[Ultrastructural observations on the asexual development of Eimeria ferrisi Levine and Ivens, 1965, in the lumen of the intestine of the mouse (Mus musculus) (author's transl)].
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Human malaria parasites in continuous culture.
Plasmodium falciparum can now be maintained in continuous culture in human erythrocytes incubated at 38 degrees C in RPMI 1640 medium with human serum under an atmosphere with 7 percent carbon dioxide and low oxygen (1 or 5 percent). The original parasite material, derived from an infected Aotus trivirgatus monkey, was diluted more than 100 million times by the addition of human erythrocytes at 3- or 4-day intervals. The parasites continued to reproduce in their normal asexual cycle of approximately 48 hours but were no longer highly synchronous. The have remained infective to Aotus.
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The release of sexual conflict after sex loss is associated with evolutionary changes in gene expression.
Sexual conflict can arise because males and females, while sharing most of their genome, can have different phenotypic optima. Sexually dimorphic gene expression may help reduce conflict, but the expression of many genes may remain sub-optimal owing to unresolved tensions between the sexes. Asexual lineages lack such conflict, making them relevant models for understanding the extent to which sexual conflict influences gene expression. We investigate the evolution of sexual conflict subsequent to sex loss by contrasting the gene expression patterns of sexual and asexual lineages in the pea aphid Acyrthosiphon pisum. Although asexual lineages of this aphid produce a small number of males in autumn, their mating opportunities are limited because of geographic isolation between sexual and asexual lineages. Therefore, gene expression in parthenogenetic females of asexual lineages is no longer constrained by that of other morphs. We found that the expression of genes in males from asexual lineages tended towards the parthenogenetic female optimum, in agreement with theoretical predictions. Surprisingly, males and parthenogenetic females of asexual lineages overexpressed genes normally found in the ovaries and testes of sexual morphs. These changes in gene expression in asexual lineages may arise from the relaxation of selection or the dysregulation of gene networks otherwise used in sexual lineages.
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[The effect of clotrimazole on the pathogen of toxoplasmosis, Toxoplasma gondii].
By means of a toxoplasma infection in the mouse it was tested whether the antimycotic agent bis-phenyl-(2-chlorophenyl)-1-imidazolyl-methane (clotrimazol, Canesten¿) is also effective against the asexual stages of replication of T. gondii as they occur in man. Canesten did not influence the forms of the proliferative phase of replication of T. gondii (trophozoites, pseudocysts = tachyzoites) either in vivo in infected mice or in vitro in the tissue culture.
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The site of action of the anticoccidial salinomycin (Coxistac).
The anticoccidial salinomycin has a cidal effect against chicken coccidia. Restricted and unrestricted medication studies and histopathological examinations of chicks infected with Eimeria acervulina, E. maxima, or E. tenella showed that parasites were destroyed within host cells during asexual development. Most sporozoites failed to become trophozoites and were destroyed 30--72 hr after ingestion of oocysts. The drug also affected schizonts during initial nuclear replication by either destroying or significantly delaying their maturation. Parasites affected by the drug were distorted grossly. Drug action against gametogony was not observed histologically, but when medication was restricted to this period of the life cycle, subsequent oocyst shedding of all 3 species was reduced by 20--70% compared to unmedicated controls. When drug was provided during the entire parasite life cycle, activity against asexual stages was so complete that only a limited number of parasites survived to form gamonts, and oocyst shedding was reduced by 80--90% relative to controls. As with other ionophores, salinomycin had no effect upon rate of oocyst sporulation.
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Light and electron microscopic observations of the life cycle of Sarcocystis orientalis sp. n. in the rat (Rattus norvegicus) and the Malaysian reticulated python (Python reticulatus).
A light and electron microscopic study of Sarcocystis orientalis sp. n. was made. The life cycle of this parasite is in two hosts. Gametogony is in the intestinal epithelial cells of a predator, Python reticulatus. Isospora-like oocysts developed. Sporocysts average 9.1 by 7.7 mum. Rats (Rattus norvegicus) were infected with sporocysts and asexual stages developed. Ten days after infection large zoites (average 7.85 by 2.48 mum) were observed free in peripheral blood and within white blood cells. Small schizonts producing merozoites 2-3 mum long were seen in lung tissue. Tissue cysts developed in skeletal muscle and produced numerous cystozoites (average 5.53 by 1.38 mum). Fine structure was similar to previously described Sarcocystis spp.
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Isolation of stages of the human parasite Plasmodium falciparum from culture and from animal blood.
Procedures for isolation of various forms of the asexual erythrocytic stages of the human parasite Plasmodium falciparum are outlined. The procedures employ the plasma expander Physiogel, which is composed of a chemically modified, partially hydrolysed gelatin dissolved in Ringer's lactate. Based on the observation that parasitized cells which are easily separable by this technique differ appreciably at the ultrastructural level, a mechanism by which separation occurs is proposed.
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[Life cycle of Frenkelia. IV. Pathomorphological findings in the organs of experimentally infected bank voles].
In 1975 the buzzard (Buteo buteo) was found to be the final host of Frenkelia clethrionomyobuteonis. After this discovery it became possible to investigate systematically the pathomorphology of the infection in the intermediate host, the bank vole (Clethrionomys glareolus). Fifty bank voles were infected orally with a suspension of sporocysts recovered from the faeces of experimentally infected buzzards. Each rodent receive 7000 sporocysts. Six controls each were given a faecal suspension from a non-infected buzzard. The voles were killed between 1 and 140 days after infection and examined histologically. Between the 5th and 8th day of the infection during the schizogonic multiplication of the parasite a focal necrosis of liver cells and of the liver parenchyma is observed followed by a reversible resorptive inflammation associated with siderophagia and the occurrence of giant cells. The spleen was spodogenously enlarged up to twice its normal size. There also was haemosiderosis of the bone marrow, the liver and the spleen up to 25 days after infection. At the same time the erythropoiesis in the bone morrow, the spleen and in the lymph nodes increased; there also was a lymphoid hyperplasia in spleen and lymph nodes. About 10 days after infection a reversible infiltration with lymphocytes and plasma cells developed in the liver, heart and brain. This infiltration was again detectable as perivascular and meningeal reactions in the brain after the 49th day after infection. The second asexual multiplication of the parasite was seen histologically in the grey and white matter of the central nervous system after the 18th day of infection. The developing cysts increased in size continuously thereby compressing the surrounding nervous tissue. Disseminated focal necrosis with resorptive inflammatory components was prominent in the parenchyma of the brain after the 49th day of infection. It was possible to differentiate between damage in single organs and systemic pathological lesions. The lesions in single organs were directly connected with the development of parasitic stages in the liver (schizonts) and in the brain (cysts). The generalized lesions occurred in the haemopoietic system after an impairment of the blood during the first asexual multiplication. They also occurred in the immunocytic systems after the first and during the second asexual multiplication and during the relatively late cystic phase of the parasite in the brain. The pathogenesis of the disintegration of blood cells is not clear. The immunocytic reaction can be considered an immunological response of the host against the parasite. The effect of the development of the cysts on the function and structure of the central nervous system is expected to lead to an increasing impairment of the motility of the intermediate host.
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Hydra hymanae: regulation of the life cycle by time and temperature.
Hydra hymanae, a hermaphroditic freshwater coelenterate, reproduces asexually at 24 degrees C and sexually at 15 degrees C. The appearance of gonads begins 12 days after transfer from 24 degrees to 15 degrees C and is complete 35 days after the temperature transition. Testes appear before eggs. Fifty percent of the mature embryos maintained at 15 degrees C hatch by day 61, but they have a low level of survival. Fifty percent of the mature embryos pretreated for from 5 to 25 days at 4 degrees C hatch by about day 45, and these have a high level of survival. Embryos maintained at 4 degrees C for longer periods (55 to 85 days) accumulate in a prehatching state and hatch with a high degree of synchrony approximately 7.5 days after return to 15 degrees C. Populations derived from newly hatched polyps are refractory to sex induction for approximately 120 days. The system is well adapted to ensure a regular alternation of reproductive modes in the natural environment.
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Life cycle studies with Eimeria magna Pérard, 1925.
Excystation of Eimeria magna required exposure to CO2 at body temperature followed by trypsin and bile. Incubation in the presence of CO2 produced marked effects on the inner layer of the oocyst wall. The evidence suggests that CO2 stimulates enzymic activity from within the oocyst rather than exerting a physico-chemical effect on the oocyst wall from the outside. Released sporozoites measured 19.65 X 3.33 mum. In the rabbit, E. magna undergoes at least 5 cycles of asexual schizogony before gametogony takes place. First-generation schizonts were observed at 30 hr, measured 15 X 11 mum and contained 4, 6, 8 or occasionally 12 merozoites; the merozoites were characterised by two very large and prominent refractile granules. As the infection progressed, schizont size and merozoite numbers became more variable; some schizonts contained 2-8 fat merozoites, many probably multinuclear, while other schizonts contained 12-100 thinner merozoites. First generation schizogony took place in the glands; all subsequent stages developed in the upper parts of the villi of the small intestine. Sexual forms have been seen as early as 96 hr, but maximum sexual activity was noted at 120-192 hr. Oocysts measured 35.87 X 24.05 mum. The first oocysts were passed 6-7 days after inoculation, with peak production at 8-9 days. Sporulation was optimal at 30 degrees C; higher temperatures inhibited sporulation, and were in time lethal, while sporulation would take place normally after suppression by cold for at least 11 months. Single oocyst inoculations indicated a maximum reproductive potential of 26.15 million. Pathogenic effects were mostly mild, amounting to growth depression over days 4-7 and softening of the faeces; occasionally diarrhoea and/or death occurred.
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Transgenerational chromosome repair in the asexual bdelloid rotifer Adineta vaga.
Homologous recombination is an essential DNA repair mechanism that also promotes chromosome pairing and ensures allele segregation during meiosis in sexual organisms. Here, we explore the dual function of homologous recombination in the bdelloid rotifer Adineta vaga, an asexual species known for its remarkable resilience to extreme genotoxic stresses. Genomic analyses reveal that A. vaga uses meiotic recombination to promote spontaneous crossovers and gene conversion during oogenesis and to repair the genome in response to DNA damage. The data also support a model of transgenerational DNA repair, termed break-induced homologous extension repair (BIHER), in which broken chromosomes are progressively restored over multiple generations. Our findings suggest that meiotic BIHER, coupled with the holocentric structure of chromosomes, may represent a key adaptation of life in extreme environments.
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Life cycles of two isopora species in the canary, Serinus canarius Linnaeus.
The endogenous stages of Isospora serini Arogão and Isospora canaria Box are described from experimentally infected canaries, Serinus canarius Linnaeus. Unlike other Coccidia, the first part of the I. serini life cycle takes place in mononuclear phagocytes. Five asexual generations are described from this cell type; 2 additional asexual generations and the sexual stages take place in the intestinal epithelium. Isospora canaria, on the other hand, has a conventional coccidian life cycle in that all of the endogenous stages are in the epithelium of the small intestine, with 3 asexual generations and the sexual generation described in the duodenal epithelium. The 2 species differ in their position relative to the nucleus of the intestinal epithelial cell. Isospora serini is usually on the lumenal side of the nucleus while I. canaria is below the nucleus, toward the basement membrane. The prepatent period is 4-5 days for I. canaria and 9-10 days for I. serini. Patency lasts for 11-13 days in I. canaria infections, but duration of oocyst output is more chronic in I. serini infections, persisting for as long as 231 days. Both species have a diurnal periodicity of oocyst discharge which occurs in late afternoon and evening.
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Unequal distribution of DNA in the macronuclear division of the ciliate Euplotes eurystomus.
During asexual fission in the ciliate Euplotes eurystomus, the macronucleus divides amitotically. The macronucleus was found to divide unequally, yielding sister pairs having a mean difference in DNA content of 11.6% DNA content was determined by the Feulgen reaction using a fluorescent Schiff's reagent, and measuring fluorescence by cytophotometry. Variability in macronuclear DNA content was also examined in randomly-paired non-sister cells, and found to be greater than in sister cells. This greater variability could be due to accumulation of differences over a number of divisions, or to interclonal differences in equality of division. Two categories of non-sister cells were examined: recently divided, and "parents" constructed by averaging the DNA contents of progeny. Both showed similar variability in quantity of macronuclear DNA. The fact that cells surviving to divide showed no less variability in amount of DNA than cells immediately after division suggests that extremes in amounts of DNA resulting from unequal division are not selected against.
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[Contributions to the life-cycle of Frenkelia. II. The asexual development of Frenkelia clethrionomyobuteonis in the bank vole (author's transl)].
A description of the asexual development of Frenkelia clethrionomyobuteonis in the European bank vole (Clethrionomys glareolus) is given as observed in experimental infections with sporocysts from buzzards' faeces. Between the 5th and the 8th day following the oral administration of sporocysts a first schizogony could be observed in liver parenchymal cells of the mammalian host. In impression smears the banana-shaped merozoites measured on an average 7.6 X 2.2 mum. Only after the 18th day were small round cysts filled with metrocytes detected in the brain and spinal cord. During the first month after infection the cysts increased their size only gradually measuring 15 to 40 mum. After 2 months they accelerated their growth and reached in the course of 3-4 months a diameter of 300 to 400 mum. Cyst formation could not be observed in organs other than the central nervous system. Cysts older than half a year frequently showed central degeneration, but in all cases viable cystozoites persisted in the peripheral zones. The infection could be transmitted from vole to vole by intraperitoneal injection of merozoites in a suspension of liver cells from the 7th day p.i. Congential infections did not occur in the offspring of mothers infected during or before pregnancy. The infectivity of the final products of the sexual development in the buzzard is limited to the bank vole.
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Budding in Hydra attenuata: bud stages and fate map.
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Studies on the formation of germ cells in a compound ascidian Botryllus primigenus Oka.
Gametogenesis of a compound ascidian Botryllus primigenus was studied histologically. On either side of the zooid (stage 9), in the gonadal space between the epidermis and the atrial epithelium, either a single testis or a complex of an egg follicle and a testis can be formed. The egg follicle consists of a single ovum (occasionally two ova) and its accessory cells and is connected with the atrial epithelium by the follicle stalk. The eff follicle is always accompanied by the brood pouch, a diverticulum of the atrial cavity. The testis is equipped with a vestigial spermiduct and is attached to the atrial epithelium. Buds of stage 8 comprise, besides the developing testes and egg follicles, loose aggregations of hemoblasts and oocytes of early developmental stages, which are already accompanied by primary follicular cells. Both the oocytes and the primary follicular cells seem to arise from the hemoblasts. The young oocytes are isolated in the gonadal space of the buds and are transferred to buds of the succeeding generations until they finally mature. In the bud of stage 3, a compact mass of cells appears, attaching to the inner vesicle on either side of the body. It is derived from the hemoblasts lodged there in the preceding generation and presumably also from the circulating hemoblasts. When the cell mass receives a large oocyte derived from the preceding generation, part of the cell mass differentiates into egg envelopes, forming an egg follicle, and a follicle stalk and the remainder into a testis. When the cell mass receives no oocyte, it differentiates as a whole into a testis. In the egg follicle thus formed, the outer and inner follicular cells increase in number by mitotic division. Subsequently, initial test cells are derived from the inner follicle by migration across the developing chorion; then they increase in number by mitosis. In the testis, meiosis and spermiogenesis take place.
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The evolution of sexual reproduction as a repair mechanism. Part II. Mathematical treatment of the wheel model and its significance for real systems.
The dynamics of populations of self-replicating, hierarchically structured individuals, exposed to accidents which destroy their sub-units, is analyzed mathematically, specifically with regard to the roles of redundancy and sexual repair. The following points emerge from this analysis: 1. A population of individuals with redundant sub-structure has no intrinsic steady-state point; it tends to either zero or infinity depending on a critical accident rate alpha c. 2. Increased redundancy renders populations less accident prone initially, but population decline is steeper if alpha is greater than a fixed value alpha d. 3. Periodic, sexual repair at system-specific intervals prevents continuous decline and stabilizes the population insofar as it will now oscillate between two fixed population levels. 4. The stabilizing sexual interval increases with increased complexity provided this is accompanied by appropriate levels of redundancy. 5. The model closely simulates the dynamics of heterosis effects. 6. Repair fitness is a population fitness: the chance of an individual being repaired is a function of the statistical make-up of the population as a whole at the particular period. Populations living at alpha greater than alpha c either engage in sexual repair at the appropriate time or they die out. 7. The mathematical properties of the model illustrate mechanisms which possibly played a role in the evolution of a mortal soma in relation to sexual reproduction.
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Ultrastructure of the ascospores of some species of the Torulaspora group.
Development and germination of the ascospores in species of the Torulaspora group of yeasts have been described. Most species had warty spores which, in sections, showed a dark outer layer consisting of the outer unit membrane of the prospore wall and a layer underneath formed at an early stage of development of the spores. In mature spores the light inner layer of the wall was delimited at the outside by a thin dark layer. The warts often contained dark material. The ascospores of two Pichia and three Debaryomyces species were studied for comparison; they differed in sections from the Torulaspora spores. The taxonomic implications of the ultrastructural observations have been discussed.
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