(A) By both in-situ hybridization (a, b) and immunohistochemistry (c, d), Foxn1 is weakly expressed in nail matrix cells excluding the basal layer and is dramatically upregulated in the keratogenous zone (A.a, c, inset, arrows). No expression is detected in the nail bed (A.b, d, inset, arrows). MSX2 protein is weakly expressed in the proximal nail unit and elevated in the more distal matrix including the basal layer, the keratogenous zone (A.e, inset, arrow) and the nail bed (A.f, inset, arrow). Proximal and distal indicate the nail unit near the phalanx and digit tip, respectively. Black and white dashed lines demarcate the border between epithelial structures and the underlying mesenchyme. (B) Foxn1 expression level is reduced in Msx2 mutant nails, as evidenced by in-situ hybridization (B.a, b, arrow). Digit 2 from the hind limbs is used for this assay. In all panels, the nail tips are orientated towards the left side. (C) A schematic outline of the nail unit.