Chromatin morphology and cytokinesis in pleurocapsalean cyanobacteria

Chromatin morphology and cytokinesis are described in the cyanobacterium Pleurocapsa sp. CALU 1126 capable of multiple fission (multiple reproduction of the mother cell, the macrocyte, with the formation of unique reproductive cells, the baeocytes by means of differential interference contrast (DIC) and fluorescence microscopy). Two kinds of chromatin behavior in the cell cycle are revealed, including (1) the formation of numerous chromatin areas prior to their compartmentalization by multiple fission and (2) chromatin condensation in the phase of binary fission and chromatin decondensation in growth period. The cytokinetic essence of multiple fission is shown to consist of successive binary fissions of the macrocyte, while in between, the mother cells (prebaeocytes) do not grow.     

Cell division in baeocyte producing cyanobacteria

Summary An ultrastructural examination of cell division in two baeocyte producing cyanobacteria,Pleurocapsa minor andDermocarpa violaceae, reveals two distinct patterns of binary (transverse) fission. Septate binary fission, inPleurocapsa minor, involves centripetal synthesis and deposition of the mucopolymer cell wall layer (L 2). The ingrowth of the cytoplasmic membrane and L 1 cell wall layer, along with the synthesis of the L 2 cell wall layer, results in the formation of a prominent septum. Partitioning of the cell occurs by the constriction of the outer cell wall layers (L 3 and L 4) through the septum. InDermocarpa violaceae, constrictive binary fission occurs by the simultaneous ingrowth or constriction of the cytoplasmic membrane and all cell wall layers (L1, L2, L3, L4). Septate and constrictive binary fission may proceed symmetrically (medially) or asymmetrically (nonmedially). Multiple fission occurs regularly inDermocarpa violaceae and provides for a rapid means of reproduction when compared to binary fission. Successive radial and tangential divisions of the protoplast result in formation of many small daughter cells (baeocytes). The process of multiple fission is similar to septate binary fission with reduced septa being formed. However, constriction of the outer cell wall layers, through the septa, proceeds concurrently with septum formation.     

Endogenous Bud Formation in Histriculus vorax, a New Asexual Reproductive Process In the Hypotrichida

SYNOPSIS. Histriculus vorax (Stokes) Corliss, a hypotrichous ciliate, has been separated from activated sludge and cultured monoxenically in the laboratory. The asexual life cycle has been observed and the stages of development photographed. There are large variations in shape and size of cells within clonal cultures. Both large (190–250 μ long) and small (70–140 μ long) cells are capable of normal asexual binary fission but only the large cells are able to grow endogenous buds, which, when mature, are extruded through the body wall of the mother cell. Newly deposited buds can either develop directly into an embryonic form, or, if unfavorable conditions prevail, first encyst. Similar embryonic stages bearing caudal and frontal cirri are produced both by direct development and by excystment of the encysted bud. Embryos develop rapidly into trophic forms which finally grow into small adults capable of asexual binary fission. During binary fission the nuclei behave as described previously for other members of the Oxytrichidae. A reorganization band forms at the outer end of each macronucleus, and these bands move along the macronuclei towards each other, finally disappearing at the inner ends. A fusion nucleus is then formed which splits into 4 pieces, 2 of which pass to the proter and 2 to the opisthe. During bud formation the reorganisation bands form and move as in binary fission. No fusion nucleus is formed, but the macronuclei divide immediately after reorganization, and the anterior macronucleus of each pair so produced migrates to the budding region. The infraciliature of H. vorax resembles that of Opisthotricha monspessulana. 'Erratic' kinetosomes, which are present in the adult, divide during binary fission and so produce the infraciliature of the proter and opisthe. During bud formation the budding region receives a number of these 'erratic' kinetosomes from the mother cell, and these divide to form the infraciliature of the bud.     

Cultivation of Three Species of Theileria in Lymphoid Cells in vitro

SYNOPSIS. The intralymphocytic stages of Theileria parva, T. lawrencei and T. annulata have been cultivated for several months in tissue cultures of bovine lymphocytes associated with baby hamster kidney cells. In established cultures the theilerial particles multiplied at about the same rate as the host cells, the percentage of infected cells and the mean number of parasite particles per cell remaining nearly constant.
During mitotic division of the host cell the theilerial body becomes closely associated with the spindle fibres and is pulled apart and distributed to both daughter cells in late anaphase. The single theilerial particles (chromatin) within the theilerial body divide by binary fission; their division is not synchronous with that of the host cell.     

Patterns of asexual reproduction in <Emphasis Type="Italic">Nannochloris bacillaris</Emphasis> and <Emphasis Type="Italic">Marvania geminata</Emphasis> (Chlorophyta,Trebouxiophyceae)

Non-flagellated vegetative green algae of the Trebouxiophyceae propagate mainly by autosporulation. In this manner, the mother cell wall is shed following division of the protoplast in each round of cell division. Binary fission type Nannochloris and budding type Marvania are also included in the Trebouxiophyceae. Phylogenetic trees based on the actin sequences of Trebouxiophyceae members revealed that the binary fission type Nannochloris bacillaris and the budding type Marvania geminata are closely related in a distal monophyletic group. Our results suggest that autosporulation is the ancestral mode of cell division in Trebouxiophyceae. To elucidate how non-autosporulative mechanisms such as binary fission and budding evolved, we focused on the cleavage of the mother cell wall. Cell wall development was analyzed using a cell wall-specific fluorescent dye, Fluostain I. Exfoliation of the mother cell wall was not observed in either N. bacillaris or M. geminata. We then compared the two algae by transmission electron microscopy with rapid freeze fixation and freeze substitution; in both algae, the mother cell wall was cleaved at the site of cell division, but remained adhered to the daughter cell wall. In N. bacillaris, the cleaved mother cell wall gradually degenerated and was not observed in the next cell cycle. In contrast, M. geminata daughter cells entered the growth phase of the next cell cycle bearing the mother and grandmother cell walls, causing the uncovered portion of the plane of division to bulge outward. Such a delay in the degeneration and shedding of the mother cell wall probably led to the development of binary fission and budding.     

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.     

Fission yeast Cdc23/Mcm10 functions after pre-replicative complex formation to promote Cdc45 chromatin binding

Using a cytological assay to monitor the successive chromatin association of replication proteins leading to replication initiation, we have investigated the function of fission yeast Cdc23/Mcm10 in DNA replication. Inactivation of Cdc23 before replication initiation using tight degron mutations has no effect on Mcm2 chromatin association, and thus pre-replicative complex (pre-RC) formation, although Cdc45 chromatin binding is blocked. Inactivating Cdc23 during an S phase block after Cdc45 has bound causes a small reduction in Cdc45 chromatin binding, and replication does not terminate in the absence of Mcm10 function. These observations show that Cdc23/Mcm10 function is conserved between fission yeast and Xenopus, where in vitro analysis has indicated a similar requirement for Cdc45 binding, but apparently not compared with Saccharomyces cerevisiae, where Mcm10 is needed for Mcm2 chromatin binding. However, unlike the situation in Xenopus, where Mcm10 chromatin binding is dependent on Mcm2-7, we show that the fission yeast protein is bound to chromatin throughout the cell cycle in growing cells, and only displaced from chromatin during quiescence. On return to growth, Cdc23 chromatin binding is rapidly reestablished independently from pre-RC formation, suggesting that chromatin association of Cdc23 provides a link between proliferation and competence to execute DNA replication.     

Baeocytes in the cyanobacterium Pleurocapsa sp.: characterization of the differentiated cells produced by multiple fission

Electron microscopy of cyanobacteria Pleurocapsa sp. CALU 1126 revealed that multiple fission proceeds by successive binary fissions. The cultivation conditions were determined when the number of baeocytes (products of multiple fission) was comparable with that of macrocytes (products of binary fission), and cell sorting was achieved for the first time. Juvenile baeocytes were shown to differ from macrocytes in: (1) the absence of sheath; (2) the linear-peripheral configuration of their lamellar system; (3) lower content of phycobiliproteins and higher content of carotenoids; (4) the set of PSII polypeptides. Baeocytes can therefore be considered differentiated cells characterized by the uncoupling between energy and biosynthetic metabolism.     

Microgemma vivaresi n. sp. (Microsporidia, Tetramicridae), infecting liver and skeletal muscle of sea scorpions, Taurulus bubalis (Euphrasen 1786) (Osteichthyes, Cottidae), an inshore, littoral fish

The ultrastructure of a new microsporidian species Microgemma vivaresi n. sp. causing liver cell xenoma formation in sea scorpions, Taurulus bubalis, is described. Stages of merogony, sporogony, and sporogenesis are mixed in the central cytoplasm of developing xenomas. All stages have unpaired nuclei. Uninucleate and multinucleate meronts lie within vacuoles formed from host endoplasmic reticulum and divide by binary or multiple fission. Sporonts, no longer in vacuoles, deposit plaques of surface coat on the plasma membrane that cause the surface to pucker. Division occurs at the puckered stage into sporoblast mother cells, on which plaques join up to complete the surface coat. A final binary fission gives rise to sporoblasts. A dense globule, thought to be involved in polar tube synthesis, is gradually dispersed during spore maturation. Spores are broadly ovoid, have a large posterior vacuole, and measure 3.6 microm x 2.1 microm (fresh). The polar tube has a short wide anterior section that constricts abruptly, then runs posteriad to coil about eight times around the posterior vacuole with granular contents. The polaroplast has up to 40 membranes arranged in pairs mostly attached to the wide region of the polar tube and directed posteriorly around a cytoplasm of a coarsely granular appearance. The species is placed alongside the type species Microgemma hepaticusRalphs and Matthews 1986 within the family Tetramicridae, which is transferred from the class Dihaplophasea to the class Haplophasea, as there is no evidence for the occurrence of a diplokaryotic phase.     

Analysis of Mcm2-7 chromatin binding during anaphase and in the transition to quiescence in fission yeast

Mcm2-7 proteins are generally considered to function as a heterohexameric complex, providing helicase activity for the elongation step of DNA replication. These proteins are loaded onto replication origins in M-G1 phase in a process termed licensing or pre-replicative complex formation. It is likely that Mcm2-7 proteins are loaded onto chromatin simultaneously as a pre-formed hexamer although some studies suggest that subcomplexes are recruited sequentially. To analyze this process in fission yeast, we have compared the levels and chromatin binding of Mcm2-7 proteins during the fission yeast cell cycle. Mcm subunits are present at approximately 1 x 10(4) molecules/cell and are bound with approximately equal stoichiometry on chromatin in G1/S phase cells. Using a single cell assay, we have correlated the timing of chromatin association of individual Mcm subunits with progression through mitosis. This showed that Mcm2, 4 and 7 associate with chromatin at about the same stage of anaphase, suggesting that licensing involves the simultaneous binding of these subunits. We also examined Mcm2-7 chromatin association when cells enter a G0-like quiescent state. Chromatin binding is lost in this transition in a process that does not require DNA replication or the selective degradation of specific subunits.     

Baeocytes in the cyanobacterium <Emphasis Type="Italic">Pleurocapsa</Emphasis> sp.: Characterization of the differentiated cells produced by multiple fission

Electron microscopy of cyanobacterium Pleurocapsa sp. CALU 1126 revealed that multiple fission proceeds by successive binary fissions. The cultivation conditions were determined when the number of baeocytes (products of multiple fission) was comparable with that of macrocytes (products of binary fission), and cell sorting was achieved for the first time. Juvenile baeocytes were shown to differ from macrocytes in: (1) the absence of sheath; (2) the linear-peripheral configuration of their lamellar system; (3) lower content of phycobiliproteins and higher content of carotenoids; (4) the set of PSII polypeptides. Baeocytes can therefore be considered differentiated cells characterized by the uncoupling between energy and biosynthetic metabolism.     

Assembly of the SpoIIIE DNA translocase depends on chromosome trapping in Bacillus subtilis

Sporulation in Bacillus subtilis is an attractive system in which to study the translocation of a chromosome across a membrane. Sporulating cells contain two sister chromosomes that are condensed in an elongated axial filament with the origins of replication anchored at opposite poles of the sporangium. The subsequent formation of a septum near one pole divides the sporangium unequally into a forespore (the smaller compartment) and a mother cell. The septum forms around the filament, trapping the origin-proximal region of one chromosome in the forespore. As a consequence, the trapped chromosome transverses the septum with the remainder being left in the mother cell. Next, SpoIIIE assembles at the middle of the septum to create a translocase that pumps the origin-distal, two-thirds of the chromosome into the forespore. Here, we address the question of how the DNA translocase assembles and how it localizes to the septal midpoint. We present evidence that DNA transversing the septum is an anchor that nucleates the formation of the DNA translocase. We propose that DNA anchoring is responsible for the assembly of other SpoIIIE-like DNA translocases, such as those that remove trapped chromosomes from the division septum of cells undergoing binary fission.     

Centromere positioning and dynamics in living Arabidopsis plants

The organization and dynamics of the genome have been shown to influence gene expression in many organisms. Data from mammalian tissue culture cells have provided conflicting conclusions with regard to the extent to which chromatin organization is inherited from mother to daughter nuclei. To gain insight into chromatin organization and dynamics, we developed transgenic Arabidopsis lines in which centromeres were tagged with a green fluorescent protein fusion of the centromere-specific histone H3. Using four-dimensional (4-D) live cell imaging, we show that Arabidopsis centromeres are constrained at the nuclear periphery during interphase and that the organization of endoreduplicated sister centromeres is cell type dependent with predominant clustering in root epidermal cells and dispersion in leaf epidermal cells. 4-D tracking of the entire set of centromeres through mitosis, in growing root meristematic cells, demonstrated that global centromere position is not precisely transmitted from the mother cell to daughter cells. These results provide important insight into our understanding of chromatin organization among different cells of a living organism.     

Schizosaccharomyces pombe Noc3 is essential for ribosome biogenesis and cell division but not DNA replication

The initiation of eukaryotic DNA replication is preceded by the assembly of prereplication complexes (pre-RCs) at chromosomal origins of DNA replication. Pre-RC assembly requires the essential DNA replication proteins ORC, Cdc6, and Cdt1 to load the MCM DNA helicase onto chromatin. Saccharomyces cerevisiae Noc3 (ScNoc3), an evolutionarily conserved protein originally implicated in 60S ribosomal subunit trafficking, has been proposed to be an essential regulator of DNA replication that plays a direct role during pre-RC formation in budding yeast. We have cloned Schizosaccharomyces pombe noc3(+) (Spnoc3(+)), the S. pombe homolog of the budding yeast ScNOC3 gene, and functionally characterized the requirement for the SpNoc3 protein during ribosome biogenesis, cell cycle progression, and DNA replication in fission yeast. We showed that fission yeast SpNoc3 is a functional homolog of budding yeast ScNoc3 that is essential for cell viability and ribosome biogenesis. We also showed that SpNoc3 is required for the normal completion of cell division in fission yeast. However, in contrast to the proposal that ScNoc3 plays an essential role during DNA replication in budding yeast, we demonstrated that fission yeast cells do enter and complete S phase in the absence of SpNoc3, suggesting that SpNoc3 is not essential for DNA replication in fission yeast.     

Ultrastructure of trichoblasts in the red alga Osmundea spectabilis var. spectabilis (Rhodomelaceae,Ceramiales)

The apex of the tetrasporangial branches of Osmundea spectabilis var. spectabilis (= Laurencia spectabilis var. spectabilis) exhibits cavities in which tufts of multicellular trichoblasts occur. Trichoblast development in Osmundea spectabilis var. spectabilis begins with the differentiation of an epidermal cell within the crypt. This cell differentiates into a trichoblast mother cell (TMC). The TMC divides to form a two-celled incipient trichoblast. Successive periclinal divisions of the apical cell of the young trichoblast result in the formation of a multicellular developing trichoblast. With the exception of the apical cell all trichoblast cells are at the same developmental stage. They possess a large nucleus, abundant plastids with peripheral and some internal thylakoids and dictyosomes. Daughter chloroplasts result from one constriction or multiple fission of a single chloroplast. Dictyosomal cisternae and mucilage sacs contribute material to wall formation. Each differentiating trichoblast cell is surrounded by a bi-layered wall. The outer wall layer represents the trichoblast mother cell wall and the inner wall layer is the trichoblast cell wall. Mature trichoblast cells have thin walls, probably as a consequence of mucilage extrusion, the most likely function of trichoblasts in Osmundea.     

EVOLUTIONARY RELATIONSHIPS AMONG MULTIPLE MODES OF CELL DIVISION IN THE GENUS NANNOCHLORIS (CHLOROPHYTA) REVEALED BY GENOME SIZE, ACTIN GENE MULTIPLICITY, AND PHYLOGENY

A single cell divides to multiply, but not all cells follow the same pattern of division. We studied cell division in seven strains from six species belonging to the genus Nannochloris Naumann and classified their modes of cell division into three types: binary fission ( N. bacillaris Naumann), budding ( N. coccoides Naumann), and autosporulation resulting in the formation of two to four daughter cells ( N. maculata Butcher, N . sp. SAG 251-2, N. atomus Butcher CCAP 251/7 and SAG 14.87, and N. eucaryotum [Wilhelm et al.] Menzel and Wild). To determine the evolutionary relationships among these multiple modes of cell division, we investigated the strains' genome sizes, copy number of actin genes, and phylogeny. The genome sizes were determined by counter-clamped homogeneous electric fields electrophoresis and fluorimetry. The genomes are very small and range from 12.6 Mbp ( N. maculata ) to 47.4 Mbp ( N. atomus SAG 14.87). The genomes of Nannochloris species seem to be among the smallest for free-living eukaryotes. Nannochloris bacillaris (binary fission), N. coccoides (budding), Nannochloris sp. (two-cell type of autosporulation), and N. eucaryotum (multicell type of autosporulation) contain a single actin gene, whereas N. maculata (two-cell type of autosporulation) and two strains of N. atomus (two-cell type of autosporulation) contain two actin genes. This suggests that the actin gene was duplicated in this eukaryote, which has a very small genome. Phylogenetic analyses of partial actin gene sequences suggest that autosporulation is the ancestral mode of cell division.     

Cytochemical Localization of Adenosine Triphosphataes Activity During Cytomixis in Pollen Mother Cells of David Lily and Its Relation to the Intercellular Migrating Chromatin Substance

Standard lead precipitation procedures have been used to examine the localization of ATPase activity during cytomixis in pollen mother cells of Lilium davidii var. willmottiae (Wilson) Roffill. Before cytomixis, cells at this stage of development show ATPase activity on plasma membrane, in the endoplasmic reticulum, dictyosomes, plastids, plasmodesmata, and in part of the groundplasm; however, there is no ATPase activity on the chromatin and nucleolus. During cytomixis, the chromatin substance begin to transfer from one cell to an adjacent cell, reaction product indicating ATPase activity is observed associated with the chromatin and nucleolus. ATPase activity is also found with the cistenae of both endoplasmic reticulum and dictyosomes, and some plastids. There is no deposition of ATPase reaction product associated with the plasm membrane and intercellular spaces. After cytomixis, the chromatin is little or no deposition of enzyme reaction product. ATPase activity, however, is consistenlly found within the intercellular space and on the plasm membrane, and also occur in the endoplasmic reticulum, dictyosome and plastid. The presence or absence of ATPase activity in the cell structure of pollen mother cells before, during or after eytomixis is discussed in relation to the active uptake or export of water for short-distance transport. It is also suggested that the intensive ATPase activity in the nucleus during cytomixis of pollen mother cells is evidence for a transport system involved in the active movement of the intercellular migrating ebromatin substance.     

百合花粉母细胞间细胞融合期间腺苷三磷酸酶活性的细胞化学定位及其与染色质胞间转移的关系

用标准的磷酸铅沉淀的细胞化学方法,对百合花粉母细胞间染色质穿壁运动期间及其前后三个时期中的腺苷三磷酸酶(ATP 酶)活性进行了超微结构的定位。结果表明:(1)在穿壁前,ATP 酶活性主要定位于质膜、胞间连丝及细胞间隙;在内质网、高尔基体、质体和某些局部的基质(groundplasm)中,也表现有 ATP 酶活性反应的产物;但在染色质和核仁中,一般都没有这种反应。(2)在穿壁时,染色质从一个细胞穿壁转移到另一个相邻细胞,同时看到染色质和核仁内出现密集的 ATP 酶活性反应产物;在内质网和高尔基体的腔内以及质体的片层上也产生明显的 ATP 酶活性反应;而在质膜、胞间连丝及细胞间隙内 ATP 酶活性明显降低,甚至看不到明显的活性反应。(3)在穿壁后,质膜及细胞间隙中又产生明显的 ATP 酶活性反应产物,但核内染色质上的 ATP 酶活性则显著降低,而核仁内则仍有较高的活性。同前二个时期一样,内质网、高尔基体和质体上的 ATP 酶仍表现明显的活性反应。最后讨论了三个不同发育时期 ATP 酶活性及其分布部位的改变与染色质胞间转移的关系。