Zinc finger transcription factor Sp7/Osterix acts on bone formation and regulates col10a1a expression in zebrafish

Sp7/Osterix as a zinc finger transcription factor is expressed specifically in osteoblasts. Embryonic lethality of Sp7 knockout mice, however, has prevented from examining the functions of Sp7 in osteoblast and bone formation in live animals. Here we used TALEN, a versatile genome-editing tool, to generate one zebrafish sp7 mutant line. Homozygous sp7-/- mutant zebrafish are able to survive to adulthood. Alizarin Red staining and Micro-CT analysis showed that sp7-/- larvae and adult fish fail to develop normal opercula, and display curved tail fins and severe craniofacial malformation, while Alcian Blue staining showed no obvious cartilage defects in sp7-/- fish. Quantitative RT-PCR showed that a number of osteoblast markers including spp1, phex, col1ala, and col1a1b are significantly down-regulated in sp7-/- fish. Furthermore, col10a1a, whose ortholog is the cartilage marker in mice, was shown to be a novel downstream gene of Sp7 as an osteoblast marker in zebrafish. Together, these results suggest that Sp7 is required for zebrafish bone development and zebrafish sp7 mutants provide animal models for investigating novel aspects of bone development.