SIX1 and neoplasm: However, the expression levels of genes governing mesodermal cell lineage (TBX6, WNT11, PITX1, FEV, and CYP26B1) and functioning in the specification of mesodermal cells (MESP1, TBX1, NKX2. 5, SIX1, SIX2, GATA2, and MYOD1) were enriched in organoids (and tumor), compared with fetal retina (Fig. 4c).