Visualizing Active Replication Regions in S-Phase Chromosomes

A basic question of cell biology is how DNA folds to chromosome. A number of recently accumulated evidences have suggested that folding of chromosome proceeds tightly coupled with DNA replication progresses. Drug-induced PCC is a useful tool for visualization of the interphase nuclei, in particular, S-phase, as S-phase prematurely condensed chromosomes (S-phase PCC). Active replicating DNA is labeled directly with Cy3-dUTP by bead loading method, and then S-phase nuclei is immediately condensed prematurely by calyculin A to obtain S-phase PCC. Active replicating regions on S-PCC are observed under a scanning confocal microscope. Cy3-dUTP-labeled S-phase PCCs clearly reveal the drastic transitional change of chromosome formation through S-phase, starting from a "cloudy nebula" to numerous numbers of "beads on a string" and finally to "striped arrays of banding structured chromosome" known as G- or R-banding pattern. The number, distribution, and shape of replication foci were also measured in individual subphase of S-phase; maximally ~1400 foci of 0.35 μm average radius size were scored at the beginning of S-phase, and the number is reduced to ~100 at the end of S-phase. Drug-induced PCC clearly provided the new insight that eukaryote DNA replication is tightly coupled with the chromosome condensation/compaction for construction of eukaryote higher-ordered chromosome structure.

Chromosome length ratio as a biomarker of DNA damage in cells exposed to high dose ionizing radiation

The premature chromosome condensation (PCC) assay is considered as complementary bio-dosimetry tool for chromosome aberration assay and the PCC assay can be used to estimate high dose exposure. Though the PCC ring is considered as prospective biomarker, chromosome length ratio (ratio of longest and shortest chromosome length in PCC spreads) of chemically induced PCC is shown to be very good indicator of ionizing radiation. In view of this, an in-vitro study has been performed using PCC assay to suggest chromosome length ratio (LR) as potential bio-dosimeter induced by high dose ionizing radiation. Blood samples were collected from healthy subjects (n = 3) after prior consent and irradiated to ten different doses ranging between 0 and 20 Gy using 6 MV LINAC X-rays with dose rate of 5.6 Gy/min. Irradiated lymphocytes were cultured and calyculin induced PCC spreads were prepared. PCC spreads were captured using image analysis system and chromosome lengths were measured using open-source ImageJ software. For each dose, LR for 50 chromosome spreads were computed and mean LR value was calculated. LR varies between 6.0 ± 0.08 and 23.6 ± 0.55 for the dose range between 2 and 20 Gy. The dose response curve for LR was observed to be linear with y = 1.02x + 3.36, R² = 0.97. Linear dose response relationship obtained in the present study confirms the prospective use of LR measurement. This study is first of its kind to examine chromosome length ratio as a biomarker of DNA damage in cells exposed to high dose X-ray exposure.

Construction of dose response curve for 6 MV LINAC X-rays using Premature Chromosome Condensation assay for radiation dosimetry

Quantification of chromosomal aberrations in the exposed personnel blood samples is considered as a 'gold standard' and sensitive biomarker in biological dosimetry. Despite technological developments, culture of cells for 48-52 h remains an unmet need in case of triage biodosimetry. Moreover, it is difficult to get sufficient number of metaphase spreads for scoring after high doses of exposures. The technique which causes condensation of chromatin before mitosis using biological or chemical agent is named as Premature Chromosome Condensation (PCC) assay. This assay is considered as an alternative to chromosome aberration assay, particularly at high acute doses of low and high LET radiation. To establish the PCC assay, blood samples were collected from healthy non-smoking individuals (n = 3) and exposed to various doses (0-20 Gy) of 6 MV X-rays at a dose rate of 5.6 Gy/min, using a high energy Linear accelerator (LINAC). Irradiated blood samples were subjected to Calyculin-A induced PCC. About 500 cells or more than 100 Ring Chromosomes (RC) were scored at each dose. Dicentric chromosomes (DC) and acentric fragments were also scored at each dose; the number of chromosomal aberrations in G1, M, G2/M and M/A phase of cell cycle were recorded and the frequency was used to construct the dose response curve. A dose dependent increase in RC and DC frequency were observed with a slope of 0.049 ± 0.002 and 0.30 ± 0.02 respectively. This study is first of its kind to construct a dose response curve for LINAC X-rays using a PCC assay.

The role of phosphorylation in the elasticity of the tethers that connect telomeres of separating anaphase chromosomes

Elastic tethers, connecting telomeres of all separating anaphase chromosome pairs, lose elasticity when they lengthen during anaphase. Treatment with phosphatase inhibitor CalyculinA causes anaphase chromosomes to move backwards after they reach the poles, suggesting that dephosphorylation causes loss of tether elasticity. We added 50nM CalyculinA to living anaphase crane-fly spermatocytes with different length tethers. When tethers were short, almost all partner chromosomes moved backwards after nearing the poles. When tethers were longer, fewer chromosomes moved backwards. With yet longer tethers none moved backward. This is consistent with tether elasticity being lost by dephosphorylation. 50nM CalyculinA blocks both PP1 and PP2A. To distinguish between PP1 and PP2A we treated cells with short tethers with 50nM okadaic acid which blocks solely PP2A, or with 1µM okadaic acid which blocks both PP1 and PP2A. Only 1µM okadaic acid caused chromosomes to move backward. Thus, tether elasticity is lost because of dephosphorylation by PP1.

Actomyosin-dependent invasion of endothelial sprouts in collagen

During sprouting angiogenesis-the growth of blood vessels from the existing vasculature-endothelial cells (ECs) adopt an elongated invasive form and exert forces at cell-cell and cell-matrix interaction sites. These cell shape changes and cellular tractions require extensive reorganizations of the actomyosin network. However, the respective roles of actin and myosin for endothelial sprouting are not fully elucidated. In this study, we further investigate these roles by treating 2D-migrating and 3D-sprouting ECs with chemical compounds targeting either myosin or actin. These treatments affected the endothelial cytoskeleton drastically and reduced the invasive response in a compound-specific manner; pointing toward a tight control of the actin and myosin activity during sprouting. Clusters in the data further illustrate that endothelial sprout morphology is sensitive to the in vitro model mechanical microenvironment and directs future research toward mechanical substrate guidance as a strategy for promoting engineered tissue vascularization. In summary, our results add to a growing corpus of research highlighting a key role of the cytoskeleton for sprouting angiogenesis.

Effects of digoxin on full-type hyperactivation in bovine ejaculated spermatozoa with relatively lower survivability for incubation with stimulators of cAMP signaling cascades

Previous researches of our laboratory reported that addition of cAMP analog cBiMPS and protein phosphatase inhibitor calyculin A (stimulators of cAMP signaling cascades) improved the capacity of incubation medium to induce full-type hyperactivation in bovine ejaculated spermatozoa. However, this modified medium was valid only for samples with relatively good survivability for incubation with stimulators of cAMP signaling cascades. Thus, it is necessary to make further modified medium for evaluation of potentials to exhibit full-type hyperactivation in bovine sperm samples with relatively lower survivability. Na⁺/K⁺-ATPase is an integral membrane protein and involved with the regulation of rodent sperm motility. To make further modification of the medium, we examined effects of Na⁺/K⁺-ATPase inhibition with digoxin on motility, full-type hyperactivation and protein tyrosine phosphorylation in bovine ejaculated spermatozoa with relatively lower survivability for incubation with stimulators of cAMP signaling cascades and also performed the immunodetection of bovine sperm Na⁺/K⁺-ATPase. The addition of Na⁺/K⁺-ATPase inhibitor digoxin to the incubation medium containing cBiMPS and calyculin A had the tendency to lessen the decreases in the percentages of motile spermatozoa in all of 12 samples after the incubation for 1-3 h and significantly increased the percentages of full-type hyperactivation in one group of 4 samples (Sample-A1) and another group of 4 samples (Sample-A2) after 1 and 2 h respectively, though it had no significant effects on full-type hyperactivation in the other group of 4 samples (Sample-B). In addition, incubation time-related changes in the sperm protein tyrosine phosphorylation (a good marker for sperm capacitation) were correlated with those in the percentages of full-type hyperactivation in Sample-A1 containing digoxin. Immunodetection showed that Na⁺/K⁺-ATPase is present in the middle and principal pieces of the flagella, indicating that Na⁺/K⁺-ATPase has possible relations with sperm motility. These results obtained with bull ejaculated spermatozoa with relatively lower survivability indicate that incubation method using digoxin is useful to evaluate potentials of sperm samples to exhibit full-type hyperactivation, that digoxin has effects on suppressing reduction of sperm motility, and that prolonged incubation with digoxin induces reduction of capacitation state which may suppress the maintenance of full-type hyperactivation.

Identification of isoforms of calyculin A-sensitive protein phosphatases which suppress full-type hyperactivation in bull ejaculated spermatozoa

In bull spermatozoa, extracellular Ca²⁺-dependent full-type hyperactivation, which is characterized by the asymmetrical beating in whole parts of the middle/principal pieces, is suppressed by calyculin A-sensitive protein phosphatases. The aim of this study was to identify isoforms of these protein phosphatases. Ejaculated spermatozoa were used for the investigation on effects of protein phosphatase inhibitors (calyculin A with high specificity for both of protein phosphatases 1 and 2A, and okadaic acid with relatively higher specificity for protein phosphatase 2A than protein phosphatase 1) on the induction of extracellular Ca²⁺-dependent full-type hyperactivation by incubation with CaCl₂ and cAMP analog (cBiMPS). They were also used for the immunodetection of protein phosphatases 1α, 1β, 1γ, 2Aα and 2Aβ. Percentages of full-type hyperactivated spermatozoa significantly increased after incubation with calyculin A (10 nM) in a concentration-dependent manner of CaCl₂ (0-3.42 mM), though only minor increases in the percentages of full-type hyperactivated spermatozoa were observed after incubation with okadaic acid (10 nM). Moreover, the immunodetection of protein phosphatase isoforms showed sperm connecting piece and flagellum included protein phosphatases 1α and 1γ, but did not do the other isoforms. These results suggest that calyculin A-sensitive and okadaic acid-less sensitive protein phosphatases (1α and 1γ) are suppressors for the extracellular Ca²⁺-dependent full-type hyperactivation in bull ejaculated spermatozoa.

G2 Premature Chromosome Condensation/Chromosome Aberration Assay: Drug-Induced Premature Chromosome Condensation (PCC) Protocols and Cytogenetic Approaches in Mitotic Chromosome and Interphase Chromatin for Radiation Biology

Chromosome analysis is a fundamental technique for a wide range of cytogenetic studies. Chromosome aberrations are easily introduced by many kinds of clastogenic agents such as ionizing irradiation, UV, or alkylating agents, and damaged chromosomes may be prone to cancer. Chromosomes are conventionally prepared from mitotic cells arrested by the colcemid block method. However, obtaining of mitotic chromosomes is sometimes hampered under several circumstances, for example after high-dose (over several Gys of γ-rays) ionizing irradiation exposure accident. As a result, cytogenetic analysis will be often difficult or even impossible in such cases. Premature chromosome condensation (PCC) is an alternative technique that has proved to be a unique and useful way in chromosome analysis. Previously, PCC has been achieved following cell fusion mediated either by fusogenic viruses (for example Sendai virus) or by polyethylene glycol (PEG) (cell-fusion PCC), but the cell-fusion PCC has several drawbacks. The novel drug-induced PCC use of specific inhibitors for serine/threonine protein phosphatase was introduced about 20 years ago. This method is much simple and easy even than the conventional mitotic chromosome preparation using colcemid block protocol and the obtained PCC index (equivalent to mitotic index for metaphase chromosome) is much higher. Furthermore, this method allows the interphase chromatin to be condensed and visualized like mitotic chromosomes, and thus has been opening the way for chromosome analysis not only in metaphase chromosomes but also in interphase chromatin. The drug-induced PCC has therefore proven the usefulness in cytogenetics and other many cell biology fields. Since the first version of drug-induced PCC protocol has been published in 2009 (Gotoh, Methods in molecular biology. Humana Press, New York, 2009), many newer applications of drug-induced PCC in radiation biology and chromosome science fields in a wide range of species from animal to plant have been reported (Gotoh et al., Biomed Res 16:63-68, 1995; Lamadrid Boada et al., Mutat Res 757:45-51, 2013; Ravi et al., Biochimie 95:124-33, 2013; Ono et al., J Cell Biol 200:429-41, 2013; Vagnarelli, Exp Cell Res 318:1435-41, 2012; Roukos et al., Nat Protoc 9:2476-92, 2014; Miura and Blakely, Cytometry A 79:1016-22, 2013; Zabka et al., J Plant Physiol 174:62-70, 2015; Samaniego et al., Planta 215:195-204, 2002; Rybaczek et al., Folia Histochem Cytobiol 40:51-9, 2002; Gotoh and Durante J Cell Physiol 209:297-304, 2006). Therefore as a new edition, I will write in this chapter the drug-induced PCC technique with newer findings, in particular focused drug-induced PCC protocols in radiation biology with referring updated articles published recently.

Biodosimetry estimation using the ratio of the longest:shortest length in the premature chromosome condensation (PCC) method applying autocapture and automatic image analysis

The combination of automatic image acquisition and automatic image analysis of premature chromosome condensation (PCC) spreads was tested as a rapid biodosimeter protocol. Human peripheral lymphocytes were irradiated with (60)Co gamma rays in a single dose of between 1 and 20 Gy, stimulated with phytohaemaglutinin and incubated for 48 h, division blocked with Colcemid, and PCC-induced by Calyculin A. Images of chromosome spreads were captured and analysed automatically by combining the Metafer 4 and CellProfiler platforms. Automatic measurement of chromosome lengths allows the calculation of the length ratio (LR) of the longest and the shortest piece that can be used for dose estimation since this ratio is correlated with ionizing radiation dose. The LR of the longest and the shortest chromosome pieces showed the best goodness-of-fit to a linear model in the dose interval tested. The application of the automatic analysis increases the potential use of the PCC method for triage in the event of massive radiation causalities.

Assessment of simulated high-dose partial-body irradiation by PCC-R assay

The estimation of the dose and the irradiated fraction of the body is important information in the primary medical response in case of a radiological accident. The PCC-R assay has been developed for high-dose estimations, but little attention has been given to its applicability for partial-body irradiations. In the present work we estimated the doses and the percentage of the irradiated fraction in simulated partial-body radiation exposures at high doses using the PCC-R assay. Peripheral whole blood of three healthy donors was exposed to doses from 0-20 Gy, with ⁶⁰Co gamma radiation. To simulate partial body irradiations, irradiated and non-irradiated blood was mixed to obtain proportions of irradiated blood from 10-90%. Lymphocyte cultures were treated with Colcemid and Calyculin-A before harvest. Conventional and triage scores were performed for each dose, proportion of irradiated blood and donor. The Papworth's u test was used to evaluate the PCC-R distribution per cell. A dose-response relationship was fitted according to the maximum likelihood method using the frequencies of PCC-R obtained from 100% irradiated blood. The dose to the partially irradiated blood was estimated using the Contaminated Poisson method. A new D₀ value of 10.9 Gy was calculated and used to estimate the initial fraction of irradiated cells. The results presented here indicate that by PCC-R it is possible to distinguish between simulated partial- and whole-body irradiations by the u-test, and to accurately estimate the dose from 10-20 Gy, and the initial fraction of irradiated cells in the interval from 10-90%.

The Giardia cell cycle progresses independently of the anaphase-promoting complex

Most cell cycle regulation research has been conducted in model organisms representing a very small part of the eukaryotic domain. The highly divergent human pathogen Giardia intestinalis is ideal for studying the conservation of eukaryotic pathways. Although Giardia has many cell cycle regulatory components, its genome lacks all anaphase-promoting complex (APC) components. In the present study, we show that a single mitotic cyclin in Giardia is essential for progression into mitosis. Strikingly, Giardia cyclin B lacks the conserved N-terminal motif required for timely degradation mediated by the APC and ubiquitin conjugation. Expression of Giardia cyclin B in fission yeast is toxic, leading to a prophase arrest, and this toxicity is suppressed by the addition of a fission yeast degradation motif. Cyclin B is degraded during mitosis in Giardia cells, but this degradation appears to be independent of the ubiquitination pathway. Other putative APC substrates, aurora and polo-like kinases, also show no evidence of ubiquitination. This is the first example of mitosis not regulated by the APC and might reflect an evolutionary ancient form of cell cycle regulation.