“…SSCs are definitively defined by their stem-like qualities (proliferation, self-renewal, expansion) using functional assays, such as in vivo transplantation, in vitro clonal proliferation, and in vitro cobblestone assays; it has proven difficult to determine SSCs precisely in vivo with a single molecular marker, because many of their phenotypic characteristics overlap with their progeny, the A-type undifferentiated spermatogonia (Ploemacher et al 1989, Brinster & Zimmermann 1994, Dobrinski et al 1999, Kubota & Brinster 2006, Kanatsu-Shinohara et al 2012). Classically, SSCs are characterized in many mammalian systems by the expression of a combination of markers, such as cadherin 1 (CDH1), glial cell line derived neurotrophic factor family receptor alpha 1 (GFRA1), inhibitor of differentiation 4 (ID4), integrins alpha 6 and beta 1, strong expression of zinc finger and BTB domain containing 16 (ZBTB16 HI ; also known as promyelocytic leukemia zinc finger (PLZF HI )), ret proto-oncogene (RET), and Thy1, and the lack of kit oncogene (KIT) and stimulated by retinoic acid 8 (STRA8) expression (Meng et al 2000, Giuili et al 2002, Kubota et al 2003, Naughton et al 2006, Kanatsu-Shinohara et al 2008, Tolkunova et al 2009, Sun et al 2015, Takashima et al 2015). …”