The cell cycle of symbiotic Chlorella. III. Numbers of algae in green hydra digestive cells are regulated at digestive cell division

1986 ◽  
Vol 85 (1) ◽  
pp. 63-71
Author(s):  
P.J. McAuley
Keyword(s):  
Cell Division ◽  
Host Cell ◽  
Algal Cell ◽  
Host Cells ◽  
Digestive Cell ◽  
Digestive Cells ◽  
Daughter Cells ◽  
Green Hydra ◽  
Mother And Daughter ◽  
Chlorella Algae

Regression analysis of the relationship between the size of interphase and mitotic digestive cells of green hydra, and the numbers and total volume of the symbiotic Chlorella algae they contain showed a partial correlation only, suggesting that numbers of algae per cell are not regulated by limiting them to a specific proportion of the host cell, and that the variation observed in numbers of algae per cell is not due to variation in host cell size. After hydra were fed, which stimulates algae and digestive cells to divide at the same time, numbers of algae per cell were higher in prophase than in interphase cells, and numbers increased as mitosis proceeded. In excised regenerating peduncles algae divide before digestive cells, and at the onset of digestive cell division mitotic cells were found to contain almost twice the number of algae as before excision. Thus, almost all of the algal cell division necessary to maintain a constant population size was associated with digestive cell division. Analysis of variance in numbers of algae in telophase mother and daughter cells suggested that the proportion of algae dividing as a result of host cell mitosis was greater in digestive cells with few algae than in those with many algae. The fact that the mechanism controlling the proportion of algae dividing in host cells is expressed at host cell division and is manifested in the daughter cells may contribute to wide variation in numbers of algae per cell.

The cell cycle of symbiotic Chlorella. I. The relationship between host feeding and algal cell growth and division

1985 ◽  
Vol 77 (1) ◽  
pp. 225-239
Author(s):  
P.J. McAuley
Keyword(s):  
Cell Division ◽  
Cell Growth ◽  
Host Cell ◽  
Algal Cell ◽  
Host Cells ◽  
Digestive Cell ◽  
Host Feeding ◽  
Digestive Cells ◽  
Division Factor ◽  
Cell Mitosis

When green hydra were starved, cell division of the symbiotic algae within their digestive cells was inhibited, but algal cell growth, measured as increase in either mean volume or protein content per cell, was not. Therefore, control of algal division by the host digestive cells must be effected by direct inhibition of algal mitosis rather than by controlling algal cell growth. The number of algae per digestive cell increased slightly during starvation, eventually reaching a new stable level. A number of experiments demonstrated that although there was a relationship between host cell and algal mitosis, this was not causal: the apparent entrainment of algal mitosis to that of the host cells could be disrupted. Thus, there was a delay in algal but not host cell mitosis when hydra were fed after prolonged starvation, and algae repopulated starved hydra with lower than normal numbers of algae (reinfected aposymbionts or hydra transferred to light after growth in continuous darkness). Two experiments demonstrated a direct stimulation of algal cell division by host feeding. Relationships of algal and host cell mitosis to numbers of Artemia digested per hydra were different, and in hydra fed extracted Artemia algal, but not host cell, mitosis was reduced in comparison to that in control hydra fed live shrimp. It is proposed that algal division may be dependent on a division factor, derived from host digestion of prey, whose supply is controlled by the host cells. Numbers of algae per cell would be regulated by competition for division factor, except at host cell mitosis, when the algae may have temporarily uncontrolled access to host pools of division factor. The identity of the division factor is not known, but presumably is a metabolite needed by both host cells and algae.

scholarly journals Temporal relationships of host cell and algal mitosis in the green hydra symbiosis

1982 ◽  
Vol 58 (1) ◽  
pp. 423-431
Author(s):  
P.J. McAuley
Keyword(s):  
Cell Division ◽  
Host Cell ◽  
Digestive Cell ◽  
Digestive Cells ◽  
Symbiotic Algae ◽  
Green Hydra ◽  
Temporal Relationships ◽  
Dividing Cells ◽  
Cell Mitosis ◽  
Mitotic Cells

In fed hydra or excised regenerating peduncles there are increases in the mitotic indices of both digestive cells and the symbiotic algae that reside within them. Conversely, algal and digestive cell mitotic indices decrease in starved hydra. The temporal relationships of algal and host cell division differ in fed hydra and regenerating peduncles. After feeding, algal and digestive cell mitotic indices both reach a peak at about the same time; during regeneration, first the algae and then the digestive cells divide. Thus, mitotic digestive cells in regenerating peduncles contain more algae than those in gastric regions of fed hydra. However, in both cases mitotic digestive cells contain more algae than non-mitotic cells. The algae appear to be partitioned at random between daughter digestive cells at teleophase. It is suggested that the division of the symbiotic algae is closely related to that of the digestive cells in which they maintained. Mitosis of algae is stimulated by host cell mitosis, but in non-dividing cells algal mitosis is restricted. Possible mechanisms by which the host digestive cells could restrict algal division are discussed.

Partitioning of symbiotic Chlorella at host cell telophase in the green hydra symbiosis

1990 ◽  
Vol 329 (1252) ◽  
pp. 47-53 ◽  
Keyword(s):  
Cell Division ◽  
Host Cell ◽  
Daughter Cell ◽  
Control Cell ◽  
Culture Conditions ◽  
Digestive Cells ◽  
Density Dependent ◽  
Green Hydra ◽  
The Mean ◽  
Control Cell Division

Although there is much evidence that green hydra digestive cells control cell division of their Chlorella symbionts, so that the symbionts divide only at host cell division, it is not clear how the population size of symbionts (numbers per cell) is regulated. In constant culture conditions the mean number of symbionts per cell also remains constant, but with a very large variance about the mean. The way in which symbionts are partitioned at host cell division appears to account for that variation. By counting numbers of Chlorella in daughter cells at late telophase it was found that partitioning of Chlorella symbionts was not symmetrical, but at random, closely following that predicted by the binomial distribution if it is assumed that each symbiont had an equal probability of entering either host daughter cell. A better fit to the predicted distribution was obtained from observations of partition in digestive cells from excised regenerating peduncles than in those from recently fed gastric regions, possibly because in the former, algae have completed their division before the host cell divides, while in the latter algal and host cell division takes place at the same time. There was only a small effect of differences in daughter cell volume on numbers of symbionts received, but comparison of variance and coefficient of variation of numbers of algae in mother (post-algal division, pre-partition) and daughter telophase digestive cells (pre-division, post-partition) suggested that algal division at host mitosis was density dependent. Random partitioning of algae at host cell telophase would account for the wide variation in numbers of algae per cell, and compensatory density-dependent algal division at the next host cell mitosis would ensure stability of the mean algal population.

The green hydra symbiosis. VIII. Mechanisms in symbiont regulation

1984 ◽  
Vol 221 (1224) ◽  
pp. 291-319 ◽  
Keyword(s):  
Cell Division ◽  
Algal Cell ◽  
Algal Growth ◽  
Culture Conditions ◽  
Continuous Illumination ◽  
Digestive Cell ◽  
Green Hydra ◽  
European Strain ◽  
Standard Culture ◽  
Feeding Regimes

The relative amount of symbiotic algae and animal tissue in the European strain of green hydra was altered by changes in illumination and feeding regimes. This indicates that the host can regulate the algal population to different sizes depending on external conditions. For animals maintained in continuous illumination, 12 h light: 12 h dark, and continous darkness, each with thrice-weekly feeding, a highly significant regression of algal volume per digestive cell on digestive cell volume was demonstrated, suggesting that the space available for the algae may be one factor that determines the population size of the algal symbionts. Seven strains of Chlorella originally symbiotic with other invertebrates formed stable associations with the European strain of green hydra; this included one strain (NC64A) which released very little maltose at pH 4-5. Althought the relative amounts of algal and host biomass of these experimental associations were very similar under standard culture conditions, large numbers of cells of strain NC64A were regularly expelled from the host. This suggests that the ability of the host to control the growth rate of its symbionts is related to the alga’s capacity for maltose release. The latter characteristic is also correlated with a sensitivity of growth to acid conditions. Of the five cultured strains of symbiotic Chlorella examined, only the two strains that released substantial amounts of maltose at pH 4-5 failed to grow at pH 4.0 and pH 4.5. It is proposed that the regulation of algal cell division in the natural symbiosis is principally mediated through relatively small and temporary changes in the pH of the perialgal vacuole. At more acid values, photosynthetically fixed carbon is primarily directed towards maltose release and little or no algal growth occurs. At higher pH values, maltose release declines sharply and the carbon becomes primarily directed towards symbiont growth. Such a relatively simple hypothetical model, involving stimulation of symbiont growth by temporary alkalinization of the perialgal vacuole, can explain the observed responses to change in environmental conditions, as well as the relation between the timing of symbiont and host cell division.

The green hydra symbiosis. V. Stages in the intracellular recognition of algal symbionts by digestive cells

1982 ◽  
Vol 216 (1202) ◽  
pp. 7-23 ◽  
Keyword(s):  
Host Cell ◽  
Transport Mechanism ◽  
Digestive Cell ◽  
Digestive Cells ◽  
Maltose Transport ◽  
Green Hydra ◽  
Algal Symbionts ◽  
Wide Range ◽  
Cell Base

Aposymbiotic (alga-free) green hydra may be reinfected by injecting a suspension of Chlorella symbionts into their coelenterons. Digestive cells could phagocytose a wide range of Chlorella types, but transport to the cell base, where the symbionts normally reside, was limited to algae that release detectable amounts of maltose. Transport of their own symbionts was inhibited when maltose release was curtailed by prolonged pretreatment with a photosynthetic inhibitor. After phagocytosis, only about half of their own symbionts were transported, the rest remaining at the digestive cell apex where they disintegrated. This phenomenon was termed sorting. It was not due to damage of algae during isolation, nor to saturation of the transport mechanism. A further stage of discrimination was observed to take place up to 5 days after injection; some symbionts that had been transported to the cell bases were removed to the apices and disintegrated or were ejected (re-sorting). It is concluded that recognition of suitable algae is unlikely to involve identification of a single algal character by the European digestive cells. The establishment of the symbiosis may depend upon a number of algal properties and interactions within the host cell.

The cell cycle of symbiotic Chlorella. IV. DNA content of algae slowly increases during host starvation of green hydra

1986 ◽  
Vol 85 (1) ◽  
pp. 73-84
Author(s):  
P.J. McAuley ◽  
L. Muscatine
Keyword(s):  
Cell Size ◽  
Dna Content ◽  
Algal Cell ◽  
S Phase ◽  
Symbiotic Algae ◽  
Daughter Cells ◽  
Green Hydra ◽  
Significant Difference ◽  
Preceding Period ◽  
Chlorella Algae

The distribution of DNA content of symbiotic Chlorella algae freshly isolated from green hydra was compared with that of cultured Chlorella of the NC64A strain, using flow cytometry. In nonlogarithmic cultures of NC64A most cells had accumulated in G1 phase, while in logarithmic cultures a peak containing cells in S phase and mitosis could be distinguished from the larger G1 peak. However, symbiotic algae showed a single broad peak in which there was no clear distinction between G1 and S phase/mitosis. When hydra were starved for a prolonged period, inhibiting host cell and algal division, the DNA content of the symbiotic algae slowly increased, and the number of daughter cells produced after a single feeding increased with the length of the preceding period of starvation. This suggests that symbiotic algae are able to cycle slowly through S phase, but unless the host is fed they cannot traverse into mitosis and complete the cell division cycle. No significant difference in cell size was found between algae producing either four or eight daughter cells after 1-day- or 22-day-starved hydra were fed, suggesting that algal cell size did not determine the number of daughter cells produced. Instead, this may be dependent upon the length of time the cell had spent in S phase prior to receiving the, as yet unknown, stimulus to enter into mitosis.

scholarly journals Spindle-independent condensation-mediated segregation of yeast ribosomal DNA in late anaphase

2005 ◽  
Vol 168 (2) ◽  
pp. 209-219 ◽  
Author(s):  
Félix Machín ◽  
Jordi Torres-Rosell ◽  
Adam Jarmuz ◽  
Luis Aragón
Keyword(s):  
Cell Division ◽  
Ribosomal Dna ◽  
Budding Yeast ◽  
Mitotic Cell ◽  
Yeast Genome ◽  
Daughter Cells ◽  
Late Anaphase ◽  
Mother And Daughter ◽  
The Right ◽  
Chromosome Resolution

Mitotic cell division involves the equal segregation of all chromosomes during anaphase. The presence of ribosomal DNA (rDNA) repeats on the right arm of chromosome XII makes it the longest in the budding yeast genome. Previously, we identified a stage during yeast anaphase when rDNA is stretched across the mother and daughter cells. Here, we show that resolution of sister rDNAs is achieved by unzipping of the locus from its centromere-proximal to centromere-distal regions. We then demonstrate that during this stretched stage sister rDNA arrays are neither compacted nor segregated despite being largely resolved from each other. Surprisingly, we find that rDNA segregation after this period no longer requires spindles but instead involves Cdc14-dependent rDNA axial compaction. These results demonstrate that chromosome resolution is not simply a consequence of compacting chromosome arms and that overall rDNA compaction is necessary to mediate the segregation of the long arm of chromosome XII.

The green hydra symbiosis. VII. Conservation of the host cell habitat by the symbiotic algae

1982 ◽  
Vol 216 (1205) ◽  
pp. 415-426 ◽  
Keyword(s):  
Host Cell ◽  
Lysosomal Degradation ◽  
Normal Complement ◽  
Calcofluor White ◽  
Digestive Cells ◽  
Symbiotic Algae ◽  
Green Hydra ◽  
Fluorescent Agent ◽  
Almost All ◽  
Cell Base

Freshly isolated ‘European’ algae phagocytosed by digestive cells of ‘European’ green hydra were distinguished from the pre-existing popu­lation of algae by prestaining with the fluorescent agent Calcofluor White. Only a small number of phagocytosed ‘European’ algae or algae cultured from Paramecium bursaria avoided lysosomal degradation and were transported to the cell base in symbiotic digestive cells, although in aposymbionts up to 50% of phagocytosed algae were transported. Degradation of almost all phagocytosed algae also occurred in digestive cells of hydra containing only half the normal complement of algae, and in those of hydra symbiotic with algae cultured from Paramecium . The presence of algae at the bases of digestive cells appears to negate the mechanism by which potentially symbiotic algae normally avoid lysosomal attack. This protects the host cell and its symbionts from invasion by ‘foreign’ algae and suggests that once established the green hydra symbiosis is conservative in nature.

The role of algal antigenic determinants in the recognition of potential algal symbionts by cells of Chlorohydra

1979 ◽  
Vol 35 (1) ◽  
pp. 367-379
Author(s):  
R.R. Pool
Keyword(s):  
Cell Surface ◽  
Algal Cell ◽  
Antigenic Determinants ◽  
Digestive Cells ◽  
Green Hydra ◽  
Algal Symbionts ◽  
Two Systems

Algal cells grown in the green hydra Chlorohydra viridissima were shown to possess characteristic antigenic determinants not found in algae cultured in vitro. These antigenic determinants, including those localized on the algal cell surface, were shown to be responsible for the phagocytic recognition of potential algal symbionts by digestive cells of Chlorohydra. The results of this study indicate the existence of two systems governing phagocytosis in Chlorohydra, one specific for algal cells grown in hydra, another governing the uptake of other particles by the hydra digestive cells.

scholarly journals Mechanisms for Curing Yeast Prions

2020 ◽  
Vol 21 (18) ◽  
pp. 6536
Author(s):  
Lois E. Greene ◽  
Farrin Saba ◽  
Rebecca E. Silberman ◽  
Xiaohong Zhao
Keyword(s):  
Quality Control ◽  
Cell Division ◽  
Protein Quality ◽  
Prion Proteins ◽  
Amyloid Fibers ◽  
Yeast Prions ◽  
Daughter Cells ◽  
Mother And Daughter ◽  
Infectious Proteins ◽  
Β Sheet

Prions are infectious proteins that self-propagate by changing from their normal folded conformation to a misfolded conformation. The misfolded conformation, which is typically rich in β-sheet, serves as a template to convert the prion protein into its misfolded conformation. In yeast, the misfolded prion proteins are assembled into amyloid fibers or seeds, which are constantly severed and transmitted to daughter cells. To cure prions in yeast, it is necessary to eliminate all the prion seeds. Multiple mechanisms of curing have been found including inhibiting severing of the prion seeds, gradual dissolution of the prion seeds, asymmetric segregation of the prion seeds between mother and daughter cells during cell division, and degradation of the prion seeds. These mechanisms, achieved by using different protein quality control machinery, are not mutually exclusive; depending on conditions, multiple mechanisms may work simultaneously to achieve curing. This review discusses the various methods that have been used to differentiate between these mechanisms of curing.

Sign in / Sign up

Export Citation Format

Share Document