Exp Mol Med.  2002 Dec;34(6):426-433.

Spatio-temporal expression patterns of Runx2 isoforms in early skeletogenesis

• Choi KY
• Lee SW
• Park MH
• Bae YC
• Shin HI
• Nam SH
• Kim YJ
• Kim HJ
• Ryoo HM

Abstract

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.

Keyword

chondrocytes; chondrogenesis; collagen type-II; osteoblasts; osteogenesis; transcription factors

MeSH Terms

Animals
*Bone Development
Cartilage/cytology/growth & development/metabolism
Embryo and Fetal Development/genetics
*Gene Expression Profiling
*Gene Expression Regulation, Developmental
In Situ Hybridization
Mice
Mice, Inbred ICR
Protein Isoforms/genetics/metabolism
Time Factors
Transcription Factors/*genetics/metabolism