London C et al. (1988), Expression of Epi 1, an epidermis-specific mark...

XB-ART-27270

Dev Biol 1988 Oct 01;1292:380-9. doi: 10.1016/0012-1606(88)90385-5.

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Expression of Epi 1, an epidermis-specific marker in Xenopus laevis embryos, is specified prior to gastrulation.

London C , Akers R , Phillips C .

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The induction of morphologically observable neural structures occurs as the result of tissue interactions between chordamesoderm and overlying ectoderm beginning at gastrulation. Since the future dorsal, and hence neural, side of the embryo is determined around the time of fertilization, we questioned whether the presumptive neural epithelium might have received some developmental instructions prior to contact with the migrating chordamesoderm. Epi 1, a cell surface antigen present only on epidermal epithelium was used as a marker to determine when epithelial cells have been programmed to express (or not express) this epidermal-specific molecule. We find that ligated animal halves of precleavage embryos already contain all the information necessary for expression of Epi 1 at the appropriate developmental time (early neurula). By at least the eight-celled stage, the epithelial cells derived from ventral animal blastomeres are much better at expressing the Epi 1 antigen than their dorsal counterparts. We suggest that the mechanisms responsible for expression of the Epi 1 antigen are localized within the animal hemisphere prior to the onset of cleavage. By the third cleavage division, dorsal animal cells appear to have received information which inhibits the subsequent expression of this epidermal antigen.

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	FIG. 1. In viwo expression pattern of Epi 1. (a) Cross section through an early neural plate (stage 13) embryo. NP, neural plate. (b) Wholemount of the dorsal anterior portion of a stage 15 embryo. CG, cement gland. (a) 67X. (b) 428X.
	FIG. 2. Detection of Epi 1 expression in cultured explants. Early stage blastomeres were removed and cultured until control embryos reached midneurula when they were fixed and assayed for Epi 1 expression. (a) Whole-mount stain of a cultured explant of the four animal hemisphere blastomeres removed at the eight-cell stage. (b) Whole-mount stain of the four vegetal blastomeres explanted at the eight-cell stage and cultured to the equivalent of midneurula. (a) 168X. (b) 150x.
	FIG. 3. The animal half of a precleavage embryo ligated free of the vegetal half, cultured, and stained for the presence of Epi 1. 150x.
	FIG. 4. Whole mounts of explants removed at midblastula (a) and early gastrula (b), cultured until control embryos reached midneurula, and stained for the presence of the Epi 1 antigen. The boundaries between areas expressing or not expressing Epi 1 become sharper when the cells are explanted later in development. (a) 150X. (b) 300X.
	FIG. 5. A cultured, stained explant containing cells from the marginal zone of the embryo. The area of non-Epi 1 expression normally resides near the base of the protrusion. 150X.
	FIG. 6. A whole-mount staining of a single cultured ventral animal cell removed at the eight-cell stage. All ventral cell cultures show nearly homogeneous expression of the Epi 1 antigen. 162X.
	FIG. 7. Whole-mount staining of 40 cultured animal caps of uv-irradiated embryos. Ninety percent of the stage 10 explanted caps expressed the Epi 1 antigen completely (a). Four cultured explants showed the same pattern of partial expression as observed from nonirradiated stage 10 explants.