A vertebrate specific and essential role for sp7/osterix in osteogenesis revealed by gene knock-out in the teleost medaka

Abstract

Sp7/osterix (osx) encodes a zinc-finger transcription factor that controls osteoblast differentiation in mammals. Although identified in all vertebrate lineages, its role in non-mammalian bone formation remains elusive. Here we show that an osx mutation in medaka results in severe bone defects and larval lethality. Pre-osteoblasts fail to differentiate leading to severe intramembranous and perichondral ossification defects. The notochord sheath mineralizes normally supporting the idea of an osteoblast-independent mechanism for teleost vertebral centra formation. This study establishes a key role for Sp7/Osx for bone formation also in a non-mammalian species, and reveals conserved and non-conserved features in vertebrate bone formation.