WITHOUT PARENTS

Evening Post, Volume CXXV, Issue 20, 25 January 1938, Page 18

WITHOUT PARENTS

THE CREATION OF LIFE

REMARKABLE EXPERIMENT

EFFECT ON BIOLOGY

Chemical creation in the laboratory of early embryonic forms of life from microscopic fragments of eggs which contained neither the male nor the female nucleus, thus bringing into existence for the first time living creatures that had neither father nor the principal element provided by the mother, was described before the autumn meeting of the American Philosophical Society at Philadelphia, writes William L. Laurence in the "New York Times." The experiments, reported by. Dr. Ethel Browne Harvey, of the Princeton University Department of Biology, throw new light on the mechanisms of the development of life in its early stages and mark a further step towards that "brave new world," predicted by J. B. S. Haldane, Aldous Huxley, and George Bernard Shaw, in which mammalian creatures, including men, would be fathered by a chemical and brought into the world In a glass jar. All creatures, from the lowest form of life to man, are brought into the realm of the living from a single cell, which divides itself first in two, then in four, and so on, until the cells reach into the billions. At a certain stage the cells begin differentiating themselves into the specific organs of the animal, each egg developing itself only "into the animal from which it originally came. Egg gives birth to animal and animal to egg, in an endless cycle which keeps reproducing itself, and, in the words of Weismann, the "hen is just the egg's way of making another egg." The egg of each species contains within itself an animal part and a vegetable part. The former develops into the animal, the latter provides food for the animal in its embryonic development. Those eggs, that are carried inside the mother during development have but a very small vegetable part, for* they are fed directly through the mother's circulation. STORES OF FOOD. On the other hand, eggs such as bird's eggs, which develop outside the mother's body, contain proportionately large quantities of food material, the whites and yolks of such eggs consisting largely of such nutrient substances. The original germ cell from which the animal is developed is but a tiny speck which always floats on the top part of the yolk. This germ cell consists of two principal parts, a nucleus and a cytoplasm. The nucleus is the heart of the germ cell, and it carries within it the chromosomes, rod-like bodies that, in turn, contain the genes, the entities by which the hereditary characteristics of the animal are transmitted from one generation to the next. All living things, throughout Nature contain a specific number of chromosomes and genes, the number being specific for each species. This is true ■with plants and insects as well as with the highest forms of life. Thus a horse has sixty chromosomes, while man has forty-eight. Each body cell, known as somatic cells, has a full set of chromosomes and genes. However, whereas the body cells each carry a full set of these chromosomes, and genes, this is not true of the germ cglls out of which' the animal's progeny comes into life. These germ cells, male as well as female, have only half of the set of chromosomes and genes. From' these observations the belief became general that the nucleus of the female egg, together with the nucleus of the male sperm, were the principal elements out of which life was generated, and that at least one was necessary to begin the process of cell-division, which marks all embryonic development. On the other hand, the cytoplasm, the protoplasm in the germ cell which surrounds the nucleus, because it does not contain any chromosomes, was not believed capable of developing into any form of embryonic life, or to have any potentialities for starting the process of cell-division. BELIEF NOW UPSET.. . The experiments of Dr. Harvey upset this belief, and show for the first time that even the cytoplasm, life's most elemental clay, has the power to develop itself into the early embryonic stages of life, notwithstanding the fact that it had been deprived of life's "dynamo"—the nucleus. "We must change our views about the role of the cytoplasm at least in the process of initiation of life, and possibly may be compelled later to assign to it a much more important part in the development of the embryo," Dr. Harvey stated. The development of eggs without nuclei was described by Dr. Harvey technically as "parthenogenic merogony," which combines parthenogensis and merogony. In parthenogenesis the egg has the female nucleus but is developed without being fertilised. In merogeny, a portion of the egg without the egg nucleus is fertilised. In such cases, therefore, the male nucleus is present but the female nucleus is lacking. Parthenogenic merogeny is a combination of the two processes, namely, the development of an egg without any nucleus at all, neither male nor female. Parts of eggs without nuclei are obtained by centrifuging. When sea urchin eggs are centrifuged. at about 10,000 times the pull of gravity in a solution of the same density as the egg, that is. sea water and sugar, so they, remain suspended, they become stratified, elongate, and then break into two almost equal parts, Dr. Harvey reported. "The nucleus," she stated, "always goes to the lighter pole, so that the heavier halves of the eggs are entirely and always without a nucleus. With further centrifuging, the halves can be broken into quarters, three of which are without a nucleus. METHOD OF EXPERIMENTATION. "By treating these non-nucleate fractions with parthenogenetic agents such as hypertonic sea water they are activated and start to develop. They throw off normal fertilisation membranes, division takes place, cleavage following cleavage in a fairly orderly fashion. More and more cells are formed, until there is a group of some 500 cells forming a fairly normal blastula (early embryonic form). "Some of these activated nonnucleate eggs have lived for four weeks. The normal unfertilised egg with a nucleus lives only a day 01 two. "Stained sections of the eggs alter cleavage show well-formed asters (radiating structures in the protoplasrr that appear when the chomosomes an ready to divide) often in pairs, but n< nuclei and no cromosomes. The reac tion -which is specific for cromatin (pig mer^-masterM in-thaHfltrompspmes) 1

negative, showing the absence of cromosomes."

The experiments were carried out with the type of sea urchin known as arabacia punctulato, from Woods Hole, Massachusetts. In several other species of sea urchin from Naples, Italy, nonnucleate halves of eggs can be obtained similarly by centrifuging, Dr. Harvey reported. The nucleus in all the species always goes to the lighter pole. "However," she added, "the granules stratify differently in the different species, so that in some species the non-nucleate halves contain mitochondria and in some species they do not. The non-nucleate halves of all the species can be activated, throw off fertilisation membranes and cleaves, but the cleavage is not so regular as in the Woods Hole species, though many- | celled blastulae are obtained. | "We thus see that an egg fragment lacking both maternal and paternal chromosomes has given rise by repeated cleavages to an embryo containing about 500 cells with a certain amount of differentiation. An embryo arising from a non-nucleate egg has lived a month. It is probable but not certain that these have cilia and are free-swimming. NO CHROMOSOMES. "The early stages of development can, therefore, take place without chromosomes. This means that the maternal cytoplasm is of great importance and has within itself the potentialities of determining at least the early stages of development. "These potentialities must either (1) be given to the cytoplasm by the nucleus previously, or (2) be innate in the maternal cytoplasm and entirely non-nuclear. They might be given to the cytoplasm either at, the time of the breakdown of the germinal vesicle, or else earlier by the chromosomes of a preceding generation. "The supposition that the potentialities of early development are innate in the cytoplasm restricts inheritance by genes to later developmental stages, and it may very well be that only the more specific and differential characters are controlled by the genes, whereas the general and fundamental characteristics of living matter are cytoplasmic. "However, if further work shows that the development of the parthenogenetic merogones does not stop with the blastula, but that they will develop to further stages, the results will be difficult to harmonise with the accepted ideas of the mechanism of genetical inheritance." Other work by Dr. Harvey has shown, she reported, that any part of the egg seems capable of development, and many parts, when fertilised, have given rise to quite normal plutei with skeletons. "Any difficulty in development seems to be mechanical rather than structural," she stated. "No particular type of visible and movable granules seems essential to development. These must me concerned with metabolism and respiration. "It must therefore be the 'ground substance' which is the material fundamental for development—-the matrix which is not moved by centrifugal force, and which, in the living egg, is optically empty." Dr. Harvey's investigations were furthered by a grant from the American Philosophical Society.