Expression of Pluripotent Stem Cell Markers in the Human Fetal Testis

¹ Institute for Cellular Engineering, Department of Gynecology and Obstetrics, Johns Hopkins University School of Medicine, Baltimore, MD 21205
² Department of Gynecology and Obstetrics, Stanford University, 300 Pasteur Drive, Stanford, California 94305

^* To whom correspondence should be addressed. E-mail: ckerr{at}jhmi.edu.

	Abstract

Human primordial germ cells (PGCs) have proven to be a source of pluripotent stem cells called embryonic germ cells (EGCs). However, the developmental potency of these cells in the fetal gonad still remains elusive. Thus, the following study provides a comprehensive analysis of pluripotent and germ cell marker expression in human fetal testis, 7–15 weeks postfertilization (pF) and compares this expression to their ability to derive EGCs. While the majority of germ cells expressed stem cell markers SSEA1, SSEA4, EMA-1 and alkaline phosphatase only a small percentage of those (<1%) expressed OCT4, CKIT and NANOG. Specifically, the number of OCT4⁺/CKIT⁺/NANOG⁺ cells significantly increased in the developing cords during week 7–9 followed by a gradual decline into week 15 pF. By week 15 pF the remaining OCT4⁺/CKIT⁺/NANOG⁺ cells were found in the cords surrounding the periphery of the testis and the predominate germ cells, CKIT⁺ cells no longer expressed OCT4 or NANOG. Based on morphology and early germ cell marker expression including VASA, PUM2 and DAZL we suggest these cells are mitotically-active gonocytes or prespermatogonia. Importantly, the number of OCT4⁺ cells correlated with an increase in the number of EGC colonies derived in culture. Interestingly, two pluripotent markers, Tra-1-60 and Tra-1-81 although highly expressed in EGCs, were not expressed by PGCs in the gonad. Together, these results suggest that PGCs maintain expression of pluripotent stem cell markers during and after sexual differentiation of the gonad albeit in very low numbers.