Background
Embryonic stem (ES) cells were first derived from the blastocysts of mice in 1981 [1,2] and humans in 1998 [3]. ES cells have two important properties: theability to maintain pluripotency, which is the ability to differentiate into a wide variety of cells, and rapid proliferation. These characteristics make mouse ES cells an essential component of gene targeting technology. These qualitiesalso make human ES cells attractive sources for cell transplantation therapy to treat various diseases, including spinal cord injuries and juvenile diabetes. The molecular mechanisms underlying the pluripotency and rapid proliferation of ES cells are currently a major focus of the field of stem cell biology [4-6].
To identify molecules essential in ES cells for these properties, several groups have utilized transcriptome analyses to identify genes specifically expressed in ES cells and early embryos. These analyses, including DNA microarray analyses [7] and expressed sequence tag analyses [8-12], identified several common transcripts, including ESG1 that was also designated dppa5 or ECAT2.
ESG1 was originally identified as a transcript Ph34 that was down-regulated by retinoic acid in embryonic carcinoma cells [13]. The expression of this gene was confined in mice to early embryos and germ cells [14]. It is also expressed in pluripotent cells, including ES cells, embryonic germ cells, and multipotent germline stem cells [15]. ESG1 encodes a polypeptide of 118 amino acids that contains a single KH domain, which is an RNA-binding domain [16]. It remains unclear, however, if ESG1 functions as an RNA-binding protein or the roles it plays in ES cells and mice.
Previous genomic library screening by identified genomic clones containing the mouse ESG1 gene and seven pseudogenes [17]. Two of these pseudogenes exhibit a similar exon-intron structure as the ESG1 gene, indicating their generation by gene duplication. The five remaining pseudogenes did not contain any introns, indicating that these were generated by retrotransposition of ESG1 transcripts. The chromosomal localizations of the mouse ESG1 gene and pseudogenes, however, have not been reported.
In this study, we determined the structure of the mouse gene encoding this protein and related pseudogenes. We also performed gene targeting to determine the physiological function of ESG1.