| Summary: | Summary: Rat embryonic stem cells (rESCs) are capable of contributing to all differentiated tissues, including the germ line in chimeric animals, and represent a unique, authentic alternative to mouse embryonic stem cells for studying stem cell pluripotency and self-renewal. Here, we describe an EGFP reporter transgene that tracks expression of the benchmark naive pluripotency marker gene Rex1 (Zfp42) in the rat. Insertion of the EGFP reporter gene downstream of the Rex1 promoter disrupted Rex1 expression, but REX1-deficient rESCs and rats were viable and apparently normal, validating this targeted knockin transgene as a neutral reporter. The Rex1-EGFP gene responded to self-renewal/differentiation factors and validated the critical role of β-catenin/LEF1 signaling. The stem cell reporter also allowed the identification of functionally distinct sub-populations of cells within rESC cultures, thus demonstrating its utility in discriminating between cell states in rat stem cell cultures, as well as providing a tool for tracking Rex1 expression in the rat. : Rat embryonic stem cells (ESCs) differentiate into all adult cells, including functional gametes, and uniquely qualify as a comparator with mouse ESCs to study self-renewal and pluripotency. In this article, Burdon and colleagues generated a Rex1-EGFP stem cell reporter as a sensitive tool to monitor and interrogate the regulation of rat ESCs, and contribute to understanding stem cells and fate determination in mammals. Keywords: rat, embryonic stem cell, Rex1, Zfp42, fluorescent reporter, EGFP, pluripotency, self-renewal, genetic engineering, transgenic, single cell sequencing
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