BMI1 enables interspecies chimerism with human pluripotent stem cells

Abstract

Human pluripotent stem cells (hPSCs) exhibit very limited contribution to interspecies chimeras. One explanation is that the conventional hPSCs are in a primed state and so unable to form chimeras in pre-implantation embryos. Here, we show that the conventional hPSCs undergo rapid apoptosis when injected into mouse pre-implantation embryos. While, forced-expression of BMI1, a polycomb factor in hPSCs overcomes the apoptosis and enables hPSCs to integrate into mouse pre-implantation embryos and subsequently contribute to chimeras with both embryonic and extra-embryonic tissues. In addition, BMI1 also enables hPSCs to integrate into pre-implantation embryos of other species, such as rabbit and pig. Notably, BMI1 high expression and anti-apoptosis are also indicators for naïve hPSCs to form chimera in mouse embryos. Together, our findings reveal that the apoptosis is an initial barrier in interspecies chimerism using hPSCs and provide a rational to improve it.

Chicken Interspecies Chimerism Unveils Human Pluripotency

“…hPSCs (3–5 × 10 3 ) (hESCs, primed RH6; pRH6) suspended in 8—5 μL culture medium were engrafted into HH2, HH3, and HH4 PS stages ( Table S1 ). Since anti-apoptotic factors improve interspecies chimera formation of primed pluripotent cells ( Huang et al., 2018 ; Masaki et al., 2016 ; Wang et al., 2018 ), the cell suspension was supplemented with 10 μM Y27632 (ROCK inhibitor). Similar to the results obtained for injection of medium, 40% of chicken embryos injected at HH4 survived, while survival after injection of HH2 and HH3 was poor (6% and 14% survival, respectively) ( Table S1 ).…”

“…Previous studies indicated that heterochronic chimera formation is feasible when enhancing survival of primed PSCs ( Huang et al., 2018 ; Kang et al., 2018 ; Masaki et al., 2016 ; Wang et al., 2018 ). To test this hypothesis, we injected primed pRH6 and piPSCs into BLD-stage chicken embryos after treatment with Y27632.…”

“…On the other hand, some studies indicated that interspecies chimerism can be achieved with non-stage-matching (NSM) rat EpiSCs or primed hPSCs and mouse pre-implantation embryos when the survival of primed cells was enhanced by overexpression of anti-apoptotic genes. These findings questioned the necessity of an SM approach ( Huang et al., 2018 ; Masaki et al., 2016 ; Wang et al., 2018 ).…”

Apoptosis, G1 phase stall and premature differentiation account for low chimeric competence of Human and rhesus monkey naïve pluripotent stem cells

“…Previous studies have shown that inhibiting apoptosis either by the addition of the Rock inhibitor Y27632 (Kang et al, 2018), or by overexpression of the anti-apoptotic genes BCL2 (Masaki et al, 2016) or BMI1 (Huang et al, 2018) enables primed PSCs to colonize host embryos. Therefore, in a final series of microinjections, we asked whether inhibition of apoptosis could improve the engraftment of naïve PSCs into the host embryo.…”

A Novel Strategy for Xeno-Regenerative Therapy

“…Given that human iPSCs fundamentally lack the ability to form chimeras, blastocyst complementation cannot be applied directly to humans. Inducing the expression of anti-apoptotic genes could give some chimera-forming ability to human iPSCs [40,41], but the long-term safety would require clarification because these are also recognized oncogenes. Another issue is that basing this method on systemic chimera formation leads to the serious ethical concern of chimera formation in host gametes or neural tissue other than the target organs.…”