Living in the post-genomic era.

The completion of the sequencing of the human genome and at an accelerating pace of the genome of many other organisms has undoubtedly changed the outlook of biological research, to the point that biologists define the present one as "the post-genomic era", marking the need to approach the study of living organisms with a different perspective. To understand this transition, we must recall that much of the research in biology and medicine in the past two to three decades has been characterized by the efforts to identify the gene(s) responsible for a given biological function (or disease, for much of human pathology), isolate it and determine the DNA sequence bearing the information for it. Instead, today the researcher investigating a function of the human organism or any interesting organism, whether microbe, plant or animal, for which the data on the genome sequence are already or will be available in the near future, is offered all the necessary information concerning the complete DNA sequence.

The media hype on the completion of the human genome sequencing--which, in fact, is not quite complete since a number of gaps and uncertainties are still extant, but will undoubtedly be eliminated in the near future--has led the public to believe that the task of understanding the details of the function (and dysfunctions) of the human organism is almost attained or lust around the corner. The reality is much more sobering, and in order to assess it the International Centre for Genetic Engineering and Biotechnology (ICGEB) organized in October 2001 a scientific symposium, gathering some of the most qualified biologists of the world scientific community to review "the biology of the post-genomic era".

Besides the purely scientific interest in the matter, the symposium had also a practical operational character, namely to help in orienting the scientific programme of ICCEB in the near and not-too-distant future. The Centre, which was initially promoted by the United Nations Industrial Development Organization (UNIDO) and is an autonomous international organization with a membership of 46 countries, has the mandate of providing a centre of excellence for research and training in genetic engineering and biotechnology of the developing countries. The reasons that prompted UNIDO to create ICGEB stem from the realization emerging in the late seventies that the extraordinary progress of molecular biology and genetics offered unprecedented potential tools to alleviate or solve the most pressing problems of the developing countries, namely health and nutrition, as well as poverty, considering that biotechnology-based industrial productions have a very high added value, are little demanding in terms of capital inves tment and energy or raw materials, and depend essentially on the availability of well-trained scientists and technicians.

The International Centre was so created as a sort of twin centre, with a component (laboratory) in Trieste, Italy, and the other in New Delhi, India, plus a network of 32 affiliated centres in as many member countries. Most of the financial support has been and is given by the Governments of the two host countries, and the activity in the two components initiated in 1987 to reach in a few years a level of approximately 200 scientists, equally distributed, over 100 peer-reviewed scientific publications per year and a programme of grants to the affiliated centres subsidizing approximately fifty research projects.

The Centre's general direction is located in Trieste, expanding the tradition of this city in international scientific cooperation initiated in the early sixties with the creation of the International Centre for Theoretical Physics (an emanation of the International Atomic Energy Agency and the UN Educational, Scientific and Cultural Organization, and founded by the late Pakistani Nobel laureate Abdus Salam) and continued with the Third World Academy of Sciences, of ICGEB, and of the International Centre for Science and High Technology (an emanation of UNIDO).

The novel scientific landscape, as it emerged during the symposium, can be summarized as an apparent paradox: how can a highly complex organism like the human one be codified by a number of genes, probably as small as 30,000, and in any case not greater than 60,000, which is only five to ten times greater than the number contained in a unicellular microbe like yeast? The solution of this paradox shows the complexities and difficulties facing today's biologists. In fact, even though we can identify the "genes" in the genome, i.e. the sequences that code for a protein--with a certain degree of uncertainty, as shown above--we are still far from even knowing the number of proteins actually present in a cell, let alone the organism.

This may sound surprising and requires some explanation. The proteins are polymeric molecules made of linear chains of many monomers called amino acids--they are of twenty different kinds, whereas the long DNA chains codifying for them are polymers made of monomers, called bases, of four different kinds. The proteins are the effectors of all the reactions and interactions that characterize living organisms.

The amino-acid sequence of any protein, having lengths ranging from a few hundreds to a few thousands of amino acids, is codified in a sequence of bases on the DNA (each amino-acid being specified by three subsequent bases). In order to pass from the sequence of bases present on the DNA to that of amino acids of a given protein, the cell utilizes a short intermediate made of four bases similar to those of DNA called RNA. This "messenger" molecule copies the gene sequence, but immediately afterwards undergoes, in complex organisms like the human one (contrary to bacteria), a process of splicing that removes portions of the sequence and leaves a processed, "mature" RNA molecule bearing the information for a given amino-acid sequence. This splicing may occur in different ways on the same RNA molecule, which can therefore code for several different proteins, and we cannot yet predict exactly how many. Furthermore, a given protein can be split in different fragments, each with a different function and properties.

But this is not all. Each protein may undergo a number of chemical modifications consisting in the addition in specific positions of chemical residues, like different sugar, acetyl, methyl or phosphate residues, and others still, each conferring different physico-chemical and functional properties to the protein. Thus, as indicated above, the number of different proteins producible in a cell is much greater than the number of genes, and we are not yet in a condition of even knowing the exact number.

And this is not all. Another very important element of complexity is given by the fact that, particularly in complex multi-cellular organisms like the human one, the proteins do not function as single molecules but mainly as multi-protein complexes made by the combination, via weak chemical bonds, of different molecules; the same protein may thus be part of different multi-protein complexes performing quite different functions, It should be clear from all this that the complexity of a living organism is not a linear function of the size of the genome or of the related number of genes, but rather an exponential function of this number.

What then are the challenges facing today's biologists in trying to give a comprehensive picture of the development and functions of a living being? In the first place, identify the detailed three-dimensional structure of any given protein or multi-protein complex of a cell, and relate this structure univocally to the function it performs. From what we have indicated above, it will be evident that this represents a formidable task that will mobilize the activity of thousands of laboratories worldwide for many decades.

No less demanding will be the study of how novel functions and properties emerge from the dynamic web of interactions and feedbacks brought about by the molecules of a living organism. This task will require, among others, the exploitation of recently developed technologies, which allow the simultaneous analysis of the presence and amount of many different RNA or protein molecules, giving a great wealth of data often of arduous interpretation and integration.

Also, the study of laboratory organisms (typically mice) bearing specific mutations, introduced by the scientists in specific portions of the genome, will be extremely valuable for associating complex biological functions or dysfunctions to specific genes. Finally, all this knowledge will undoubtedly allow great progress in curing important diseases, especially, but not only, by the application of gene therapy approaches, and in obtaining novel improved organisms for agriculture and breeding.

ICGEB will not remain behind in this challenge. The scientists working in the two components and in the network of affiliated centres will strive to remain at the forefront of scientific research as they are today, as witnessed by the quality of the scientific output in international peer-reviewed scientific journals. Two novel initiatives will also be pursued, with the help of external funds, for the study of the safety of genetically-modified organisms for agriculture and for the production of model animals for the study of human diseases. In the course of the next year, we expect to initiate, in collaboration with the Government of India, field experimentation of a possible malaria vaccine. With these and all the other activities of the Centre, the action initiated in 1987 to bring the benefits of advanced biological research to the peaceful development of all world countries will be continued and possibly strengthened.

Arturo Falaschi is Director General of ICGEB and member of the Executive Council of the Italian National Research Council. The former Chairman of the Council of Scientists of the Human Frontier Science Programme was Professor of Molecular Biology at the University of Pavia, Italy from 1966 to 1979.