Fig. 9

fras1 and hmcn1 mutants display blister formation at identical sites below the basement membrane; however, in contrast to Frem2/3 proteins, Hmcn1 is dispensable for Fras1 stabilisation.

(A–C) Electron micrographs of the sub-epidermal space of medial fin folds at 30 hpf in WT (A), pif^te262/te262 (B), and nel^tq207/tq207 (C) embryos. Epidermal cells (indicated by ‘ep’ in A) are at the top of all panels as well as in the lower part of A. The lamina densa of the basement membrane (labelled with ‘bm’ in A), including the sublamina densa, is attached to the epidermal cells in all three panels. Below the bm, electron dense material is evident as actinotrichia (ac) or dermis material (de), which appears disorganized and in the two mutants (B,C). (D–G) Low power electron micrographs of the apical portion of the fin fold in WT (D), pif^te262/te262 (E), and nel^tq207/tq207 (F–G) embryos at 30 hpf (D–F) and 48 hpf (G). Cell–cell adhesion is well preserved in both mutants at 30 hpf (E–F), but at 48 hpf, when the blister begins to collapse, cell-cell boundaries become compromised (G, red arrows). The basal and outer enveloping layers are indicated with yellow and green bars respectively. (H–L) Transverse sections fluorescently immunostained for Fras1 (green), epidermal p63 (red) and counterstained with DAPI (blue) at 30 hpf (H–K) and 48 hpf (L). Fras1 immunoreactivity is evident between the fin folds in WT embryos (H), but lost in pif^te262/te262 mutants (I) as well as in embryos injected with MOs against frem2a, frem2b, and frem3 (J). In contrast, it is retained in nel^tq207/tq207 embryos at both 30 hpf (K) and 48 hpf (L), when blistering is even more severe.