Effects of asymmetric division on a stochastic model of the cell division cycle

The stochastic model of cell division formulated by Alt and Tyson is generalized to the case of imprecise binary fission. Closed-form expressions are derived for the generation-time distribution, the birth-size and division-size distributions, the beta curve, and the correlation coefficient of generation times of sister cells. The theoretical results are compared to observations of cell division statistics in a culture of fission yeast.     

Studies on the control of cell division in a green alga,Ankistrodesmus gracilis (Chlorococcales)

The effects of various kinds of nitrogen compounds on the proliferation patterns ofAnkistrodesmus gracilis were examined. Among the tested compounds, the addition of peptone, arginine or glutamine to the N-free medium was the most effective on cell growth. The effectiveness was also shown in media containing one of several kinds of amino acid. In both peptone and arginine media the alga proliferated with multiple fission type of cell division, whereas the cultures grown in glutamine or serine medium contained 2-celled colonies at high frequencies. The latter was an efficient culture condition for cell reproduction with binary fission. The evidence for the behavior of nuclear and cytoplasmic division in these growth patterns were obtained from observations of thin sectioned materials.     

Life cycle of the multiarmed sea star Coscinasterias acutispina (Stimpson, 1862) in laboratory culture: sexual and asexual reproductive pathways

The multiarmed sea star Coscinasterias acutispina generally has 7-10 arms and 2-5 madreporites. It is known to be able to reproduce by asexual fission, and we have previously observed that this species also has the ability to reproduce sexually; however, there has been no report until now of spawning in this species. We succeeded in establishing a long-term culture of juveniles produced by artificial fertilization. Twelve months after the completion of metamorphosis, three individuals had six arms of the same length and a madreporite. At this time, fission occurred in two of these individuals, while the remaining individual underwent fission four months later. Each sea star divided into two halves, provided with three arms each. Thereafter, four or five new arms and two or four madreporites were formed anew in each of the six daughter sea-stars, so that by 30 days after the first fission the number of arms and madreporites in each was similar to that in adults. A second fission occurred in four of these six individuals, four or five months after the first fission, and in three of them the plane of division was the same as that of the first fission. The original three individuals eventually proliferated to 12 by undergoing fission. All individuals had fully developed gonads by 1-3 months after the second fission. Some of them eventually spawned under laboratory culture, and the resulting larvae metamorphosed into juveniles. Our observations demonstrate that individuals of C. acutispina possess the potential for both sexual and asexual reproduction.     

Bacterial Degradation of Diphenylmethane, a DDT Model Substrate

A strain of Hydrogenomonas was isolated by elective culture in a solution with diphenylmethane, an analogue of DDT, as the sole carbon source. Constitutive enzymes effected the oxidation and fission of one of the benzene rings of diphenylmethane, and phenylacetic acid was found as a major degradation product. Small amounts of phenylglyoxylic and benzoic acids were also generated from diphenylmethane by the bacterium. Phenylacetic acid, which contains the second benzene ring of diphenylmethane, was metabolized by inducible enzymes.     

Multi-patterned dynamics of mitochondrial fission and fusion in a living cell

Mitochondria are highly-dynamic organelles, but it is challenging to monitor quantitatively their dynamics in a living cell. Here we developed a novel approach to determine the global occurrence of mitochondrial fission and fusion events in living human epithelial cells (Hela) and mouse embryonic fibroblast cells (MEF). Distinct patterns of sequential events including fusion followed by fission (Fu-Fi), the so-called "kiss and run" model previously described, fission followed by fusion (Fi-Fu), fusion followed by fusion (Fu-Fu), and fission followed by fission (Fi-Fi) were observed concurrently. The paired events appeared in high frequencies with short lifetimes and large sizes of individual mitochondria, as compared to those for unpaired events. The high frequencies of paired events were found to be biologically significant. The presence of membrane uncoupler CCCP enhanced the frequency of paired events (from both Fu-Fi and Fi-Fu patterns) with a reduced mitochondrial size. Knock-out of mitofusin protein Mfn1 increased the frequency of fission with increased lifetime of unpaired events whereas deletion of both Mfn1 and Mfn2 resulted in an instable dynamics. These results indicated that the paired events were dominant but unpaired events were not negligible, which provided a new insight into mitochondrial dynamics. In addition to kiss and run model of action, our data suggest that, from a global visualization over an entire cell, multiple patterns of action appeared in mitochondrial fusion and fission.     

Experimental induction of two inner cell masses in mouse embryos by vinblastine treatment in vitro

Induction of artificial fission of the inner cell mass in an in vitro embryonal culture system was attempted. Mouse blastocysts were collected from uteri on day 3 of gestation and exposed to vinblastine sulfate after removal of zona pellucida. Embryos in the control group had a single inner cell mass on the trophectoderm and developed to the postblastocyst stage. On the other hand, the inner cell masses of the embryos in experimental groups subdivided into two or more. The present results, therefore, revealed that the vinblastine treatment at the blastocyst stage induced fission of the inner cell mass in mouse embryos. Further studies are planned in improved culture conditions to determine whether each inner cell mass subdivision develops into independent embryos.     

Cell division in marine Ceratium. I

The binary fission of 3 forms of marine Ceratium, C.gibberum, C.gibberum f.sinsitra and C.tripos f.atlantica was observed in culture. In either of the 3 forms, it is possible to make cell division take place under the condition of single cell culture. Both binary fission and chain formation have been observed. Concerning the relationship between binary fission and chain formation, light intensity may be considered as a controlling factor.     

Planeticovorticella finleyi n.g., n.sp. (Peritrichia, Vorticellidae), a planktonic ciliate with a polymorphic life cycle

Abstract. Free-swimming trophonts of a sessiline peritrich ciliate were discovered in plankton samples from the Rhode River, Maryland, and main-stem Chesapeake Bay. Cultures revealed that the species comprises both free trophonts that swim with their peristomial cilia and sessile trophonts that attach to substrates with a contractile, helically-twisted talk. Trophonts with a short, rigid stalk or no definite stalk also were seen in culture. Binary fission of free-swimming trophonts usually produced a pair of trophonts attached scopula to scopula by a short, rigid stalk. These persisted for some time as distinctive, spinning doublets before their stalks broke and they separated. Binary fission of free-swimming trophonts also yielded trophont-telotroch pairs that stayed together for only a short time. Telotrochs from these pairs were presumably the source of attached trophonts. Conjugation occurred in both free and attached trophonts. Formation of microconjugants involved at least 2 successive divisions of a trophont. Possession of a helically-twisted, contractile stalk placed the peritrich in the family Vorticellidae, but its unique combination of life-cycle stages marks it as a new genus and species, Planeticovorticella, finleyi The morphology and life cycle of P. finleyi raise questions about the present classification of sessiline peritrichs and suggest that it may be at least partly artificial. Stalkless planktonic peritrichs that swim with their oral cilia as do trophonts of P. finleyi may have evolved from sessile ancestors by an alteration in the life cycle that created unstable clusters of trophonts on a single parental stalk. Free-swimming trophonts would originate from breakup of these clusters.     

Expression of human antithrombin III in Saccharomyces cerevisiae and Schizosaccharomyces pombe

Recombinant plasmids were constructed that direct the synthesis of human antithrombin III in baker's yeast, Saccharomyces cerevisiae, and the fission yeast, Schizosaccharomyces pombe. The signal sequence of antithrombin III was recognized by both yeast species, and antithrombin III was secreted into the medium. When the signal sequence was replaced by a sequence of ten arbitrary amino acids, the product expressed from such a construct stayed inside the cell. Antithrombin III was glycosylated by the baker's and fission yeast and was immunologically identical to antithrombin III isolated from human plasma. Antithrombin III isolated from the culture media of recombinant yeasts was biologically active, as could be shown by progressive inhibitor activity and heparin cofactor activity.     

The Relationship of the Nutritive State of the Prey Organism Paramecium aurelia to the Growth and Encystment of Didinium nasutum

SYNOPSIS. Only well fed Paramecium aurelia , grown either monoflorally or on a mixture of 2 species of bacteria, are adequate to maintain optimal fission rates and encystment rates for Didinium nasutum. Progressive starvation of paramecia prior to their being fed to didinia leads to decreased fission rates, the appearance of abnormal cells and a loss of ability to encyst by the didinia. This depression can be fully overcome by allowing the didinia to feed again upon well nourished paramecia. A minimum of 45 well-fed paramecia is required daily for each Didinium if maximal fission rates are to be maintained. Encystment and fission appear to be mutually exclusive processes, but encystment rates are related to fission rates and seem to be exclusive of the density of the didinial culture.     

Bacterial Metabolism of para- and meta-Xylene: Oxidation of a Methyl Substituent

Pseudomonas Pxy was isolated on p-xylene as sole source of carbon and energy. Substrates that supported growth were toluene, p-methylbenzyl alcohol, p-tolualdehyde, p-toluic acid, and the analogous m-methyl derivatives, including m-xylene. Cell extracts prepared from Pseudomonas Pxy after growth with either p-xylene or m-xylene oxidized the p- and m-isomers of tolualdehyde as well as p-methylbenzyl alcohol. The same cell extracts also catalyzed a "meta" fission of both 3- and 4-methylcatechol. Treatment of Pseudomonas Pxy with N-methyl-N'-nitro-N-nitrosoguanidine led to the isolation of two mutant strains. Pseudomonas Pxy-40, when grown on succinate in the presence of p-xylene, accumulated p-toluic acid in the culture medium. Under the same conditions Pseudomonas Pxy-82 accumulated p-toluic acid and also 4-methylcatechol. When Pseudomonas Pxy-82 was grown on succinate in the presence of m-xylene, 3-methylcatechol and 3-methylsalicylic acid were excreted into the culture medium. A pathway is proposed for the initial reactions utilized by Pseudomonas Pxy to oxidize p- and m-xylene.     

Relative biological effectiveness and tolerance dose of fission neutrons in canine skin for a potential combination of neutron capture therapy and fast-neutron therapy

To investigate the potential efficacy of fission neutrons from a fast-neutron reactor for the treatment of radioresistant tumors, the relative biological effectiveness (RBE) and tolerance dose of fission neutrons in canine skin were determined. The forelimbs of 34 healthy mongrel dogs received a single dose of fission neutrons (5.6, 6.8, 8.2, 9.6 or 11 Gy) or 137Cs gamma rays (10, 15, 20, 25 or 30 Gy). Based on observations of radiodermatitis for each radiation, the single-fraction RBE of fission neutrons in the sixth month was calculated as approximately 3. The tolerance doses of fission neutrons and gamma rays, defined as the highest doses giving no moist desquamation on the irradiated skin in the recovery phase, were estimated as 7.6 Gy and 20 Gy, respectively. The tolerance dose of 7.6 Gy of fission neutrons included 5.0 Gy of fast neutrons possessing high anti-tumor effects and 1.4 x 10(12) n/cm2 of thermal neutrons, which could be applicable to neutron capture therapy (NCT). The combination of fast-neutron therapy and NCT using a fast-neutron reactor might be useful for the treatment of radioresistant tumors.     

Mitochondrial fusion, fission and autophagy as a quality control axis: the bioenergetic view

The mitochondrial life cycle consists of frequent fusion and fission events. Ample experimental and clinical data demonstrate that inhibition of either fusion or fission results in deterioration of mitochondrial bioenergetics. While fusion may benefit mitochondrial function by allowing the spreading of metabolites, protein and DNA throughout the network, the functional benefit of fission is not as intuitive. Remarkably, studies that track individual mitochondria through fusion and fission found that the two events are paired and that fusion triggers fission. On average each mitochondrion would go though ~5 fusion:fission cycles every hour. Measurement of Deltapsi(m) during single fusion and fission events demonstrates that fission may yield uneven daughter mitochondria where the depolarized daughter is less likely to become involved in a subsequent fusion and is more likely to be targeted by autophagy. Based on these observations we propose a mechanism by which the integration of mitochondrial fusion, fission and autophagy forms a quality maintenance mechanism. According to this hypothesis pairs of fusion and fission allow for the reorganization and sequestration of damaged mitochondrial components into daughter mitochondria that are segregated from the networking pool and then becoming eliminated by autophagy.     

Stable telocentric chromosomes produced by centric fission in chinese hamster cells in vitro

Metaphase examination of pseudodiploid Chinese hamster cells revealed that spontaneous breaks or fission occurred rather frequently (2.9%) at the centromeric regions of subtelo- or metacentric chromosomes, resulting in the production of telocentric chromosomes. The centromeric fission appeared to occur in every member of the chromosome complement. An attempt was made to isolate cells possessing thus derived telocentrics from the cell population and gave two clonal lines which were retaining one and two telocentric chromosomes, respectively. Both banding and labeling patterns of these chromosomes indicated unequivocally their X chromosome origin. They were transmitted successively to the daughter cells during a 3-month culture period, showing no tendency to fuse to produce a metacentric chromosome.Contribution No. 897 from the National Institute of Genetics, Japan.     

Who is Responsible for Fission in a Free-ranging Troop of Baboons?

The study troop of chacma baboons (Papio cynocephalus ursinus) at Mkuzi Game Reserve, Zululand, South-Africa, comprised of about 76 members that split into two new troops. The events leading to this troop fission will be described and its possible causes will be discussed. Troop fission among baboons is generally attributed to the withdrawal of low-ranking females from the main group, as a result of the cost of food competition and its effect on their reproductive success. At Mkuzi, no evidence for food competition among females was recorded in terms of rank-related time spent feeding or other time—budget components, feeding-bout length, diet composition or context of female aggression. Moreover, no evidence for rank-related differential reproductive success was found in terms of inter-birth intervals or infant survival. Female mortality was, however, related to dominance rank, with circumstantial evidence suggesting that cause of mortality was predation by leopards. Rate of female disappearances, aggression levels among females, and the percentage of time they spent in proximity to other adult troop members increased after fission. Relatively short inter-birth intervals and extremely low infant mortality rate at Mkuzi resulted in a small number of receptive females at any one time, and therefore in high costs of male sexual competition as expressed in the high levels of male aggression and woundings, both reduced after fission. It is suggested that this troop fission may have been initiated by the resident males, triggered by the high cost of sexual competition, and forced on the females, who were, consequently, subjected to higher risk of predation. The troop fission was preceded by a long process of increasing tendency for sub-trooping. It was initiated by the four resident males who kept a large distance apart from each other, herded oestrous female associates away from others and were followed by other females. The females generally tended to stay close to associates, males and females. These parties were followed by the peripheral and immigrant males who had no female associates, and eventually two distinct daughter troops were formed.     

Mitochondrial fusion, fission and autophagy as a quality control axis: The bioenergetic view

The mitochondrial life cycle consists of frequent fusion and fission events. Ample experimental and clinical data demonstrate that inhibition of either fusion or fission results in deterioration of mitochondrial bioenergetics. While fusion may benefit mitochondrial function by allowing the spreading of metabolites, protein and DNA throughout the network, the functional benefit of fission is not as intuitive. Remarkably, studies that track individual mitochondria through fusion and fission found that the two events are paired and that fusion triggers fission. On average each mitochondrion would go though ~ 5 fusion:fission cycles every hour. Measurement of Δψ_m during single fusion and fission events demonstrates that fission may yield uneven daughter mitochondria where the depolarized daughter is less likely to become involved in a subsequent fusion and is more likely to be targeted by autophagy. Based on these observations we propose a mechanism by which the integration of mitochondrial fusion, fission and autophagy forms a quality maintenance mechanism. According to this hypothesis pairs of fusion and fission allow for the reorganization and sequestration of damaged mitochondrial components into daughter mitochondria that are segregated from the networking pool and then becoming eliminated by autophagy.     

Effect of Adenine on Paramecium multimicronucleatum*

SYNOPSIS. The addition of adenine to the culture medium of Paramecium multimicronucleatum caused an inhibition of conjugation and fission and also an increase in the number of food vacuoles. The inhibition of conjugation was observed at the stage of adhesion of cell membranes. With adenine, the duration of fission was prolonged and L-shaped cells were formed. Adenine apparently repressed the excretion of food vacuoles and thus caused an accumulation of food vacuoles within the cells. All these effects were observed at similar concentrations of adenine higher than 2 mM. The addition of uridine to the adenine-containing medium reversed the inhibition of fission; conjugation and vacuole accumulation remained unaffected.     

Evolution of a novel developmental trajectory: fission is distinct from regeneration in the annelid Pristina leidyi

Understanding how novelty arises has been a major focus of evolutionary developmental biology. While the origin of new genes, gene functions, and morphological features has been studied intensely, the origin of entire developmental trajectories, such as regeneration or agametic reproduction, remains poorly understood. Agametic reproduction by fission is a novel trajectory evolved numerous times among animal phyla, including Annelida, in which it is thought to arise by co-option of regeneration. To gain insight into how a novel trajectory may evolve, we investigated a relatively recent origin of fission. We performed a detailed comparison of morphogenesis during regeneration and fission in the annelid Pristina leidyi (Clitellata, Naididae), from the onset of these trajectories to the achievement of the final morphology. We find extensive similarities between fission and regeneration morphogenesis, and, of particular note, find evidence for a synapomorphy of fission and regeneration (apparently not shared with embryogenesis) in peripheral nervous system development, providing strong support for the hypothesis that fission is derived from regeneration. We also find important differences between fission and regeneration, during development of multiple organ systems. These are manifested by temporal shifts in developmental events and by the presence of elements unique to only one process. Differences are not obviously temporally clustered at the beginning, middle, or end of development but rather occur throughout, indicating that divergence has occurred along the entire developmental course of these trajectories.     

Binary fission of Pneumocystis carinii trophozoites grown in vitro

Trophozoites grown in vitro were shown to undergo binary fission by transmission electron microscopy (TEM). Standard fixation with subsequent embedding in Spurr was employed using 3% glutaraldehyde and 1% osmium tetroxide with 5% sucrose added to both fixatives and 0.1 M cacodylate buffer washes. Trophozoites were grown on WI-38 cells in vitro. Trophozoites were found in various stages of fission. The dividing trophozoite has daughter cells that are rounder than the pleomorphic, non-dividing trophozoites. Tubular forms external to the dividing trophozoites were decreased in number; tubular forms when present were concentrated around the forming septa. Nuclear material was sometimes, but not always, well defined in both daughter cells. There was no concentration of nuclear material at the poles. Vacuoles without membrane were present in the dividing forms. Separate nuclear regions were sometimes found in the dividing trophozoites. These observations suggest that binary fission does occur in culture; however, the significance of binary fission to the life cycle of Pneumocystis carinii (Pc) is not yet clear.