Regulation of ES Cell Self Renewal and Pluripotency by Foxd3

¹ Center for Stem Cell Biology, Department of Cell and Developmental Biology, 2213 Garland Ave, 9465 MRB IV, Vanderbilt University School of Medicine, Nashville, TN 37232-0494, USA

^* To whom correspondence should be addressed. E-mail: trish.labosky{at}vanderbilt.edu.

	Abstract

The Foxd3 forkhead transcription factor is required for maintaining pluripotent cells in the early mouse embryo and for the establishment of murine embryonic stem (ES) cell lines. To begin to understand the role of Foxd3 in ES cell maintenance, we derived ES cell lines from blastocysts that carried two conditional Foxd3 alleles and a tamoxifen-inducible Cre transgene. Tamoxifen treatment produced a rapid and near complete loss of Foxd3 mRNA and protein. Foxd3- deficient ES cells maintained a normal proliferation rate but displayed increased apoptosis, and clonally dispersed ES cells showed a decreased ability to selfrenew. Under either self-renewal or differentiationpromoting culture conditions we observed a strong, precocious differentiation of Foxd3 mutant ES cells along multiple lineages including trophectoderm, endoderm and mesendoderm. This profound alteration in biological behavior occurred in the face of continued expression of factors known to induce pluripotency including Oct4, Sox2 and Nanog. We present a model for the role of Foxd3 in repressing differentiation, promoting self-renewal and maintaining survival ofmouse ES cells.