Osteoclasts in bone modeling, as revealed by in vivo imaging, are essential for organogenesis in fish

Abstract

Bone modeling is the central system controlling the formation of bone including bone growth and shape in early development, in which bone is continuously resorbed by osteoclasts and formed by osteoblasts. However, this system has not been well documented, because it is difficult to trace osteoclasts and osteoblasts in vivo during development. Here we showed the important role of osteoclasts in organogenesis by establishing osteoclast-specific transgenic medaka lines and by using a zebrafish osteoclast-deficient line. Using in vivo imaging of osteoclasts in the transgenic medaka carrying an enhanced GFP (EGFP) or DsRed reporter gene driven by the medaka TRAP (Tartrate-Resistant Acid Phosphatase) or Cathepsin K promoter, respectively, we examined the maturation and migration of osteoclasts. Our results showed that mononuclear or multinucleated osteoclasts in the vertebral body were specifically localized at the inside of the neural and hemal arches, but not at the vertebral centrum. Furthermore, transmission electron microscopic (TEM) analyses revealed that osteoclasts were flat-shaped multinucleated cells, suggesting that osteoclasts initially differentiate from TRAP-positive mononuclear cells residing around bone. The zebrafish panther mutant lacks a functional c-fms (receptor for macrophage colony-stimulating factor) gene crucial for osteoclast proliferation and differentiation and thus has a low number of osteoclasts. Analysis of this mutant revealed deformities in both its neural and hemal arches, which resulted in abnormal development of the neural tube and blood vessels located inside these arches. Our results provide the first demonstration that bone resorption during bone modeling is essential for proper development of neural and vascular systems associated with fish vertebrae.

Rankl-induced osteoclastogenesis leads to loss of mineralization in a medaka osteoporosis model

“…1A). This line shows expression comparable with the CTSK-GFP line reported recently in a study that used a slightly shorter promoter (Chatani et al, 2011). Stable ctsk:mEGFP transgenic embryos first showed GFP expression at 5 dpf in head and tail regions (Fig.…”

The Phosphate Exporter xpr1b Is Required for Differentiation of Tissue-Resident Macrophages

“…Osteoclasts are cells derived from macrophages that have the primary function of resorbing bone during remodelling, and mutations that affect osteoclasts number and function disrupt bone remodelling (Segovia-Silvestre et al, 2009). Indeed the zebrafish panther mutant, which has a mutation in the macrophage colony-stimulating factor 1 receptor ( csf1ra ), has a reduced number of osteoclasts and narrower neural and hemal canals due to increased bone mass (Chatani et al, 2011). Interestingly, csfr1a mutants also had impaired blood vessel formation, with the formation of an ectopic blood vessel that bypassed the occluded hemal canals.…”

Retinoic acid-induced premature osteoblast-to-preosteocyte transitioning has multiple effects on calvarial development

“…To assess further whether osteoclasts are required for RA-induced calvarial fragmentation, pfeffer ( pfe) mutant fish in the receptor tyrosine kinase colony stimulating factor 1 receptor a (csf1ra) gene, also named c-fms (Maderspacher and Nüsslein-Volhard, 2003), which have been reported to lack osteoclasts (Chatani et al, 2011), were treated with RA. Upon RA treatment, pfe mutants, in contrast to wildtype fish, lacked ectopic TRAP-positive areas above the epiphyseal bar ( Fig.…”