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Fig. 1. Arnt-null TS cells differentiate into chorionic trophoblasts and
syncytiotrophoblasts. Undifferentiated wild-type (A) and Arnt-null
(B) TS cells grown on fibroblast feeders exhibited identical morphological
features. Differentiated wild-type cells (C) formed large trophoblast giant
cells and smaller spongiotrophoblasts. Differentiated Arnt-null TS
cells (D) produced large multinucleated syncytiotrophoblasts and smaller
chorionic trophoblasts. E-cadherin staining of differentiated wild-type cells
revealed one or occasionally two nuclei per cell (E), whereas
Arnt-null cells formed syncytia containing multiple nuclei (F). In
some cases, multinucleated cells with peripherally distributed nuclei (G,
arrowheads) and central clearing appeared to form epithelial-lined spaces. (H)
RNA FISH analysis of Xist RNA revealed a single inactive X chromosome per
nucleus in differentiated Arnt-null TS cells, additional evidence for
lack of endoreduplication. (I) Analysis of lineage-specific markers by
northern blot hybridization and RNase protection assays confirmed these
findings.