Figure 4. Schematic representation of the effects of deregulated ephrin-B2 expression on the mammary epithelial differentiation pathway. Expression of truncated ephrin-B2 (red arrows) leads to an accumulation of the stem and bipotent progenitor population and shifts differentiation toward the estrogen receptor-positive lineage, thereby further favoring the basal lineage (shaded in red). Overexpression of the native ephrin-B2 leads (yellow arrows) to an accumulation of the bipotent progenitor population and shifts differentiation toward the luminal lineage (shaded in yellow), thereby not affecting steroid receptor expression.