2013) (n = 436+ embryos). PCR for human mitochondria is a more sensitive assay, identifying even the presence of 1/10,000 human cells, but this also failed to detect mouse-human chimerism. Although the generation of interspecies chimeras by injection of human ESCs into mouse morulae was proposed as a stringent assay for naive human pluripotency (Gafni et al., 2013), the assay may be too inefficient for use as a routine functional assay. Instead, Jaenisch suggested that expression profiling is the best method to define naive versus primed ESCs, noting that principal component analysis (PCA) of gene expression from naive hESCs clusters close to mESCs and far from primed hESCs.
