Early neoplasias express high levels of ECAD, NANOG and SOX2. Arrowheads indicate morphologically wild-type germ cells and arrows indicate neoplasias. E-cadherin (ECAD; red) labels both germ cells and neoplasias in all frames. The frequency of neoplasia formation is strain-dependent. (A-C) Neoplasias do not form in double mutants on a C57BL/6J background. Germ cells express MVH (A) and lack expression of the pluripotency genes NANOG (B) and SOX2 (C) (arrowheads). (D-F) On a mixed background, ECAD-positive, morphologically distinct neoplasias form in double mutants (arrows). These clusters do not express MVH (D, arrow), although many germ cells persist that express MVH normally (arrowheads) and lack NANOG (E, arrowheads) and SOX2 (F, arrowheads). Cells within neoplasias maintain expression of NANOG (E, arrow) and SOX2 (F, arrow). (G-I) Many neoplasias form on a 129/SvJ background that lack MVH (G) and ectopically maintain expression of NANOG (H) and SOX2 (I). No MVH-positive, morphologically normal germ cells are detected at this stage in 129/SvJ mutants. Scale bars: 50 μm.