Investigating the role of FOXM1 in the maintenance of human embryonic stem cell pluripotency

Abstract

Human embryonic stem cells (hESCs) are capable of infinite proliferation and hold the potential to differentiate into various cell lineages for cell and tissue transplantation. Many factors have been identified to regulate the self renewal and pluripotency of hESCs, yet the complete regulatory mechanism has not be fully elucidated1. The proliferation-associated Forhkead box transcription factor FOXM1 has been reported to be involved in the maintenance of pluripotency in mouse embryonal carcinoma cells. In this study, we showed that FOXM1 is expressed in the hESC line VAL3, with expression found in both the nucleus and the cytoplasm. Using bivariate flow cytometry analysis, FOXM1 was shown to display cell cycle-dependent changes in expression in asynchronus VAL3 cells, with peak levels observed at the G2/M phase. Using chromatin immunoprecipitation assay, FOXM1 was demonstrated to bind the promoters of OCT4 and NANOG, as well as the promoters of cell cycle genes. However, depleting FOXM1 in undifferentiated VAL3 cells using siRNAs did not result in significant down-regulation of OCT4 and NANOG. As VAL3 differentiated, either as embryoid bodies or after retinoic acid induction, FOXM1 expression was found to decrease gradually and reach low levels at late differentiation stages. Taken together, our findings suggest that FOXM1 is not likely to be an upstream regulator of the core pluripotent network in hESCs. Future work will focus on the role of FOXM1 in mediating the self renewal and proliferation of hESCs.