Gene expression profiling of cells and tissues

Abstract

The behaviour of individual human cells and of tissues in health and disease has long been a focus for study. Increasingly, we recognize the roles that alterations in the pattern of cellular gene expression play in normal processes, such as human embryonic development, and in abnormal processes, such as tumourigenesis. The Human Genome Project, which aims to identify and sequence all of the approximately 80 000 genes within the human genome, is already at an advanced stage. As this wealth of information becomes available, the focus in research is shifting towards the functional analysis of human genes in health and disease. This requires methods which allow the global pattern of gene expression in cells and/or tissues to be sampled and analysed rapidly. The human genome consists of approximately 3.3 x 10 9 base-pairs of double-stranded deoxyribonucleic acid (DNA) and contains approximately 80000 genes. Within the genome, a gene is that amount of DNA base sequence which codes for a single protein. A gene is said to be expressed when its base sequence is transcribed from DNA into an intermediate form known as messenger RNA (mRNA). Base triplets (codons) within the mRNA determine the incorporation of amino acids into the newly synthesized protein in the order determined by the original DNA strand. Most human genes are expressed in the majority of cell types; however, a minority of genes (15% or less) are expressed only in a specific cell type or at a specific developmental timepoint) These genes confer defined structural and functional properties on the cell. Gene expression and its regulation are processes which determine many aspects