The expression of genes in human preimplantation embryos

The study of gene expression in human preimplantation embryos is establishi ng itself as a necessary dimension of developmental biology and medical gen etics. Transcripts identified in human preimplantation embryos include hous ekeeping genes, transcription and growth factor genes, sex-determining gene s, tissue-specific genes and novel genes, as well as genes of unknown funct ion. Strategies are being developed which will eventually permit the most s ophisticated gene expression studies on single human embryos of co-ordinate d transcription and translational regulation. There is both a need for inte rnational co-operation for the systematic construction of expression maps a nd a need to establish databases of expression patterns during different st ages of human development. Understanding how genes are regulated in humans is essential for understand ing both normal development and disease. Until recently, studies of gene ex pression and regulation during embryogenesis were almost exclusively limite d to prokaryotes and to eukaryotes other than man. The introduction of arti ficial reproductive technologies in conjunction with the development of rec ombinant molecular technologies applicable to single cells has made possibl e the study of human development at its earliest stages (Pergament and Bonn icksen, 1994). Although there are still enormous technical challenges, robu st strategies have been, and continue to be, developed for connecting DNA s equence to such endophenotypes as timing and level of gene expression at th e single cell level. Questions currently being asked in human developmental genetic studies concern the pronucleus, the zygote and the preimplantation embryo: what genes are expressed? When are they expressed? What functions do they perform and how, in sequence or in combination? And, what elements control and regulate their expression? This review provides an overview of current knowledge about the expression of different embryonic genes during early human development and discusses future prospects, which includes a ne ed for international co-operation similar to the Human Genome Project. Copy right (C) 1998 John Wiley & Sons, Ltd.