggest that March retains cytosolic pools of Dvl protein and leads subsequent limitation of Wnt signaling for vertebrate head development. Citation Format: Hyeyoon Lee, Seong-Moon Cheong, Jin-Kwan Han. March E3 ubiquitin ligase is required for head formation by mediating Dishevelled degradation during Xenopus development. [abstract]. In: Proceedings of the AACR Special Conference: Developmental Biology and Cancer; Nov 30-Dec 3, 2015; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(4_Suppl):Abstract nr B12.

Identification of an Alternative Splicing Product of the Otx2 Gene Expressed in the Neural Retina and Retinal Pigmented Epithelial Cells.

To investigate the complexity of alternative splicing in the retina, we sequenced and analyzed a total of 115,706 clones from normalized cDNA libraries from mouse neural retina (66,217) and rat retinal pigmented epithelium (49,489). Based upon clustering the cDNAs and mapping them with their respective genomes, the estimated numbers of genes were 9,134 for the mouse neural retina and 12,050 for the rat retinal pigmented epithelium libraries. This unique collection of retinal of messenger RNAs is maintained and accessible through a web-base server to the whole community of retinal biologists for further functional characterization. The analysis revealed 3,248 and 3,202 alternative splice events for mouse neural retina and rat retinal pigmented epithelium, respectively. We focused on transcription factors involved in vision. Among the six candidates suitable for functional analysis, we selected Otx2S, a novel variant of the Otx2 gene with a deletion within the homeodomain sequence. Otx2S is expressed in both the neural retina and retinal pigmented epithelium, and encodes a protein that is targeted to the nucleus. OTX2S exerts transdominant activity on the tyrosinase promoter when tested in the physiological environment of primary RPE cells. By overexpressing OTX2S in primary RPE cells using an adeno associated viral vector, we identified 10 genes whose expression is positively regulated by OTX2S. We find that OTX2S is able to bind to the chromatin at the promoter of the retinal dehydrogenase 10 (RDH10) gene.

In-depth characterization of the salivary adenoid cystic carcinoma transcriptome with emphasis on dominant cell type.

Adenoid cystic carcinoma (ACC), 1 of the most common salivary gland malignancies, arises from the intercalated ducts, which are composed of inner ductal epithelial cells and outer myoepithelial cells. The objective of this study was to determine the genomic subtypes of ACC with emphasis on dominant cell type to identify potential specific biomarkers for each subtype and to improve the understanding of this disease. A whole-genome expression study was performed based on 42 primary salivary ACCs and 5 normal salivary glands. RNA from these specimens was subjected to expression profiling with RNA sequencing, and results were analyzed to identify transcripts in epithelial-dominant ACC (E-ACC), myoepithelial-dominant ACC (M-ACC), and all ACC that were expressed differentially compared with the transcripts in normal salivary tissue. In total, the authors identified 430 differentially expressed transcripts that were unique to E-ACC, 392 that were unique to M-ACC, and 424 that were common to both M-ACC and E-ACC. The sets of E-ACC-specific and M-ACC-specific transcripts were sufficiently large to define and differentiate E-ACC from M-ACC. Ingenuity pathway analysis identified known cancer-related genes for 60% of the E-ACC transcripts, 69% of the M-ACC transcripts, and 68% of the transcripts that were common in both E-ACC and M-ACC. Three sets of highly expressed candidate genes-distal-less homeobox 6 (DLX6) for E-ACC; protein keratin 16 (KRT16), SRY box 11 (SOX11), and v-myb avian myeloblastosis viral oncogene homolog (MYB) for M-ACC; and engrailed 1 (EN1) and statherin (STATH), which are common to both E-ACC and M-ACC)-were further validated at the protein level. The current results enabled the authors to identify novel potential therapeutic targets and biomarkers in E-ACC and M-ACC individually, with the implication that EN1, DLX6, and OTX1 (orthodenticle homeobox 1) are potential drivers of these cancers. Cancer 2016;122:1513-22. © 2016 American Cancer Society.

Global transcriptional expression in ovarian follicles from Tsaiya ducks (Anas platyrhynchos) with a high-fertilization rate

Novel candidates for biomarkers of a high-fertilization rate were identified here through global transcriptional profiling of ovarian follicles. Some other differentially expressed candidate genes were first noted to influence animal reproduction in our previous cDNA microarray analysis and are now recognized as markers for marker-assisted selection. In the present study, we compared gene expression in ovarian follicles from animals with high- and low-fertilization rates using an oligonucleotide array. On the basis of a fold change of greater than 1.2 and less than −1.2, a difference of >100 Affymetrix arbitrary units between the two groups, and a P value of less than 0.05, 47 genes were found to be associated with fertilization rate. GOEAST and MetaCore software were further used to identify the functional categories of genes that were differentially expressed. Then, we focused on three interesting genes associated with a high-fertilization rate: one of these genes was discovered to participate in signaling pathways of fertilization, and two genes take roles in lipid metabolism. An oligonucleotide array showed that the levels of orthodenticle homeobox 2 (OTX2) and lecithin:cholesterol acyltransferase (LCAT) gene expression were 1.62-fold and 1.95-fold higher in the high-fertilization rate group than in the low-fertilization rate group, respectively (P < 0.05). The level of apolipoprotein A-I (APOA1) gene expression was also higher in the high-fertilization rate group, with a difference of 2.31-fold (P < 0.05). The data were validated through quantitative polymerase chain reaction analysis. These results confirm the usefulness of the array technique and data mining methods in the discovery of new biomarkers and add knowledge to our understanding of the factors affecting fertilization rates in ovarian follicles.

OTX1 Contributes to Hepatocellular Carcinoma Progression by Regulation of ERK/MAPK Pathway.

Orthodenticlehomeobox 1 (OTX1) overexpression had previously been associated with the progression of several tumors. The present study aimed to determine the expression and role of OTX1 in human hepatocellular carcinoma (HCC). The expression level of OTX1 was examined by quantitative real-time PCR (qRT-PCR) in 10 samples of HCC and paired adjacent non-cancerous tissues, and by immunohistochemistry (IHC) analysis in 128 HCC samples and matched controls. The relationship between OTX1 expression and the clinicopathological features werealso analyzed. Furthermore, the effects of OTX1 knockdown on cell proliferation and migration were determined in HCC cell lines. Axenograft mouse model was also established to investigate the role of OTX1 in HCC tumor growth. TheqRT-PCR and IHC analyses revealed that OTX1 was significantly elevated in HCC tissues compared with the paired non-cancerous controls. Expression of OTX1 was positively correlated with nodal metastasis status (P = 0.009) and TNM staging (P = 0.001) in HCC tissues. In addition, knockdown of OTX1 by shRNA significantly inhibited the proliferation and migration, and induced cell cycle arrest in S phase in vitro. Tumor growth was markedly inhibited by OTX1 silencing in the xenograft. Moreover, OTX1 silencing was causable for the decreased phosphorylation level of ERK/MAPK signaling. In conclusion, OTX1 contributes to HCC progression possibly by regulation of ERK/MAPK pathway. OTX1 may be a novel target for molecular therapy towards HCC.

GENETIC DISORDERS OF PITUITARY DEVELOPMENT IN PATIENTS WITH SHEEHAN'S SYNDROME.

Genetic disorders associated with the development of the pituitary gland and cranial bones may cause a genetic tendency toward Sheehan's syndrome (SS). Our aim in this study was to investigate expression disorders in the genes responsible for the development of the pituitary gland and cranial bones in patients with SS. Forty-four patients who were previously diagnosed with SS and 43 healthy women were compared in terms of the mean expression values of genes including the prophet of PIT-1 (PROP1), HESX homeobox 1 (HESX1), POU class 1 homeobox 1 (POU1F1), LIM homeobox 3 (LHX3), LHX4, glioma-associated oncogene homolog 2 (GLI2), orthodenticle homeobox 2 (OTX2), SIX homeobox 3 (SIX3), SIX6, T-box transcription factor 19 (TBX19), transducin-like enhancer protein 1 (TLE1), TLE3, distal-less homeobox 2 (DLX2), DLX5, MSH homeobox 2 (MSX2), and paired box 3 (PAX3). The mean expression values of the HESX1, TLE1, TLE3, and MSX2 genes were significantly different in the SS group from the healthy control group, while the mean expression values of the remaining genes were similar. The present study concludes that abnormal expressions of HESX1, TLE1, TLE3, and MSX2 genes may cause a genetic predisposition to the development of SS.

Wnt/β-Catenin Signaling Mediates Regeneration of Retinal Pigment Epithelium After Laser Photocoagulation in Mouse Eye

Laser photocoagulation of retinal pigment epithelium (RPE) is used to stimulate the regenerative processes of the RPE. However, the molecular mechanisms that control RPE proliferation and the epithelial-mesenchymal transition (EMT) during regeneration remain poorly understood. We investigated the role of Wnt/β-catenin signaling in the regeneration of mouse RPE after laser photocoagulation. C57BL/6J mice were photocoagulated unilaterally. To determine the β-catenin-dependent Wnt signal transduction in the photocoagulated RPE, the expression levels of Wnts, β-catenin, and their target genes were analyzed using real time-PCR and Western blotting. Retinal pigment epithelium proliferation and EMT were determined by 5-ethynyl-2'-deoxyuridine (EdU) incorporation assay and by profiling expression of EMT markers, respectively, in eyes injected intravitreally with a Wnt/β-catenin signaling antagonist, Dkk-1, after laser photocoagulation. Expression of several of the 19 Wnt genes was significantly increased in laser-treated RPE. The expression levels of β-catenin signaling target genes cyclin D1, Otx2, and Mitf were higher in laser-treated RPE than in control RPE. The number of EdU-positive cells in the laser-treated area was significantly lower in the Dkk-1-injected group than in the laser-treated group or laser-treated + vehicle-injected group. There were more Otx2- and Mitf-positive cells after laser photocoagulation and markedly fewer in the Dkk-1-injected group. Otx2- and Mitf-positive cells were colocalized with EdU-positive cells. The EMT markers vimentin and α-smooth muscle actin (α-SMA) were upregulated in the laser-treated area and significantly downregulated in the Dkk-1-injected group. Laser photocoagulation activates a Wnt/β-catenin signal transduction pathway, promoting both RPE proliferation and EMT. Wnt/β-catenin signaling also upregulates the expression of Otx2 and Mitf, key transcription factors in RPE formation. Our results demonstrate an important role for Wnt/β-catenin signaling in RPE proliferation and EMT, and suggest that manipulating Wnt/β-catenin signaling may have therapeutic potential for RPE regeneration.

Investigation of Melanogenic Factors Gene Expression in Human Adult and Neonate Retinal Pigment Epithelium Cell Cultures

Retinal pigment epithelium is responsible for maintaining the structural integrity of the retina by an efficient defense against free radicals, photo-oxidative exposure and light energy. For this purpose the main RPE line of defense is melanosomes. Melanin content of retinal pigment epithelium cells in adults and neonates reveals remarkable variations. In the current study we compared melanogenic factors gene expression levels in human adult and neonate RPE cells in culture. RPE cells from adult and neonate human eye globes were isolated and then cultured in DMEM: F12 (1:1) containing 10% FBS. Expression of RPE65 and Cytokeratin 8/18 markers in isolated cells was confirmed by immunocytochemistry. To evaluate the responsible factors in the pathway of melanin biosynthesis, gene expression of orthodenticle homeobox 2, microphthalmia-associated transcription factor A and H as prominent transcription factors, tyrosinase and dopachrome tautomerase as effective enzymes in the melanin biosynthetic pathway were examined in human neonate derived RPE cells compared to human adult derived RPE cells in culture. According to the Real-Time RT-PCR data, gene expression of MITF-H, OTX2, TYR and DCT in RPE cells of the neonates showed a significant increase compared to the adults. With increasing passage number, gene expression of MITF-H, OTX2, TYR and DCT showed remarkable decline. According to the role of OTX2 and MITF-H as the main transcription factor effectors on the TYR and DCT, restoration of OTX2 and MITF-H gene expression may be retain melanin content in RPE cells.

Mitochondrial Protection by Exogenous Otx2 in Mouse Retinal Neurons

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.

Aberrant expression of homeobox gene SIX1 in Hodgkin lymphoma.

In Hodgkin lymphoma (HL) we recently identified deregulated expression of homeobox genes MSX1 and OTX2 which are physiologically involved in development of the embryonal neural plate border region. Here, we examined in HL homeobox gene SIX1 an additional regulator of this embryonal region mediating differentiation of placodal precursors. SIX1 was aberrantly activated in 12 % of HL patient samples in silico, indicating a pathological role in a subset of this B-cell malignancy. In addition, SIX1 expression was detected in HL cell lines which were used as models to reveal upstream factors and target genes of this basic developmental regulator. We detected increased copy numbers of the SIX1 locus at chromosome 14q23 correlating with enhanced expression while chromosomal translocations were absent. Moreover, comparative expression profiling data and pertinent gene modulation experiments indicated that the WNT-signalling pathway and transcription factor MEF2C regulate SIX1 expression. Genes encoding the transcription factors GATA2, GATA3, MSX1 and SPIB - all basic lymphoid regulators - were identified as targets of SIX1 in HL. In addition, cofactors EYA1 and TLE4, respectively, contrastingly mediated activation and suppression of SIX1 target gene expression. Thus, the protein domain interfaces may represent therapeutic targets in SIX1-positive HL subsets. Collectively, our data reveal a gene regulatory network with SIX1 centrally deregulating lymphoid differentiation and support concordance of lymphopoiesis/lymphomagenesis and developmental processes in the neural plate border region.

Aberrantly Expressed OTX Homeobox Genes Deregulate B-Cell Differentiation in Hodgkin Lymphoma.

In Hodgkin lymphoma (HL) we recently reported that deregulated homeobox gene MSX1 mediates repression of the B-cell specific transcription factor ZHX2. In this study we investigated regulation of MSX1 in this B-cell malignancy. Accordingly, we analyzed expression and function of OTX homeobox genes which activate MSX1 transcription during embryonal development in the neural plate border region. Our data demonstrate that OTX1 and OTX2 are aberrantly expressed in both HL patients and cell lines. Moreover, both OTX loci are targeted by genomic gains in overexpressing cell lines. Comparative expression profiling and subsequent pathway modulations in HL cell lines indicated that aberrantly enhanced FGF2-signalling activates the expression of OTX2. Downstream analyses of OTX2 demonstrated transcriptional activation of genes encoding transcription factors MSX1, FOXC1 and ZHX1. Interestingly, examination of the physiological expression profile of ZHX1 in normal hematopoietic cells revealed elevated levels in T-cells and reduced expression in B-cells, indicating a discriminatory role in lymphopoiesis. Furthermore, two OTX-negative HL cell lines overexpressed ZHX1 in correlation with genomic amplification of its locus at chromosomal band 8q24, supporting the oncogenic potential of this gene in HL. Taken together, our data demonstrate that deregulated homeobox genes MSX1 and OTX2 respectively impact transcriptional inhibition of (B-cell specific) ZHX2 and activation of (T-cell specific) ZHX1. Thus, we show how reactivation of a specific embryonal gene regulatory network promotes disturbed B-cell differentiation in HL.

OTX2 is a therapeutic target for retinoblastoma and may function as a common factor between C-MYC, CRX, and phosphorylated RB pathways.

The homeobox transcription factor orthodenticle homeobox 2 (OTX2) plays a critical role in very early neurogenesis, but can become oncogenic when aberrantly expressed later in life. We previously discovered its novel oncogenic role in the malignant childhood brain tumor medulloblastoma and hypothesize an oncogenic role in retinoblastoma. Primary retinoblastoma tumors and cell lines were analyzed by quantitative-PCR, immunoblotting and immunohistochemistry for OTX2. The effect of modulating OTX2 expression on tumorigenesis was tested pharmacologically and by siRNA. A lentiviral shRNA-engineered vector was used for conditional knockdown studies on tumor growth in vivo. A luciferase reporter assay was used to analyze ATRA's effect on OTX2's promoter. In this study on retinoblastoma, OTX2 was frequently amplified and/or overexpressed in primary tumors and cell lines. Knockdown of OTX2 expression by siRNA or pharmacologic inhibition by all-trans retinoic acid (ATRA) repressed OTX2 expression and cell proliferation and significantly decreased tumor growth in vivo. Loss of OTX2 expression also resulted in decreased expression of C-MYC and CRX, genes previously implicated in retinoblastoma tumorigenesis. Loss of OTX2 expression increased the phosphorylation of RB, a potential mechanism of modulating cell proliferation. Aberrant expression of OTX2 may contribute to the development of retinoblastoma. OTX2 may serve as a common transcription factor that interlinks multiple tumor-driving pathways. These results also show that OTX2 can be genetically and pharmacologically targeted, providing an exciting new therapeutic option that may be less toxic and more efficacious than current treatments.

CRISPR/Cas9-based generation of knockdown mice by intronic insertion of artificial microRNA using longer single-stranded DNA

Knockdown mouse models, where gene dosages can be modulated, provide valuable insights into gene function. Typically, such models are generated by embryonic stem (ES) cell-based targeted insertion, or pronuclear injection, of the knockdown expression cassette. However, these methods are associated with laborious and time-consuming steps, such as the generation of large constructs with elements needed for expression of a functional RNAi-cassette, ES-cell handling, or screening for mice with the desired knockdown effect. Here, we demonstrate that reliable knockdown models can be generated by targeted insertion of artificial microRNA (amiRNA) sequences into a specific locus in the genome [such as intronic regions of endogenous eukaryotic translation elongation factor 2 (eEF-2) gene] using the Clustered Regularly Interspaced Short Palindromic Repeats/Crispr associated 9 (CRISPR/Cas9) system. We used in vitro synthesized single-stranded DNAs (about 0.5-kb long) that code for amiRNA sequences as repair templates in CRISPR/Cas9 mutagenesis. Using this approach we demonstrate that amiRNA cassettes against exogenous (eGFP) or endogenous [orthodenticle homeobox 2 (Otx2)] genes can be efficiently targeted to a predetermined locus in the genome and result in knockdown of gene expression. We also provide a strategy to establish conditional knockdown models with this method.

PM-01 * NEURAL DERIVATIVES FROM HUMAN EMBRYONIC STEM CELLS: A CELLULAR SYSTEM TO STUDY THE ROLE OF Otx2 IN MEDULLOBLASTOMA PROGRESSION

Medulloblastoma (MB) is the most common malignant primary pediatric brain tumor and is currently divided into 4 subtypes based on different genomic alterations, gene expression profiles and response to treatment: Wnt, Sonic Hedgehog (Shh), Group 3 and Group 4. This extensive heterogeneity has made it difficult to assess the functional relevance of genes to malignant progression. For example, expression of the transcription factor, Orthodenticle homeobox2 (Otx2) is frequently dysregulated in multiple MB variants; however, its role may be subtype-specific. We recently demonstrated that neural precursors derived from transformed human embryonic stem cells (trans-hENs), but not their normal counterparts (hENs), resemble Groups 3 and 4 MB in vitro and in vivo. These trans-hENs have >12-fold overexpression of Otx2. Here, we tested the utility of this model system as a means of dissecting the role of Otx2 in MB using gain and loss of function studies in hENs and trans-hENs respectively. Parallel experiments with MB cells revealed that Otx2 exerts tumor suppressive effects in hEN and Shh MB cells, likely by regulating self-renewal and decreasing expression of pluripotent genes such as Sox2, Lin28A, Oct4 and Nanog. Concomitant to the negative regulation of hESC genes, we observed a decrease in levels of the active histone mark, H3K4me3 at promoter loci of pluripotent genes as well as an increase in Otx2 recruitment at the Sox2 promoter by chromatin immunoprecipitation assays. This was supported by overexpression of Sox2 in Otx2+ Shh MB and hENs that resulted in significant rescue of self-renewal and cell migration. In contrast, Otx2 is oncogenic and promotes self-renewal of trans-hENs and Groups 3/4 MB independent of pluripotent genes. These results demonstrate a cell context-dependent function of Otx2. Our study underscores the value of hESC derivatives as developmental models of MB and for investigating key biological questions related to embryonal childhood cancers.

Demonstration of the preoral coelom in the brachiopod Lingula anatina with consideration of its phylogenetic significance

The origin of the Bilateria and reconstruction of the last common bilaterian ancestor (LCA) are fundamental problems in zoology, including the question whether the LCA was a coelomic creature or not? Insight into the nature of the LCA might be obtained by investigating the coelomic system of poorly studied bilaterians. The Brachiopoda is a relict group of marine invertebrates whose anatomy has been seldom studied with modern methods. For most brachiopods, the coelomic system has been described as bipartite, i.e., as consisting of two parts: the lophophore coelom and trunk coelom. In the present report, a tripartite coelomic system is described for the first time in adult brachiopods, the linguliform Lingula anatina. In addition to a lophophoral and trunk coelom, L. anatina has a preoral coelom. The protocoel is located at the base of the epistome and has its own lining, which consists of non-muscular monociliated epithelial cells connected by desmosomes and tight junctions. Among brachiopods there are two types of the coelom: bipartite and tripartite. The same is known in phoronids and bryozoans (=ectoprocts). These three phyla – brachiopoda, phoronida, and bryozoa – are traditionally united into clade called lophophorata. An analysis of coelomic system organization revealed that the trimeric coelom is plesiomorphic for the lophophorates. The trimeric coelom is typical for the most of deuterostomes. The presence of the trimeric coelom in two main lineages of the bilateria allows to suggest that the LCA may have had a tripartite coelom and strongly specialized two the most anterior parts of the body – the prosome and the mesosome. This suggestion is consistent with published gene expression studies, in which Hox genes are never expressed in the two first segments of the body, whereas Otx genes are expressed in the most anterior segments of some bilaterians.

DNase I hypersensitivity analysis of the mouse brain and retina identifies region-specific regulatory elements.

BackgroundThe brain, spinal cord, and neural retina comprise the central nervous system (CNS) of vertebrates. Understanding the regulatory mechanisms that underlie the enormous cell-type diversity of the CNS is a significant challenge. Whole-genome mapping of DNase I-hypersensitive sites (DHSs) has been used to identify cis-regulatory elements in many tissues. We have applied this approach to the mouse CNS, including developing and mature neural retina, whole brain, and two well-characterized brain regions, the cerebellum and the cerebral cortex.ResultsFor the various regions and developmental stages of the CNS that we analyzed, there were approximately the same number of DHSs; however, there were many DHSs unique to each CNS region and developmental stage. Many of the DHSs are likely to mark enhancers that are specific to the specific CNS region and developmental stage. We validated the DNase I mapping approach for identification of CNS enhancers using the existing VISTA Browser database and with in vivo and in vitro electroporation of the retina. Analysis of transcription factor consensus sites within the DHSs shows distinct region-specific profiles of transcriptional regulators particular to each region. Clustering developmentally dynamic DHSs in the retina revealed enrichment of developmental stage-specific transcriptional regulators. Additionally, we found reporter gene activity in the retina driven from several previously uncharacterized regulatory elements surrounding the neurodevelopmental gene Otx2. Identification of DHSs shared between mouse and human showed region-specific differences in the evolution of cis-regulatory elements.ConclusionsOverall, our results demonstrate the potential of genome-wide DNase I mapping to cis-regulatory questions regarding the regional diversity within the CNS. These data represent an extensive catalogue of potential cis-regulatory elements within the CNS that display region and temporal specificity, as well as a set of DHSs common to CNS tissues. Further examination of evolutionary conservation of DHSs between CNS regions and different species may reveal important cis-regulatory elements in the evolution of the mammalian CNS.Electronic supplementary materialThe online version of this article (doi:10.1186/1756-8935-8-8) contains supplementary material, which is available to authorized users.