Fig. 5. Msk protein is apically sequestered in the morphogenetic furrow and ectopically expressed Msk at the furrow reduces both pMAPK and Atonal. Third instar eye-imaginal discs, anterior right. A,B and C-J are at the same scale, as indicated. (A,B) Apical (A) and basal (B) view of Msk staining (Dim7 antigen, black) at the morphogenetic furrow (arrowheads) Note the apical Msk expression (arrows, A), and that this is lost from cells surrounding the preclusters (black asterisk, B). Note also the higher level of Msk antigen anterior to the furrow (white asterisks). (C-J) pMAPK (black, C-F) and Atonal (white, G-J) expression at the morphogenetic furrow (arrowheads). pMAPK antigen stained with Ni/Co intensified DAB; Atonal by immunofluorescence. Genotypes and heat-induction times are indicated above the panels. pMAPK antigen is lost from the furrow after one hour of hsp70 promoter-driven Msk expression (compare F with arrows in C-E. Atonal expression is greatly reduced by the same treatment, on the anterior side of the furrow (arrows, J).