TRANSCRIPTION OF TISSUE-SPECIFIC GENES IN HUMAN PREIMPLANTATION EMBRYOS

We have recently detected de-novo transcripts of the predominantly mus cle-specific myotonin protein kinase gene in human preimplantation emb ryos from the 1-cell to the 4-cell stages. Others have shown de-novo t ranscripts of the Y-linked genes, ZFY and SRY, in the 1-cell zygote. I n order to assess the significance of early transcription of these pre dominantly tissue-specific genes in preimplantation development, we ha ve analysed individual human oocytes and preimplantation embryos for t he presence of transcripts of two further tissue-specific genes, alpha -globin and beta-globin, and two house-keeping genes, HPRT and APRT. R everse transcriptase polymerase chain reaction assays were developed t o the required single cell sensitivity, using human red blood cells an d fibroblasts, prior to their application to human oocytes and embryos . As expected: transcripts of the house-keeping genes, HPRT and APRT. were detected at all stages of preimplantation development. Transcript s of 'tissue-specific' alpha-globin were readily detected in preimplan tation embryos from the 1-cell stage. However, transcripts of beta-glo bin were detected only rarely (in only one of the 11 embryos analysed) . This difference may be due to the fact that alpha-globin contains a CpG island. A survey of the data on gene expression in early human dev elopment suggests that CpG-island-containing genes may be expressed in preimplantation embryos. Expression of these genes in gametes and ear ly embryos may be involved in the survival of CpG islands in evolution .