Fig. 8. A Myc-Slug/Twist regulatory circuit directs vasculogenesis and lymphangiogenesis. Xc-Myc is required for the normal expression of the XSlug and XTwist transcription factors, either of which are sufficient to rescue the defects in vascular and lymphatic development provoked by knockdown of Xc-Myc. Knockdown of XSlug also disrupts normal patterns of Xc-Myc expression, indicating a positive-feedback loop. Knockdown of both XSlug and XTwist in lateral plate mesoderm, but not neural crest, results in the vascular defects observed after knockdown of Xc-Myc, indicating both genes operate in the same pathway and downstream of Myc. Either ectopic Slug or Twist rescue defects in endogenous XSlug or XTwist expression induced by Xc-Myc knockdown, indicating that they also regulate each the expression of one another.