Amoeba Discoides Research Articles

Cytoplasmic DNA-containing bodies and the inheritance of certain cytoplasmically determined characters in amoeba.

THE results of experiments involving the transfer of nuclei or of small quantities of cytoplasm between cells of Amoeba proteus and Amoeba discoides indicate that certain cellular properties, including nuclear diameter and sensitivity to streptomycin, are influenced by self-replicating hereditary determinants in the cytoplasm of both species1–6. In cells of the A. discoides strain (T1D), but not in cells of the A. proteus strain (T1P) used in. these experiments, cytoplasmically located DNA- and RNA-containing bodies of the type described by Rabinovitch, Wolstenholme and Plaut7,8,10 have been found9.

Cytoplasmic deoxyribonucleic acid-containing bodies in Amoebae.

EVIDENCE has been presented, from investigations involving techniques of nuclear transfer and injections of cytoplasm, that certain cellular properties of Amoeba proteus and Amoeba discoides, such as nuclear diameter and sensitivity to streptomycin, are influenced by self-replicating cytoplasmic hereditary determinants1–6. The finding of DNA- and RNA-containing bodies in the cytoplasm of Amoeba proteus7–9, followed by the demonstration that these bodies are self-replicating within the cell8,9 and that they show a certain degree of interaction with the nucleus of amoeba8, has stimulated interest in the possibility that they contain the physical basis of this cytoplasmic inheritance6.

Electron microscopic identification of the interphase chromosomes of Amoeba proteus and Amoeba discoides using autoradiography; with some notes on helices and other nuclear components

Data obtained from light and electron microscope autoradiographs of cells of Amoeba proteus and Amoeba discoides previously incubated in medium supplemented with H3 thymidine, indicate that fibrous material, the basic unit of which is about 150 A in diameter, represents the interphase chromosomes of these amoebae. The helices of interphase nuclei do not appear to incorporate H3 thymidine, which is in opposition to the hypothesis of Taylor (1963) that they are G2 chromosomes, and makes it unlikely that they represent any form of the DNA-containing component of the amoeba's interphase nucleus. Stereo-electron microscopy reveals that the direction of spiralization of helices may be either left or right handed and that the direction of spiralization of a single helix can reverse. The specific location of helices and of 850 A–1150 A electron dense bodies suggests that they are either primary chromosome products which subdivide before entering the cytoplasm, or units for the intranuclear transportation of primary chromosome products. In each nuclear membrane pore complex one central and eight peripheral regions of dense material are found. At each of the nine points, the dense material appears to traverse the nuclear membrane.

CYTOPLASMIC INHERITANCE IN AMOEBAE: NUCLEAR TRANSFER INVESTIGATIONS.

INVESTIGATIONS into the molecular basis of cytoplasmic inheritance in the large, uninucleate amœbae, Amoeba proteus and Amoeba discoides, have shown that certain self-replicating cytoplasmically inherited determinants can be transferred from one strain to the other, by the micro-injection of relatively small quantities of non-homologous cytoplasm1,2.

A COMPARISON OF THE PROTEIN COMPOSITION OF THREE SPECIES OF AMOEBAE.

SYNOPSIS. A comparison has been made of the characteristics of proteins present in two strains of Amoeba proteus, Amoeba discoides, and Chaos chaos. Extractable protein mixtures of each of the strains have been compared with respect to electrophoretic mobilities, enzyme activities, and immunological reactivities. With one slight exception, the three Amoeba strains appear to be identical by all the tests that have been performed but each of the three strains is dearly different from C. chaos by the same tests. The exception may be a difference of a single immunologically active component between A. discoides and one of the A. proteus strains, according to a preliminary observation.

Nuclear-cytoplasmic interactions in the responses of Amoeba proteus and Amoeba discoides to streptomycin

The growth rates of clones of various strains of Amoeba proteus, in growth limiting concentrations of streptomycin, have been measured. These experiments have shown the existence of naturally occurring inter-strain differences in resistance to this drug. The growth of sensitive strains is retarded in concentrations higher than 0.06 μg/ml. “Moderately resistant” and “resistant” strains can be differentiated, four times and six times, respectively, as resistant as the most sensitive strain. All strains of A. proteus investigated absorb the same amount of streptomycin per individual amoeba in standard conditions. The level of resistance of clones originating from heterotransfers between sensitive and resistant A. proteus strains, produced by the de Fonbrune technique of nuclear transplantation, is the same as the sensitive parent. Therefore the mechanisms conferring higher levels of resistance on some strains of A. proteus cannot be transmitted by either nuclear factors or cytoplasmic factors independently. A single strain of A. discoides was also investigated and found to be six times as resistant as the most sensitive A. proteus and to absorb only half as much streptomycin in similar conditions. Both heterotransfer strain types [resistant nucleus ( A. discoides) in sensitive cytoplasm ( A. proteus) and sensitive nucleus ( A. proteus) in resistant cytoplasm ( A. discoides)] are more resistant and absorb less streptomycin than the sensitive parent. No additive effects between factors from resistant A. proteus and A. discoides occurred in the relevant heterotransfer strains. It is concluded that independent nuclear and cytoplasmic factors determine the higher resistance of A. discoides, which is probably based on lower permeability to streptomycin, and that the cytoplasmic system is self-replicating.

Nuclear Transplantation in Amoebae. II: The immediate results of transfer of nuclei between Amoeba proteus and Amoeba discoides

ABSTRACT 1. A description is given of a method for replacing the original nucleus of an amoeba by a nucleus from another amoeba. This method has been used to study transfers of nuclei within a species (homotransfers) and between species (heterotransfers). The species used were A. proteus and A. discoides. 2. Removal of the nucleus from an amoeba inactivates the animal, so that movement is sporadic and unco-ordinated, digestion ineffective, and death results after 10—20 days. 3. Renucleation results in reactivation with both homo-and heterotransfers. Reactivated homotransfers normally are able to divide and form mass cultures. Heterotransfers are less often able to divide and very seldom form mass cultures. 4. Amoebae taken at random from a mass culture divide after an interval which appears to be composed of a lag t; in which the processes leading to division are inactive, followed by an interdivision period id during which preparation for division is active. Experiments are given showing the effect of nuclear transfer on Z; and td. 5. After heterotransfer nuclei of either species may grow and divide in foreign cytoplasm. Before the first division after heterotransfer a cytoplasmic effect on nuclear size is observable, and after the first division the cytoplasm has a dominant effect in determining nuclear diameter. 6. When curves are plotted of the frequency of occurrence of nuclei of various diameters in pure cultures, maxima are found in the curves characteristic of the species. After nuclear transfer the cytoplasm and nucleus both have a strong influence in determining the position of the maxima. 7. Studies of the form assumed by heterotransfers show that, although there is a measurable influence of the nucleus on the form soon after transfer, this influence disappears almost entirely in 6-12 days, after which the determination of form is almost entirely cytoplasmic. 8. The results given under points 4, 5, 6, and 7 are based on the study of animals immediately after transfer and for the subsequent two divisions only. Longer-term effects will be discussed in another paper.

Amoeba lescherae (nov. spec.)—Its morphology, cytology, and life-history

ABSTRACT 1. The discovery of a new species of large, free-living freshwater amoeba is recorded, and a description of the adult and of its reproduction is given. Although provisionally called Amoeba lescherae, it may have to be placed in the genus Chaos. 2. A method of cultivating it in the laboratory on a diet of small flagellates and ciliates subsisting on a pabulum of wheat grains is detailed. By starting them in Petri dishes pure line cultures are shown to be easily obtainable. 3. The resting nucleus, discoid in shape, has been shown to bear a general resemblance to that of Amoeba discoides as well as Amoeba proteus Y. Division is mitotic, and occurs once in twenty-four hours under optimum conditions. In contrast to Amoeba proteus Y the separation of the daughter amoeba is facilitated by the mechanical support of minute fragments of floating debris. 4. The cytoplasmic contents include square prismatic crystals, nutritive spheres, fat globules, neutral red bodies, and mitochondria. 5. It has been shown that while the adult has a general resemblance to Amoeba proteusY the respective developmental stages of the two amoebae are in marked contrast. 6. Agametogony is seen to begin with the emission of ‘chromidia’ from the nucleus. These chromidia form the rudiments of the agametes which differentiate into cysts. Excystationis described. 7. Agametogony occurs more frequently in Amoeba lescherae than in Amoeba proteus Y, the intervals between the ‘depression’ periods being shorter in the former than in the latter. 8. The development of the nucleus from the newly hatched amoeba to its adult condition has been traced, and the immature nucleus has been contrasted with that of species of M a y o r e l l a.

Memoirs: An Account of Amoeba Discoides; its Culture and Life History

1. A large free-living amoeba found by Mr. Harry Watkinson in the tropical fish tanks of Mr. Albert Sutcliffe of Grimsby has been identified as Amoeba discoides (Schaeffer, 1916) = Metachaos discoides (Schaeffer, 1926). 2. From the inoculation material obtained from these tanks Amoeba discoides has been successfully cultivated in the Notre Dame Training College Laboratory by a technique similar to that used for the cultivation of Amoeba proteus: wheat being the pabulum employed. In contrast to what obtains in the cultivation of Amoeba proteus , however, Amoeba discoides flourishes more luxuriantly in shallow Petri dishes, than in deeper troughs. 3. The nucleus in the resting and dividing stages is described; division is amitotic. 4. The more important cytoplasmic contents, including nutritive spheres, and crystals are likewise described. 5. The life-history has been worked out. The adult amoeba becomes an agamont giving rise to agametes which eventually grow into adult amoebae, the life-cycle occupying roughly about four months. 6. Descriptions of the nucleus of the newly hatched and developing amoebae are deferred. I wish to offer my sincerest thanks to Professor Graham Kerr under whom this work was begun, and who has continued from afar to watch over it with ever kindly interest and encouragement and who has read the paper in typescript. My thanks are also extended to Professor Hindle, under whom the work was completed, for his kind advice and for reading the paper in typescript. In conclusion I would like to express my appreciation of her skill and of the care and trouble bestowed by Miss Brown Kelly in the execution of the original drawing of fig. 1, PI. 31.