Nuclear Transplantation in Amoebae. I. - Journal of Cell Science

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45° Larch and Danielli—Nuclear Transplantation in Amoebae. I A. discoides graphs (at 34 //. and 40 JJL). See, for example, fig. 4. A. proteus graphs were never found to have a 'peak' below 38 fi, whereas in the A. discoides graphs the 'peak' at 50 /x was absent. This is illustrated by table 5. We are not able to express an opinion on the significance of the maxima in the graphs of nuclear diameter. Under the relatively constant culture conditions we used, the maxima were constantly found. Fig. 5 shows two sets of measurements made on the same culture with an interval of two years between the two sets. These two sets are closely similar. Fig. 3 shows that even when FIG. 5. Nuclear diameters in a mass culture of a clone of A. proteus. There was an interval of 2 years between the two sets of measurements. Note that the maxima are at the same diameters (40, 44, and 5Ofi) in both cases. O, 1949; X, 1951. cultures are compared in widely different states of nutrition, displacements of the maxima are not very striking. Although individual amoebae cannot necessarily be classified by their nuclear diameter, the average nuclear diameter of a random sample of at least 50 amoebae from a healthy culture usually enables one to identify the culture, as may be seen by comparing tables 1 and 2 with tables 3 and 4. Differences in the mode of binary fission sometimes provide diagnostic features for the classification of protozoa. For instance, Singh (1951) revised the classification of some soil amoebae according to type of nuclear division. It has been mentioned that no difference in the mode of cytoplasmic division of A. proteus and A. discoides was found by Doljanski (1954). An examination of stained preparations of division-stages of the two species also yielded negative results: the mitotic figures of the two species were indistinguishable. Doljanski was unable to confirm the differences in the shape of the spindle described by Hayes (1946). Certain species of amoebae form typical cysts which aid in their identification (Singh, 1951). The question of the encystment of the large fresh-water amoebae has recently been brought up again by Galbraith and Taylor (1950), who claim to have demonstrated that 'Amoeba proteus in the young encysted
Lorch and Daniellt—Nuclear Transplantation in Amoebae. I 457 stage can survive desiccation and is thus capable of dispersal by wind. . . .' The authors do not, however, present any conclusive evidence of the existence of such encysted stages, either in this or in earlier publications (Taylor, 1924, 1927) and we fully agree with Johnson (1930) and Halsey (1936), who, after a critical study of the alleged life cycle of A. proteus and A. dubia, concluded that these amoebae reproduce only by binary fission. The same seems to apply to A. discoides and we were unable to confirm Hayes's (1938) observations of agamontogony in this species. Hence the life cycles of A. proteus and A. discoides do not provide any features which might serve to differentiate between the two species. So far only morphological differences between the species have been studied. It is not unlikely that significant differences may be found in their physiological or serological properties. That this may be so is suggested for instance by the work of Dawson and Belkin (1928, 1929), who studied the digestion of oils by A. proteus and A. dubia. They found significant differences between the species, both in their ability to digest certain oils and in the nature of the pellicle. Thus under certain conditions A. dubia undergoes the phenomenon of 'capping' with oil, but no permanent capping was found to take place with A. proteus. (In some preliminary experiments with A. discoides it was found that it behaves like A. proteus in this respect, i.e. oil droplets did not form permanent 'caps'.) Physiological differences between species of amoebae were also found by Andresen and Holter (1949), who examined the proteolytic enzyme contents of A. proteus, Chaos chaos (Schaeffer), and Pelomyxa palustris (Greef). Work on possible physiological and serological differences between A. proteus and A. discoides is still in progress. However, the only differences which we have found between the two species which at present permit of quantitative study are the form assumed in moving and the distribution of nuclear diameters in a culture. These two factors were studied after making nuclear transfers between species. The results will be discussed in a subsequent paper. ACKNOWLEDGEMENTS The preliminary stages of this work were financed by a grant from the British Empire Cancer Campaign, and the later stages by a grant from the Nuffield Foundation. We are indebted to the Rockefeller Foundation for a gift of microscopes, to Professor A. Haddow of the Chester Beatty Research Institute for loan of apparatus, and to the Royal Society for the loan of micromanipulators.
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Nuclear Transplantation in Amoebae. I. - Journal of Cell Science

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