| Popis: |
Embryonic germ cells (EGCs) are pluripotent stem cells derived from primordial germ cells (PGCs), which are unipotent cells that in vivo give rise to the gametes (McLaren, 2003). Specification of PGCs takes place in the proximal posterior part of the epiblast shortly before gastrulation, when the epiblast is about to give rise to the three germ layers ectoderm, mesoderm, and endoderm. PGCs can be identified by expression of tissue non-specific alkaline phosphatase (TNAP) activity, various surface antigens stage specific embryonic antigen (SSEA1,3,4), mouse vasa homolog (Mvh) and intracellular proteins (Stella, Fragilis, Oct-4, Nanog and Blimp1 among others). From the proximal epiblast, PGCs migrate along the extraembryonic mesoderm at the base of the allantois, and then move into the epithelium of the hindgut. Later, PGCs start to move through the dorsal mesentery reaching the aorta-gonad-mesonephros (AGM) region and finish their migration at the developing genital ridges. When in gonads, PGC proliferate by mitosis until males enter in mitotic quiescence and in females enter into meiosis (De Felici, 2009). Under special conditions, PGCs become pluripotent stem cells. In vivo PGCs can generate embryonal carcinoma cells (ECC), the pluripotent stem cells of testicular tumors (Stevens, 1967; Oosterhuis& Looijenga, 2005), while in vitro they can generate EGCs (Matsui et al., 1992; Resnick et al., 1992; Surani, 2007; De Felici et al., 2009; De Miguel et al., 2010). PGCs could be isolated and cultured as such during short periods (up to 10 days) maintaining their phenotype, until they undergo apoptosis. When exposed to a specific mixture of growth factors, PGCs generate EGC colonies. EGCs could be an important source of cells for germ cell or stem cell therapy and a valuable model for understanding development processes involved in reprogramming such as the acquisition of pluripotency. EGCs were first derived in mice (Matsui et al., 1992; Resnick et al., 1992), and afterwards in a wide variety of mammals like cow (Cherny et al., 1994), goat (Jia et al., 2008), pig (Shim et al., 1997), and sheep (Ledda et al., 2010) among others. Importantly, in 1998 Shamblott et al. derived the first human EGC line, providing a potential source of pluripotent stem cells for therapy. In this chapter, differences and similarities of EGC derivation and culture of different species are discussed, including species in which long term EGC lines derivation has not yet been achieved. |
