Deriving rabbit embryonic stem cells by small molecule inhibitors.

We previously developed pluripotent rabbit embryonic stem cells (rbES) using a culture system supplemented with basic fibroblast growth factor (bFGF) and leukemia inhibitory factor (LIF), noggin and Y-27632 (referred to as iFLY). In present work, we explored multiple approaches to enhance the chance of deriving domed pluripotent rbES cells by inhibition of MEK, GSK, and PKC signaling pathways. Domed stated rbES were derived in defined medium supplemented with 15% KOSR, 10³ IU/mL mouse LIF, 10 ng/mL bFGF and three inhibitors to the MEK (PD0325901, 1 µM), GSK3 (CHIR99021, 3 µM) and PKC (Gö6983, 5 µM) (3i). Domed rbES were passaged every 3-4 days till passage 3-4 for the designated experiments. We showed that bFGF and LIF are indispensable for the derivation and maintenance of rbES; whereas the 3i medium containing inhibitors to the MEK (PD0325901), GSK3 (CHIR99021) and PKC (Gö6983) were necessary for deriving domed rbES. Domed rbES possessed naïve ES markers as <i>Rex1</i> and <i>ERAS</i> in addition to <i>Oct4, Klf4, Sox 2</i> and <i>c-myc</i> by RT-PCR. Domed rbES showed positive staining for Rex1, Fgf4, Klf4, Nanog and Oct4 by immunofluorescence chemistry. Further deleting either one factor in 3i medium as CHIR99021, PD0325901, Gö6983 or bFGF resulted in disappearing of domed rbES colonies. The optimal concentrations of 3i contained 0.75 µM PD0325901, 2.25 µM CHIR99021, and 4.5 µM Gö6983. Our work, in combination of different inhibitors for deriving rabbit ES, supports that the network of signal pathways plays an important role in ES self-renew, propagation and maintenance, and sheds light on deriving authentic properties of rbES in an important yet understudied model animal species.