Chapter 7: UNRAVELING THE HUMAN GENOME AND ITS FUTURE IMPLICATIONS FOR CARDIOLOGY
FUNCTIONAL GENOMICS (PROTEOMICS)
One of the great accomplishments-and perhaps the greatest of the twenty-first century or even the new millenium-will be the identification of all the genes responsible for humankind. This development is often compared to another great landmark in physics, namely, the identification of the table of physical elements. This analogy emphasizes a very important point for the future. The table of physical elements (periodic table) provided the physicists with the tools to determine the composition of the earth, to understand many natural phenomena, and also to create artificial constructs, many that were essential to modern civilization and others that were destructive, such as the atomic bomb. Identification of the genes will be to the biologist or physician what discovering the physical elements was to the physicist. Leroy Hood refers to the human genetic map as the "periodic table of life." The identification of all human genes provides the tools for the first step: determining gene function and how to manipulate genes to benefit humankind. Determining the function of known and unknown genes was addressed at a recent workshop in Cold Spring Harbor, New York.15 At present, we know of only about 2000 proteins. Thus, we do not know the protein composition of most genes and so would not be expected to know their function. It was estimated that determining the function of 100,000 genes by conventional techniques-namely, eliminating the gene from the mouse by homologous recombination or overexpressing the gene (transgenic mouse)-would take a century. The theme of Human Genome Project II will undoubtedly be determining functions of the proteins, and the project has been referred to by several names emphasizing function, such as The Proteome, Gene Health and Disease, or Functional Genome II. It is imperative that the efforts to determine the functions of human genes receive a boost from improved technology and increased awareness. New approaches are already emerging from the Human Genome Project to address this issue.
In parallel with the progress for sequencing the human genome has been the success of efforts to sequence simpler genomes of single-cell organisms. The first organism for which the genome was sequenced and the genes identified was Haemophilus influenzae, in 1995, consisting of 1.4 million base pairs and 1740 genes. Within 3 years of this initial effort, the genomes of over 40 single-cell organisms were completely sequenced and all of the genes identified. Several notable organisms were sequenced: Saccharomyces cerevisiae,16 which is the cause of vaginitis, and spirochete Treponema pallidum,17 which causes syphilis. These organisms, many of which are bacterial, offer the potential for the diagnosis and treatment of human infectious diseases, whether they affect the heart or other organs. Identification of the genes responsible for these various organisms has ushered in a new era for antibiotics based on a variety of molecular mechanisms made possible through the identification of genes and the various pathways they regulate. A significant step forward in our understanding of the function of human genes came with the sequencing of the genome responsible for Caenorhabditis elegans (C. elegans).18 This was the first multicellular organism for which the genome and all of its genes have been sequenced. C. elegans, although a tiny worm that is not visible to the naked eye, has 959 cells, all of which have been identified and characterized. Its genome consists of over 97,000,000 base pairs, with a total of over 19,000 genes. This represents one-fifth of the number of genes present in the human genome. The more important features are, however, that 36 percent of the genes in C. elegans are virtually identical to human genes, with many others having homologous consensus. The C. elegans is a transparent worm, and, thus, it is possible under the microscope to observe development from a single cell to a multicellular organism and now to do so with the armamentarium of knowing all the genes. Thus, it should be possible, by determining the function of many genes in C. elegans homologous to human genes, to learn of their approximate function in humans. Several other multicellular organisms are being sequenced, including the fruit fly (Drosophila)19 and the mouse, which will provide an immense opportunity for determining the function of human genes with similar functions.20 This will considerably accelerate our efforts to determine the function of human genes and how to utilize them to diagnose, prevent, and cure disease.
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