Fig. 2. ncp fin regenerates display defects in proximal blastemal cells during regenerative outgrowth. (A) Longitudinal sections of 1-day postamputation fin regenerates during blastema formation, with the distal, regenerating end shown at the top. At this stage, ncp regenerates display a typical blastema with normal msxb expression (violet stain). (B) Sections of regenerates at the onset of outgrowth. (Top) Hematoxylin stains of ncp regenerates indicate a mesenchymal compartment with a reduced number of blastemal cells. (Middle) msxb expression is maintained and even expanded in ncp regenerates despite blastemal reduction. (Bottom) The antibody Zns-5 detects scleroblasts, or bone-depositing cells (brown stain), which align bilaterally in the patterning zone by 2 days postamputation and begin to deposit mineral. Note that the ncp regeneration defect was first apparent at the onset of regenerative outgrowth and had little or no effect on the establishment of the distal blastema or patterning zone. Arrows indicate point of amputation. Original magnification is 250x.