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PubMed1980

Flow cytometric analysis of megakaryocytopoiesis: strategy for defining mitotic and endoreduplicative events in the committed progenitor compartment.

A new cellular approach to the analysis of the physiology and regulation of the megakaryocyte progenitor cell compartment is proposed. It utilizes initial progenitor cell separation by centrifugal elutriation followed by flow cytometry and viable cell sorting using quantitative, vital DNA stains and secondary cytoplasmic and/or membrane markers to isolate megakaryocyte progenitors on the basis of DNA content for subsequent analysis of proliferative (mitotic) activity in an in vitro clonogenic assay. It should be possible to delineate whether mitosis (as measured by the number of CFU-M per culture) is limited to diploid cells and determine the distribution of CFU-M in subclasses of cells identified by the secondary label. This kind of study will provide new information on the relationship between progenitor cell size, DNA content and proliferative activity within the framework of a working model of progenitor cell kinetics.

Animals↗
PubMed1994

DNA endoreduplication, RNA and protein synthesis during growth and development of the antheridial basal cell in Chara vulgaris L.

Cytophotometric measurements of nuclear DNA contents and morphometric analyses indicate that the level of endopolyploidy plays an important role in determining the maximum size, transcriptional and translational activity that the antheridial basal cell attains during successive stages of spermatogenesis in Chara vulgaris. During the proliferative period of antheridial development, the metabolic activity of basal cell, expressed as the total incorporation of radioactive uridine and leucine was found to increase gradually with the increasing DNA C-values, yet both the synthesis of RNA and then the synthesis of proteins become reduced at the stage preceding spermiogenesis. In accordance with some earlier data [2], the obtained results seem to support the hypothesis that regulatory mechanisms of symplasmic connections between the antheridium and a thallus participate in the regulation of morphogenesis of the male sex organs in Chara.

Autoradiography↗
PubMed2005

RHL1 is an essential component of the plant DNA topoisomerase VI complex and is required for ploidy-dependent cell growth.

How cells achieve their final sizes is a pervasive biological question. One strategy to increase cell size is for the cell to amplify its chromosomal DNA content through endoreduplication cycles. Although endoreduplication is widespread in eukaryotes, we know very little about its molecular mechanisms. Successful progression of the endoreduplication cycle in Arabidopsis requires a plant homologue of archaeal DNA topoisomerase (topo) VI. To further understand how DNA is endoreduplicated and how this process is regulated, we isolated a dwarf Arabidopsis mutant, hyp7 (hypocotyl 7), in which various large cell types that in the wild type normally endoreduplicate multiple times complete only the first two rounds of endoreduplication and stall at 8C. HYP7 encodes the RHL1 (ROOT HAIRLESS 1) protein, and sequence analysis reveals that RHL1 has similarity to the C-terminal domain of mammalian DNA topo IIalpha, another type II topo that shares little sequence homology with topo VI. RHL1 shows DNA binding activity in vitro, and we present both genetic and in vivo evidence that RHL1 forms a multiprotein complex with plant topo VI. We propose that RHL1 plays an essential role in the topo VI complex to modulate its function and that the two distantly related topos, topo II and topo VI, have evolved a common domain that extends their function. Our data suggest that plant topo II and topo VI play distinct but overlapping roles during the mitotic cell cycle and endoreduplication cycle.

Amino Acid Sequence↗
PubMed2005

Cell reproduction and genome multiplication in the proliferative and invasive trophoblast cell populations of mammalian placenta.

Spatiotemporal "time-table" of ways of cell reproduction (mitosis, restitutional mitosis, endomitosis, endoreduplication) of trophoblast cell populations is described. The populations of mitotically active trophoblast cells (diploid and low-polyploid) are located mostly out of contact with maternal tissues. In rodent placenta they mainly switch from mitotic cycle to polyploidizing (restitutional) mitoses and reach 4c-8c. Thereafter they switch to endoreduplication and reach 16c-64c. Following a series of endoreduplication cycles a part of this cell population sets apart and penetrates deeply into the decidualized endometrium and myometrium, their capabilities for replication being lost progressively (in rodent--256c-1024c). The invasive trophoblast cells that reach 256c-1024c via endoreduplication simultaneously form a barrier between semiallogenic fetal and maternal tissues. Arrest of mitoses and complete repression of DNA replication after a series of endoreduplication cycles makes hardly probable the renewal of mitotic activity in the deeply invading tertiary giant trophoblast cells, thereby preventing the possibility of their ectopic expanding in the maternal tissues during the normal pregnancy.

Animals↗
PubMed2005

The DP-E2F-like gene DEL1 controls the endocycle in Arabidopsis thaliana.

Endoreduplication or DNA replication without mitosis is widespread in nature. Well-known examples are fruit fly polytene chromosomes and cereal endosperm. Although endocycles are thought to be driven by the same regulators as those that control the G1-S transition of the mitotic cell cycle, the molecular mechanisms that differentiate mitotically dividing cells from endoreduplicating ones are largely unknown. A novel class of atypical E2F-like proteins has recently been identified and is designated E2F7 in mammals and DP-E2F-like (DEL) in Arabidopsis thaliana . We demonstrate that loss of DEL1 function resulted in increased ploidy levels, whereas ectopic expression of DEL1 reduced endoreduplication. Ploidy changes were correlated with altered expression of a subset of E2F target genes encoding proteins necessary for DNA replication. Because DEL1 proteins were postulated to antagonize the E2F pathway, we generated DEL1-E2Fa-DPa triple transgenics. DEL1 inhibited the endoreduplication phenotype, but not the ectopic cell divisions that resulted from the overexpression of both E2Fa and DPa, illustrating that DEL1 specifically represses the endocycle. Because DEL1 transcripts were detected exclusively in mitotically dividing cells, we conclude that DEL1 is an important novel inhibitor of the endocycle and preserves the mitotic state of proliferating cells by suppressing transcription of genes that are required for cells to enter the DNA endoreduplication cycle.

Arabidopsis↗
PubMed1996

In situ hybridization and flow cytometric analysis of colorectal tumours suggests two routes of tumourigenesis characterized by gain of chromosome 7 or loss of chromosomes 17 and 18.

Chromosomal aberrations in colonic tumourigenesis were investigated by fluorescence in situ hybridization (FISH) with centromere-specific DNA probes and correlated to flow cytometry (FCM) results in a series of tissues including normal colonic epithelium, adenomas, and carcinomas, as well as adenomas adjacent to carcinomas. No numerical chromosome aberrations were detected in normal colonic epithelium, except for an extra chromosome X in one case. In the adenomas, the most frequently occurring chromosome aberration was a trisomy for chromosome 7, occurring in 37 per cent of the cases. In the carcinomas, two distinct routes of genetic aberration could be established on the basis of correlation with FCM: one with and one without endoreduplication. In the carcinomas without endoreduplication, trisomy or tetrasomy for chromosome 7 was detected in 12 out of 15 cases (80 per cent). In three of these cases, trisomy 7 was found in combination with loss of chromosome 17 and/or chromosome 18. In 87 per cent of the carcinomas with endoreduplication, loss of chromosome 17 and/or 18 was found, while in only one case was gain of chromosome 7 detected. In the adenomas adjacent to carcinomas, trisomy 7 was found in 36 per cent of the cases. In these cases, the concomitant adenocarcinomas showed the same numerical chromosome 7 aberration, plus extra aberrations for other chromosomes. In only two cases the carcinoma demonstrated trisomy 7 with a normal adjacent adenoma. These results suggest that gain of chromosome 7 is a significant aberration in the tumourigenesis of colonic carcinomas in which no endoreduplication has occurred. No marked clinico-pathological differences were observed between tumours of either route of tumourigenesis in this series.

Adenocarcinoma↗