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Fig. 2 Zebrafish epcam is expressed in multiple epithelia, including the skin.
(A–J) In situ hybridizations with anti-sense epcam probe. (A) Maternally provided epcam RNA is uniformly distributed in all blastomeres of 4-cell stage embryo (1 hpf). (B–D) At the 50% epiboly stage (early gastrula; 5.5 hpf), epcam expression is restricted to the outer EVL layer. (C,D) show 8 μm thick paraffin sections; in (D) epcam-negative deep cells (dc) and yolk syncitial layer (ysl) are indicated. (E–G) Mutant epcam mRNA is unstable, and zygotic epcam transcription is initiated before gastrulation. (E) Wild-type (WT) embryos at 8–16 cell stage; (F,G) embryos from cross of homozygous mutant female (M-/-) and heterozygous male, 50% of which are zygotic heterozygotes (Z+/-), and 50% zygotic homozygous mutants (Z-/-). At the 8–16 cell stage (F), all embryos lack (maternally supplied) epcam transcripts. At the 50% epiboly stage (G), Z-/- embryos still lack epcam mRNA, whereas zygotically derived transcripts are detectable in Z+/- embryos, indicating that zygotic epcam transcription starts shortly after midblastula transition [88]. (H–K) At 24 hpf (H–J) and 48 hpf (K), epcam is expressed in the olfactory placodes (olf), otic vesicles (ot), head and lateral line neuromasts (nm), pronephric ducts (pd) and the skin; (I,J) transverse sections through trunk of 24 hpf embryo labeled for epcam RNA (in blue) and p63 protein (in brown). epcam is expressed both in the (p63-negative) outer EVL (arrow in J), and in the underlying layer of p63-positive basal keratinocytes (arrowhead in J). (L, M) Epifluorescent images of live embryo at 9 hpf. Upon injection of mRNA encoding EpCAM-GFP, the fusion protein localizes to the cell membrane of both EVL cells (L) and the underlying deep cells (M). Note the size differences between the two cell types.