Isolation of novel developmental genes from human germ cell, oocyte and embryo cDNA by differential display

Due to the difficulties inherent in research on human embryos, almost nothing is known about genes active in human early development. Although the human genome project will provide resources that theoretically provide access to every human gene, those genes specific to human early development may be difficult to define. Also, by definition, genes specific to early development will not be represented in cDNA databases derived from human somatic cells. Yet these unknown human developmental genes are likely to be of key importance for several areas of human health, including assisted reproduction and contraception, embryo stem cell research and tissue transplantation, ageing and cancer. In order to identify and isolate these human developmental genes, we have prepared amplified cDNA from human primordial germ cells, oocytes and embryos, and used differential display to compare patterns of gene expression in these embryonic cells and in the cells of somatic tissues of a 10-week human fetus. This paper reviews the highly sensitive procedures used to create amplified cDNA representing expressed genes in a single cell and the use of differential display to identify developmental genes. Several such genes have been isolated, but their full-length sequences and function are yet to be elucidated. Genes active in human early development are expected to play key roles in the maintenance of the archetypal stem cell state, potential immortality and the invasiveness of trophectoderm and primordial germ cells. They represent candidate genes regulating these functions for targeting in clinical research in human reproduction, stem cell differentiation and cancer.