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At least 19 recordsLinked to original sources
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↗
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↗
PubMed1975

Distribution of neoblasts and mitoses during the asexual reproduction of the planarian Dugesia tigrina (Girard).

The neoblast distribution in the prepharyngeal portion of the body remains unchanged during the asexual reproduction of planaria. During the first few days after fission, the number of neoblasts decreases in the portion of the body immediately adjoining the site of daughter zooid detachment and considerably increases in the regenerative bud. Starting with the fourth day after division, there is an increase in the number of neoblasts in the region of future fission, which can be regarded as one preparatory mechanism for the next fission. The mitosis distribution pattern is just the reverse: the regions of the body with the highest neoblast density are characterized by a low mitotic index or no dividing cells at all. The neoblast and mitosis distributions in the daughter zooid during its asexual reproduction cycle duplicate those observed in the maternal zooid.

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 light and electron microscope study of the interaction of soil bacteria with Phytophthora cinnamomi Rands.

Light- and electron-microscopic examination showed that bacteria became associated with the hyphae and asexual reproductive structures of P. cinnamomi in soil. In suppressive soils this association appears to be correlated with hyphal lysis, inhibition of zoospore production, and sporangial breakdown. One notable feature of the microbial association between P. cinnamomi and soil bacteria is the formation of extensive slime material. Many of the bacteria isolated from the fungal hyphosphere display antagonism to the growth of P. cinnamomi in vitro. The bacteria are morphologically varied and include Pseudomonas, Bacillus, and Streptomyces spp. These observations suggest that the appropriate manipulation of the antagonistic bacteria may provide a means of biological control of P. cinnamomi.

Fungi↗
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↗
PubMed2026

Development of a low-coverage whole genome sequencing screen for apomixis using a diverse set of Malus germplasm.

In the past decade, plant biologists have made several major discoveries pertaining to the genetic basis of apomixis (clonal propagation by seed) that have shown promise in preserving high-value hybrid rice and sorghum genotypes. This progress was made possible by foundational gene discovery efforts in model species and natural apomicts, but pleiotropic obstacles still limit its broad agricultural adoption, especially in eudicots. Thus, it follows that investigations of novel apomicts should lead to the development of new molecular tools for plant breeding. The two most common ways to identify clonal seed production are flow-cytometry seed screens and genome sequencing to compare the DNA sequences of the maternal parent and progeny, traditionally using low-throughput markers. While flow-cytometry has been the dominant method for more than two decades, it provides indirect information on the genetics of a resulting embryo and can be ineffective in certain species. Here we developed a method using short-read whole-genome sequencing at moderately low coverage (averaging 3X and 6X) to screen diverse Malus genotypes maintained in a USDA germplasm collection for clonal seed production. In total, we sequenced 55 genotypes, 1,216 of their embryos, and identified 17 previously undescribed apomictic genotypes. Several more were detected with the flow cytometry seed screen, which helped resolve certain types of reproduction and sources of noise in low-coverage datasets. This low-pass screening-by-sequencing method is a relatively low-cost, rapid method for detecting apomictic genotypes in diverse plant germplasm and when used thoughtfully in conjunction with flow cytometry, provides a new way to visualize the genetic outcomes of sexual and asexual reproduction in plants.

Apomixis↗
PubMed2025

Reviving Élie Metschnikoff's Monospora: the obligately parasitic yeast Australozyma monospora sp. nov.

A vast literature explores a model system that consists of a prey crustacean, the water flea Daphnia spp., and an obligately pathogenic yeast that has been referred to as Metschnikowia bicuspidata and thought to represent the material used by Metschnikoff in his study of innate immunity. Typification of species bearing that name and indeed the whole genus has been problematic as regards yeasts that only grow or form aciculate ascospores in hospite. The neotype of M. bicuspidata, unlike the Daphnia parasite, is easily cultured on a variety of laboratory media, although it too can cause serious infections in a variety of mostly aquatic animals. It has become evident that the Daphnia parasite studied by Metschnikoff or current workers is not closely related to M. bicuspidata as currently understood. Analysis of whole genome DNA extracted from the yeast repeatedly found in infected Daphnia specimens shows that it belongs to the recently circumscribed genus Australozyma. The yeast is described here as Australozyma monospora sp. nov. The species, although haplontic and heterothallic, forms single-spored asci without mating. It also appears that all species in the genus are restricted to asexual reproduction, which may explain their rare status. The holotype is MICH 346683. The name is registered in Mycobank under the number MB 859667.

Animals↗
PubMed1979

[Sequence of reconversion of the sporocysts of Schistosoma mansoni producing cercariae, to the production of new generations of sporocysts (author's transl)].

During the life cycle of Schistosoma mansoni the production of sporocysts of a higher order than secondary is a normal mode of larval multiplication which intervenes in asexual reproduction of the parasite. The sequence of reconversion of sporocysts producing cercariae to those producing sporocysts III, IV, etc... can be divided into three principal steps: (1) cessation of cercariae production; (2) degeneration of cercariae contained in the sporocyst, and (3) production of the new generation of sporocysts. Degeneration of intrasporocystic larval material seems to be an indispensable step for the new orientation of production. The signifance of this method os multiplication in the ecology of transmission is discussed.

Animals↗
PubMed1976

Is sex maintained to facilitate or minimise mutational advance?

There are two alternative hypotheses for the selective advantages of sex: (i) The "Fisher-Muller" model:sex facilitates evolutionary adaptation to chaning environments. (ii) The "Rachet" model: sex minimises the mutational load. The relative importance of these hypotheses is discussed with reference to (a) comparative data on sexual and asexual reproduction, (b) the timing of sex in species with asexual/sexual alternation, (c) the advantages of haploid/diploid alternation, (d) the disadvantage associated with the recombinational load. It is concluded that the Ratchet model may well be the major mechanism which maintains sex.

Genes, Lethal↗
PubMed2026

Co-option of ancestral stem regulators drove recurrent evolution of underground storage organs.

Geophytes are plants that produce underground storage organs such as tubers, rhizomes, and bulbs, to facilitate asexual reproduction and withstand a myriad of environmental challenges. While the potato (Solanum tuberosum L.) serves as the primary model for studying tuberization, the genetic mechanisms encoding this trait across diverse angiosperm lineages remains unclear. This study utilized a phylogenomic-transcriptomic approach to compare tuber development across nine tuberizing species with five nontuberizing sister taxa. We identified orthologs of key potato tuberization genes that exhibit similar expression in the stolons or tubers of these distant relatives. In nontuberizing species, these orthologs exhibit distinct expression profiles and are primarily expressed in the stem. This suggests that the independent evolution of tubers across angiosperms resulted from shifts in the expression of preexisting genes that led to their co-option. This process, also known as exaptation, occurs when existing genetic suites are recruited for entirely new biological functions. This mechanism stands in contrast to the repeated loss or gain of genes, which has been associated with the origin of other adaptive plant traits. Furthermore, the co-option of the same genes was observed in species with other stem-derived storage organs, such as rhizomes and runners. These findings reveal a conserved evolutionary model for the development of stem-derived geophyte organs that evolved independently across the flowering plants over the past 160 My.

Plant Tubers↗
PubMed1978

Bidder's hypothesis revisited. Solution to some key problems associated with general molecular theory of ageing.

In this paper I consider three major difficulties associated with the general molecular theory of ageing, namely: (1) How can molecular damage accumulate in the face of the constellation of repair mechanisms that is found in cells? (2) How can the obvious programmatic nature of ageing be reconciled with underlying stochastic processes? (3) How do some organisms avoid ageing? As a solution to points 1 and 2, I propose that the repair mechanisms themselves deteriorate in a programmed fashion with age. However, I argue that this programming is unlikely to be a result of direct selection for life-shortening but, rather, is more likely to be a result of an indirect selection for other characters. This idea is very similar to the theory of senescence first formulated by Bidder. The solution to point 3 is that the repair mechanisms in systems which avoid ageing, in particular cellular and molecular turnover, are not impaired with age. The rejuvenating capacities of sexual and asexual reproduction are also discussed.

Aging↗
PubMed1976

[Reorganization of the nervous system during regeneration in Dugesia tigrina].

The normal structure of the nervous system in Dugesia tigrina Girard and the total morphodynamics of the nervous system during regeneration have been studied by means of choline esterase assay. The nervous system reacts to local damages of the planarian body; accumulations of nervous elements form in the wound region. Following the transverse cut of a planarian, the regeneration of the nervous system is not reduced to the completion of lacking parts. In this case (as well as in that of asexual reproduction) the nervous system manifests a considerable morphological lability and undergoes morphological rearrangements accompanied by the appearance of additional, frequently unpaired, nerve trunks. The data obtained are to be taken into account in neurobiological studies on planarians.

Animals↗
PubMedDate not supplied

[Toxoplasmids, their life cycle and systematic position].

Recent evidence on the life cycles of the toxoplasmids (Toxoplasma, Besnoitia, Sarcocystis, Hammondia, Frenkelia) has been analysed. The availability of the complex life cycles, including the alternation of sexual and asexual reproduction, in addition to gametogenesis involving the independent development of gametes that produce unequal numbers of gametes, makes it possible to include the toxoplasmids into the family Eimeriidae within the order Coccidiida. A detailed evidence recently provided for Isospora has suggested a kinship of this typical coccidian genus with toxoplasmids. At the same time much similarity is obvious between Isospora and Eimeria in the general pattern of their life cycles. Hence, the family Eimeriidae is suggested to be divided into two subfamilies: Eimeriinae Wenyon, 1926 with Eimeria as the type genus and Isosporinae Wenyon, 1926 with Isospora, Toxoplasma, Besnoitia, Sarcocystis, Frenkelia and Hammondia. The main features of the former subfamily are: various oocyst structures, the lack of the extra-intestinal development, obligatory monoxeny. The main characters of the latter subfamily: oocysts of the same pattern, the involvement of extra-intestinal development, shifts from facultative to obligatory heteroxeny.

Animals↗
PubMedDate not supplied

The cytoplasmic differentiation of jumelle Stylonychia.

Jumelle Stylonychia with oppositely oriented peristomes, which we obtained by artificial operations, carried on not only asexual reproduction and generation, but sexual reproduction and encystment as well, and seemingly tended to form a new species [7-10]. Our recent experimental analysis revealed that the sinister grew more and more dependent on its dextral sister organism, losing the ability of independent existence. Once cut off from the dexter, the organelles of the sinister ceased to regenerate, and the sinister died. But, if, when cutting, a portion is left connected to the dexter, the sinister will then be able to regenerate, and all its organelles become completely revealed. This indicates that dependence on the dexter weakened the metabolic functions of the sinister, primarily influencing the cytoplasm, which is manifested by the formation and development of its organelles. This, in effect, is a phenomenon of cytoplasmic differentiation induced by co-existence of the jumeaux.

Animals↗