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At least 19 recordsLinked to original sources
PubMed1978

Malaria immunization in Rhesus monkeys. A vaccine effective against both the sexual and asexual stages of Plasmodium knowlesi.

Rhesus monkeys were immunized with a preparation of Plasmodium knowlesi parasites containing principally microgametes with lesser numbers of macrogametes and asexual trophozoites. The antigen mixture was emulsified in Freund's complete adjuvant (FCA) and administered intramuscularly. After one or two inoculations of from 10(5) to 10(7) microgametes in FCA, monkeys showed high levels of circulating anti-gamete antibodies as demonstrated by various in vitro microgamete immobilization or transmission blocking tests. After challenge with P. knowlesi, immunized monkeys developed low level asexual parasitemias and were not infectious to feeding mosquitoes as measured by growth of the parasite on the mosquito gut. Control monkeys developed rapidly rising, usually fatal infections and were highly infectious to mosquitoes. Anti-gamete antibodies appear to neutralize the sexual parasites and prevent mosquito infection within the gut of the recently fed mosquito vector. Suppression of asexual parasitemia in immunized monkeys may be due to the presence of asexual trophozoites in the antigen mixture or to antigens common to both sexual and asexual stages of the parasite. A vaccine effective as a single injection capable of interrupting malaria transmission from man to man whereas reducing the severity of the disease in infected individuals offers a new approach to the control of one of the major diseases affecting man.

Animals↗
PubMed2026

High levels of mitotic gene conversion are needed to effectively purge deleterious mutations in asexual organisms.

Self-fertilisation and asexual reproduction are both hypothesised to cause long-term extinction due to inefficient selection against deleterious mutations. Self-fertilisation can counter these effects through creating homozygous genotypes and purging deleterious mutations. Although complete asexuality lacks meiotic gene exchange, mitotic gene conversion creates homozygous regions that could limit deleterious mutation accumulation in an analogous manner. We compare mutation accumulation in self-fertilising and facultative sexual populations subject to mitotic gene conversion, and quantify the efficacy of purging in the latter. We first show analytically that purging is most effective with high levels of asexuality and gene conversion, and when deleterious mutations are recessive. We further show using simulations that, when mitotic gene conversion becomes sufficiently high in obligate asexuals, there is a reduction in the mutation count and a jump in homozygosity, reflecting purging. However, this mechanism is not necessarily as efficient at purging under high self-fertilisation, and elevated rates of mitotic gene conversion seem to be needed for widespread purging compared to empirical estimates. If gene conversion rates are allowed to evolve, then elevated rates that increase mean fitness can arise, but only if there is sufficient variance in the gene conversion rate. Conversely, if gene conversion rates are already high and rates are not constrained then they will slightly decrease, reducing mean fitness.

Self-fertilisation↗
PubMed2025

Investigating the Functions of Hox Genes Using Planarian Asexual Reproduction.

Hox genes are highly conserved developmental regulators instrumental to the formation of a wide range of diverse body plans across metazoans. While significant progress in the field of Hox gene research has been made, persistent challenges in unraveling their mechanisms of action and full repertoire of functions remain. To date, investigations of Hox gene function have been primarily conducted in research models belonging to ecdysozoa and vertebrata. Herein we summarize recent findings on Hox genes' roles in the asexual reproduction of the regenerative flatworm planaria, a member of the understudied superphylum Spiralia. We detail our optimized methods for planarian culture, gene perturbation, and induction of asexual reproduction. We aim to provide an experimentally tractable means to dissect Hox gene adult tissue functions underlying planarian asexual reproduction with broader relevance to Hox genes' established and emerging roles in regulating cellular behaviors, developmental patterning, animal behavior, and tissue regeneration.

Animals↗
PubMed1976

Genetics and asexual reproduction of the sea anemone Metridium senile.

1. Metridium senile was studied for phosphohexose-isomerase variation at three locations on Cape Cod, Massachusetts: Woods Hole, Cape Cod Canal, and Barnstable Town Boat Harbor. 2. All three locations exhibited significant polymorphism for PHI. 3. Mapping of individual polyps was performed at Barnstable to analyze spatial distributions of clones and genotypes. 4. In Barnstable, PHI does not depart significantly from Hardy-Weinberg expectations at the time of establishment of new polyps, and establishment of larvae is spatially random with respect to PHI genotype. 5. Asexual reproduction was uses as a meausre of the relative success of different PHI genotypes. There are indications that not all genotypes are equally likely to produce large clones. 6. There is significant heterogeneity among the three locations with respect to PHI genotype frequencies, suggesting that there may be geographical differentiation of the populations. 7. Sessile, asexual organisms provide powerful tools for examining the dynamic aspects of genetic structure in natural populations.

Animals↗
PubMed1977

A mutation (gad) linked to mt and affecting asexual plasmodium formation in Physarum polycephalum.

Amoebae of the acellular slime mold Physarum polycephalum convert to plasmodia both asexually and sexually. Genetic analysis of a mutant that exhibits enhanced asexual plasmodium formation is reported. The mutant carries a single lesion (gad-11) located 12.3 map units from mt, a gene that controls mating specificity in sexual plasmodium formation. The mutation, which was isolated in an mt3 strain, is also expressed in mth and mt4 strains.

Chromosome Mapping↗
PubMed2026

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.

Animals↗
PubMed1977

Repression of asexual embryogenesis in vitro by some plant growth regulators.

A factor that represses asexual embryogenesis has been observed in the Rutaceae, with particularly high concentrations in the naturally monoembryonic cultivars. This investigation was an initial step towards identifying the factor. Citrus reticulata Blanco Ponkan mandarin nucellus explants and Daucus carota L. 'Queen Anne's Lace' callus were employed to examine effects of known plant growth regulators and to determine possible identity of one or more of them with the repressive factor. The chalazal halves of ovules of C. media L. 'Citron of Commerce' were used as control repressor source. Embryo initiation and growth of both test tissues were depressed markedly by 2,4-D, abscisic acid and ethephon. Slight inhibitions were obtained with IAA, kinetin and gibberellic acid. Recovery from the repressor did not occur readily in Citrus nucellus following recultures in citron-ovule-free medium; carrot callus resumed normal embryogenesis immediately upon transfer to suppressor-free medium. The repression by natural sources apparently involved the combined action of some or all natural hormones that are generically related to the above.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1977

An extracellular inducer of asexual plasmodium formation in Physarum polycephalum.

Asexual conversion of amoebae to plasmodia was studied in the Colonia isolate of the myxomycete, Physarum polycephalum. When a culture of Colonia amoebae is grown on a bacterial lawn, a period of amoebic growth precedes the appearance of cells committed to the plasmodial state. The onset of plasmodium production appears to be related to amoebic nutrition since cultures supplied with fewer bacteria display earlier differentiation. For a period of time after differentiation is initiated, conversion of amoebae to plasmodia is rapid and proceeds as an exponential function of time. A filter-transmissible substance, apparently released by differentiating cells, is implicated in the control of this rapid conversion.

Cell Differentiation↗
PubMed1978

Suprahypophyseal dysfunction in a patient with asexual ateleiosis.

The neuroendocrine function of a 19 years old female dwarf with primary amenorrhoea and lack of sexual development (asexual ateleiosis) was studied. Undetectable fasting plasma levels of growth hormone (GH) and a lack of response to three different provocative stimuli was observed. Oestrogen administratin did not modify the GH response. Thyroid and adrenal function were within normal limits. Undetectable plasma levels of immunoreactive oestradiol and lack of oestrogenic activity in vaginal smears indicated absence of ovarian function. Low levels of circulating gonadotrophins with a significant rise after synthetic LH-RH administration was demonstrated, while clomiphene citrate failed to induce ovulation. Following 6 months of continuous GH administration a significant increase in the growth rate was evident, whereas no pubertal development was observed. These data are interpreted as demonstrating the suprahypophyseal origin of the sexual infantilism in a patient with inappropriate GH secretion. It is suggested that a combined deficiency of LH-RH and GH-RH may account for the aetiology of this disorder.

Adrenocorticotropic Hormone↗
PubMed1979

Ultrastructure of the asexual apparatus in Mycotypha (Mucorales).

The development of the asexual apparatus of Mycotypha africana and Mycotypha poitrasii observed by means of scanning electron microscopy is reported. Using ultrathin sections and freeze-fracture replicas, sporangiole structure is described. Sporangiospore structure is compared with that of other members of the Thamnidiaceae.

Cell Membrane↗
PubMed1979

Stomatogenesis during sexual and asexual reproduction in an amicronucleate strain of Paramecium caudatum.

Amicronucleate cells of Paramecium caudatum, whose micronuclei have been artifically removed by micropipetting, are characterized by the appearance of a deciliated area at the posterior part of the buccal opening. These cells form food vacuoles at a slightly lower rate than micronucleate cells. Their mean interfission time is longer than that in micronucleates. The exconjugants of amicronucleate cells can not form food vacuoles and eventually die witout fission, though conjugation proceeds normally in them as well as in their micronucleate mate. The oral apparatus of amicronucleate exconjugants seems to be shallower than that of micronucleates. The membranellar cilia, therefore, can be seen through the buccal overture by scanning electron microscope. The results obtained from the cross of micronucleate and amicronucleate strains and from the induction of autogamy in amicronucleate strains suggest that the micronucleus has a primary role in developing the normal oral apparatus after nuclear reorganization.

Animals↗
PubMed1978

[Investigations into the fire structure of the asexual developmental stages of Frenkelia in the liver of the bank vole (author's transl)].

Bank voles (Clethrionomys glareolus) were infected by stomach tube with Frenkelia sporocysts from the faeces of buzzards (Buteo buteo). The voles were sacrificed at regular intervals and their livers examined electronmicroscopically. Seven days p.i. developmental stages of Frenkelia could be detected in liver parenchymal cells. The youngest schizonts detected are enveloped by a pellicle consisting of two membranes. This pellicle, which is in direct contact with the host cell mitochondria, shows marked invaginations which increase with the development of the schizont. A parasitophorous vacuole is not detectable. In developing schizonts numerous sections through nuclei with nucleic spindles and merozoite anlagen (dome-shaped) structures) are visible. It is not clear whether there are several nuclei or a section through one large and lobed nucleus. Within the merozoite anlagen the conoid and the subpellicular microtubules are formed first. By the prolongation of the dome-shaped structures towards the posterior pole, the nucleus and the other newly formed cell organelles are incorporated into the forming merozoite. The posterior pole of the merozoite still remains open at this stage of development. With increasing differentiation the merozoites become lancet-shaped, their apical poles bing always directed towards the periphery of the schizont. The outer membrane of the pellicle of the schizont forms the outer part of the pellicle of the merozoites by invaginating around them. At this stage of development the inner membrane of the pellicle of the schizont is no longer detectable. Thus the typical pellicle of the motile stages of sporozoaonsisting of three membranes is formed. In the centre of the merozoites which lie freely in the liver cell a residual body is present. The host cell reacts against the parasites by forming a thick border of mitochondria and distinct endoplasmic reticulum.

Animals↗