NES and fibrosarcoma: It is noteworthy that about 90% of mice in this GFAP-Cre activated cohort and 100% in the Nestin-Cre; PdgfrαK/+ or J/+; INK4A/Arf−/− cohort were affected by aggressive subcutaneous fibrosarcomas (Fig. S3c), presumably derived from Nestin-Cre or GFAP-Cre activation of PDGFRα J/K in fibroblastic cell lineages in the skin (Fig. S1a).