by Academician Alexander SPIRIN
Humankind has moved into the third millennium with an immense knowledge in the life sciences and a colossal potential of its practical uses. By manipulating DNA molecules biologists are now able to modify heredity of the ambient world, and this applies to bacteria, plants, animals and even man. All that has become possible owing to the unprecedented possibilities of technological progress (biotechnology), revolutionary breakthroughs in medicine (gene therapy) and farming (transgene plants and animals). Hence the vital importance of biological safety. But the present situation of Russia - specifically, in the life sciences and biotechnology, and in biological safety for that matter - is lackluster. Neither our public nor our government has realized yet: humanity is already in a biological era.
THE BIRTH OF MOLECULAR BIOLOGY
The mid-20th century saw a real revolution in the life sciences. At first it touched basic knowledge and afterwards, decades later, spread to hands-on fields to give rise to what is now known as biotechnology. The heart of the matter is that the molecular mechanism of reproduction, i.e. the molecular mechanism of heredity, was uncovered.
It became clear by the 1950s: heredity and the main process of its realization - the biosynthesis of proteins - depend on a definite group of biological polymers, or nucleic acids. Two types of them were discovered - RNA (ribonucleic acid) and DNA (deoxyribonucleic acid). DNA was regarded as "the substance of heredity", while RNA was assigned the role of a heredity effector in the form of synthesizing proteins which determine the structure, metabolism and other characters of an organism.
In 1953 Francis Harry Crick and James Dewey Watson (who were subsequently awarded a Nobel Prize) published a work in which they set out the main principles of the DNA molecular structure: two long, loosely bonded polymer strands that wind around each other in a spiral manner to form what is known as a double helix (duplex) interact by their side groups (nitrogen base residues) so that adenine (A) pairs with thymine (T), and guanine (G) - with cytosine (C). Though different in their chemical structure, the A-T and G-C pairs are identical geometrically and thus make possible a symmetrical structure (helical symmetry) of the DNA double helix. In their second work F.H. Crick and J.D. Watson showed that the principle of complementarity they had discovered - the complementarity of base pairing in a DNA molecule (A, T, G and С in one strand complementary with Т, А, С and G in the other) automatically predetermines a mechanism of the exact reproduction (reduplication) of a similar structure.
Articles in this rubric reflect the opinion of the author. - Ed.
When separated (unwound), each of the two DNA strands can become the template for replication of a new complementary strand. Two duplexes are then formed from the original duplex and are identical with it. This is the mechanism of self-reproduction (reduplication); and so DNA molecules are the unique substances in living nature to have this mechanism inherent in their structure. That discovery gave birth to a new discipline in the life sciences, the molecular biology.
THE CENTRAL DOGMA OF MOLECULAR BIOLOGY
Thus, the primary structure of "the substance of heredity", DNA, carries a living organism's genetic information; and its tertiary structure enables its reproduction in generations of cells and organisms. Yet DNA is not directly implicated in the realization of genetic information. This is done by RNA, a polymer of ribonucleotides which is chemically similar to DNA but is not coupled to a complementary chain and hence not organized into a double helix.
For side groups a RNA chain has the same nitrogen base residues as DNA (A, G and C); but present instead of thymine (T) is its demethylated derivative uracil (2,6-Dihydroxypyrimidine) [U]. All these four side groups of RNA are likewise capable of interacting (pairing) with corresponding bases of the other chain of DNA and RNA. So it becomes clear how the genetic information recorded as a linear sequence of DNA nitrogen bases is transcribed (rerecorded) into an identical sequence of single-chain RNAs with the substitution of U for T. Assuming the separation (unwinding) of two DNA strands, with a complementary chain of RNA built on one of them, we get a RNA identical with the parent strand of DNA (with U substituting for T). In this fashion the genetic material (DNA) is copied (replicated) in RNA chains; and a great number of RNA copies are made from various DNA segments, or genes. It is these copies that are directly involved in the realization of the transcribed genetic information.
This information is realized through protein synthesis. Proteins, in fact, determine the characters of organisms - their structure, metabolism and the like. RNA chains copying genes - what we call messenger, or template RNAs (mRNAs) - serve as templates for the synthesis of the organism's proteins. This synthesis occurs on subcellular particles, the ribosomes. The latter, programmed by mRNA chains, are concerned with decoding, or translation from the language of nucleic acids to that of proteins; likewise polymers, such proteins are of quite different chemical nature though. So: DNA (genes) is transcribed into RNA, while RNA is translated into proteins. This principle is known as "the central dogma of molecular biology" * (summarized as DNA -> RNA -> Protein).
From the 1950s to the 1970s molecular biology developed as a purely basic science. The dramatic breakthrough in the knowledge of the very essence of life held little, if any, promise of practical uses. Besides, molecular biology was (and still is) a high-cost science. And yet the governments of the industrial countries - the United States, Great Britain, France, Germany and Japan in the first place - kept subsidizing it heavily. The general culture of those nations and of their governments must have prodded them to act so: basic knowledge, they felt, sooner or later was bound to culminate in major spin-offs. And they were not wrong: a decade between
* See:Ye. Blagonravova, "Gene Structure Still a Mystery", Science in Russia, No. 5-6, 1993. - Ed.
1970 and 1980 ushered in a biotechnological revolution when molecular biology gave life to new methodic approaches that led to the appearance of gene engineering.
Since the heredity of organisms, their geno- and phenotype are determined by genes (and these are a substance having a definite structure, i.e. DNA), corresponding methods have been developed for manipulating them outside the organism. Biologists learned to isolate individual genes, or definite fragments of DNA. They discovered enzymes capable of cleaving DNA strands at certain points and, conversely, those that could join DNA segments and thus restore the continuous structure of DNA strands. In other words, methods of the artificial recombination of genes in vitro have been developed, when a gene or its fragment from one organism is linked to a gene or its fragment from another organism to produce a new-recombinant, or chimeric - hereditary material (genes). A real possibility was opened up of inducing selective changes in the isolated genes, that is effecting artificial mutagenesis and thus modifying heredity outside the organism. Furthermore, methods of chemical synthesis of DNA have been devised and, consequently, it became possible to synthesize new genes with preassigned encoding qualities. And last, the technique of a polymerase chain reaction was developed to enable biologists to breed genes and their artificial variants outside living organisms, in a test tube. *
But gene engineering in vitro would have been a dead letter had it not become possible to discover and further develop methods of the introduction of DNA (that is any genes-foreign, mutant, chimeric, synthetic genes, among many others) into live cells and organisms. The first experiment toward this end was outlined in a work of O. Avery, C. McLeod and М. McCarthy which was published way back in 1944: the transfer of pure DNA into bacteria and consequently, the transfer of genetic characters from one organism (donor) to another (recipient) by means of DNA. This and other suchlike manipulations came to be known as cell transformation. Subsequently other techniques were developed for the transfer of genetic material (DNA) into living cells. One of the most effective methods is transfection, when a foreign gene is introduced through viral DNA supplemented with the DNA of the gene. Foreign genes can be transferred also to the egg cells of higher organisms, plants and animals. As a result, we obtain a transgene organism.
Today humanity is making use of a great variety of transgene organisms. The first object of that kind was represented by bacteria carrying some of the human or animal genes and producing human insulin or interferon. Next came microbes synthesizing viral antigens in man, say, to the hepatitis virus - for obtaining antiviral vaccines; furthermore, there were microorganisms producing hormones, enzymes and other useful proteins. ** Here are some of the examples of transgene animals: a milch cow with genes responsible for the synthesis of vital proteins in human milk and hence producing milk for suckling infants; a goat giving milk with human interferon in it; a hog yielding human immunoglob-ulin or antibodies to human infections. *** Among the transgene plants are these: pea with a gene from a bacterium coding for a protein killing a dangerous pest, the weevil; cabbage containing a gene making this plant resistant to herbicides and thus allowing to destroy the weeds without damaging the crop... Many transgene plants and domestic animals carry foreign genes responsible for the synthesis of proteins useful as nutrients.
Gene therapy is the latest trend in medicine. Medics can now introduce DNA into cells of human organs and tissues. **** The first clinical application of this technique was registered in 1992 in the United States. A young female patient suffered from hereditary myocardial infarction. It was a hopeless case, she was doomed to certain death. That woman had a defective gene responsible for the synthesis of a protein (in liver) adsorbing low- density lipoproteins in blood (such proteins constrict blood vessels and cause myocardial infarction). The attending doctors took a piece of her liver and, using the method of transfection, introduced a DNA (gene) encoding the normal protein. The thus transformed cells were reimplanted into the liver. They took on and started producing the required protein. The hereditary disease was vanquished.
Seven years later US doctors applied gene therapy for the noninvasive prevention of ordinary - not hereditary - infarctions too. Instead of the conventional coronary by-pass surgery, they implanted a capsule saturated with a DNA coding for a protein called "the endothelial factor of vascular growth". Penetrating the cells surrounding the constricted vessel, the DNA stimulates the growth of by-pass vessels.
Today gene therapy is finding ever broader uses for treating other hereditary diseases of man and for correcting various gene anomalies that may develop in human organs in the course of natural life. This applies to certain malignancies as well.
Yet another and very promising trend related to gene therapy: present-day molecular biology enables one to make a specific, strictly selective attack at any definite part of the organism's genome, i.e. at a particular designated gene. This is done by means of nucleic acids or their derivatives complementary with a given site of the selected gene. These
* See: A. Bayev, "A Glimpse into the 21st Century", Science in Russia, No. 4, 1994. - Ed.
** See: S. Vinokurova, "Biotechnology: Achievements and Problems", Science in Russia, No. 5-6, 1993 . - Ed.
*** See: K. Ernst, "The Start of the Transgenes' Era", Science in the USSR, No. 5, 1990. - Ed.
**** See: V. Pereverzev, "Genetics Lies in the Center of Biological Problems", No. 1, 1993 .- Ed.
are the "anti-sense nucleic acids", mostly corresponding RNAs or their derivatives. Injected into a cell, such RNAs bind specifically only to a complimentary site and block its function; or, in another scenario, if they carry a chemically active group, they modify or destroy that site. Thus we can inactivate a noxious (mutant) gene responsible for the cell's malignant degeneration and other pathologies. Lately a new possibility has been opened up - that of a selective inactivation of genes with the aid of synthetic RNA duplexes (double helices).
And yet the turbulent development of molecular biology has certain negative sides to it too. Here's the lurking danger: the achievements of gene engineering, gene therapy and biotechnology may be put to military uses by developing a new generation of biological weapons. One has just to replace the object of gene interference.
The "classical" biological weapon - the particularly dangerous infections like plague, cholera, anthrax - may be rendered invulnerable to immunoprofylaxis, immunotherapy and antibiotics through gene-engineering modifications of respective bacterial genomes. And more: on the basis of viruses (similar to the native smallpox virus or smallpox vaccine) it would be not difficult to design various types of bio-arms by inoculating their genome with harmful genes - namely, toxin genes, activators of malignization * , activators of apoptosis, inhibitors of immunity, and so on. Developing recombinant viruses is but a matter of technique, including those that will kill people infected with viruses of incurable haemorrhagic fevers (causative agents similar to Abola viruses), and do it fast. Or conversely, one can develop "sluggish" and latent viruses activated at a specified time by a signal. Transgene plants can also be employed as weapon: say, weeds inoculated against herbicides and pests; or grain, fruits and vegetables containing genes harmful to man. Even a ghastlier threat is posed by a molecular gene weapon in the form of stabilized anti-sense DNAs and RNAs capable of immobilizing vital human genes; or by stabilized penetrating genes coding for toxic and other harmful proteins. Also, infective nucleic acids could be designed: polymers coding for their own replication systems in a host cell or uncontrolled replication of host mRNA. **
As a mass-destruction weapon, a new generation of bio-arms will not need huge investments and large production facilities. What one needs just knowledge and top skills in molecular biology. Therefore biological warfare is within reach of any small country, or a bunch of terrorists. Besides, the bio-weapon can be easily disguised to make the attackers virtually undetectable. That is why biological terrorism poses the worst threat among the array of up- to-date weaponry.
Another danger lurks in what may seem peaceful intentions-say, developing new recombinant genes and transgene organisms to boost the productivity and quality of farm produce, and for uses in the food and pharmaceutical industries. Unfortunately it is very difficult to predict the negative effects of new genes on live organisms, man including. Cases of such negative aftereffects have already been reported in the press. One cannot rule out a runaway spread of artificial genetic frankensteins that could wreak havoc by upsetting the natural and ecological equilibrium. Apart from that, an open-ended propagation of genes may prove to be adverse for the metabolic equilibrium of individual live systems, the living organisms.
And yet another menance: the technique of creating transgene organisms may be misused with the aim of modifying man's heredity. In fact, relatively simple procedures of transferring foreign genes to animals may tempt someone to go ahead and try this technique on the Homo sapiens so as to get transgene human individuals with prescribed properties.
Mention should also be made of the deferred dangers of gene therapy. It is a double-edged weapon. The point is that treating hereditary defects and mutations in man by means of immunization of his organs and tissues with sound genes or by means of a blockade (destruction) of mutant, i.e. abnormal, genes may correct such defects in a particular individual for the rest of his natural life; however, such manipulations do not affect hereditary characters. And this means that the patient's progeny will inherit the defect(s). It is clear therefore that gene therapy, if used on a wide scale on individuals beset by various hereditary defects and mutations, lethal among them, would result in the degeneracy of the progeny; such offspring might likewise be treated by gene engineering methods. As a consequence, defective and lethal genes would be accumulating in the human population to usher in a gradual degradation of the human gene pool (genofond).
So the headway made by molecular biology in the domain of its practical uses poses a number of formidable problems. Hence the vital importance of biological security and safety. This task is bound to feature prominently in the new century, and in the new millennium for that matter.
* Malignization - degeneration of a benign cell into a malignant one . - Ed.
** See: Yu. Lopukhin, B. Yudin, "Bioethics in Russia and for Russia", Science in Russia, No. 5-6, 1993 . - Ed.
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