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Journal of Postgraduate Medicine, Vol. 49, No. 1, Jan-March, 2003, pp. 3-4 To Clone or Not to Clone Lakshmi Rajgopal Department of Anatomy, Seth G. S. Medical College and K. E. M. Hospital, Parel, Mumbai, India. Code Number: jp03001 'There is perhaps no phenomenon in the field of biology that touches so many fundamental questions as the union of the germ cells in the act of fertilisation; in the supreme event all the strands of webs of two lives are gathered in one knot, from which they diverge again and are rewoven in a new individual life history …The elements that unite are single cells each at the point of death; but by their union a rejuvenated individual is formed which constitutes a link in the eternal process of life' Thus quoting Lillie, Patten emphasises the importance of sexual reproduction, which has been the hallmark of speciation or species variation.1 This involves the union of haploid male and female gametes. Given the segregation and crossing-over of the genetic material that takes place during the meiosis of gametogenesis, the new individual formed by sexual reproduction has a good genetic variation. As opposed to this, a clone is defined as an organism or a group of cells derived from a single cell or organism through asexual reproduction. Offspring thus obtained are mere genomic copies.2 The latter may be in the form of 'Parthenogenesis' in which the unfertilised egg undergoes cleavage due to some chemical or ionic stimulus and results in a new individual.3 This keeps happening in nature all the time in plants and probably some invertebrates. 'Embryonic cloning' may also be a naturally occurring phenomenon resulting in the formation of monozygotic twins by splitting of the zygote. The birth of 'Dolly' was achieved through 'Reproductive cloning' - by a technique called as ' Somatic Cell Nucleus Transfer' (SCNT) wherein the nucleus of a somatic cell (in the case of Dolly, it was an adult mammary gland cell) was transplanted into an enucleated unfertilised egg resulting in further development into an 'embryo' and later, an individual. This in itself created a scientific furore as it opened up a 'Pandora's box' of possibilities. Reproductive cloning may be presumed to have achieved a newer landmark, if reports4 about the birth of the first human clone as claimed by 'Clonaid' are true. Unfortunately, the secrecy shrouding the latter report has only helped the scientific community not to believe it upfront but to question its authenticity. Amidst a horde of criticisms and question-marks about the longevity and health of a cloned animal, comes the report of death of 'Dolly' who had to be euthanised because of the morbidity caused by a fulminant lung infection.5 One of the reasons put forth for Dolly's morbidity was that the nucleus of the somatic cell used, was as old as the adult from whom it had been harvested. Germ cells, because of repeated cell divisions, are relatively younger and when they unite as in sexual reproduction, there is no fear of senility of the daughter cells. Cloned animals are fraught with birth defects, immune deficiency and inadequate renal function leading to premature death. All or some of these may be due to incomplete reprogramming of the adult cell used in cloning, thus resulting in inappropriate gene expression.6 In contrast to 'Reproductive cloning', 'Therapeutic cloning' aims at producing cloned cell lines as a source of stem cells which have been suitably modified genetically, so as to produce a deficient enzyme or protein or some such factor. Therapeutically cloned cell lines would help in research as well as in treatment; production of alpha-1-antitrypsin or Factor IX would help in the treatment whereas production of transgenic cell lines as disease models would provide a viable alternative to animal experiments.2 Countries involved in stem cell research are evolving their own rules and regulations to address the ethical issues concerning this field of research. The last-mentioned advantage of preparing stem cell lines as disease models has prompted the National Academy of Sciences of the U.S.A. to allow reasearch cloning while seeking a ban on human cloning.7 Steps are also being taken to establish an International Stem Cell Repository.8 In India, Indian Council of Medical Research (ICMR) in 1998 had prepared ethical guidelines pertaining to research in stem cells under the chairmanship of former Supreme Court Justice MN Venkatachalaiah, called as the 'ICMR Code'.9 This code, while asking to enact a law banning human cloning, stipulates a time-limit for research on embryos as 14 days when the embryo is still in the developmental stage. As per the ICMR code 'Harm cannot be done to such an organism until the capacity for sentience has been established.' More recently, Department of Biotechnology (DBT) has asked ICMR to provide ethical guidelines on therapeutic cloning.10 According to DBT, reproductive cloning is unanimously opposed; but therapeutic cloning is still in nascent stage. The purpose of therapeutic cloning is to create only early-stage embryos from which stem cells could be harvested that could yield perfectly matched tissues. So far, stem cells have been sourced from spare embryos in IVF clinics. There are still a lot of unanswered questions with regard to the future of cloning and its role in therapeutics and research. Only time will tell whether cloning and clones pass the 'survival of the fittest' test. Lakshmi Rajgopal Department of Anatomy,
References
Copyright 2003 - Journal of Postgraduate Medicine. Online full-text also available at http://www.jpgmonline.com/ |
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