Hdac1 is essential for redifferentiation of osteoblast during regeneration. (A-B) Longitudinal sections of fin regenerates at 4 dpa treated with DMSO (A) or MGCD0103 (B) and triply stained with BrdU (green), ZNS5 antibody (red), and DAPI (blue). Dashed lines indicate the amputation plane. Proximal osteoblast nuclei acquired an elongated shape in control fins (A′), whereas osteoblast nuclei rarely presented an elongated shape in MGCD0103-treated fins (B′). (C) Percentage of ZNS5-positive cells at 4 dpa that were also positive for BrdU relative to the total number of ZNS5-positive cells in fin regenerates treated with DMSO or MGCD0103. Error bars represent the SEM. n = 15. *P < 0.01. (D-I) Caudal fins of runx2:GFP (D-E), osterix:mcherry (F-G) or osteocalcin:GFP (H-I) transgenic fish treated with DMSO or MGCD0103 at 3 and 7 dpa. Constant exposure times were used. Dashed lines indicate the amputation plane. In DMSO-treated fish, the amputation plane is below the photographed part of the fin at 7 dpa. Scale bars: 100 μm (A,D,F,H), 50 μm (A′).