Basic FGF and Activin/Nodal but not LIF signaling sustain undifferentiated status of rabbit embryonic stem cells.

Recently, we proposed that rabbit embryonic stem (ES) cells can be stable mammalian ES cells and can be a small animal model for human ES cell research. However, the signaling pathways controlling rabbit ES cell pluripotency remain largely unknown. Here we report that bFGF can maintain the undifferentiated status of rabbit ES cells and found that Activin/Nodal signaling through Smad2/3 activation is necessary to maintain the pluripotent status of rabbit ES cells. We further show that in spite of STAT3 in rabbit ES cells, LIF is dispensable for maintenance of undifferentiated status in rabbit ES cells. Although phosphorylation of Janus Kinase signal transducer and activator (JAK/STAT) disappeared after JAK-inhibitor treatment, OCT4 is constantly produced. When rabbit ES cells were cultured for more than 40 passages in the absence of LIF, expression of stem cell markers and teratoma formation were observed. Additionally, treatment with Rho-associated kinase (ROCK) inhibitor, Y27632, to rabbit ES cells significantly enhanced cell growth. These findings suggest that molecular mechanisms underlying rabbit ES cell self-renewal and pluripotency are similar to primate ES cells. Rabbit ES cells may provide a translational research model for the study of human diseases in vitro and applications to transplantation therapy.