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PubMed2006

Interference of Mycobacterium tuberculosis cell division by Rv2719c, a cell wall hydrolase.

The genetic factors responsible for the regulation of cell division in Mycobacterium tuberculosis are largely unknown. We showed that exposure of M. tuberculosis to DNA damaging agents, or to cephalexin, or growth of M. tuberculosis in macrophages increased cell length and sharply elevated the expression of Rv2719c, a LexA-controlled gene. Overexpression of Rv2719c in the absence of DNA damage or of antibiotic treatment also led to filamentation and reduction in viability both in broth and in macrophages indicating a correlation between Rv2719c levels and cell division. Overproduction of Rv2719c compromised midcell localization of FtsZ rings, but had no effect on the intracellular levels of FtsZ. In vitro, the Rv2719c protein did not interfere with the GTP-dependent polymerization activity of FtsZ indicating that the effects of Rv2719c on Z-ring assembly are indirect. Rv2719c protein exhibited mycobacterial murein hydrolase activity that was localized to the N-terminal 110 amino acids. Visualization of nascent peptidoglycan (PG) synthesis zones by probing with fluoresceinated vancomycin (Van-FL) and localization of green fluorescent protein-Rv2719c fusion suggested that the Rv2719c activity is targeted to potential PG synthesis zones. We propose that Rv2719c is a potential regulator of M. tuberculosis cell division and that its levels, and possibly activities, are modulated under a variety of growth conditions including growth in vivo and during DNA damage, so that the assembly of FtsZ-rings, and therefore the cell division, can proceed in a regulated manner.

Animals↗
PubMed1999

Chromosomal aberrations in peripheral lymphocytes from healthy subjects as detected in first cell division.

Baseline frequencies of chromosomal aberrations were analysed in human peripheral lymphocytes and the influence of age, sex and smoking habits was considered. From 53 healthy subjects (29 males, 24 females) 54,689 exclusively first division cells (M1) were scored. The frequencies of chromosome aberrations per 1000 cells were 1.15 +/- 0.15 dicentrics (dic), 2.6 +/- 0.3 excess acentric fragments (ace) and 7.0 +/- 0.6 chromatid breaks (crb). An age dependency could only be established for ace. Between males and females no differences in any of the aberration types were observed. For heavy smokers (> 30 cigarettes per day) a significant increase was only found for dic (2.5 +/- 0.6 per 1000 cells). Dicentric frequency was compared with background levels of other studies in which results were reported also from exclusively M1 cells. Despite cell cycle control, differences between laboratories can be observed which may be partly influenced by environmental conditions. But on the other hand the mean frequency of dic (excluding heavy smokers) of 0.95 per 1000 cells reported here is consistent for more than one decade. Since such a consistency of the mean frequency of dic is reported also from another laboratory, the conclusion is drawn that especially for the detection of low-level exposures, each laboratory should establish its own base line data, otherwise, the interpretation of the findings is dependent on the selected background level from the literature.

Adult↗
PubMed2002

Nuclear injection of anti-pigpen antibodies inhibits endothelial cell division.

Endothelial cell proliferation is required for angiogenesis in both embryonic and adult tissues. In rat brain tumors, it has recently been shown that the nuclear protein pigpen is expressed selectively in endothelial cells of developing microvasculature but not in the established peritumoral vessels (Blank, M., Weinschenk, T., Priemer, M., and Schluesener, H. (2001) J. Biol. Chem. 276, 16464-16468). This finding suggests that pigpen may be important for promoting the undifferentiated, or "angiogenic" endothelial cell phenotype. Our studies show that pigpen protein and mRNA are expressed in actively dividing endothelial cells and down-regulated as they become confluent. Protein distribution is regulated in a cell cycle-dependent manner. We conclude that this expression pattern is important for and not simply ancillary to proliferation because nuclear microinjection of anti-pigpen Fab fragments inhibited endothelial cell division. Moreover, expression of the proliferating cell marker Ki67 was inhibited in antibody-injected cells. The absence of Ki67 suggests exit from rather than arrest within (for example, at the G(1)/S interface) the cell cycle. Together with earlier observations on the structure and expression of this molecule, our data support the hypothesis that pigpen helps regulate endothelial cell differentiation state.

Animals↗
PubMed2001

FtsQ, FtsL and FtsI require FtsK, but not FtsN, for co-localization with FtsZ during Escherichia coli cell division.

During cell division in Gram-negative bacteria, the cell envelope invaginates and constricts at the septum, eventually severing the cell into two compartments, and separating the replicated genetic materials. In Escherichia coli, at least nine essential gene products participate directly in septum formation: FtsA, FtsI, FtsL, FtsK, FtsN, FtsQ, FtsW, FtsZ and ZipA. All nine proteins have been localized to the septal ring, an equatorial ring structure at the division site. We used translational fusions to green fluorescent protein (GFP) to demonstrate that FtsQ, FtsL and FtsI localize to potential division sites in filamentous cells depleted of FtsN, but not in those depleted of FtsK. We also constructed translational fusions of FtsZ, FtsA, FtsQ, FtsL and FtsI to enhanced cyan or yellow fluorescent protein (ECFP or EYFP respectively), GFP variants with different fluorescence spectra. Examination of cells expressing different combinations of the fusions indicated that FtsA, FtsQ, FtsL and FtsI co-localize with FtsZ in filaments depleted of FtsN. These localization results support the model that E. coli cell division proteins assemble sequentially as a multimeric complex at the division site: first FtsZ, then FtsA and ZipA independently of each other, followed successively by FtsK, FtsQ, FtsL, FtsW, FtsI and FtsN.

Bacterial Proteins↗
PubMed1984

Doubling of cell mass is not necessary in order to achieve cell division in cultured human cells.

When exponentially growing NHIK 3025 cells were shifted from medium containing 30% serum to medium containing 0.03% serum the rate of net protein accumulation was reduced due to both a reduction in the rate of protein synthesis and an increase in the rate of protein degradation. This change in growth conditions increased the protein doubling time from 18 to 140 h. The cell cycle duration of cells synchronized by mitotic selection was, however, only increased from 17 to 26 h by this treatment. Therefore, when the cells divide by the end of the first cell cycle following synchronization, the cells shifted to 0.03% serum contained far less protein than those growing continuously in 30% serum. Hence, the attainment of a critical cell mass is probably not controlling cell division for cells growing in a balanced state.

Cell Cycle↗
PubMed1981

Effect of inhibitors of plant cell division on mammalian tumor cells in vitro.

We studied the activity of 14 compounds, all of which have been shown to interfere in plant cell division, in two animal tumor cell cultures, EL-4 and L1210. Four compounds [propham, chlorpropham, bensulide S-(O,O-diisopropylphosphorodithioate) ester of N-(2-mercaptoethyl)benzenesulfonamide), and siduron] had a 50% inhibitory dose less than 10(-4) M; six [2,3,5-triiodobenzoic acid, (2,4-dichlorophenoxy)acetic acid, bromacil, (2,4,5-trichlorophenoxy)acetic acid, naptalam, and (4-chloro-2-methylphenoxy)acetic acid] had a 50% inhibitory dose between 10(-4) and 10(-3) M, and the remaining four 2,3:4,6-di-O-isopropylidene-2-keto-L-gulonate, eptam, maleic hydrazide, and 4-(methylsulfonyl)-2,6-dinitro-N,N,-dipropylaniline] had a 50% inhibitory dose at higher than 10(-3) M. There was a significant correlation between the effect on the two cell lines as well as between the inhibition of cell proliferation and that of thymidine and leucine uptake. More detailed study of cell proliferation and leucine and thymidine uptake for bensulide and 2,3,5-triiodobenzoic acid revealed a dose-response pattern of inhibition starting shortly after exposure of the cells to the compounds. These results indicate that some inhibitors of plant cell division are capable of inhibiting the proliferation of animal tumor cells.

Animals↗
PubMed2001

G protein signaling and asymmetric cell division.

Asymmetric cell division depends on the polarization of the dividing cell for the correct alignment of the mitotic spindle and the localization of cytoplasmic determinants. Receptor-independent activation of heterotrimeric G proteins by the Drosophila GoLoco protein Partner of Inscuteable seems to represent a novel mechanism to control these events.

Animals↗
PubMed1996

Bifunctional protein required for asymmetric cell division and cell-specific transcription in Bacillus subtilis.

During sporulation in Bacillus subtilis an asymmetric cell division gives rise to unequal progeny called the prepore and the mother cell. Gene expression in the prespore is initiated by cell-specific activation of the transcription factor sigma(F). Three proteins participate in the regulation of sigma(F) activity. The first, SpoIIAB, is an inhibitor of sigma(F), that is, an anti-sigma factor. SpoIIAB is also a protein kinase that catalyzes phosphorylation of the second regulatory protein SpoIIAA (the anti-anti-sigma factor), and thus inactivates it. A third protein, SpoIIE, was shown recently to be able to dephosphorylate SpoIIAA-P in vitro. Here we show that SpoIIE is a bifunctional protein with two critical roles in the establishment of cell fate. First, we confirm by the use of in vivo experiments that it regulates the release of sigma(F) activity by dephosphorylating SpoIIAA-P. Second, we show that SpoIIE is needed for normal formation of the asymmetric septum that separates the prespore from the mother cell. Combination of these two functions in a single polypeptide may serve to couple the release of the cell-specific transcription factors with the formation of the differentiating cells.

Bacillus subtilis↗
PubMed2001

Frizzled regulates localization of cell-fate determinants and mitotic spindle rotation during asymmetric cell division.

Cell-fate diversity is generated in part by the unequal segregation of cell-fate determinants during asymmetric cell divisions. In the Drosophila pupa, the pI sense organ precursor cell is polarized along the anterior-posterior axis of the fly and divides asymmetrically to generate a posterior pIIa cell and an anterior pIIb cell. The anterior pIIb cell specifically inherits the determinant Numb and the adaptor protein Partner of Numb (Pon). By labelling both the Pon crescent and the microtubules in living pupae, we show that determinants localize at the anterior cortex before mitotic-spindle formation, and that the spindle forms with random orientation and rotates to line up with the Pon crescent. By imaging living frizzled (fz) mutant pupae we show that Fz regulates the orientation of the polarity axis of pI, the initiation of spindle rotation and the unequal partitioning of determinants. We conclude that Fz participates in establishing the polarity of pI.

Animals↗
PubMedDate not supplied

Interdependence of filamentous actin and microtubules for asymmetric cell division.

Asymmetric cell divisions are crucial to the generation of cell fate diversity. They contribute to unequal distribution of cellular factors to the daughter cells. Asymmetric divisions are characterized by a 90 degrees rotation of the mitotic spindle. There is increasing evidence that a tight cooperation between cortical, filamentous actin and astral microtubules is indispensable for successful spindle rotation. Over the past years, the dynactin complex has emerged as a key candidate to mediate actin/microtubule interaction at the cortex. This review discusses our current understanding of how spindle rotation is accomplished by the interplay of filamentous actin and microtubules in a variety of experimental systems.

Actins↗
PubMed1987

The structural characterization of endogenous factors from Vinca rosea crown gall tumors that promote cell division of tobacco cells.

The ability of two compounds, a cytokinin and an auxin, to stimulate tobacco cell growth and differentiation has been known for greater than 30 years, but the molecular mechanism of this activation is still unknown. Previous reports of factors endogenous in crown gall tumors of Vinca rosea that could replace the cytokinin requirement in tobacco cell culture has motivated an investigation of these tissues. The optimization of a reverse-phase isolation scheme has led to the purification of sufficient material to allow for the identification of six different related compounds. The structures of two of these compounds have been assigned as a set of epimeric dehydrodiconiferyl alcohol beta-D-glycosides. The structure of these compounds suggests that they would most likely be derived from the plant cell wall.

Cell Division↗
PubMed1987

When and how does cell division order influence cell allocation to the inner cell mass of the mouse blastocyst?

Aggregate 8-cell embryos were constructed from four 2/8 pairs of blastomeres, one of which was marked with a short-term cell lineage marker and was also either 4 h older (derived from an early-dividing 4-cell) or 4 h younger (derived from a late-dividing 4-cell) than the other three pairs. The aggregate embryos were cultured to the 16-cell stage, at which time a second marker was used to label the outside cell population. The embryos were then disaggregated and each cell was examined to determine its labelling pattern. From this analysis, we calculated the relative contributions to the inside cell population of the 16-cell embryo of older and younger cells. Older cells were found to contribute preferentially. However, if the construction of the aggregate 8-cell embryo was delayed until each of the contributing 2/8 cell pairs had undergone intercellular flattening and then had been exposed to medium low in calcium to reverse this flattening immediately prior to aggregation, the advantage possessed by the older cells was lost. These results support the suggestion that older cells derived from early-dividing 4-cell blastomeres contribute preferentially to the inner cell mass as a result of being early-flattening cells.

Animals↗