Tbx3 improves the germ-line competency of induced pluripotent stem cells

Induced pluripotent stem (iPS) cells can be obtained through the introduction of defined factors into somatic cells1. The combination of Oct4, Sox2 and Klf4 (OSK) constitutes the minimal requirement for generating iPS cells from mouse embryonic fibroblasts (MEFs). These cells are thought to resemble embryonic stem cells (ESCs) based on global gene expression analyses; but, few studies have tested their ability and efficiency in contributing to chimerism, colonization of germ tissues, and most importantly, germ-line transmission and life-birth from iPS cells produced with tetraploid complementation. Through the genomic analyses of ESC genes that have roles in pluripotency and fusion-mediated somatic cell reprogramming, we identified Tbx3 as a transcription factor that significantly improves the quality of iPS cells. Induced-PS cells generated with OSK + Tbx3 (OSKT) are superior in both germ cell contribution to the gonads and germ-line transmission frequency. However, global gene expression profiling could not distinguish between OSK and OSKT iPS cells. Genome-wide ChIP-sequencing analysis of Tbx3 binding sites in ESCs suggests that Tbx3 regulates pluripotency-associated and reprogramming factors, in addition to sharing many common downstream regulatory targets with Oct4, Sox2, Nanog and Smad1. This study underscores the intrinsic qualitative differences between iPS cells generated by different methods and highlights the need to rigorously characterize iPS cells beyond in vitro studies.