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PLoS One. 2014 Sep 22;9(9):e108294. doi: 10.1371/journal.pone.0108294. eCollection 2014.

Runx2-I isoform contributes to fetal bone formation even in the absence of specific N-terminal amino acids.

Author information

1
Division of Mucosal Immunology, Department of Microbiology and Immunology, The Institute of Medical Science, The University of Tokyo, Tokyo, Japan; Department of Medical Genome Science, Graduate School of Frontier Science, The University of Tokyo, Chiba, Japan.
2
Division of Mucosal Immunology, Department of Microbiology and Immunology, The Institute of Medical Science, The University of Tokyo, Tokyo, Japan; Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency, Tokyo, Japan.
3
Division of Mucosal Immunology, Department of Microbiology and Immunology, The Institute of Medical Science, The University of Tokyo, Tokyo, Japan.
4
Department of Cell Signaling, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo, Japan.
5
Laboratory of Developmental Genetics, The Institute of Medical Science, The University of Tokyo, Tokyo, Japan.
6
Department of Immunology, Graduate School of Medicine and Faculty of Medicine, The University of Tokyo, Tokyo, Japan.
7
Division of Mucosal Immunology, Department of Microbiology and Immunology, The Institute of Medical Science, The University of Tokyo, Tokyo, Japan; Department of Medical Genome Science, Graduate School of Frontier Science, The University of Tokyo, Chiba, Japan; Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency, Tokyo, Japan.

Abstract

The Runt-related transcription factor 2 (Runx2) gene encodes the transcription factor Runx2, which is the master regulator of osteoblast development; insufficiency of this protein causes disorders of bone development such as cleidocranial dysplasia. Runx2 has two isoforms, Runx2-II and Runx2-I, and production of each isoform is controlled by a unique promoter: a distal promoter (P1) and a proximal promoter (P2), respectively. Although several studies have focused on differences and similarities between the two Runx2 isoforms, their individual roles in bone formation have not yet been determined conclusively, partly because a Runx2-I-targeted mouse model is not available. In this study, we established a novel Runx2-manipulated mouse model in which the first ATG of Runx2-I was replaced with TGA (a stop codon), and a neomycin-resistant gene (neo) cassette was inserted at the first intron of Runx2-I. Homozygous Runx2-Ineo/neo mice showed severely reduced expression of Runx2-I, whereas Runx2-II expression was largely retained. Runx2-Ineo/neo mice showed neonatal lethality, and in these mice, intramembranous ossification was more severely defective than endochondral ossification, presumably because of the greater involvement of Runx2-I, compared with that of Runx2-II in intramembranous ossification. Interestingly, the depletion of neo rescued the above-described phenotypes, indicating that the isoform-specific N-terminal region of Runx2-I is not functionally essential for bone development. Taken together, our results provide a novel clue leading to a better understanding of the roles of Runx2 isoforms in osteoblast development.

PMID:
25244033
PMCID:
PMC4171521
DOI:
10.1371/journal.pone.0108294
[Indexed for MEDLINE]
Free PMC Article

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