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

More documents

Recommendations

Info

454 Larch and Danielli—Nuclear Transplantation in Amoebae. I Conditions of culture, rather than age, might affect nuclear diameters; hence well-fed and active as well as starved cultures were chosen for measurement. Again no marked constant difference was detected. For example, in table 2, P3 and P4 represent an underfed and a well-fed mass culture respectively: the average nuclear diameters are the same. In table 4, culture D5C is a starving culture and its average nuclear diameter, 38 /x, is intermediate between those of the two active, well-fed cultures, D15 (36 /x) and D16 (40 y). 28 26 24 22 . I 20 1 18 12 8.10 28 30 3Z 34 36 38 40 42 44 46 48 50 52 54 56 58 60 62 nuclear diameter m^x FIG. 4. Nuclear diameters of amoebae in mass cultures. Solid line: A. discoides (cultures D5C, 15 and 16, table 4). Broken line: A. proteus (cultures P2-5, table 2). Yet it should not be concluded that external conditions have no effect on the nuclear diameters, otherwise it would be difficult to explain why the same culture examined at different times gives slightly different average values, e.g. table 3, D5 a and b and table 4, D5C, and why different cultures kept under as nearly as possible identical conditions give almost identical average values. For example, table 3, Dio, 11, and 12 all have a 37 p average; however, of the cultures P13, 14, and 15 on table 1, which are also under 'equalized' conditions, only two show identical average diameters. These 6 cultures were 'equalized' as follows: 10 active amoebae were picked out from each of 6 different cultures and placed in solid watch-glasses containing dense 'food' culture. After 8 days the resulting cultures were used for measurements. P20 (table 1) and D19 (table 3) were also treated in this way but not at the same time as the other six cultures. We believe we have shown that the size of the nucleus of the parent of a clone does not influence the average nuclear diameter of the resulting culture. Four cultures of A. proteus (table 1) and 4 cultures of A. discoides (table 3) illustrate this point.
Lorch and Danielli—Nuclear Transplantation in Amoebae. I 455 Also the operation of nuclear transfer between amoebae of the same species does not appear to influence the average nuclear diameter of the resulting clone (table i, Pio and 11a; table 3, Dza, 8a, 13, 14, 17, 18) nor the distribution of nuclear diameters in a culture: such cultures may be considered normal in every respect (see Lorch and Danielli, 1953, for methods used in nuclear transfer). The difference between the nuclear diameters of A. proteus and A. discoides is illustrated in fig. 4, which shows the nuclear diameters of 250 specimens of A. discoides and 340 of A. proteus, both from mass cultures under various conditions. It is seen that the shapes of the curves are markedly different, but there is considerable overlap. The average nuclear diameters for these amoebae were 38-2 (s.d. 3-6) p for A. discoides and 45 (s.d. 5-6) /u, for A. proteus. DISCUSSION The following main points emerge from a review of the results obtained. 1. Observation of the mode of pseudopod formation and of the cytoplasmic inclusions did not reveal any constant difference between A. proteus and A. discoides. Specimens of the former species are usually larger, but there is much variation in size in both species. 2. The pattern of locomotion as demonstrated by successive outline drawings was found to be typical for each species, but some atypical amoebae were found in each culture tested. 3. The nucleus of A. proteus is generally larger than that of A. discoides and is often notched or folded, whereas that of A. discoides is usually discoid with a smooth outline. Again there are exceptional specimens in respect of each of these features. It is perhaps not remarkable that no clear-cut differences between individuals of A. proteus and A. discoides were found under the present conditions. The extent of biological variation among protozoa of the same species and even within a clone is always considerable. The variation is much reduced when the animals are cultured under constant conditions, preferably in a sterile medium as has been found with various ciliates. Some soil amoebae (Singh, 1950) have been cultured under relatively constant conditions on solid media. Singh's method of using a single strain of bacteria as food-supply for amoebae on non-nutrient agar greatly reduces the variability within the clones of soil amoebae used. Unfortunately the large free-living amoebae of the proteus group are not bacterial feeders, nor have they ever been cultured in the absence of living food animals. Hence, without a controllable food supply, the conditions for a comparison of the two species are necessarily imperfect. Nevertheless we have shown that certain characters are species-characteristic, namely the shape of the active animal and the distribution of nuclear diameters within a clone. An analysis of the graphs of nuclear diameters of the cultures set out in tables 1-4 shows that there tend to be 3 maxima or well defined 'shoulders' in the A. proteus graphs (at 40 p, 44 ft, and 50 p), and two maxima in the
Page 1 and 2: 445 Nuclear Transplantation in Amoe
Page 3 and 4: Lorch and Danielli—Nuclear Transp
Page 5 and 6: Larch and Danielli—Nuclear Transp
Page 9: Lorch and Danielli—Nuclear Transp
Page 13 and 14: Lorch and Daniellt—Nuclear Transp

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

Create successful ePaper yourself

Delete template?

Save as template?