Stage-specific induction and regulation by genomic imprinting of the mouse U2afbp-rs gene during preimplantation development.

The mouse U2afbp-rs gene is imprinted and expressed exclusively from the paternal allele in the adult. To determine whether the U2afbp-rs gene is regulated by imprinting in the early embryo and to examine its normal temporal pattern of expression, we used a new quantitative RT-PCR approach to compare U2afbp-rs gene expression between androgenetic and gynogenetic embryos and to monitor U2afbp-rs expression during normal preimplantation embryogenesis. The U2afbp-rs gene is transcriptionally induced transiently at the 2-cell stage, making it one of the first genes ever identified with this pattern of regulation. At the 2-cell stage, androgenones express approximately twice as much U2afbp-rs mRNA as normal embryos, while gynogenones express much less. Thus, genomic imprinting regulates the U2afbp-rs gene from the time of its initial induction, distinguishing it from some other autosomal imprinted genes that have been analyzed (e.g., Igf2r and Igf2). Because the function of the U2afbp-rs protein has not been determined, the significance of transient induction of the U2afbp-rs gene at the 2-cell stage is not clear. Our data indicate that abundant expression of the U2afbp-rs gene is not essential for early development since gynogenones form blastocysts at a high frequency.