Activation of ERK pathway in skin melanocytes of Grey horses. (A) Double immunofluorescence staining was performed for P-ERK1/2 (green in a1-a2, c1-c2) or ERK1/2 (green in b1-b2, d1-d2) and MITF (red in a2, b2, c2, d2) in skin tissue sections from non-grey and Grey horses; a3, b3, c3, d3, bright field images of the sections. Dotted lines, skin basal membrane; e, epidermis; d, dermis. Scale bar, 10 μm. Note an increase in P-ERK1/2 signal (arrow heads in c1-c2) in the surrounding keratinocytes in Grey horse skin. (B) Quantification of P-ERK1/2 and ERK1/2 immunofluorescent signals in relation to the respective total number of MITF+ cells in skin tissue sections from non-grey (n =9; dark grey bars) and Grey (n =12; light grey bars) horses shown as the mean ± s.e. of three independent experiments. ***P <0.001.