Oct4GiP reporter assay to study genes that regulate mouse embryonic stem cell maintenance and self-renewal.

Pluripotency and self-renewal are two defining characteristics of embryonic stem cells (ES cells). Understanding the underlying molecular mechanism will greatly facilitate the use of ES cells for developmental biology studies, disease modeling, drug discovery, and regenerative medicine (reviewed in (1,2)). To expedite the identification and characterization of novel regulators of ES cell maintenance and self-renewal, we developed a fluorescence reporter-based assay to quantitatively measure the self-renewal status in mouse ES cells using the Oct4GiP cells (3). The Oct4GiP cells express the green fluorescent protein (GFP) under the control of the Oct4 gene promoter region (4,5). Oct4 is required for ES cell self-renewal, and is highly expressed in ES cells and quickly down-regulated during differentiation (6,7). As a result, GFP expression and fluorescence in the reporter cells correlates faithfully with the ES cell identity (5), and fluorescence-activated cell sorting (FACS) analysis can be used to closely monitor the self-renewal status of the cells at the single cell level (3,8). Coupled with RNAi, the Oct4GiP reporter assay can be used to quickly identify and study regulators of ES cell maintenance and self-renewal (3,8). Compared to other methods for assaying self-renewal, it is more convenient, sensitive, quantitative, and of lower cost. It can be carried out in 96- or 384-well plates for large-scale studies such as high-throughput screens or genetic epistasis analysis. Finally, by using other lineage-specific reporter ES cell lines, the assay we describe here can also be modified to study fate specification during ES cell differentiation.