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Constitutive GFP-UTF1 Expression Interferes with ES and EC Cell Differentiation

Rajkumar P. Thummer, Loes J. Drenth-Diephuis and Bart J.L. Eggen

Embryonic stem cells have the ability to self-renew and can differentiate into all cell types of the three embryonic germ lineages. The undifferentiated embryonic cell Transcription Factor 1 (UTF1) gene is highly expressed in ES cells and we previously reported that UTF1 is tightly associated with chromatin and is required for differentiation of pluripotent mouseembryonic stem (ES) and embryonic carcinoma (EC) cells. In this study, we generated ES and EC cell lines constitutively expressing GFP-UTF1 to further investigate its role in differentiation. ES and EC cells constitutively expressing GFP-UTF1were suppressed in their proliferation and were still dependent on LIF for self-renewal. Embryoid body (EB) differentiation of GFP-UTF1 overexpressing ES cells showed both normal differentiation as well as a delayed or incomplete differentiation of a subset of cells. GFP-UTF1 was persistently expressed in undifferentiated cells whereas GFP-UTF1 expression was not detected in differentiated cells. Where GFP-UTF1 expressing ES cells differentiated normally in response to DMSO, EC cell differentiation was completely blocked. When ES and EC cells expressing GFP-UTF1 were treated with RA, differentiation markers were induced and endogenous UTF1 and GFP-UTF1 protein levels decreased. However, GFP-UTF1 and UTF1 (in ES cells) mRNA was still detected indicating that degradation of (GFP-)UTF1 protein preceded down regulation of (GFP-) UTF1 mRNA, suggesting that RA induced UTF1 degradation. Summarizing these data indicate that similar to UTF1 depletion, overexpression of GFP-UTF1 interfered with ES and EC cells differentiation.