Our studies show that retrogenes are preferentially expressed in preimplantation embryos. These genes carry a short noncoding exon 1 that contributes directly to expression of the gene, and a second exon that contains the coding sequence without intron interruption. We show that preimplantation gene expression is first regulated by developmentally regulated transcription factors that target exon 1 and the solitary intron, followed by promoter hypermethylation on implantation and in adult tissues. An understanding of the mechanisms of gene expression during preimplantation development should have an impact on the understanding and treatment of spontaneous abortion and infertility. [J Chin Med Assoc 2009; 72(7):346-350]
