The Early Human Germ Cell Lineage Does Not Express SOX2 During In Vivo Development or upon In Vitro Culture1

Abstract

NANOG, POU5F1, and SOX2 are required by the inner cell mass of the blastocyst and act cooperatively to maintain pluripotency in both mouse and human embryonic stem cells. Inadequacy of any one of them causes loss of the undifferentiated state. Mouse primordial germ cells (PGCs), from which pluripotent embryonic germ cells (EGCs) are derived, also express POU5F1, NANOG, and SOX2. Thus, a similar expression profile has been predicted for human PGCs. Here we show by RT-PCR, immunoblotting, and immunohistochemistry that human PGCs express POU5F1 and NANOG but not SOX2, with no evidence of redundancy within the group B family of human SOX genes. Although lacking SOX2, proliferative human germ cells can still be identified in situ during early development and are capable of culture in vitro. Surprisingly, with the exception of FGF4, many stem cell-restricted SOX2 target genes remained detected within the human SOX2-negative germ cell lineage. These studies demonstrate an unexpected difference in gene expression between human and mouse. The human PGC is the first primary cell type described to express POU5F1 and NANOG but not SOX2. The data also provide a new reference point for studies attempting to turn human stem cells into gametes by normal developmental pathways for the treatment of infertility.

Essential Role of Sox2 for the Establishment and Maintenance of the Germ Cell Line

“…Even though SOX2 has been reported not to be expressed in human PGCs [53], it is expressed in human intratubular germ cell carcinoma in situ [54], and in embryonal carcinoma [8], which are thought to be derived from PGCs. Moreover, human PGCs have been found to express SOX17 [55], which is a strictly related transcription factor showing the same DNA binding properties of SOX2 and interchangeable partner specificity [56].…”

Primordial Germ Cells in Mice

“…Thus, the genes associated with pluripotency are critical in PGC specification and proliferation/survival. Among the core pluripotency factors, SOX2 is not present in human PGCs, indicating that a different mechanism may underpin the pluripotency between the mouse and the human (Perrett et al 2008).…”

Elucidating human male germ cell development by studying germ cell cancer

“…1B). Furthermore, ECs show only weak to absent expression of cKIT as well as cytoplasmic localization of PRDM1 (Rajpert-De Meyts & Skakkebaek 1994, Leroy et al 2002, Almstrup et al 2005, Eckert et al 2008 (Fig. 1B).…”

“…Vice versa, human PGCs lack the expression of the pluripotency marker SOX2, which is expressed in murine PGCs aside with OCT3/4 and NANOG (Perrett et al 2008). Further, PRDM14, which is essential for murine PGC maintenance, shows only low levels of expression in human PGC-like cells and seminomatous TCam-2 cells, which also share a similar gene expression profile with PGCs (Irie et al 2015, Nettersheim et al 2015, Sugawa et al 2015, Tang et al 2015.…”

“…From seminoma patients, three cell lines have been derived so far, namely TCam-2, JKT-1 and SEM-1 (Table 1) (Mizuno et al 1993, Kinugawa et al 1998, Russell et al 2013. Thorough analyses revealed that TCam-2, but not JKT-1 cells, resemble seminoma in vitro (de Jong et al 2008, Eckert et al 2008, Nettersheim et al 2012, while SEM-1 cells show intermediate characteristics between seminoma and nonseminoma (Russell et al 2013).…”