Functional heterogeneity of embryonic stem cells revealed through translational amplification of an early endodermal transcript.

Abstract

Author SummaryEmbryonic stem (ES) cells are karyotypically normal, embryo-derived cell lines that are pluripotent, i.e. capable of generating all the cell types of the future organism, but not the extra-embryonic lineages. What gives ES cells this unique capacity? Here, we use a fluorescent reporter cell line that employs translational amplification to visualize single ES cells expressing low levels of lineage-specific genes. With this reporter we split ES cell cultures into two fractions that both express certain stem cell markers but only one of which expresses low levels of an endodermal marker gene. Following purification, single cells from either fraction are equally competent to re-establish a heterogeneous culture. However, when challenged to differentiate immediately after purification, each exhibits strong lineage bias, with the endoderm marker-expressing fraction unexpectedly able to contribute to the extra-embryonic endoderm in chimeric embryos. These data suggest that ES cells expand under steady-state conditions as a heterogeneous mix of lineage-biased—but not lineage-committed—cell types. We propose that these observed uncommitted substates exist temporarily in vivo, but are perpetuated in vitro under the selectively self-renewing conditions of ES cell culture. Our findings suggest that pluripotency is determined by the capacity of a mixed population of lineage-biased intermediates to commit to different cell fates in specific contexts.