title: Runx1 and Runx2 cooperate during sternal morphogenesis.
abstract: Chondrocyte differentiation is strictly regulated by various transcription factors, including Runx2 and Runx3; however, the physiological role of Runx1 in chondrocyte differentiation remains unknown. To examine the role of Runx1, we generated mesenchymal-cell-specific and chondrocyte-specific Runx1-deficient mice [Prx1 Runx1(f/f) mice and alpha1(II) Runx1(f/f) mice, respectively] to circumvent the embryonic lethality of Runx1-deficient mice. We then mated these mice with Runx2 mutant mice to obtain mesenchymal-cell-specific or chondrocyte-specific Runx1; Runx2 double-mutant mice [Prx1 DKO mice and alpha1(II) DKO mice, respectively]. Prx1 Runx1(f/f) mice displayed a delay in sternal development and Prx1 DKO mice completely lacked a sternum. By contrast, alpha1(II) Runx1(f/f) mice and alpha1(II) DKO mice did not show any abnormal sternal morphogenesis or chondrocyte differentiation. Notably, Runx1, Runx2 and the Prx1-Cre transgene were co-expressed specifically in the sternum, which explains the observation that the abnormalities were limited to the sternum. Histologically, mesenchymal cells condensed normally in the prospective sternum of Prx1 DKO mice; however, commitment to the chondrocyte lineage, which follows mesenchymal condensation, was significantly impaired. In situ hybridization analyses demonstrated that the expression of alpha1(II) collagen (Col2a1 - Mouse Genome Informatics), Sox5 and Sox6 in the prospective sternum of Prx1 DKO mice was severely attenuated, whereas Sox9 expression was unchanged. Molecular analyses revealed that Runx1 and Runx2 induce the expression of Sox5 and Sox6, which leads to the induction of alpha1(II) collagen expression via the direct regulation of promoter activity. Collectively, these results show that Runx1 and Runx2 cooperatively regulate sternal morphogenesis and the commitment of mesenchymal cells to become chondrocytes through the induction of Sox5 and Sox6.
authors.affiliation: Department of Orthopaedics, Graduate School, Tokyo Medical and Dental University, Tokyo 113-8519, Japan.
authors.forename: Ayako
authors.initials: A
authors.lastname: Kimura
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Inose
authors.forename: Fumiko
authors.initials: F
authors.lastname: Yano
authors.forename: Koji
authors.initials: K
authors.lastname: Fujita
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Ikeda
authors.forename: Shingo
authors.initials: S
authors.lastname: Sato
authors.forename: Makiko
authors.initials: M
authors.lastname: Iwasaki
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Jinno
authors.forename: Keisuke
authors.initials: K
authors.lastname: Ae
authors.forename: Seiji
authors.initials: S
authors.lastname: Fukumoto
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Takeuchi
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Itoh
authors.forename: Takeshi
authors.initials: T
authors.lastname: Imamura
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kawaguchi
authors.forename: Ung-il
authors.initials: UI
authors.lastname: Chung
authors.forename: James F
authors.initials: JF
authors.lastname: Martin
authors.forename: Sachiko
authors.initials: S
authors.lastname: Iseki
authors.forename: Ken-ichi
authors.initials: K
authors.lastname: Shinomiya
authors.forename: Shu
authors.initials: S
authors.lastname: Takeda
mesh_terms: D000818:Animals; D001842:Bone and Bones / Q000166:cytology / Q000378:metabolism; D002356:Cartilage / Q000166:cytology / Q000502:physiology; D002454:Cell Differentiation; D019070:Cell Lineage; D019902:Chondrocytes / Q000166:cytology / Q000378:metabolism; D050659:Core Binding Factor Alpha 1 Subunit / Q000235:genetics / Q000378:metabolism*; D050676:Core Binding Factor Alpha 2 Subunit / Q000235:genetics / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental; D006367:HeLa Cells; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008648:Mesoderm / Q000166:cytology / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D009024:Morphogenesis / Q000502:physiology*; D055755:SOXD Transcription Factors / Q000235:genetics / Q000378:metabolism; D013234:Stem Cells / Q000166:cytology / Q000378:metabolism; D013249:Sternum / Q000002:abnormalities / Q000033:anatomy & histology / Q000196:embryology* / Q000378:metabolism; D019076:Transgenes
chemical_list: D050659:Core Binding Factor Alpha 1 Subunit; D050676:Core Binding Factor Alpha 2 Subunit; D018398:Homeodomain Proteins; C489936:Prrx1 protein, mouse; C493726:Runx1 protein, mouse; C493716:Runx2 protein, mouse; D055755:SOXD Transcription Factors; C089186:Sox5 protein, mouse; C095939:Sox6 protein, mouse