Spatio-temporal expression patterns of Runx2 isoforms in early skeletogenesis.
Skeletogenesis occurs through either intramembranous or endochondral ossification. In addition, some parts of the skeletal components maintain their cartilaginous characteristics throughout life without mineralization. Runx2 is known to be a pivotal transcription factor for all skeletogenic processes. In this study, we examined the expression patterns of two major isoforms of Runx2 in early skeletogenesis. During intramembranous bone formation, Runx2-type I (Runx2-I) was widely expressed in osteoprogenitor cells and active osteoblasts, while Runx2-type II (Runx2-II) expression was stringently restricted to cells lining mineralized bones. Cells in permanent cartilage expressed collagen type II (Col-II) but never expressed Runx2 or Col-X. These permanent cartilages were well circumscribed by Runx2-I positive cells, in which Runx2-II was negative. In endochondral bone formation, Runx2 expression temporarily disappeared in Col-II-positive proliferating chondrocytes, but a secondary surge of Runx2-I expression occurred in the prehypertrophic zone before the mineralization of cartilage. Collectively, both Runx2 isoforms showed very similar expression patterns in active bone forming areas; however, Runx2-I has an exclusive role in the early commitment stage of intramembranous or endochondral bone forming processes or in cells surrounding permanent cartilage.
Choi
Kang-Young
KY
Department of Biochemistry, School of Dentistry, Kyungpook National University, Daegu, Korea.
Lee
Sang-Won
SW
Park
Mi-Hyun
MH
Bae
Yong-Chul
YC
Shin
Hong-In
HI
Nam
Soon- Hyeun
S
Kim
Young-Jin
YJ
Kim
Hyun-Jung
HJ
Ryoo
Hyun-Mo
HM
D000818:Animals; D001846:Bone Development; D002356:Cartilage / Q000166:cytology / Q000254:growth & development / Q000378:metabolism; D050659:Core Binding Factor Alpha 1 Subunit; D005314:Embryonic and Fetal Development / Q000235:genetics; D020869:Gene Expression Profiling; D018507:Gene Expression Regulation, Developmental; D017403:In Situ Hybridization; D051379:Mice; D008813:Mice, Inbred ICR; D009363:Neoplasm Proteins; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D013997:Time Factors; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism
D050659:Core Binding Factor Alpha 1 Subunit; D009363:Neoplasm Proteins; D020033:Protein Isoforms; D014157:Transcription Factors