Odd-skipped related 2 splicing variants show opposite transcriptional activity

Downregulation of Odd-Skipped Related 2, a Novel Regulator of Epithelial-Mesenchymal Transition, Enables Efficient Somatic Cell Reprogramming

Somatic cell reprogramming proceeds through a series of events to generate induced pluripotent stem cells (iPSCs). The early stage of reprogramming of mouse embryonic fibroblasts (MEFs) is characterized by rapid cell proliferation and morphological changes, which are accompanied by downregulation of mesenchyme-associated genes. However, the functional relevance of their downregulation to reprogramming remains poorly defined. In this study, we have screened transcriptional regulators that are downregulated immediately upon reprogramming, presumably through direct targeting by reprogramming factors. To test if these transcriptional regulators impact reprogramming when expressed continuously, we generated an expression vector that harbors human cytomegalovirus upstream open reading frame 2 (uORF2), which reduces translation to minimize the detrimental effect of an expressed protein. Screening of transcriptional regulators with this expression vector revealed that downregulation of odd-skipped related 2 (Osr2) is crucial for efficient reprogramming. Using a cell-based model for epithelial-mesenchymal transition (EMT), we show that Osr2 is a novel EMT regulator that acts through induction of TGF-β signaling. During reprogramming, Osr2 downregulation not only diminishes TGF-β signaling but also allows activation of Wnt signaling, thus promoting mesenchymal-epithelial transition (MET) toward acquisition of pluripotency. Our results illuminate the functional significance of Osr2 downregulation in erasing the mesenchymal phenotype at an early stage of somatic cell reprogramming.

Identification of Long Non-Coding RNAs Related to Skeletal Muscle Development in Two Rabbit Breeds with Different Growth Rate

Skeletal muscle development plays an important role in muscle quality and yield, which decides the economic value of livestock. Long non-coding RNAs (lncRNAs) have been reported to be associated with skeletal muscle development. However, little is revealed about the function of lncRNAs in rabbits' muscle development. LncRNAs and mRNAs in two rabbit breeds (ZIKA rabbits (ZKR) and Qixin rabbits (QXR)) with different growth rates at three developmental stages (0 day, 35 days, and 84 days after birth) were researched by transcriptome sequencing. Differentially expressed lncRNAs and mRNAs were identified for two rabbit breeds at the same stages by DESeq package. Co-expression correlation analysis of differentially expressed lncRNAs and mRNAs were performed to construct lncRNA⁻mRNA pairs. To explore the function of lncRNAs, Gene Ontology (GO) analysis of co-expression mRNAs in lncRNA⁻mRNA pairs were performed. In three comparisons, there were 128, 109, and 115 differentially expressed lncRNAs, respectively. LncRNAs TCONS_00013557 and XR_518424.2 differentially expressed in the two rabbit breeds might play important roles in skeletal muscle development, for their co-expressed mRNAs were significantly enriched in skeletal muscle development related GO terms. This study provides potentially functional lncRNAs in skeletal muscle development of two rabbit breeds and might be beneficial to the production of rabbits.

Functional Networks of Highest-Connected Splice Isoforms: From The Chromosome 17 Human Proteome Project

Alternative splicing allows a single gene to produce multiple transcript-level splice isoforms from which the translated proteins may show differences in their expression and function. Identifying the major functional or canonical isoform is important for understanding gene and protein functions. Identification and characterization of splice isoforms is a stated goal of the HUPO Human Proteome Project and of neXtProt. Multiple efforts have catalogued splice isoforms as "dominant", "principal", or "major" isoforms based on expression or evolutionary traits. In contrast, we recently proposed highest connected isoforms (HCIs) as a new class of canonical isoforms that have the strongest interactions in a functional network and revealed their significantly higher (differential) transcript-level expression compared to nonhighest connected isoforms (NCIs) regardless of tissues/cell lines in the mouse. HCIs and their expression behavior in the human remain unexplored. Here we identified HCIs for 6157 multi-isoform genes using a human isoform network that we constructed by integrating a large compendium of heterogeneous genomic data. We present examples for pairs of transcript isoforms of ABCC3, RBM34, ERBB2, and ANXA7. We found that functional networks of isoforms of the same gene can show large differences. Interestingly, differential expression between HCIs and NCIs was also observed in the human on an independent set of 940 RNA-seq samples across multiple tissues, including heart, kidney, and liver. Using proteomic data from normal human retina and placenta, we showed that HCIs are a promising indicator of expressed protein isoforms exemplified by NUDFB6 and M6PR. Furthermore, we found that a significant percentage (20%, p = 0.0003) of human and mouse HCIs are homologues, suggesting their conservation between species. Our identified HCIs expand the repertoire of canonical isoforms and are expected to facilitate studying main protein products, understanding gene regulation, and possibly evolution. The network is available through our web server as a rich resource for investigating isoform functional relationships (http://guanlab.ccmb.med.umich.edu/hisonet). All MS/MS data were available at ProteomeXchange Web site (http://www.proteomexchange.org) through their identifiers (retina: PXD001242, placenta: PXD000754).

The OSR1 rs12329305 polymorphism contributes to the development of congenital malformations in cases of stillborn/neonatal death

Background

Involvement of development-related gene polymorphisms in multifactorial/polygenic etiology of stillborn/neonatal deaths due to malformations has been insufficiently tested. Since these genes showed evolutional stability and their mutations are very rare, we can assume that their polymorphic variants may be a risk factor associated with the occurrence of developmental disorders of unknown etiology or can enhance the phenotypic variability of known genetic disorders.

Material/Methods

To determine the association of 3 polymorphisms involved in the regulation of the early embryonic development of different organs, we conducted an association study of their relation to the particular malformation. We selected 140 samples of archived paraffin tissue samples from deceased patients in which fetal/neonatal autopsy examination had shown congenital abnormalities as the most likely cause of death. The polymorphisms of OSR1 rs12329305, rs9936833 near FOXF1, and HOXA1 rs10951154 were genotyped using the TaqMan allelic discrimination assay.

Results

After Bonferroni correction for multiple testing, significant allelic association with stillborn/neonatal deaths was observed for rs12329305 (p=7×10⁻⁴). In addition, association analysis for the same polymorphism was shown in the subgroup with isolated anomalies (1.25×10⁻⁵), particularly in the subgroup of cases with kidney and heart anomalies (p=4.18×10⁻⁵, p=5.12×10⁻⁸, respectively).

Conclusions

The findings of the present study showed, for the first time, the role of the OSR1 rs12329305 polymorphism in the development of congenital malformations in cases of stillborn/neonatal death, particularly in those with congenital kidney and heart developmental defects.

Distinct splice variants and pathway enrichment in the cell-line models of aggressive human breast cancer subtypes

This study was conducted as a part of the Chromosome-Centric Human Proteome Project (C-HPP) of the Human Proteome Organization. The United States team of C-HPP is focused on characterizing the protein-coding genes in chromosome 17. Despite its small size, chromosome 17 is rich in protein-coding genes; it contains many cancer-associated genes, including BRCA1, ERBB2, (Her2/neu), and TP53. The goal of this study was to examine the splice variants expressed in three ERBB2 expressed breast cancer cell-line models of hormone-receptor-negative breast cancers by integrating RNA-Seq and proteomic mass spectrometry data. The cell lines represent distinct phenotypic variations subtype: SKBR3 (ERBB2+ (overexpression)/ER-/PR-; adenocarcinoma), SUM190 (ERBB2+ (overexpression)/ER-/PR-; inflammatory breast cancer), and SUM149 (ERBB2 (low expression) ER-/PR-; inflammatory breast cancer). We identified more than one splice variant for 1167 genes expressed in at least one of the three cancer cell lines. We found multiple variants of genes that are in the signaling pathways downstream of ERBB2 along with variants specific to one cancer cell line compared with the other two cancer cell lines and with normal mammary cells. The overall transcript profiles based on read counts indicated more similarities between SKBR3 and SUM190. The top-ranking Gene Ontology and BioCarta pathways for the cell-line specific variants pointed to distinct key mechanisms including: amino sugar metabolism, caspase activity, and endocytosis in SKBR3; different aspects of metabolism, especially of lipids in SUM190; cell-to-cell adhesion, integrin, and ERK1/ERK2 signaling; and translational control in SUM149. The analyses indicated an enrichment in the electron transport chain processes in the ERBB2 overexpressed cell line models and an association of nucleotide binding, RNA splicing, and translation processes with the IBC models, SUM190 and SUM149. Detailed experimental studies on the distinct variants identified from each of these three breast cancer cell line models that may open opportunities for drug target discovery and help unveil their specific roles in cancer progression and metastasis.

odd-skipped related 2 is required for fin chondrogenesis in zebrafish

BACKGROUND

odd-skipped related 2 (osr2) encodes a vertebrate ortholog of the Drosophila odd-skipped zinc-finger transcription factor. Osr2 in mouse is required for proper palate, eyelid, and bone development. Zebrafish knock-down experiments have also suggested a role for osr2, along with its paralog osr1, in early pectoral fin specification and pronephric development.

RESULTS

We show here that osr2 has a specific function later in development, independent of osr1, in the regulation of sox9a expression and promoting fin chondrogenesis. mRNA in situ hybridization demonstrated osr2 expression in the developing floorplate and later during organogenesis in the pronephros and gut epithelium. In the pectoral fin buds, osr2 was specifically expressed in fin mesenchyme. osr2 knock down in zebrafish embryos disrupted both three and five zinc finger alternatively spliced osr2 isoforms and eliminated wild-type osr2 mRNA. osr2 morphants exhibited normal pectoral fin bud specification but exhibited defective fin chondrogenesis, with loss of differentiated chondrocytes. Defects in chondrogenesis were paralleled by loss of sox9a as well as subsequent col2a1 expression, linking osr2 function to essential regulators of chondrogenesis.

CONCLUSIONS

The zebrafish odd-skipped related 2 gene regulates sox9a and col2a1 expression in chondrocyte development and is specifically required for zebrafish fin morphogenesis.

Expression pattern of zinc-finger transcription factor Odd-skipped related 2 in murine development and neonatal stage

The Odd-skipped gene, first identified as a Drosophila pair-rule zinc-finger transcription factor, plays an important role in Drosophila development. The mammalian homolog, Odd-skipped related 2 (Osr2), regulates limb, tooth, and kidney development in mouse embryos. However, the detailed expression pattern of Osr2 during neonatal development remains unclear. In this study, we investigated Osr2 expression patterns in mouse neonatal and embryo tissues using qPCR and in situ hybridization methods. First, we examined the tissue distribution of Osr2 by qPCR, and found it to be highly expressed in the uterus and moderately in the testes, small intestine, and prostate. That expression was also found in eye, kidney, placenta, lung, thymus, lymph node, stomach, and skeletal muscle tissues, and in all embryonic stages. On the other hand, Osr2 was not expressed in brain, heart, liver, or spleen samples. Next, we examined the tissue localization of Osr2 using in situ hybridization. Osr2 was found in the craniofacial region on E13.5, with notable expression in dental germ mesenchyme as well as the renal corpuscle on E17.5. As for neonatal tissues, Osr2 was expressed in the dental papilla, dental follicle, Harderian gland, nasal bone, eyelid dermis, synovial joint, and tibial subcutis. Our findings suggest that Osr2 functions in reproductive system organs, such as the uterus, testes, prostate, placenta, and ovaries. Furthermore, based on its expression in kidney, Harderian gland, eyelid dermis, and tibial subcutis tissues, this transcription factor may be involved in hormone synthesis and function. Together, our results demonstrate the role of Osr2 in postnatal development and embryogenesis.

Innovations in proteomic profiling of cancers: alternative splice variants as a new class of cancer biomarker candidates and bridging of proteomics with structural biology

Alternative splicing allows a single gene to generate multiple RNA transcripts which can be translated into functionally diverse protein isoforms. Current knowledge of splicing is derived mainly from RNA transcripts, with very little known about the expression level, 3D structures, and functional differences of the proteins. Splicing is a remarkable phenomenon of molecular and biological evolution. Studies which simply report up-regulation or down-regulation of protein or mRNA expression are confounded by the effects of mixtures of these isoforms. Besides understanding the net biological effects of the mixtures, we may be able to develop biomarker tests based on the observable differential expression of particular splice variants or combinations of splice variants in specific disease states. Here we review our work on differential expression of splice variant proteins in cancers and the feasibility of integrating proteomic analysis with structure-based conformational predictions of the differences between such isoforms.

Negative regulation of Odd-skipped related 2 by TGF-beta achieves the induction of cellular migration and the arrest of cell cycle

The transcription factor Odd-skipped related 2 (Osr2) functions in craniofacial and limb developments in mammals. We previously found that Osr2 gene expression is regulated by intracellular transcription factors such as Runx2, and C/EBP, whereas it remains unclear if extracellular factors would functionally regulate the Osr2 expression. In this study, we showed that TGF-β down-regulated the Osr2 expression, which is involved in regulation of cellular migration and cell cycle. Furthermore, the down-regulation was found to be mediated by Smad3/Smad4 and p38/ATF2 signaling molecules. The Osr2 promoter was shown to possess Smad3/4 binding element and ATF2 binding element between -647 and -64 of promoter. TGF-β induced cellular migration in C3H10T1/2 cells and arrested cell cycle at G1 phase in NMuMG-Fucci cells. In contrast, the Osr2 reduced the migration and also stimulated the cell-cycle progression. These results suggest that Osr2 is involved in TGF-β regulating cell migration and cell cycle via a Smad3-ATF2 transcriptional complex mediating pathway.

Functional implications of structural predictions for alternative splice proteins expressed in Her2/neu-induced breast cancers

Alternative splicing allows a single gene to generate multiple mRNA transcripts, which can be translated into functionally diverse proteins. However, experimentally determined structures of protein splice isoforms are rare, and homology modeling methods are poor at predicting atomic-level structural differences because of high sequence identity. Here we exploit the state-of-the-art structure prediction method I-TASSER to analyze the structural and functional consequences of alternative splicing of proteins differentially expressed in a breast cancer model. We first successfully benchmarked the I-TASSER pipeline for structure modeling of all seven pairs of protein splice isoforms, which are known to have experimentally solved structures. We then modeled three cancer-related variant pairs reported to have opposite functions. In each pair, we observed structural differences in regions where the presence or absence of a motif can directly influence the distinctive functions of the variants. Finally, we applied the method to five splice variants overexpressed in mouse Her2/neu mammary tumor: anxa6, calu, cdc42, ptbp1, and tax1bp3. Despite >75% sequence identity between the variants, structural differences were observed in biologically important regions of these protein pairs. These results demonstrate the feasibility of integrating proteomic analysis with structure-based conformational predictions of differentially expressed alternative splice variants in cancers and other conditions.

Osr2 acts downstream of Pax9 and interacts with both Msx1 and Pax9 to pattern the tooth developmental field

Mammalian tooth development depends on activation of odontogenic potential in the presumptive dental mesenchyme by the Msx1 and Pax9 transcription factors. We recently reported that the zinc finger transcription factor Osr2 was expressed in a lingual-to-buccal gradient pattern surrounding the developing mouse molar tooth germs and mice lacking Osr2 developed supernumerary teeth lingual to their molars. We report here generation of a gene-targeted mouse strain that allows conditional inactivation of Pax9 and subsequent activation of expression of Osr2 in the developing tooth mesenchyme from the Pax9 locus. Expression of Osr2 from one copy of the Pax9 gene did not disrupt normal tooth development but was sufficient to suppress supernumerary tooth formation in the Osr2(-/-) mutant mice. We found that endogenous Osr2 mRNA expression was significantly downregulated in the developing tooth mesenchyme in Pax9(del/del) mice. Mice lacking both Osr2 and Pax9 exhibited early tooth developmental arrest with significantly reduced Bmp4 and Msx1 mRNA expression in the developing tooth mesenchyme, similar to that in Pax9(del/del) mutants but in contrast to the rescue of tooth morphogenesis in Msx1(-/-)Osr2(-/-) double mutant mice. Furthermore, we found that Osr2 formed stable protein complexes with the Msx1 protein and interacted weakly with the Pax9 protein in co-transfected cells. These data indicate that Osr2 acts downstream of Pax9 and patterns the mesenchymal odontogenic field through protein-protein interactions with Msx1 and Pax9 during early tooth development.

The nephrogenic potential of the transcription factors osr1, osr2, hnf1b, lhx1 and pax8 assessed in Xenopus animal caps

BACKGROUND

The three distinct types of kidneys, pronephros, mesonephros and metanephros, develop consecutively in vertebrates. The earliest form of embryonic kidney, the pronephros, is derived from intermediate mesoderm and the first expressed genes localized in the pronephros anlage are the transcription factors osr1, osr2, hnf1b, lhx1 and pax8, here referred to as the early nephrogenic transcription factors. However, the pathway inducing nephrogenesis and the network of theses factors are poorly understood. Treatment of the undifferentiated animal pole explant (animal cap) of Xenopus with activin A and retinoic acid induces pronephros formation providing a powerful tool to analyze key molecular events in nephrogenesis.

RESULTS

We have investigated the expression kinetics of the early nephrogenic transcription factors in activin A and retinoic acid treated animal caps and their potential to induce pronephric differentiation. In treated animal caps, expression of osr1, osr2, hnf1b and lhx1 are induced early, whereas pax8 expression occurs later implying an indirect activation. Activin A alone is able to induce osr2 and lhx1 after three hours treatment in animal caps while retinoic acid fails to induce any of these nephrogenic transcription factors. The early expression of the five transcription factors and their interference with pronephros development when overexpressed in embryos suggest that these factors potentially induce nephrogenesis upon expression in animal caps. But no pronephros development is achieved by either overexpression of OSR1, by HNF1B injection with activin A treatment, or the combined application of LHX1 and PAX8, although they influenced the expression of several early nephrogenic transcription factors in some cases. In an additional approach we could show that HNF1B induces several genes important in nephrogenesis and regulates lhx1 expression by an HNF1 binding site in the lhx1 promoter.

CONCLUSIONS

The early nephrogenic transcription factors play an important role in nephrogenesis, but have no pronephros induction potential upon overexpression in animal caps. They activate transcriptional cascades that partially reflect the gene activation initiated by activin A and retinoic acid. Significantly, HNF1B activates the lhx1 promoter directly, thus extending the known activin A regulation of the lhx1 gene via an activin A responsive element.

Odd-skipped related 2 is epigenetically regulated in cellular quiescence

Cellular behavior and development are extensively altered during the transition from cell cycle into quiescence, though the mechanism involved in establishing and maintaining quiescence is largely unknown. We found that Odd-skipped related 2 (Osr2) was up-regulated during cellular quiescence by serum starvation as well as culturing to confluence. To investigate the regulatory mechanism of Osr2 under these conditions, we characterized the mouse Osr2 promoter. CpG islands in the flanking region of the transcription start site were predominantly methylated in exponentially growing cells, resulting in silencing of Osr2 expression. In addition, CpG demethylation in quiescence caused activation of Osr2 expression, while acetylation of the H3 and H4 histones during quiescence also led to an increase in Osr2 expression. These results suggest that epigenetically regulated Osr2 plays an important role in cellular quiescence and proliferation.

Functional exploration of the adult ovarian granulosa cell tumor-associated somatic FOXL2 mutation p.Cys134Trp (c.402C>G)

Background

The somatic mutation in the FOXL2 gene c.402C>G (p.Cys134Trp) has recently been identified in the vast majority of adult ovarian granulosa cell tumors (OGCTs) studied. In addition, this mutation seems to be specific to adult OGCTs and is likely to be a driver of malignant transformation. However, its pathogenic mechanisms remain elusive.

Methodology/Principal Findings

We have sequenced the FOXL2 open reading frame in a panel of tumor cell lines (NCI-60, colorectal carcinoma cell lines, JEG-3, and KGN cells). We found the FOXL2 c.402C>G mutation in the adult OGCT-derived KGN cell line. All other cell lines analyzed were negative for the mutation. In order to gain insights into the pathogenic mechanism of the p.Cys134Trp mutation, the subcellular localization and mobility of the mutant protein were studied and found to be no different from those of the wild type (WT). Furthermore, its transactivation ability was in most cases similar to that of the WT protein, including in conditions of oxidative stress. A notable exception was an artificial promoter known to be coregulated by FOXL2 and Smad3, suggesting a potential modification of their interaction. We generated a 3D structural model of the p.Cys134Trp variant and our analysis suggests that homodimer formation might also be disturbed by the mutation.

Conclusions/Significance

Here, we confirm the specificity of the FOXL2 c.402C>G mutation in adult OGCTs and begin the exploration of its molecular significance. This is the first study demonstrating that the p.Cys134Trp mutant does not have a strong impact on FOXL2 localization, solubility, and transactivation abilities on a panel of proven target promoters, behaving neither as a dominant-negative nor as a loss-of-function mutation. Further studies are required to understand the specific molecular effects of this outstanding FOXL2 mutation.

Functional equivalence of the zinc finger transcription factors Osr1 and Osr2 in mouse development

Osr1 and Osr2 are the only mammalian homologs of the Drosophila odd-skipped family developmental regulators. The Osr1 protein contains three zinc-finger motifs whereas Osr2 exists in two isoforms, containing three and five zinc-finger motifs respectively, due to alternative splicing of the transcripts. Targeted null mutations in these genes in mice resulted in distinct phenotypes, with heart and urogenital developmental defects in Osr1(-/-) mice and with cleft palate and open eyelids at birth in Osr2(-/-) mice. To investigate whether these contrasting mutant phenotypes are due to differences in their protein structure or to differential expression patterns, we generated mice in which the endogenous Osr2 coding region was replaced by either Osr1 cDNA or Osr2A cDNA encoding the five-finger isoform. The knockin alleles recapitulated endogenous Osr2 mRNA expression patterns in most tissues and completely rescued cleft palate and cranial skeletal developmental defects of Osr2(-/-) mice. Mice hemizygous or homozygous for either knockin allele exhibited open-eyelids at birth, which correlated with differences in expression patterns between the knockin allele and the endogenous Osr2 gene during eyelid development. Molecular marker analyses in Osr2(-/-) and Osr2(Osr1ki/Osr1ki) mice revealed that Osr2 controls eyelid development through regulation of the Fgf10-Fgfr2 signaling pathway and that Osr1 rescued Osr2 function in maintaining Fgf10 expression during eyelid development in Osr2(Osr1ki/Osr1ki) mice. These results indicate that the distinct functions of Osr1 and Osr2 during mouse development result from evolutionary divergence of their cis regulatory sequences rather than distinct biochemical activities of their protein products.

Zinc-finger transcription factor odd-skipped related 2 is one of the regulators in osteoblast proliferation and bone formation

We report that Osr2 is one of the regulators of osteoblast function, because dominant-negative Osr2 transgenic mice exhibited decreased osteoblast activity and delayed mineralization in calvarial and tibial bone tissues. Our results indicate that Osr2 functions in regulation of osteoblast proliferation.

INTRODUCTION

Molecular mechanisms that control bone formation have received attention with increasing knowledge related to genetic control of osteoblast differentiation. The odd-skipped related (Osr) gene is a zinc-finger transcription factor recently suggested to be involved in bone formation, although little is known about its role.

MATERIALS AND METHODS

To elucidate the in vivo function of Osr2, we generated transgenic mice overexpressing dominant-negative Osr2.

RESULTS

In this study, N-terminal-deleted Osr2 was found to act as a dominant-negative mutant toward both Osr1 and Osr2. Dominant-negative Osr2 (Osr2DeltaN) transgenic mice showed delayed mineralization in calvarial and cortical bone tissues. Furthermore, soft X-ray analysis of transgenic mice bones revealed distinctly increased radiolucency. Examinations of newborn Osr2DeltaN transgenic mice skeletons stained with alcian blue and alizarin red showed reduced intensities in the skull and skeletal elements. Morphologically, calvariae and tibias of Osr2DeltaN transgenic mice were composed of markedly thinner parietal and cortical bones and lower numbers of osteoblastic cells on bone surfaces, indicating a reduced proliferation of osteoblasts. Furthermore, calvarial osteoblasts obtained from Osr2DeltaN transgenic mice showed highly attenuated osteoblast differentiation and proliferation, confirming that Osr2 is needed for osteogenesis. Finally, results of Runx2-deficient cell assays suggested that Osr2 induces alkaline phosphatase (ALP) expression, but to a lesser degree than Runx2-expressing cells.

CONCLUSIONS

Our genetic observations showed that the Osr2 gene plays a key role in osteoblastic cell proliferation.

Odd-skipped genes encode repressors that control kidney development

Odd-skipped family of proteins (Odd in Drosophila and Osr in vertebrates) are evolutionarily conserved zinc finger transcription factors. Two Osr genes are present in mammalian genomes, and it was recently reported that Osr1, but not Osr2, is required for murine kidney development. Here, we show that in Xenopus and zebrafish both Osr1 and Osr2 are necessary and sufficient for the development of the pronephros. Osr genes are expressed in early prospective pronephric territories, and morphants for either of the two genes show severely impaired kidney development. Conversely, overexpression of Osr genes promotes formation of ectopic kidney tissue. Molecularly, Osr proteins function as transcriptional repressors during kidney formation. We also show that Drosophila Odd induces kidney tissue in Xenopus. This might be accomplished through recruitment of Groucho-like co-repressors. Odd genes may also be required for proper development of the Malpighian tubules, the Drosophila renal organs. Our results highlight the evolutionary conserved involvement of Odd-skipped transcription factors in the development of kidneys.

Odd-Skipped Related 2 gene transcription is regulated by CCAAT enhancer-binding protein δ in mesenchymal C3H10T1/2 cells

Odd-skipped related 2 (Osr2) gene is mouse homolog of Drosophila Odd-skipped gene involved with the pair-rule segmentation phenotype in Drosophila mutant embryos. In this study, to examine Osr2 expression regulation, the mouse Osr2 promoter region was cloned and characterized, and found to have two enhancer elements in the -1463/-1031 (distal) and -581/+3 (proximal) regions, and a repressor region (-4845/-1463, far distal). CCAAT/enhancer binding protein (C/EBP) binding sites were found in both the distal and proximal enhancer elements. Osr2 promoter activity was enhanced by C/EBPdelta, a member of the C/EBP family, in a dose-dependent manner. Electrophoresis mobility shift assays showed that purified GST-C/EBPdelta bound to distal (-1295/-1261) and proximal (-89/-55) C/EBP binding motifs. Chromatin immunoprecipitation demonstrated that acetylated histones H3, H4, and C/EBPdelta in the proximal region (-280/-43), but not the distal region (-1438/-1196), indicating that the Osr2 promoter proximal region was transcriptionally activated in C3H10T1/2 cells. Our results suggest that Osr2 expression is regulated by C/EBP regulatory elements.