Embryonic pluripotent stem cells (ESC) and induced pluripotent stem cells (iPSC) were reported capable of differentiating into primordial germ cell-like (PGCL) and functional gametes in vitro in the murine model (Hikabe et al. 2016 Nature 539, 299-303). The in vitro generation of primordial germ cells (PGC) and gametes from farm animals would greatly contribute to enhance animal production technologies and to the creation of adequate models for several disorders. The present study aimed at the generation of PGC in vitro (iPGC) from iPSC in cattle and their characterisation through pluripotency and germ cell markers. For that, bovine iPSC previously generated and characterised (Bressan et al. 2015 Reprod. Fertil. Dev. 27, 254) were submitted to in vitro differentiation into epiblast-like cells (EpiLC) and iPGC by the protocol adapted from mice (Hayashi et al. 2011 Cell 146, 519-532). The biPS cells were induced into EpiLC by culture in fibronectin-coated (16.7 µg mL−1) 6-well plates in N2B27 culture medium supplemented with 20 ng mL−1 activin A, 12 ng mL−1 basic fibroblast growth factor (bFGF), and 1% knockout serum replacement (KSR) for 48 h and further differentiated into iPGC by non-adherent culture (Agreewell plates, StemCell Technologies, Vancouver, BC, Canada) with GK15 medium (GMEM supplemented with 15% KSR, 0.1 mM nonessential amino acids, 1 mM sodium pyruvate, 0.1 mM 2-mercaptoethanol, 2 mm l-glutamine, and 1% antibiotics) in the presence of 500 ng mL−1 BMP4, 100 ng mL−1 SCF, 500 ng mL−1 BMP8b, and 50 ng mL−1 epidermal growth factor for 4 days. The cells were then characterised regarding morphology, detection of alkaline phosphatase, immunofluorescence for OCT4, DDX4, VASA, and c-Kit proteins, and transcripts of pluripotency-related genes OCT4 and SOX2, as well as of imprinted genes (H19, SNRPN) and imprinted-related (DNMT1, DNMT3B) genes were analysed through RT-qPCR and compared with constitutive genes GAPDH, NAT1, and ACTB. Alkaline phosphatase and immunofluorescence analysis were positive for all specific markers. Interestingly, although OCT4 and SOX2 expression was present in iPS, EpiLC, and iPGC, this last group presented greater OCT4 and lesser SOX2 transcript amounts compared with other groups, suggesting, as expected, that PGC are still pluripotent but may already be differentiating into germ-cell lineages. The expression of H19 was increased in iPGC, whereas the expression of SNRPN was decreased only in the fibroblast group, potentially indicating epigenetic reprogramming process in these cells. Expression of DNMT1 and DNMT3B was not different between pluripotent groups but subtly increased when compared with that in fibroblasts. The results obtained herein represent an important first step in the in vitro generation of PGC and gametes from domestic farm animals, an unprecedented and desirable tool for enhancing new reproductive technologies and providing new understanding of cellular reprogramming and pluripotent germ cell biology.
Financially supported by FAPESP grants 2013/08135-2, 2013/13686-8, 2015/26818-5; CNPq 482163/2013-5.
Germ Cell Derivation from Pluripotent Stem Cells for Understanding In Vitro Gametogenesis