The formation of testicular teratomas and other testicular germ cell tumours (TGCTs) is thought to involve defects in male germ cell development. On , Jason Heaney and co-workers provide new insights into TGCT development by studying strains of mice with different teratoma incidences, including the 129 strain, which has a high spontaneous rate of TGCTs. In 129 mice, TGCTs are visible at embryonic day (E) 15.5 as microscopic foci of pluripotent stem cells (embryonal carcinoma cells). The researchers report that germ cell proliferation, the expression of the pluripotency factor Nanog and the premature expression of genes normally expressed in pre-meiotic adult male germ cells, such as cyclin D1 and Stra8, at E15.5 are all directly related to increased tumour risk. Notably, embryonal carcinoma cells co-express genes involved in germ cell pluripotency and differentiation, and deletion of Stra8 in 129 mice reduces their teratoma incidence. Together, these results indicate that deregulation of the mitotic-meiotic switch in male germ cells contributes to teratoma initiation.
