Defining cell identity by comprehensive gene expression profiling

The human body is composed of 60 trillion cells, which have their origin in a fertilized egg. During development, the potential of a cell or tissue can be achieved by environmental manipulation. Then, what molecular determinants underlie or accompany the potential of the cells? To obtain a broader understanding of these problems, it is important to analyze all transcripts/genes in a wide selection of cell types. The development of microarray technologies, which allow us to undertake parallel analyses of many genes, has led to a new era in medical science. In this review, we show that the global expression data have clearly elucidated discernible major trends of the phenomenon in preimplantation development and epithelial-mesenchymal transition, and of the character of marrow stromal cells, which are attracting a great deal of attention as they represent a valuable source of cells for regenerative medicine. One of the interesting results is obtained from microarray data of marrow stromal cells: OP9 cells that have been recognized as a type of niche-constituting preadipocyte derived from marrow stroma, are found to be chondroblasts. We also describe what effect each type of expression data would bring to reproductive and regenerative medicine, as well as offering an excellent model of cell differentiation in biology.