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

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.

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.

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.

Odd-skipped related 1 gene expression is regulated by Runx2 and Ikzf1 transcription factors

Odd-skipped related 1 (Osr1) gene encodes a zinc-finger transcription factor that plays important roles in embryonic, heart, and urogenital development, however, it is unknown how its expression is regulated. In this study, we analyzed the promoter region of Osr1 to elucidate its regulation mechanism. The mouse Osr1 promoter region was cloned and characterized, and found to have two repressor elements in the -4504/-2766 and -1616/-109 regions, and two enhancer elements in the -2766/-1616 and -109/+199 regions. Several Runx2 and Ikzf1 binding sites were found in both mouse and human Osr1 promoters. Osr1 promoter activity was suppressed by cotransfection with Runx2- and Ikzf1-expressing vectors in a dose-dependent manner. Electrophoresis mobility shift assays showed that purified Runx2 bound to proximal (-611/-606) Runx2 binding motifs and that Ikzf1 bound to proximal (-1652/-1644) Ikzf1 binding motifs. Chrosmatin immunoprecipitation demonstrated that Runx2 bound to both the distal (-3047/-3042) and proximal regions, and that Ikzf1 bound to both the far-distal (-3036/-3028) and proximal elements. These findings indicate that Osr1 expression is regulated by Runx2 and Ikzf1, which are known as master-gene of osteogenesis and hematopoiesis, respectively.

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.