RESUMEN
Pluripotent embryonic stem cells (ESCs) were first isolated nearly three decades ago from mice, yet efficient ESC isolation has been limited to rodents and primates to date. We report a novel and robust technique for isolating ESCs from mammalian pre-implantation embryos by altering the epigenotype of embryonic explants and using pressed zona pellucida-free blastocysts. We first examined this technique for murine ESC derivation. Compared with controls, murine ESCs were efficiently derived when explants were exposed to 1 µM 5-azacytidine, an epigenetic modifier that causes DNA demethylation (56.1% vs 31.6%; P < 0.01). Mouse ESCs stained positively for alkaline phosphatase, expressed markers of pluripotency including Oct4, Rex1 and SSEA1 and formed teratomas when injected into Severe Combined Immuno-Deficient (SCID) mice. The approach was subsequently used for bovine ESC derivation. In bovine a higher concentration of 5-azacytidine (5 µM) was required to elicit a response. This technique resulted in up to 18 times more efficient isolation of pluripotent cells than traditional methods (71.4% vs 4.0%; P < 0.001). These putative bovine ESCs expressed OCT4, REX1 mRNA and SSEA-1 and SSEA-4 proteins; and were able to form embryoid bodies in vitro and teratomas when injected in Severe Combined Immuno Deficient (SCID) mice. This is the first report on derivation of ESCs with both in vitro and in vivo differentiation potential in a livestock species.
