Okadaic acid induces premature chromosome condensation reflecting the cell cycle progression in one-cell stage mouse embryos

Multifaceted applications of pre-mature chromosome condensation in radiation biodosimetry

BACKGROUND

Biodosimetry with persistent cytogenetic indicators in peripheral blood lymphocytes (PBLs) plays crucial role in regulatory/medical management of individuals overexposed to radiation. Conventional methods require ∼48 h culture and have limited dose range (0.1-5Gy) applications due to checkpoint arrest/poor stimulation. G0-Phase Premature chromosome condensation (G0-PCC) allows chromosome aberration analysis within hours after blood collection. Due to high skill demand, applications of G0-PCC were not very well explored and being re-visited worldwide. Among all aberrations, analysis of excess chromosomal fragments is quickest. Radiation dose response curve for the fragments has been reported.

PURPOSE

In present study, excess fragment analysis has been addressed in detail, in addition to validation of radiation dose response curve, gender variation in the response, dose dependent repair kinetics, minimum detection limit (MDL), duration and accuracy of final dose estimation with 5blindfolded, ex vivo irradiated samples have been studied. In extension, feasibility of multiparametric dosimetry with Fluorescent in situ hybridization (FISH) based endpoints were qualitatively explored.

MATERIAL AND METHODS

PBLs were exposed to Gamma-Radiation and G0-PCC was performed at different time points. Decay kinetics and dose response curve were established. Gender Variation of the frequency of the fragments was assessed at 0, 2 and 4 Gy. FISH was performed with G0-PCC applying centromere probe, whole chromosome paints, multi-color FISH and multi-color banding probes.

RESULTS

Radiation response curve for fragments was found to be linear (Slope 1.09 ± 0.031 Gy-1). Background frequency as well as dose response did not show significant gender bias. Based on variation in background frequency of fragments MDL was calculated to be ∼0.3 Gy. Kinetics of fragment tested at 0, 4, 8, 16 and 24 h showed exponential decay pattern from 0 to 8 h and without further decay. Final dose estimation of five samples was completed within 13 man-hours. Dicentric chromosomes, translocations, insertions and breaks were identifiable in combination with centromere FISH and WCP. Advanced methods employing multicolor FISH and multi-color banding were also demonstrated with PCC spreads.

CONCLUSION

G0-PCC, can be useful tool for high dose biodosimetry with quick assessment of fragment frequency. Further, it holds potential for multi-parametric dosimetry in combination with FISH.

Prophasing interphase chromatin for assessing genetic damages-The evolution, applications and the future prospects

Premature chromosome condensation (PCC) involves induction of near-chromosome-like morphology to interphase chromatin. Experimental induction of PCC was achieved by somatic cell hybridization (SCH), an approach which evolved into a chemical-induction process. PCC presents most probably the only way in which cytogenetic assessment of damages can be analyzed in special situations such as availability of limited numbers of sample cells and for cells which have lost their ability to divide. Initial experiments on PCC were reported in late 1960s and the technique has evolved into one with wide range of applications owing to its increased efficiency in detecting primary DNA damages. Biodosimetry remains as the primary area which utilizes PCC technique to the maximum efficiency with several multiple-groups participating in collaborative exercises for biodosimetric applications. However, in spite of the advantages that the technique offers, it is yet to reach its full potential. This is due to the inherent limitations of the manner in which PCC is induced currently; by the somatic cell hybridization and chemical-induction processes. An approach which combines these two would sure help in taking PCC to its highest potential as the preferred technique for assessment of primary DNA damages. We present the chronological events of evolution of the PCC technique along with its applications. Also, the limitations of the technique along with the suggestions for further refinement of the PCC technique are discussed.

Standardization of CalyculinA induced PCC assay and its advantages over Okadaic acid PCC assay in Biodosimetry applications

OBJECTIVE

In the present study an attempt was made to estimate coefficients of dose response curves for PCC aberrations induced by CalyculinA and Okadaic acid, using ⁶⁰Co gamma radiation and 8 MeV pulsed electron beam for biodosimetry application.

MATERIALS AND METHODS

The modified method outlined by Puig et al. 2013 was used to conduct Calyculin A and Okadaic acid induced PCC assay in human blood lymphocytes.Chemical treatment was given for the last 1 h of a 48 h culture. The study was carried out in the dose range 2.5 to 20 Gy using ⁶⁰Co gamma rays and 8 MeV pulsed electron beam.

RESULTS AND CONCLUSIONS

Results show a linear dose dependent increase with a slope of 0.047 ± 0.001 from Calycalin A PCC and 0.048 ± 0.002 form Okadaic acid PCC. The slope of the fragments curve was 0.327 ± 0.006 from Calyculin A and 0.328 ± 0.006 from Okadaic acid PCC. Further, dose calibration studies were carried out for 8 MeV electron using Calyculin A PCC assay and the obtained slope from ring yield was 0.054 ± 0.002 and 0.427 ± 0.009 from fragment yield.

A novel parameter, cell-cycle progression index, for radiation dose absorbed estimation in the premature chromosome condensation assay

The calyculin A-induced premature chromosome condensation (PCC) assay is a simple and useful method for assessing the cell-cycle distribution in cells, since calyculin A induces chromosome condensation in various phases of the cell cycle. In this study, a novel parameter, the cell-cycle progression index (CPI), in the PCC assay was validated as a novel biomarker for biodosimetry. Peripheral blood was drawn from healthy donors after informed consent was obtained. CPI was investigated using a human peripheral blood lymphocyte (PBL) ex vivo irradiation ((60)Co-gamma rays: ∼0.6 Gy min(-1), or X ray: 1.0 Gy min(-1); 0-10 Gy) model. The calyculin A-induced PCC assay was performed for chromosome preparation. PCC cells were divided into the following five categories according to cell-cycle stage: non-PCC, G1-PCC, S-PCC, G2/M-PCC and M/A-PCC cells. CPI was calculated as the ratio of G2/M-PCC cells to G1-PCC cells. The PCC-stage distribution varied markedly with irradiation doses. The G1-PCC cell fraction was significantly reduced, and the G2/M-PCC cell fraction increased, in 10-Gy-irradiated PBL after 48 h of culture. CPI levels were fitted to an exponential dose-response curve with gamma-ray irradiation [y = 0.6729 + 0.3934 exp(0.5685D), r = 1.0000, p < 0.0001] and X-ray irradiation [y = -0.3743 + 0.9744 exp(0.3321D), r = 0.9999, p < 0.0001]. There were no significant individual (p = 0.853) or gender effects (p = 0.951) on the CPI in the human peripheral blood ex vivo irradiation model. Furthermore, CPI measurements are rapid (< 15 min per case). These results suggest that the CPI is a useful screening tool for the assessment of radiation doses received ranging from 0 to 10 Gy in radiation exposure early after a radiation event, especially after a mass-casualty radiological incident.

Essential role of protein phosphatase 2A in metaphase II arrest and activation of mouse eggs shown by okadaic acid, dominant negative protein phosphatase 2A, and FTY720

Vertebrate eggs arrest at second meiotic metaphase. The fertilizing sperm causes meiotic exit through Ca(2+)-mediated activation of the anaphase-promoting complex/cyclosome (APC/C). Although the loss in activity of the M-phase kinase CDK1 is known to be an essential downstream event of this process, the contribution of phosphatases to arrest and meiotic resumption is less apparent, especially in mammals. Therefore, we explored the role of protein phosphatase 2A (PP2A) in mouse eggs using pharmacological inhibition and activation as well as a functionally dominant-negative catalytic PP2A subunit (dn-PP2Ac-L199P) coupled with live cell imaging. We observed that PP2A inhibition using okadaic acid induced events normally observed at fertilization: degradation of the APC/C substrates cyclin B1 and securin resulting from loss of the APC/C inhibitor Emi2. Although sister chromatids separated, chromatin remained condensed, and polar body extrusion was blocked as a result of a rapid spindle disruption, which could be ameliorated by non-degradable cyclin B1, suggesting that spindle integrity was affected by CDK1 loss. Similar cell cycle effects to okadaic acid were also observed using dominant-negative PP2Ac. Preincubation of eggs with the PP2A activator FTY720 could block many of the actions of okadaic acid, including Emi2, cyclin B1, and securin degradation and sister chromatid separation. Therefore, in conclusion, we used okadaic acid, dn-PP2Ac-L199P, and FTY720 on mouse eggs to demonstrate that PP2A is needed to for both continued metaphase arrest and successful exit from meiosis.

Release of phospholipase C ζand [Ca2+]i oscillation-inducing activity during mammalian fertilization

During fertilization of mammalian eggs a factor from the sperm, the sperm factor (SF), is released into the ooplasm and induces persistent [Ca2+]ioscillations that are required for egg activation and embryo development. A sperm-specific phospholipase C (PLC), PLCz, is thought to be the SF. Here, we investigated whether the SF activity and PLCζare simultaneously and completely released into the ooplasm soon after sperm entry. To accomplish this, we enucleated sperm heads within 90 min of intracytoplasmic sperm injection (ICSI) and monitored the persistence of the [Ca2+]ioscillations in eggs in which the sperm had been withdrawn. We also stained the enucleatedsperm heads to ascertain the presence/absence of PLCζ. Our results show that by 90 min all the SF activity had been released from the sperm, as fertilized enucleated eggs oscillated as fertilized controls, even in cases in which oscillations were prolonged by arresting eggs at metaphase. In addition, we found that the released SF activity became associated with the pronucleus (PN), as induction of PN envelope breakdown evoked comparable [Ca2+]iresponses in enucleated and non-manipulated zygotes. Lastly, we found that PLCzlocalized to the equatorial area of bull sperm and to the post-acrosomal region of mouse sperm and that by 90 min after ICSI all the sperm’s PLCζimmunoreactivity was lost in both species. Altogether, our findings show that during fertilization the SF activity and PLCζimmunoreactivity are simultaneously released from the sperm, suggesting that PLCζmay be the only [Ca2+]ioscillation-inducing factor of mammalian sperm.

Evidence for the existence of satellite DNA-containing connection between metaphase chromosomes

Physical connections between mitotic chromosomes have been reported previously. It was assumed that the interchromosome connection was based on the DNA-protein thread. However, the data about DNA sequences and protein component in the thread is fragmentary. We demonstrated on the mouse cultured cell line and prematurely condensed chromosomes that: (a) all four mouse satellite DNA fragments (major and minor satellite, mouse satellite 3 (MS3) and mouse satellite 4 (MS4)) were involved in the thread formation; (b) MS4 was involved in the thread to the least extent among all the other fragments; (c) telomere was never a member of the thread; (d) the thread was synthesized at a late G(2) phase; (e) RNA helicase p68 and CENP-B were among the protein components of the interchromosome connection. It was shown by FACS analysis that in mouse and human cell lines: (1) the flow karyotype spectrums were never free from chromosome aggregates; (2) chromosome association did not depend on the chromosome length and each chromosome was free to associate with the other.

Obtaining metaphase spreads from single blastomeres for PGD of chromosomal rearrangements

It has previously been shown that it is possible to obtain metaphase chromosomes from single blastomeres converted into metaphase in the cytoplasm of a mouse zygote. This method is highly labour intensive and cannot be performed outside the preimplantation genetic diagnosis (PGD) laboratory, so to overcome these limitations, a method was developed for obtaining metaphase spreads from single biopsied blastomeres using different chemicals. The substances tested were calyculin A, caffeine, paclitaxel and colcemid in a total of 496 disaggregated and 234 biopsied blastomeres from day 3 embryos. It was demonstrated that the optimal method involved a combined use of 'selective biopsy' (selection of the biopsied blastomere according to morphological criteria) and exposure to caffeine. This resulted in shortening the mean incubation time of biopsied blastomeres, with a metaphase formation rate of 80%. The method is simple for obtaining metaphases from single blastomeres, and may be implemented in clinical practice of PGD for structural rearrangements.

Transmission of modified nucleosomes from the mouse male germline to the zygote and subsequent remodeling of paternal chromatin

Rapidly after gamete fusion, the sperm nucleus loses its specific chromatin conformation and the DNA is repopulated with maternally derived nucleosomes. We evaluated the nature of paternally derived nucleosomes and the dynamics of sperm chromatin remodeling in the zygote directly after gamete fusion. We observed histone H4 acetylated at K8 or K12 already prior to full decondensation of the sperm nucleus, suggesting that these marks are transmitted by the spermatozoon. Tracking down the origin of H4K8ac and H4K12ac during spermiogenesis revealed the retention of nucleosomes with these modifications in the chromocenter of elongating spermatids. We show that sperm constitutive heterochromatin is enriched for nucleosomes carrying specific histone modifications which are transmitted to the zygote. Our results suggest an epigenetic mechanism for inheritance of chromosomal architecture. Furthermore, up to pronucleus formation, histone acetylation and phosphorylation build up in a cascade-like fashion in the paternal chromatin. After formation of the pronucleus, a subset of these marks is removed from the heterochromatin, which suggests a reestablishment of the euchromatin-heterochromatin partition.

High-resolution organization of mouse centromeric and pericentromeric DNA

We studied the organization of mouse satellite 3 and 4 (MS3 and MS4) in comparison with major (MaSat) and minor (MiSat) DNA sequences, located in the centromeric and pericentromeric regions of mouse telocentric chromosomes by fiber-FISH. The centromeric region consists of a small block of MiSat and MS3 followed by a pericentromeric block of MaSat with MS4. Inside the block of the long-range cluster, MaSat repeats intermingle mostly with MS4, while MiSat intermingle with MS3. The distribution of GC-rich satellite DNA fragments is less strict than that of AT-rich fragments; it is possible to find MS3 fragments in the MaSat array and MS4 fragments in the MiSat array. The methylation pattern does not fully correspond to one of the four families of satellite DNA (satDNA). In each satDNA fragment only part of the DNA is methylated. MS3 and MS4 are heavily methylated being GC-rich. Pericentomeric satellite DNA fragments are more methylated than centromeric ones. Among the four families of satDNA MS4 is the most methylated while MiSat is methylated only to a minimal extent. Estimation of the average fragment length and average distance between fragments shows that the range of the probes used does not cover the whole centromeric region. The existence of unknown sequences in the mouse centromere is likely.

New types of mouse centromeric satellite DNAs

Genomic databases do not contain complete sequences of the centromeric regions. We created a pUC19-based library of DNA fragments from isolated chromocentres of interphase nuclei. In this library we have found major satellite (MaSat) and two new satellite sequences - MS3 and MS4. The computer analysis of MS3 and MS4 sequences by alignment, fragment curved state and search for MAR motifs in comparison with the mouse major and minor satellite (MiSat) DNA has shown them to be new satellite fragments. Southern blot of MS3 and MS4 with total DNA digested by restriction enzymes shows the ladder characteristic of satellite DNA. 2.2% of the total DNA consists of MS3, the monomer of which is 150 bp long. The MS4 monomer is 300 bp long and accounts for 1.6% of the total DNA. On metaphase chromosomes MS3 and MS4 are located at the centromeric region. FISH analysis of L929 nuclei during the cell cycle showed relative positions of MaSat, MiSat, MS3, and MS4. All mapped satDNA fragments except MaSat belong to the outer layer of the chromocentres in the G0/G1 phase. MS3 is likely to be involved in the centromere formation. The mouse genome contains at least four satDNA types: AT-rich (MaSat and MiSat), and CG-rich (MS3 and MS4).

Satellite DNA binding and cellular localisation of RNA helicase P68

We purified a 68-kDa protein from the mouse nuclear matrix using ion exchange and affinity chromatography. Column fractions were tested for specific binding to mouse minor satellite DNA using a gel mobility shift assay. The protein was identified by mass spectrometry as RNA helicase P68. In fixed cells, P68 was found to shuttle in and out of SC35 domains, forming fibres and granules in a cell-cycle dependent manner. Analysis of the P68 sequence revealed a short potential coiled-coil domain that might be involved in the formation of P68 fibres. Contacts between centromeres and P68 granules were observed during all phases of the cycle but they were most prominent in mitosis. At this stage, P68 was found in both the centromeric regions and the connections between chromosomes. Direct interaction of P68/DEAD box RNA helicase with satellite DNAs in vitro has not been demonstrated for any other members of the RNA helicase family.

Regulation of mitogen-activated protein kinase phosphorylation, microtubule organization, chromatin behavior, and cell cycle progression by protein phosphatases during pig oocyte maturation and fertilization in vitro

We used okadaic acid (OA), a potent inhibitor of protein phosphatases 1 and 2A, to study the regulatory effects of protein phosphatases on mitogen-activated protein (MAP) kinase phosphorylation, morphological changes in the nucleus, and microtubule assembly during pig oocyte maturation and fertilization in vitro. When germinal vesicle (GV) stage oocytes were exposed to OA, MAP kinase phosphorylation was greatly accelerated, being fully activated at 10 min. However, MAP kinase was dephosphorylated by long-term (>20 h) exposure to OA. Correspondingly, premature chromosome condensation and GV breakdown were accelerated, whereas meiotic spindle assembly and meiotic progression beyond metaphase I stage were inhibited. OA also quickly reversed the inhibitory effects of butyrolactone I, a specific inhibitor of maturation-promoting factor (MPF), on MAP kinase phosphorylation and meiosis resumption. Treatment of metaphase II oocytes triggered metaphase II spindle elongation and disassembly as well as chromosome alignment disruption. OA treatment of fertilized eggs resulted in prompt phosphorylation of MAP kinase, disassembly of microtubules around the pronuclear area, chromatin condensation, and pronuclear membrane breakdown, but inhibited further cleavage. Our results suggest that inhibition of protein phosphatases promptly phosphorylates MAP kinase, induces premature chromosome condensation and meiosis resumption as well as pronucleus breakdown, but inhibits spindle organization and suppresses microtubule assembly by sperm centrosomes in pig oocytes and fertilized eggs.

Premature chromosome condensation and cell separation studies in biopsies from head and neck tumors for radiosensitivity prediction

BACKGROUND AND PURPOSE

Intrinsic radiosensitivity of tumor cells from biopsies, assayed by colony formation after in vitro irradiation, has shown significant correlations with outcome after radiotherapy. Alternatives to the colony assay have been sought due to its long and cumbersome nature. We have previously shown good correlations between colony formation and radiation-induced chromosome aberrations in human tumor cell lines. In addition, we and others have shown on cell lines that premature chromosome condensation (PCC) induced with phosphatase inhibitors can be used to aid rapid assessment of aberrations in interphase cells, reducing the selection problem with metaphases. The purpose of this study was to translate the in vitro results to human cancer, with the aim of developing a rapid assay for intrinsic radiosensitivity.

METHODS AND RESULTS

The problem of admixtures of normal and malignant cells in biopsies was addressed using magnetic bead separation (MACS) employing antibodies to human fibroblasts. This proved to be a reliable and efficient method, enriching mean tumor cell fractions from 20 to almost 80%. PCC could be induced in human normal and tumor cell lines, and in sorted or unsorted suspensions from biopsies, with the phosphatase inhibitor calyculin A. Maximum PCCs were achieved after 1-week culture of biopsy-derived cells. Mean fractions of aneuploid tumor cell PCCs were, however, less than 1%. PCCs were predominantly from S and G2 phase, of which only G2 were scorable for aberrations. Almost no G1 PCCs were found. More scorable PCCs were found after 1h of calyculin A than metaphases after 5h of colcemid, but these were calculated to be too few to yield reliable estimates of chromosome damage after radiation.CONLCUSIONS: Tumor cells can be satisfactorily separated from fibroblasts in fresh suspensions from cancer biopsies, but poor growth of tumor cells in short term culture and low yields of PCCs combine to prevent the routine use of such cytogenetic assays for pre-treatment prediction of radiotherapy outcome.

Prepregnancy genetic testing for age-related aneuploidies by polar body analysis

Current practice for prevention of chromosomal aneuploidies involves prenatal screening and termination of pregnancy, a procedure that is not universally acceptable. We introduced prepregnancy genetic testing by sampling and fluorescence in situ hybridization (FISH) analysis of the first and second polar body (PB), to avoid fertilization and transfer of embryos resulting from aneuploid oocytes. In 395 in vitro fertilization (IVF) patients of advanced maternal age, the first and second PBs were removed following their extrusion from oocytes and studied by FISH, using probes specific for chromosomes 13, 18, and 21, to detect and avoid the transfer of oocytes with common aneuploidies. Overall, 3,651 oocytes obtained from 598 IVF cycles were available for FISH analysis, with 2,952 showing interpretable FISH results (80.9%). The analysis revealed 1,271 (43.1%) oocytes with aneuploidy, which were excluded from transfer and subjected to follow-up FISH analysis to confirm PB diagnosis in the cleavage or blastocyst stage embryos. Only embryos originating from 1,681 aneuploidy-free oocytes were transferred back to patients, resulting in 119 pregnancies overall, from which 78 healthy children have already been born, 35 were spontaneously aborted, and 16 are ongoing, after confirming PB diagnosis by prenatal diagnosis. The results demonstrate that PB-based preimplantation diagnosis may be used for prepregnancy screening in women with age-related risk for common aneuploidies.

Apoptosis and mitotic arrest are two independent effects of the protein phosphatases inhibitor okadaic acid in K562 leukemia cells

Treatment of human myeloid leukemia K562 cells with the serine/threonine protein phosphatases inhibitor okadaic acid induced mitotic arrest followed by apoptosis in a synchronized manner. The effect was observed at drug concentrations that inhibited the protein phosphatase type 2A but not type 1. We investigated whether apoptosis was a consequence of the preceding mitosis arrest or was induced independently by okadaic acid. We found that (1) apoptosis, but not mitotic arrest, was inhibited in cells with constitutive expression of Bcl-2; (2) pretreatment of cells with the DNA synthesis inhibitor hydroxyurea blocked the mitotic arrest but not the apoptosis mediated by okadaic acid; (3) down-regulation of c-myc gene was associated with apoptosis, but not with mitotic arrest; and (4) inhibition of protein synthesis abrogated mitotic arrest, but not apoptosis. The results suggest that inhibition of protein phosphatase 2A by okadaic acid provokes mitotic arrest and apoptosis of leukemia cells by independent mechanisms.

Birth of healthy children after preimplantation diagnosis of common aneuploidies by polar body fluorescent in situ hybridization analysis. Preimplantation Genetics Group

OBJECTIVE

To perform preimplantation diagnosis of common aneuploidies by polar body analysis and fluorescent in situ hybridization technique using probes specific for chromosomes X, 18, and 13/21.

DESIGN

The first and/or second polar bodies were removed and studied by fluorescent in situ hybridization to detect and avoid fertilization and transfer of oocytes with common aneuploidies.

SETTING

The Reproductive Genetics Institute's IVF program at Illinois Masonic Medical Center.

PATIENTS

One hundred ninety-three couples of advanced maternal age (34 to 46 years) under-going IVF treatment volunteered to be part of a clinical trial on preimplantation polar body diagnosis of common aneuploidies.

INTERVENTIONS

Using micromanipulation procedures, the first and second polar bodies were removed after their extrusion from the oocytes.

MAIN OUTCOME MEASURE

Fluorescent in situ hybridization signals specific for chromosomes X, 18, and 13/21.

RESULTS

In 235 IVF cycles performed in 193 couples, 1,293 oocytes were biopsied and subjected to fluorescent in situ hybridization analysis, with fluorescent in situ hybridization results available in 993 oocytes (76.8%). Of 993 oocytes with fluorescent in situ hybridization results, 665 (67%) were predicted to be normal based on the chromosomes studied; 460 embryos resulting from these oocytes were transferred in 187 treatment cycles, resulting in 12 births of healthy children and 18 ongoing pregnancies after confirmation of the polar body diagnosis by chorionic villus sampling or amniocentesis.

CONCLUSION

Polar body fluorescent in situ hybridization analysis may be used for preimplantation diagnosis of common aneuploidies in IVF patients of advanced maternal age.

Polar body diagnosis of common aneuploidies by FISH

PURPOSE

The purpose of this work was to investigate the reliability and accuracy of polar body analysis for preimplantation diagnosis of common aneuploidies in IVF patients of advanced maternal age.

DESIGN

We have previously introduced polar body analysis as an approach for nondestractive evaluation of the genotype of human oocytes. The method has recently been applied in a clinical trial involving 45 infertile patients, demonstrating the feasibility of preconception diagnosis of common aneuploidies by fluorescent in situ hybridization (FISH). The present paper describes the experience of polar body diagnosis in 135 IVF patients (161 cycles) of advanced maternal age.

RESULTS

FISH results of the first and/or second polar bodies were available in 648 (72.4%) of 895 biopsied oocytes subjected to FISH analysis. Of 648 oocytes with FISH results, 208 demonstrated chromosomal abnormalities. Of 440 oocytes predicted to be free from monosomy or trisomy of chromosomes X, 18, and/or 13/21, 314 were normally fertilized, cleaved, and transferred in 122 treatment cycles, resulting in 6 healthy deliveries and 12 ongoing pregnancies following confirmation of the polar body diagnosis by CVS or amniocentesis.

CONCLUSIONS

The method may be useful for detection of oocytes with common chromosomal trisomies in IVF patients of advanced maternal age.

Detection of aneuploidy in human oocytes and corresponding first polar bodies by fluorescent in situ hybridization

PURPOSE

The purpose of the study was to investigate the reliability of the fluorescent in situ hybridization (FISH) analysis of the first polar body (IPB) for cytogenetic evaluation of human oocytes as a method of choice in preimplantation diagnosis of chromosomal aneuploidies.

DESIGN

Human unfertilized oocytes and their extruded IPB were analyzed using the directly labeled fluorescence alpha-satellite DNA probes to chromosomes X and 18.

RESULTS

Paired signals for chromosomes X and 18 were observed in the second meiotic prophase (MII) of unfertilized oocytes and their extruded IPB. In the series of 156 unfertilized oocytes in which the number of X chromosome- and chromosome 18-specific signals were analyzed in both MII and IPB, five nondisjunction events have been detected, with corresponding signals in MII and their IPB: missing signals in MII corresponded to extra signals in their IPB and extra signals in MII corresponded to missing signals in IPB. In one oocyte chromosome 18 nondisjunction was detected, with both chromosome 18 signals in MII and no chromosome 18 signal in IPB. In four oocytes chromatid malsegregations for chromosome X or chromosome 18 were detected: in two oocytes, three of four chromosome 18 signals were present in MII, with only one in IPB, and in the other two oocytes, three of four chromosome signals were present in MII, with only one left in IPB.

CONCLUSIONS

The data suggest the possibility of detecting chromosomal aneuploidy in oocytes through cytogenetic analysis of their corresponding IPB by FISH as a possible approach for preimplantation diagnosis of major chromosomal trisomies.

Chromatin condensation activity and cortical activity during the first three cell cycles of a mouse embryo

One-cell parthenogenetic haploid embryos and blastomeres of the 2- and 4-cell diploid mouse embryos were observed in vitro for the occurrence of two cytoplasmic activities: the cortical activity and the chromatin condensation activity. For this purpose anucleated halves (AHs) and nucleated halves (NHs) were produced by bisection of one-cell embryos and of blastomeres. The cortical activity (manifested by surface deformations) was observed only during the first cleavage cycle. In AHs the surface activity began at the same time as in NHs and disappeared before the time of the cleavage division of nucleated halves. Anucleate fragments of blastomeres from 2- and 4-cell embryos did not exhibit any cortical activity. In the absence of the native nucleus the chromatin condensation activity (assayed by premature chromatin condensation of interphase thymocyte nuclei introduced into cytoplasts by cell fusion) could also have been detected only in the first cleavage cycle. In AHs this activity appeared at the time when NHs started to cleave and disappeared after the NHs finished the first cleavage division. AHs obtained from 2-cell and 4-cell stage blastomeres did not reveal condensation activity.

Morphological effects of caffeine, okadaic acid and genistein in one-cell mouse embryos blocked in G2 by X-irradiation

One-cell mouse embryos of the Balb/c strain normally divide at 18.5 h p.c. (post conception), but they suffer an extremely long G2 arrest when irradiated with 2 Gy X-rays 8 h p.c. at the early pronuclear stage. This could be an indirect effect of radiation on tyrosine dephosphorylation of the p34cdc2 subunit of a maturation or mitosis promoting factor (MPF), which normally occurs at the end of G2. This, in turn, would maintain MPF in an inactivated form and block entry into mitosis. Preliminary studies were undertaken at the morphological level to assess indirectly the validity of this hypothesis. For this purpose, irradiated and control embryos were exposed to different compounds, which are known to interfere, directly or indirectly, with the state of phosphorylation/dephosphorylation of p34cdc2. Caffeine (CAF; 2 mM) did not affect the time of first division of control embryos, but it completely suppressed the radiation-induced G2 arrest of embryos exposed to this compound from 17 h p.c., i.e. 1.5 h before the normal time of first cleavage. Under the same conditions, okadaic acid (OA; 3 microM), a specific inhibitor of phosphatases I and IIA, induced a rapid pronuclear membrane breakdown and a block of all control and irradiated embryos at metaphase. Genistein (GEN; 92 or 185 microM). A potent inhibitor of tyrosine kinases, increased the radiation-induced G2 arrest and even induced a dose-dependent G2 arrest in the control embryos. Embryos were exposed at different times following irradiation to a mixture of either CAF (2 or 5 mM) or OA (3 or 10 microM), and cycloheximide (CH; 5 micrograms/ml), a potent protein synthesis inhibitor. Reversion of G2-arrest by CAF was still seen in embryos exposed to CAF+CH from 17 h p.c. However, the proportion of irradiated embryos eventually able to cleave was lower than that obtained under the conditions of exposure to CAF alone. Embryos exposed to CAF+CH before 17 h p.c. were not able to cleave, regardless of the concentration of CAF used. Nuclear envelope breakdown still occurred in 100% control and irradiated embryos, following exposure to 3 microM OA+CH from 10 h p.c., or to 10 microM OA+CH from 8.5 p.c.(ABSTRACT TRUNCATED AT 400 WORDS)

Human preimplantation diagnosis: needs, efficiency and efficacy of genetic and chromosomal analysis

One of the limitations of existing assisted reproduction practices is that couples at genetic risk to their offspring have to face the abortion of an affected fetus following prenatal diagnosis. This is not acceptable as a measure to avoid a congenital disease in many communities or ethnic groups, where there is a great need for a method to diagnose and avoid the affected embryo before implantation and establishment of the pregnancy. In fact, preimplantation diagnosis is needed also for those who accept prenatal diagnosis as an option to avoid the birth of an affected child, because in most of the cases the couples are at high (25-50%) risk of having a child with a recessive or dominant disease, leading to their unfortunate experience of undergoing two or more abortions of wanted pregnancies. Two methods for preimplantation genetic diagnosis (PGD) have been recently developed and implemented in the framework of IVF. PGD can be performed by micromanipulation and biopsy of the first polar body before fertilization, or by blastomere biopsy before implantation of the pre-embryo. Another potentially realistic approach is blastocyst biopsy, which is still under development and has not yet been tested in clinical practice. Available data suggest that preimplantation diagnosis is safe, as no detrimental effects have been observed in studies on the viability of biopsied pre-embryos. Genetic analysis of biopsied gametes and blastomeres is now possible by DNA analysis, while enzyme analysis and preimplantation diagnosis of chromosomal disorders are still at the research stage. The accuracy of DNA analysis in preimplantation diagnosis is clear from available data on the outcome of preimplantation diagnosis: eight children free of genetic disease have been born following preimplantation diagnosis of cystic fibrosis, haemophilia A and other X-linked conditions. However, two misdiagnoses have been also described, showing the need for further development and improvement in the accuracy, efficiency and efficacy of DNA analysis in single cells. A particularly important implication for assisted reproduction practices can be expected from the further development and improvement of methods for preimplantation cytogenetic analysis. Although the efficiency and efficacy of these methods are not yet acceptable for application in clinical practice, considerable progress has been made, providing clear evidence for their feasibility in the near future. In spite of the high cost of the preimplantation diagnostic technique at present, its development is highly justified for high risk families as it provides a wider range of options for avoiding the risk of having an affected child.(ABSTRACT TRUNCATED AT 400 WORDS)

Visualization and cytogenetic analysis of second polar body chromosomes following its fusion with a one-cell mouse embryo

PURPOSE

This study was designed to visualize the second polar body (2PB) chromosomes using its electrofusion with a one-cell-stage mouse embryo to approach preconception diagnosis of chromosomal disorders.

RESULTS

Eighty to 90% hybridization efficiency has been achieved by electrofusion of 2PB with mouse zygotes. 2PB chromosomes were visualized in 40-50% of hybrids. Sixty-five percent of 2PB chromosomes were visualized when fused with the cytoplast obtained microsurgically by removing pronuclei from a one-cell embryo. As much as 33-43% of these resulting metaphases appeared to contain chromosomal aberrations. The follow-up of the development of the reconstructed one cell-stage hybrids in vitro revealed a significant decrease in their viability. The hybrid embryos resulting from 2PB electrofusion with enucleated zygotes did not develop beyond the two-cell stage.

CONCLUSION

Electrofusion is an efficient approach for hybridization of 2PB with a one-cell mouse embryo and may be useful for visualization and cytogenetic analysis of 2PB chromosomes. The visualization rate of 2PB chromosomes is higher if 2PB is fused with enucleated zygotes. However, the method induces over 30% of chromosomal aberrations and may lead to a significant decrease in the viability of the resulting one-cell embryos.