Formation Of Daughter Cells Research Articles

Gigantism in a bacterium, Epulopiscium fishelsoni, correlates with complex patterns in arrangement, quantity, and segregation of DNA.

Epulopiscium fishelsoni, gut symbiont of the brown surgeonfish (Acanthurus nigrofuscus) in the Red Sea, attains a larger size than any other eubacterium, varies 10- to 20-fold in length (and >2, 000-fold in volume), and undergoes a complex daily life cycle. In early morning, nucleoids contain highly condensed DNA in elongate, chromosome-like structures which are physically separated from the general cytoplasm. Cell division involves production of two (rarely three) nucleoids within a cell, deposition of cell walls around expanded nucleoids, and emergence of daughter cells from the parent cell. Fluorescence measurements of DNA, RNA, and other cell components indicate the following. DNA quantity is proportional to cell volume over cell lengths of approximately 30 micrometers to >500 micrometers. For cells of a given size, nucleoids of cells with two nucleoids (binucleoid) contain approximately equal amounts of DNA. And each nucleoid of a binucleoid cell contains one-half the DNA of the single nucleoid in a uninucleoid cell of the same size. The life cycle involves approximately equal subdivision of DNA among daughter cells, formation of apical caps of condensed DNA from previously decondensed and diffusely distributed DNA, and "pinching" of DNA near the middle of the cell in the absence of new wall formation. Mechanisms underlying these patterns remain unclear, but formation of daughter nucleoids and cells occurs both during diurnal periods of host feeding and bacterial cell growth and during nocturnal periods of host inactivity when mean bacterial cell size declines.

Effect of growth rate on resistance of Candida albicans biofilms to antifungal agents.

A perfused biofilm fermentor, which allows growth-rate control of adherent microbial populations, was used to assess whether the susceptibility of Candida albicans biofilms to antifungal agents is dependent on growth rate. Biofilms were generated under conditions of glucose limitation and were perfused with drugs at a high concentration (20 times the MIC). Amphotericin B produced a greater reduction in the number of daughter cells in biofilm eluates than ketoconazole, fluconazole, or flucytosine. Similar decreases in daughter cell counts were observed when biofilms growing at three different rates were perfused with amphotericin B. In a separate series of experiments, intact biofilms, resuspended biofilm cells, and newly formed daughter cells were removed from the fermentor and were exposed to a lower concentration of amphotericin B for 1 h. The susceptibility profiles over a range of growth rates were then compared with those obtained for planktonic cells grown at the same rates under glucose limitation in a chemostat. Intact biofilms were resistant to amphotericin B at all growth rates tested, whereas planktonic cells were resistant only at low growth rates (</=0.13 h-1). Cells resuspended from biofilms were less resistant than intact biofilm populations but more resistant than daughter cells; the susceptibilities of both these cell types were largely independent of growth rate. Our findings indicate that the amphotericin B resistance of C. albicans biofilms is not simply due to a low growth rate but depends on some other feature of the biofilm mode of growth.

Reconstitution of Golgi stacks from vesiculated Golgi membranes in permeabilized cells

Golgi membranes are organized into stacks of flattened cisternae in the cytoplasm of eukaryotic cells. These membranes are constantly budding and receiving small transport vesicles during protein trafficking. In mammalian cells, during mitosis, the Golgi cisternae break down extensively into small vesicles and tubules, which are partitioned into the cytoplasm of the newly formed daughter cells, where they fuse and assemble into stacks of cisternae. These findings raise intriguing questions; how Golgi membranes maintain their organization in stacks of cisternae amidst the tremendous membrane flux in non-dividing cells and how is the organization of the Golgi regulated in association with the cell cycle events? The scope of this article is to describe an assay that reconstitutes the process of Golgi stack formation from vesiculated Golgi membranes (VGMs) in semi-intact cells and to highlight some of the recent findings that increase our understanding of the mechanism of Golgi stack assembly.

A Deviating Pattern of Cell Division in the Green Alga Microthamnion: Ultrastructure of Vegetative Cell Division and Zoosporogenesis

Summary The ultrastructure of cell division of the green alga Microthamnion is described. It involves a unique mechanism for both vegetative cell division and zoosporogenesis. It starts with migration of the counterclockwise oriented centriole pair along the nuclear surface from the polar interphase position towards a lateral prophase position. The centriole pair duplicates and the root templates of the parental basal bodies grow out distally. Two microtubules of each of the two microtubular roots per basal body form two four-stranded microtubular bundles running along the cell wall and oriented perpendicular to the cell axis. At metaphase the separated centriole pairs have migrated to positions at approximately 180° from each other apparently via a sliding mechanism along the newly formed microtubular bundles. The microtubular bundles lie in the equatorial plane and curve over the nucleus, thus indicating the future division plane. In this respect the microtubular bundles resemble the preprophase band in higher plants. At anaphase the centriole pairs seem to have slightly co-migrated with the separating chromosome halves and thus the microtubular bundles show a shifted orientation with respect to the long axis of the cell. In this stage the unilateral septum starts to develop from the previous prophase position of the centriolar complex and progresses between the two four-stranded microtubular bundles. At telophase the daughter nuclei are reformed and the septum development proceeds. After cytokinesis the centrioles either return to the interphase position awaiting a new division cycle (vegetative cell division) or the centrioles take the prophase position in the newly formed daughter cells and duplicate in order to repeat the division cycle (zoosporogenesis). The ultrastructural features of Microthamnion are compared with the other pleurastrophycean algae and some chlamydomonadalean algae. However, the systematic position of Microthamnion still remains a matter of discussion.

Effects of norcantharidin, a protein phosphatase type-2A inhibitor, on the growth of normal and malignant haemopoietic cells

Cantharidin is a natural toxin that inhibits protein phosphatase type 2A (PP2A) and has antitumour effects in man. We have studied the synthetic analogue, norcantharidin (NCTD), which has less nephrotoxic and phlogogenic side-effects, investigating the effects on the normal haemopoietic system and leukaemia cell growth. Daily intraperitoneal (i.p.) injection of NCTD induced dose and circadian time-dependent transient leucocytosis in normal mice, but did not accelerate bone marrow (BM) regeneration, or have haemopoietic side-effects following chronic administration. NCTD stimulated the cell cycle progression of granulocyte—macrophage colony-forming cells (GM-CFC), stimulated DNA synthesis and increased the frequency of mitotic cells in short-term human BM cultures. NCTD also stimulated the production of interleukin (IL)-1β, colony stimulating activity (CSA) and tumour necrosis factor (TNF)-α. Continuous in vitro NCTD treatment, however, inhibited both DNA synthesis and GM-CFC growth. Fluorescence-activated cell sorting (FACS) analysis of DNA profiles and cytological studies in HL-60, K-562 or MRC5V2 (fibroblast) cells indicated that low doses of NCTD accelerated the G 1/S phase transition, while higher doses or prolonged incubations inhibited the cell cycle at the G 2/M phases or during the formation of postmitotic daughter cells. Electron microscopy revealed that NCTD impaired the neogenesis of chromatin material and nuclear membrane during the M/G 1 phase transition in K-562 cells. The biphasic effect of NCTD may be due to inhibition of PP2A activity, which regulates the cell cycle, both at the restriction point and at the G2 and M phases. Our data provide new insight into the cellular and molecular actions of NCTD, and partly explain its therapeutical effects in cancer patients.

Reconstitution of Golgi stacks from vesiculated Golgi membranes in permeabilized cells.

Abstract Golgi membranes are organized into stacks of flattened cisternae in the cytoplasm of eukaryotic cells. These membranes are constantly budding and receiving small transport vesicles during protein trafficking. In mammalian cells, during mitosis, the Golgi cisternae break down extensively into small vesicles and tubules, which are partitioned into the cytoplasm of the newly formed daughter cells, where they fuse and assemble into stacks of cisternae. These findings raise intriguing questions; how Golgi membranes maintain their organization in stacks of cisternae amidst the tremendous membrane flux in non-dividing cells and how is the organization of the Golgi regulated in association with the cell cycle events? The scope of this article is to describe an assay that reconstitutes the process of Golgi stack formation from vesiculated Golgi membranes (VGMs) in semi-intact cells and to highlight some of the recent findings that increase our understanding of the mechanism of Golgi stack assembly.

Host-inhibitory Functions Encoded by Promiscuous Plasmids: Transient Arrest of Escherichia coli Segregants that Fail to Inherit Plasmid RK2

An effective strategy for a plasmid to be maintained in a growing population of bacteria is to prevent the proliferation of newly formed daughter cells that lack of plasmid. In this study, we determined that the promiscuous, incompatibility group P plasmid RK2 encodes such a system. To induce large numbers of RK2-free segregants of an RK2-containing host, we designed a genetic system that made RK2 replication temperature-sensitive. A double amber mutant of the trfA replication initiator gene was constructed to complement a trfA deletion mutant of an otherwise wild-type RK2 in an Escherichia coli supD(Ts) strain. At the permissive temperature (30°C), RK2 was maintained stably in the strain. Shifting the cells to the non-permissive temperature (42°C) resulted in the nearly synchronous appearance of cells lacking RK2. We found that the number of viable cells rose only slowly over a period of six hours, during which time the cells formed long filaments reaching 20 to 40 times the length of a normal E. coli cell. After six hours, the arrested cells regained the ability to divide and multiply exponentially, and the filaments were eventually reduced to normal-sized cells. Neither arrest nor filamentation required the host recA function. Inhibiting the replication of an RK2 mutant deleted for the par stability locus also induced the arrest of segregants lacking the plasmid, but the arrested cells were not filamented. Our results demonstrate that RK2 encodes at least two functions that are activated in a plasmidless segregant: (1) a filamentation-inducing function specified by the par stability locus, and (2) a post-segregational arrest function ( psa) that inhibits the proliferation of plasmidless segregants independent of par. We discuss the possible roles of these functions in the stable maintenance of RK2.

Evaluation of rhodamine 123 as a probe for monitoring mitochondrial function in Trypanosoma brucei spp.

Rhodamine 123, a membrane potential-specific dye, has been evaluated as a probe to monitor the function of the mitochondrion in long slender bloodstream and procyclic trypomastigotes of several Trypanosoma brucei spp. By epifluorescence microscopy, mitochondrial development has been followed in long slender bloodstream and procyclic organisms stained with rhodamine 123. To photograph stained long slender bloodstream forms, it was necessary to develop a method to completely immobilize viable organisms. In both parasite forms, as the cell cycle progressed, the mitochondrion developed from a thread-like structure to a highly branched organelle. A dramatic reorganization occurred preceding cytokinesis to produce two progeny thread-like structures which were partitioned into newly formed daughter cells. The organelle within the long slender trypomastigote was found to stain optimally at 0.3 microgram/ml of rhodamine 123, while the procyclic form required 3.0 micrograms/ml. The results suggest that the plasma membrane potential is higher in the long slender parasite than in the procyclic form. The effects of inhibitors that disrupt mitochondrial function were examined in long slender and procyclic parasites, and some of these agents were shown to affect rhodamine 123 accumulation and retention. In long slender trypomastigotes the trypanosome alternative oxidase does not appear to be coupled to proton pumping, whereas in procyclic organisms the effects of inhibitors indicate that this oxidase may be coupled to a pathway that is branched preceding an antimycin A1-sensitive site.

Effect of Beauveria bassiana and Candida albicans on the Cellular Defense Response of Spodoptera exigua

A marked difference in the cellular response of Spodoptera exigua was observed when larvae were challenged with the insect mycopathogen Beauveria bassiana versus the yeast Candida albicans. Both fungi were rapidly phagocytized by circulating hemocytes. The relative growth rate of C. albicans as measured by daughter cell formation was partially suppressed, whereas B. bassiana blastospores produced germ tubes at rates equivalent to those under in vitro conditions. Limited growth by C. albicans within the phagocytic cells stimulated nodulation by hemocytes resulting in the protection of challenged larvae to C. albicans. Alternatively, B. bassiana suppressed the spreading ability of S. exigua hemocytes. These suppressed larvae, while capable of phagocytizing C. albicans, were unable to produce multicellular nodules. Circulating vegetative cells of both C. albicans and B. bassiana were observed to proliferate within these immunosuppressed host larvae.

The essential bacterial cell-division protein FtsZ is a GTPase.

Cytokinesis defines the last stage in the division cycle, in which cell constriction leads to the formation of daughter cells. The biochemical mechanisms responsible for this process are poorly understood. In bacteria, the ftsZ gene product, FtsZ, is required for cell division, playing a prominent role in cytokinesis. The cellular concentration of FtsZ regulates the frequency of division and genetic studies have indicated that it is the target of several endogenous division inhibitors. At the time of onset of septal invagination, the FtsZ protein is recruited from the cytoplasm to the division site, where it assembles into a ring that remains associated with the leading edge of the invaginating septum until septation is completed. Here we report that FtsZ specifically binds and hydrolyses GTP. The reaction can be dissociated into a GTP-dependent activation stage that is markedly affected by the concentration of FtsZ, and a hydrolysis stage in which GTP is hydrolysed to GDP. The results indicate that GTP binding and hydrolysis are important in enabling FtsZ to support bacterial cytokinesis, either by facilitating the assembly of the FtsZ ring and/or by catalysing an essential step in the cytokinetic process itself.

Susceptibility of Pseudomonas aeruginosa and Escherichia coli biofilms towards ciprofloxacin: effect of specific growth rate

Methods of cell culture which enable the control of specific growth rate and expression of iron-regulated membrane proteins within Gram-negative biofilms were employed for various clinical isolates of Pseudomonas aeruginosa taken from the sputum of cystic fibrosis patients and of a laboratory strain of Escherichia coli. Susceptibility towards ciprofloxacin was assessed as a function of growth-rate for intact biofilms, cells resuspended from the biofilms and also for newly formed daughter cells shed from the biofilm during its growth and development. Patterns of susceptibility with growth rate were compared to those of suspended cultures grown in a chemostat. In all instances the susceptibility of chemostat cultures was directly related to growth rate. Whilst little difference was observed in the susceptibility pattern for P. aeruginosa strains with different observed levels of mucoidness, such populations were generally more susceptible towards ciprofloxacin than those of E. coli. At fast rates of growth P. aeruginosa cells resuspended from biofilms were significantly more resistant than chemostat grown cells. Intact P. aeruginosa biofilms were significantly more resistant than cells resuspended from them. This is in contrast to E. coli, where cells resuspended from biofilm and intact biofilms were, at the slower rates of growth, equivalent and significantly more susceptible than chemostat-grown cells. At high growth rates all methods of E. coli culture produced cells of equivalent susceptibility. For all strains, daughter cells dislodged from the biofilms demonstrated a high level of susceptibility towards ciprofloxacin which was unaffected by growth rate. This sensitivity corresponded to that of the fastest grown cells in the chemostat.

Switching at the cellular level in the white--opaque transition of Candida albicans

The 'white-opaque transition' in Candida albicans strain WO-1 provides a unique system for analysing high-frequency switching at the cellular level because of the difference in the budding phenotypes of the white and opaque phases. Single white and opaque cells were placed on agar and monitored for the dynamics of cell division, microcolony genesis and switching to the alternative phase. It is demonstrated that at 24 degrees C, opaque cells can switch directly to white cells but white cells first generate an elongate, pseudohyphal-shaped precursor in the transition to an opaque cell. Cells in either phase can generate a daughter cell in the alternative phase, then revert immediately to the genesis of subsequent daughter cells in the original phase. By developing a mathematical model for switching at the cellular level which subtracts mother cells and switched daughter cells from the pool of switching candidates, the probability for an opaque cell to generate a white daughter cell in any single generation was calculated to be 1.0 x 10(-1) and the probability for a white cell to generate an opaque daughter cell in any single generation was calculated to be 1.7 x 10(-5) at 24 degrees C on nutrient agar. The mean number of generations before an opaque cell generated a white daughter cell was calculated to be 3.4 and the mean number before a white cell formed an opaque cell was calculated to be 15.8 at 24 degrees C on nutrient agar. Finally, high-temperature induction of the opaque to white transition was analysed at the cellular level and demonstrated to involve frequent bipolar formation of white daughter cells on the original opaque mother cell, and in some cases intermediate phenotypes.

Microtubule distribution in dv, a maize meiotic mutant defective in the prophase to metaphase transition

Microsporogenesis in Zea mays, the meiotic reduction of diploid sporocytes to haploid microspores, proceeds through a well-defined developmental sequence. The ability to generate mutants that affect the process makes this an ideal system for elucidating the role of the cytoskeleton during plant development. We have used immunofluorescence microscopy to compare microtubule distribution in wild-type and mutant microsporocytes. During normal meiosis the distribution of microtubules follows a specific temporal and spatial pattern that reflects the polar nature of microspore formation. Perinuclear microtubule staining increases and the nucleus elongates in the future spindle axis during late prophase I. Metaphase I spindles with highly focused poles align along the long axis of the anther locule. Cytokinesis occurs perpendicular to the spindle axis. The second division axis shifts 90° with respect to the first division plane, thereby yielding an isobilateral tetrad of microspores. Microtubule distribution patterns during meiosis suggest that a nuclear envelope-associated microtubule organizing center (MTOC) controls the organization of cytoplasmic microtubules and contributes to spindle formation. The meiotic mutant dv is defective in the transition from a prophase microtubule array to a metaphase spindle. Instead of converging to form focused poles, the metaphase spindle poles remain diffuse as in prometaphase. This defect correlates with several abnormalities in subsequent developmental events including the formation of multinucleate daughter cells, multiple microspindles during meiosis II, multiple phragmoplasts, polyads of microspores, and cytoplasmic microtubule foci. These results suggest that dv is a mutation that affects MTOC organization.

Possible involvement of the division cycle in dispersal of Escherichia coli from biofilms

Growth rate control of adherent, sessile populations was achieved by the controlled perfusion of membrane-associated bacterial biofilms by the method of Gilbert et al. (P. Gilbert, D. G. Allison, D. J. Evans, P. S. Handley, and M. R. W. Brown, Appl. Environ. Microbiol. 55:1308-1311, 1989). Changes in cell surface hydrophobicity were evaluated with respect to growth rate for such sessile Escherichia coli cells and compared with those of suspended (planktonic) populations grown in a chemostat. Newly formed daughter cells shed at the various growth rates from the biofilm during its growth and development were also included in the study. Surface hydrophobicity decreased with growth rate similarly for both planktonic and sessile E. coli; no significant differences were noted between the two. Daughter cells dislodged from the biofilm, however, were significantly more hydrophilic than those remaining, indicating that hydrophobicity changed during the division cycle. Our data support the hypothesis that dispersal of cells from adhesive biofilms and recolonization of new surfaces reflect cell-cycle-mediated events.

Cytochalasin B enhances cytokinetic cleavage in miniprotoplasts isolated from cultured tobacco cells

Miniprotoplasts capable of cytokinesis were isolated from cultured tobacco cells (BY-2) at anaphase by brief centrifugation in the absence of cytochalasin B. The cytokinesis was observed both in the absence and in the presence of cytochalasin B. Formation of furrow and spherical daughter cells were enhanced in the presence of cytochalasin B.

Effect of growth-rate on resistance of Gram-negative biofilms to cetrimide

A method of cell culture, which allows control of growth rate for sessile Gram-negative populations, has been employed to assess the sensitivity of Escherichia coli biofilms to the antiseptic compound, cetrimide. Growth-rate-dependent changes in sensitivity were compared for chemostat-grown, planktonic cells, for cells resuspended from the biofilm and also for newly formed daughter cells shed from the biofilm during its growth and development. Susceptibility to cetrimide decreased in all instances with increases in growth-rate up to mu = 0.15 h-1. As growth rate was increased beyond this value then sensitivity increased in proportion to the rate of division. At rates of growth less than mu = 0.15 h-1 the susceptibility of the biofilm-derived cells and their offspring was significantly less than that of cells of planktonic origin.

Intracellular free calcium and mitosis in mammalian cells: anaphase onset is calcium modulated, but is not triggered by a brief transient.

Swiss 3T3 fibroblasts and LLC-PK epithelial cells in prometaphase or metaphase were either injected with fura-2 or loaded with the acetoxymethyl ester derivative of fura-2 (fura-2 AM) and monitored by microspectrofluorimetry. With both methods of loading, we observed two aspects of intracellular free calcium (Cai) metabolism. (a) Most fibroblasts and epithelial cells exhibited a gradual rise from 75 nM in metaphase to 185 nM during cleavage, returning to baseline by early G1. (b) Mitotic Swiss 3T3 cells exhibited rapid transient Cai changes, similar to those previously reported [Poenie, M., J. Alderton, R. Y. Tsien, R. A. Steinhardt. 1985. Nature (Lond.). 315:147-149; Poenie, M., J. Alderton, R. Steinhardt, and R. Tsien. 1986. Science (Wash. DC). 233:886-889; Ratan, R., and M. L. Shelanski. 1988. J. Cell Biol. 107:993]. These Cai transients occurred repetitively, often beginning in metaphase and continuing long after daughter cell formation. Eliminating serum or calcium from the medium abolished the transients, but delayed neither the gradual Cai elevation nor anaphase onset. Co-injection of EGTA or 1,2-bis-(2-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid (BAPTA) with fura-2 in calcium-free medium, but not in calcium containing medium, blocked both anaphase and the sustained Cai elevation in almost all cases. Blocked cells were rescued by returning calcium to the medium, whereupon Cai slowly but steadily rose as the cell entered anaphase. Spindle microtubules persisted through the EGTA block. Depolymerization of spindle microtubules by nocodazole also reversibly blocked anaphase onset and the sustained Cai elevation, but did not block transients. This study has revealed the following: (a) anaphase in mammalian fibroblasts and epithelial cells is not triggered by brief calcium transients; (b) anaphase is a calcium-modulated event, usually accompanied by a sustained elevation of Cai above 50 nM; (c) the elevation of Cai is dependent upon an intact spindle; and (d) fibroblasts progress through mitosis by drawing upon either intracellular or extracellular sources of calcium.

Division of chloroplast nucleoids and replication of chloroplast DNA during the cell cycle ofDunaliella salina grown under blue and red light

Synchronous cultures of the algaDunaliella salina were grown in blue or red light. The relationships between replication of chloroplast DNA, cell size, cell age and the number of chloroplast nucleoids were studied. The replication of chloroplast DNA and the division of chloroplast nucleoids occurred in two separate periods of the chloroplast cycle. DNA replication was concomitant with that in the nucleocytoplasmic compartment but nucleoid division occurred several hours earlier than nuclear division. Red-light-grown cells were bigger and grew more rapidly than those grown in blue light. In newly formed daughter cells, the chloroplast nucleoids were small and spherical and they were localized around the pyrenoid. During the cell cycle they spread to other parts of the chloroplast. The number of DNA molecules per nucleoid doubled during DNA replication in the first third of the cell cycle but decreased several hours later when the nucleoids divided. Their number was fairly constant independent of the different light quality. Cells grown in red light replicated their chl-DNA and divided their nucleoids before those grown in blue light and their daughter cells possessed about 25 nucleoids as opposed to 15.

Intracellular free calcium and mitosis in mammalian cells: anaphase onset is calcium modulated but is not triggered by a brief transient

Swiss 3T3 fibroblasts and LLC-PK epithelial cells in prometaphase or metaphase were either injected with fura-2 or loaded with the acetoxymethyl ester derivative of fura-2 (fura-2 AM) and monitored by microspectrofluorimetry. With both methods of loading, we observed two aspects of intracellular free calcium (Cai) metabolism. (a) Most fibroblasts and epithelial cells exhibited a gradual rise from 75 nM in metaphase to 185 nM during cleavage, returning to baseline by early G1. (b) Mitotic Swiss 3T3 cells exhibited rapid transient Cai changes, similar to those previously reported [Poenie, M., J. Alderton, R. Y. Tsien, R. A. Steinhardt. 1985. Nature (Lond.). 315:147-149; Poenie, M., J. Alderton, R. Steinhardt, and R. Tsien. 1986. Science (Wash. DC). 233:886-889; Ratan, R., and M. L. Shelanski. 1988. J. Cell Biol. 107:993]. These Cai transients occurred repetitively, often beginning in metaphase and continuing long after daughter cell formation. Eliminating serum or calcium from the medium abolished the transients, but delayed neither the gradual Cai elevation nor anaphase onset. Co-injection of EGTA or 1,2-bis-(2-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid (BAPTA) with fura-2 in calcium-free medium, but not in calcium containing medium, blocked both anaphase and the sustained Cai elevation in almost all cases. Blocked cells were rescued by returning calcium to the medium, whereupon Cai slowly but steadily rose as the cell entered anaphase. Spindle microtubules persisted through the EGTA block. Depolymerization of spindle microtubules by nocodazole also reversibly blocked anaphase onset and the sustained Cai elevation, but did not block transients. This study has revealed the following: (a) anaphase in mammalian fibroblasts and epithelial cells is not triggered by brief calcium transients; (b) anaphase is a calcium-modulated event, usually accompanied by a sustained elevation of Cai above 50 nM; (c) the elevation of Cai is dependent upon an intact spindle; and (d) fibroblasts progress through mitosis by drawing upon either intracellular or extracellular sources of calcium.

A genetic assay to detect chromosome gain and/or loss in somatic cells of Drosophila melanogaster

A genetic short-term test is described that allows (i) detection and (ii) quantitative evaluation of aneuploidy induced in somatic cells of Drosophila melanogaster. In this somatic aneuploidy test (SAT) larvae of the genotype z w −/ w +J Y are exposed to the test compound. Gain and/or loss of the w +J Y chromosome leads to the formation of aneupliod daughter cells: z w −/ w +J Y and z w −/ O, respectively. These cells are fully viable, proliferate and, when they are part of an eye primordium, form a yellow/ /white twin spot on the otherwise red background after metamorphosis. The number of eyes screened, the size and number of spots allow for a quantitative estimate of the frequency of induced aneuploidy. Induced aneuploidy was detected after exposure of larvae to X-rays and to vincristine. The somatic aneuploidy test seems to be a simple, sensitive and fast method to screen environmental chemicals for their ability to induce aneuploidy.