Osteoblast maturation occurs in overlapping proximal‐distal compartments during fin regeneration in zebrafish

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Abstract
During fin regeneration, osteoblasts must continually differentiate for outgrowth of the bony fin rays. Bone maturity increases in a distal‐proximal manner, and osteoblast maturation can be detected similarly when following gene expression. We find that early markers for osteoblast differentiation are expressed in a discrete domain at the distal end of the fin, just proximal to the adjacent germinal compartment of dividing cells. Matrix genes, required at later stages developmentally, are expressed in a population of cells proximally to the early genes. A marker for mature osteoblasts is expressed in cells further proximal. These domains of gene expression are partially overlapping, perhaps revealing additional levels of osteoblast maturity. We suggest a model for growth where new cells are continually added to the distal‐most osteoblast compartment, while osteoblasts in more proximal locations differentiate, thus translating developmental time to location on the proximal‐distal axis. Developmental Dynamics 238:2922–2928, 2009.