International Journal of Molecular Sciences Review To Be or Not to Be a Germ Cell: The Extragonadal Germ Cell Tumor Paradigm Massimo De Felici 1,*, Francesca Gioia Klinger 1 , Federica Campolo 2 , Carmela Rita Balistreri 3 , Marco Barchi 1 and Susanna Dolci 1,* 1 Department of Biomedicine and Prevention, University of Rome Tor Vergata, 00133 Rome, Italy;
[email protected] (F.G.K.);
[email protected] (M.B.) 2 Department of Experimental Medicine, University of Rome La Sapienza, 00161 Rome, Italy;
[email protected] 3 Department of Biomedicine, Neuroscience and Advanced Diagnostics (Bi.N.D.), University of Palermo, 90133 Palermo, Italy;
[email protected] * Correspondence:
[email protected] (M.D.F.);
[email protected] (S.D.) Abstract: In the human embryo, the genetic program that orchestrates germ cell specification in- volves the activation of epigenetic and transcriptional mechanisms that make the germline a unique cell population continuously poised between germness and pluripotency. Germ cell tumors, neo- plasias originating from fetal or neonatal germ cells, maintain such dichotomy and can adopt either pluripotent features (embryonal carcinomas) or germness features (seminomas) with a wide range of phenotypes in between these histotypes. Here, we review the basic concepts of cell specification, mi- gration and gonadal colonization of human primordial germ cells (hPGCs) highlighting the analogies of transcriptional/epigenetic programs between these two cell types. Keywords: germ cell tumor; primordial germ cells; germline; EG cells Citation: De Felici, M.; Klinger, F.G.; Campolo, F.; Balistreri, C.R.; Barchi, M.; Dolci, S. To Be or Not to Be a Germ Cell: The Extragonadal Germ Cell Tumor Paradigm.