Fig. 5. Expression of a dominant-negative mutant of XGrhl1 (227XGrhl1) results in global defects in epidermal differentiation. (A) Defective epidermal structures observed in tadpoles (arrowheads) in 227XGrhl1-injected (227) but not wild-type (wt) embryos. All embryos illustrated are stage 40 and were injected in one animal pole blastomere at the eight-cell stage. (B) Defects in trunk and tail structures observed in embryos injected with 227XGrhl1 transcripts. (C) Abnormal accumulation of pigment vesicles in 227XGrhl1-expressing epidermis (white arrowhead). (D) Transverse section through head structures of 227XGrhl1-injected tadpole. Left panels show normal epidermal structure with discrete outer epithelial (OEL) and inner sensorial layers (ISL). A marked increase in the thickness and disorganization of the epidermis is observed in magnified cross-section of injected regions (right). Note the persistence of yolk sac platelets (arrows) and embryonic pigment granules (arrowhead), large round nuclei and prominent nucleoli of OEL. (E,F) Transverse sections through embryonic trunk (E) and fin (F). Middle panels shows a low-power magnification through regions. Key structures are indicated: DNT, dorsal neural tube; SM, somite; NC, notochord; pnt, pronephric duct. Side panels at higher magnification show differences between normal bi-layer (left) and 227XGrhl1 RNA affected cells (right).