Figure 5. Double mutant nail bed hyperplasia results from distal matrix hyperproliferation.

(A) Ki67 antibody labels all cycling cells and Ki67+ cells are detected in the distal matrix and stratified hyponychium of wild type nails (A.a). The PAI2 positive nail bed is Ki67 negative revealed on adjacent sections (in-between two white arrows) (A.c). Similar to wild type, no Ki67 positive cell is detected in the double mutant PAI2 positive nail bed (A.b, d). (B) Under low magnification, no gross change in cell proliferation is observed in the double mutant nails (B.a, b). However, in the distal matrix, more than one layer of proliferating cells is labeled in the double mutant, as compared to a single layer in wild type (B.a′, b′, arrows). In the proximal matrix, the total number of proliferating cells (Ki67+) is not changed (B.a″, b″). In (B), a′, b′ and a″, b″ are higher magnifications of distal and proximal boxes in a and b, respectively. White dashed lines demarcate the border between the distal nail matrix and the underlying mesenchyme. Digit 2 from the hind limbs is used for this assay. In all panels, the nail tips are orientated towards the left side.