Fluorescence In Situ Hybridization Procedure Research Articles

Detection of chromosomal abnormalities by fluorescent in-situ hybridization in immotile viable spermatozoa determined by hypo-osmotic sperm swelling test.

If randomly selected immotile spermatozoa are used for intracytoplasmic sperm injection (ICSI), pregnancy rates are significantly decreased. The hypo-osmotic swelling test (HOST) is the only method available to detect the viable, but immotile spermatozoa for ICSI. However, evidence is still lacking for the chromosomal abnormalities for the normal-looking, but immotile spermatozoa positive for HOST. Sperm samples from 20 infertile men with normal chromosomal constitution were obtained. After Percoll separation, morphologically normal but immotile spermatozoa were transported individually into HOST solution for 1 min using micropipettes. Cells that showed tail curling with swelling in HOST were then transferred back into human tubal fluid solution to allow reversal of swelling. These sperm cells were fixed and processed for the multi-colour fluorescence in-situ hybridization (FISH) for chromosomes X, Y and 18. The same FISH procedure was applied for the motile spermatozoa from the same cohort, which formed the control group. The average aneuploidy rates were 1.70 and 1.54% in 1000 HOST positive immotile and motile spermatozoa respectively detected by FISH for each patient. Our results indicate that morphologically normal, immotile but viable spermatozoa have an aneuploidy rate similar to that of normal motile spermatozoa.

The management of patients with leukaemia: the role of cytogenetics in this molecular era.

The management of patients with leukaemia: the role of cytogenetics in this molecular era.

Identification of a ζ-Crystallin (Quinone Reductase)-like 1 Gene (CRYZL1) Mapped to Human Chromosome 21q22.1

To identify a new gene(s) located on the yeast artificial chromosome (YAC) clone D142H8 that was mapped to human chromosome 21q22.1, purified YAC DNA from the clone was utilized directly as a probe to screen a human brain cDNA library after the suppression of human repetitive DNA. One cDNA clone hybridizing specifically to the YAC D142H8 DNA was identified. The clone has an insert of 1341 bp and the longest open reading frame of 349 amino acids. A search of GenBank revealed that the clone has a high degree of homology to ζ-crystallin (quinone reductase) at the amino acid level, and its nucleotide sequence represents the expressed sequence from the 50-kb segment of the human chromosome 21q11.1. Thus a new gene was namedCRYZL1(ζ-crystalline-like 1). Genomic Southern blot with total human and yeast DNAs suggests thatCRYZL1might be a single-copy gene. The fluorescencein situhybridization procedure was applied, and the results showed that the gene mapped to the human chromosome 21q22.1 subband. TheCRYZL1mRNA was expressed in heart, brain, skeletal muscle, kidney, pancreas, liver, and lungs but at different levels in different tissues.

Clinical experience of sex determination by fluorescent in-situ hybridization for preimplantation genetic diagnosis.

In our centre we started using fluorescent in-situ hybridization (FISH) technique for sexing in couples with sex-linked diseases in May 1995. Probes specific for chromosomes X, Y and 18 were applied, allowing us to detect simultaneously both gender and ploidy status. The efficiency of the FISH procedure is 90.4% per biopsied blastomere or 95.2% per biopsied blastomere with a distinct nucleus visible at spreading. Up to December 1997, we treated 15 couples (20 treatment cycles) at risk for X-linked recessive disease and two couples with Yq deletion (two treatment cycles) with the aim of transferring only female embryos. In one cycle, no embryos suitable for biopsy were obtained and in five cycles no normal female embryos were available at diagnosis. In the remaining 16 cycles, transfer was possible and six pregnancies ensued: one miscarriage has occurred and six children have been born from the other five pregnancies. The implantation rate (fetal sacs) per transferred embryo was 20.8%. In 98 (61%) of the 161 diagnosed embryos, a diploid status was observed in one or in both biopsied blastomeres. In 10 out of the 161 (6.2%) embryos a heterogeneity among the two biopsied blastomeres was found: a diploid nucleus in one blastomere and a non-diploid pattern or binuclear status in the other. In the remaining 53 (32.9%) out of 161 diagnosed embryos, the biopsied blastomeres were abnormal. The embryos that were not transferred or frozen were further analysed. When two sex chromosomes and two autosomes were present in the biopsied blastomere, the sex determination of the biopsied blastomere was never in conflict with the sex determination in the rest of the embryo. Furthermore, if the biopsied cell was diagnosed as abnormal (triploid, aneuploid, chaotic) the embryo was indeed completely abnormal or at least mosaic. A FISH error could not be excluded in two embryos (1.2%); however, a wrong gender determination did not result from this.

Fluorescence in situ hybridization with y chromosome-specific probe in decondensed bovine spermatozoa

This study was carried out to demonstrate bovine Y chromosome-bearing spermatozoa by rapid fluorescence in situ hybridization (FISH), using a digoxigenin (Dig)-labeled DNA probe specific to bovine Y chromosome. Before the FISH procedure, sperm heads were treated for decondensation with dithiothreitol (DTT) and glutathione (GSH) with or without heparin supplementation. Concentrations of either above 2 mM DTT or above 100 mM GSH induced swelling of the sperm head, which resulted in sufficient detection of the Y chromosome signal in sperm nuclei by rapid FISH (49.8 to 53.4%). When FISH was used with 2 mM DTT or 100 mM GSH on specimens from 7 sires, the rate of detection of the Y chromosome signal varied among sires (5.4 to 49.6%), especially that of the GSH treatment. Supplementation of GSH with heparin (100 U/mL), however, could induce reliable, repeatable detection of the Y chromosome signal in sperm nuclei of all the 7 sires (48.4 to 50.3%). These results show that in bovine spermatozoa decondensed with GSH and heparin, rapid FISH can detect Y chromosome-bearing spermatozoa.

Chromosomal Rearrangement of the PAX-5 Locus in Lymphoplasmacytic Lymphoma with t(9; 14) (p13; q32)

B-cell non-Hodgkin's lymphoma (NHL) consists of heterogeneous subtypes based on histologic, immunophenotypic, and clinical findings. Recent advances in molecular biology have provided us new insights into the pathogenesis of this neoplasm at the genetic level, such as the deregulation of the protooncogenes adjoining the immunoglobulin gene (Ig) loci, which is a specific event in mature B-cell tumors. Moreover, involvement of certain protooncogenes corresponds to certain subtypes of NHL. Recently, we found that t(9;14)(p13;q32) chromosomal translocation associated with lymphoplasmacytic lymphoma (LPL) juxtaposes PAX-5 gene encoding for an essential transcription factor (BSAP: B-cell specific activator protein) for B-cell proliferation and differentiation to the Ig heavy chain gene (IgH) locus. This results in deregulated expression of the PAX-5 mRNA. We also developed a diagnostic FISH (fluorescence in situ hybridization) procedure which is able to detect 80% of the widely scattering 9p13 breakpoints involved in this translocation. Thus, an understanding of the PAX-5 gene's physiological role in B-cell development and the pathological role in tumorigenesis may lead to the optimal clinical treatment strategy for LPL and LPL-derived diffuse large cell lymphoma (DLCL).

Ultrarapid detection of sex chromosomes with the use of fluorescence in situ hybridization with direct label dna probes in single human blastomeres, spermatozoa, amniocytes, and lymphocytes

Objective: To assess the ultrarapid fluorescence in situ hybridization (FISH) procedure with a 1-minute hybridization time for gender determination. Design: Fluorescence in situ hybridization with direct label fluorescence DNA probes for chromosomes X and Y were tested with the use of different hybridization times and different cell types. Setting: Hospital-based IVF program. Intervention(s): The efficiency of the FISH procedure with different hybridization times was compared with the use of male lymphocytes. The same FISH procedure, but with only 1-minute hybridization, was carried out in human blastomeres, spermatozoa, uncultured amniocytes, male lymphocytes, and female lymphocytes. Main Outcome Measure(s): Percentages of nuclei with positive signals. Result(s): The percentages of nuclei with positive signals in lymphocytes with hybridization times of 1, 3, 4, 10, 30, and 45 minutes were 97%, 97%, 98%, 98%, 98%, and 98%, respectively. The percentages of nuclei with positive signals after FISH with a 1-minute hybridization time in single blastomeres, spermatozoa, amniocytes, male lymphocytes, and female lymphocytes were 94%, 96%, 96%, 98%, and 97%, respectively. Conclusion(s): Chromosomes X and Y of human blastomeres, spermatozoa, uncultured amniocytes, and lymphocytes can be detected rapidly with the use of this ultrarapid FISH procedure with a 1-minute hybridization time.

Potential use of repeated fluorescence in situ hybridization in the same human blastomeres for preimplantation genetic diagnosis

Objective: To assess the feasibility of repeated fluorescence in situ hybridization (FISH) procedures in the same nucleus of a human blastomere. Design: Three consecutive FISH procedures were performed in the same human blastomere by using direct label fluorescence CEP and WCP probes (Vysis). Setting: Hospital-based private IVF program. Patient(s): Twenty-eight infertile couples who underwent conventional IVF in our center. Intervention(s): Embryos from oocytes with three pronuclei after in vitro insemination were used in this study. Main Outcome Measure(s): The rates of nuclear loss, present signals, and absent signal were examined. Result(s): In group 1, the rates of presence of signals were 94% after the first FISH, 92% after the second FISH, and 88% after the third FISH. In group 2, the rates of presence of signals were 96% after the first FISH, 93% after the second FISH, and 87% after the third FISH. There was no statistically significant difference in the rates of nuclear loss, present signals, and absent signal between three consecutive FISH procedures and between CEP and WCP probes. Conclusion(s): Six or more chromosomes of a single blastomere may be examined with use of this repeated FISH procedure, which may be important for preimplantation genetic diagnosis.

Prenatal Detection of Aneuploidy by Directly Labeled Multicolored Probes and Interphase Fluorescence In Situ Hybridization

To detect aneuploidy of chromosomes 13, 18, 21, X, and Y with use of new, directly labeled, multicolored, commercially available DNA probes from interphase cells of amniotic fluid (AF). The hybridization sites of the five probes were validated by metaphase analysis. The fluorescence in situ hybridization (FISH) normal range was determined from a series of normal AF specimens and tested on a series of normal and abnormal specimens. The hybridization efficiencies of the five probes were 100%. The mean AF interphase disomic signal patterns for chromosomes 13, 18, 21, XX, and XY were 95.9%, 89.1%, 94.3%, 94.7%, and 98.7%, respectively. Of a total of 508 cases analyzed, 211 were aneuploid. All cases were correctly identified and no false results occurred (in comparison with karyotypic analysis), although maternal cell contamination was relatively common. Clinical screening for aneuploidy of chromosomes 13, 18, 21, X, and Y from interphase AF cells is possible with use of these probes and FISH. Cases of maternal cell contamination and mosaicism necessitate cautious interpretation. The FISH procedure is recommended for screening of common aneuploidies, followed by a complete chromosome analysis to detect anomalies.

Epididymal sperm aneuploidies in three strains of rats detected by multicolor fluorescence in situ hybridization

A multicolor fluorescence in situ hybridization (FISH) method was developed to detect aneuploidy and diploidy in epididymal sperm of rats using DNA probes specific for chromosomes 4 and Y. Fourteen healthy young-adult rats from three strains were evaluated: inbred Fisher 344/N/ehs, outbred Sprague-Dawley, and outbred WU Wistar/CPB. The hybridization efficiency of the FISH procedure was > 99.9%, the sex-ratio in sperm was approximately 1 as expected, and there was no significant variation among two independent scorers. No significant variations were detected within or among strains in the frequencies of sperm disomy for chromosome 4 (1-6.5 per 10,000 cell per animal) or the Y chromosome (0-2.5 per 10,000 cells per animal). There was a trend toward increased variation among Wistar rats. The frequencies of sperm-carrying hyper- and hypohaploidy for chromosome 4 were similar, suggesting a symmetrical mechanism of chromosome gain and loss during meiosis. The frequencies of Y-Y-4-4 sperm, which represent genomic meiosis II errors, did not differ significantly across strains (0.1-0.7 per 10,000 cells per strain). This FISH method for detecting aneuploidy in rat epididymal sperm provides a promising interspecies biomarker of male germ cell aneuploidy and introduces the rat as an animal model for investigating the heritable risk to offspring associated with paternal genotype, physiology, and exposure to environmental mutagens. There appear to be no significant differences among young healthy rats, mice, and men in the baseline frequencies of sperm with Y chromosomal disomy, the only chromosome for which data currently exists for all three species.

Estimation of aneuploidy for chromosomes 3, 7, 16, X and Y in spermatozoa from 10 normospermic men using fluorescence in-situ hybridization.

Fluorescence in-situ hybridization (FISH) is a fast and efficient method of estimating aneuploidy in human spermatozoa. In this study, we have estimated baseline disomy frequencies in spermatozoa from a group of 10 normospermic men, using stringent scoring criteria. A triple-probe FISH procedure was used for chromosomes 3, X and Y, while a double-probe FISH method was used for chromosomes 7 and 16. A total of 101273 spermatozoa were scored for chromosomes 3, X and Y, resulting in 97.83% haploidy (3X or 3Y), 0.39% disomy (33X, 33Y, 3XX, 3YY or 3XY) and 0.35% diploidy (33XX, 33YY or 33XY). A total of 100760 spermatozoa were scored for chromosomes 7 and 16, giving 98.9% haploidy (716), 0.11% disomy (7716 or 71616) and 0.27% diploidy (771616). Disomy frequencies for individual chromosomes differed (chromosome 3, 0.20%; chromosome 7, 0.05%, chromosome 16, 0.06%; X + Y, 0.19%). The frequency of disomy 3 was significantly higher than disomy 7 (P = 0.019) and disomy 16 (P = 0.022), while the frequency of sex chromosome disomy was significantly higher than disomy 7 (P = 0.0058) and disomy 16 (P = 0.0067), but not disomy 3 (P = 0.73). The disomy and diploidy (0.27-0.35%) estimates obtained for this normospermic population were generally low and were similar to other recent reports.

Application of fluorescence in situ hybridization to detect N-myc (MYCN) gene amplification on paraffin-embedded tissue sections of neuroblastomas.

Fluorescence in situ hybridization (FISH) was applied to neuroblastoma for detection of N-myc (MYCN) oncogene amplification, and the results were compared with Southern blot analysis (Southern). In nine neuroblastomas (formalin-fixed paraffin-embedded tissues were available in seven cases including two cases with touch preparations, and two cell lines), all five cases with N-myc amplification detected by Southern had cells with multiple N-myc signals by FISH, and three cases showed no N-myc amplification either by Southern or FISH procedure. One case, not examined by Southern, showed amplified signals of N-myc by FISH. These data indicate that FISH results for N-myc amplification have close correlation with Southern blot analysis. The chromosome 2-specific repetitive DNA probe was also applied for the analysis of ploidy by FISH. Six cases with N-myc amplification by Southern and/or FISH had diploid tumors and two cases without amplified N-myc showed aneuploidy. The remaining one case consisted of heterogeneous elements showing diploidy in undifferentiated tissue and both aneuploidy (ganglionic cells) and diploidy (Schwann cells) in differentiated area. We conclude that FISH is a practical, useful and reliable method over Southern especially for analysis of N-myc amplification in neuroblastoma, and simultaneous cohybridization with a specific chromosome probe is of great value in predicting the prognosis of patients.

Interphase cytogenetics of workers exposed to benzene.

Fluorescence in situ hybridization (FISH) is a powerful new technique that allows numerical chromosome aberrations (aneuploidy) to be detected in interphase cells. In previous studies, FISH has been used to demonstrate that the benzene metabolites hydroquinone and 1,2,4-benzenetriol induce aneuploidy of chromosomes 7 and 9 in cultures of human cells. In the present study, we used an interphase FISH procedure to perform cytogenetic analyses on the blood cells of 43 workers exposed to benzene (median = 31 ppm, 8-hr time-weighted average) and 44 matched controls from Shanghai, China. High benzene exposure (> 31 ppm, n = 22) increased the hyperdiploid frequency of chromosome 9 (p < 0.01), but lower exposure (< or = 31 ppm, n = 21) did not. Trisomy 9 was the major form of benzene-induced hyperdiploidy. The level of hyperploidy in exposed workers correlated with their urinary phenol level (r = 0.58, p < 0.0001), a measure of internal benzene dose. A significant correlation was also found between hyperdiploidy and decreased absolute lymphocyte count, an indicator of benzene hematotoxicity, in the exposed group (r = -0.44, p = 0.003) but not in controls (r = -0.09, p = 0.58). These results show that high benzene exposure induces aneuploidy of chromosome 9 in nondiseased individuals, with trisomy being the most prevalent form. They further highlight the usefulness of interphase cytogenetics and FISH for the rapid and sensitive detection of aneuploidy in exposed human populations.

Evidence for a parent-of-origin effect on sperm aneuploidy in mice carrying Robertsonian translocations as analyzed by fluorescence in situ hybridization

Multi-color fluorescence in situ hybridization (FISH) was employed to investigate variations in the frequency of aneuploid spermatids produced by males derived from three separate lines of Robertsonian translocations in mice: Rb(2.8)2Lub, Rb(8.12)22Lub, and Rb(8.14)16Rma, each with one arm involving chromosome 8. The DNA probes used were specific for repetitive sequences on chromosomes 8 and X. Heterozygous males for these Robertsonian translocations produced ~1% of spermatids with hyperhaploid for chromosome 8, which was > 80 times higher than the frequency of sperm hyperhaploid for chromosome X within the same animals; consistent elevations in chromosome-8 sperm disomy were observed among lines. In addition, ~25% higher fractions of sperm aneuploidy were observed when the Robertsonian translocation was inherited from the father rather than from the mother ( p = 0.009). These findings illustrate the sensitivity of the FISH procedure for detecting small differences in the hyperhaploidy in male germ cells and suggest that imprinted factors may influence sperm aneuploidy.

Differential sensitivity of 16S rRNA targeted oligonucleotide probes used for fluorescence in situ hybridization is a result of ribosomal higher order structure.

The use of 16S rRNA targeted gene probes for the direct analysis of microbial communities has revolutionized the field of microbial ecology, yet a comprehensive approach for the design of such probes does not exist. The development of 16S rRNA targeted oligonucleotide probes for use with fluorescence in situ hybridization (FISH) procedures has been especially difficult as a result of the complex nature of the rRNA target molecule. In this study a systematic comparison of 16S rRNA targeted oligonucleotide gene probes was conducted to determine if target location influences the hybridization efficiency of oligonucleotide probes when used with in situ hybridization protocols for the detection of whole microbial cells. Five unique universal 12-mer oligonucleotide sequences, located at different regions of the 16S rRNA molecule, were identified by a computer-aided sequence analysis of over 1000 partial and complete 16S rRNA sequences. The complements of these oligomeric sequences were chemically synthesized for use as probes and end labeled with either [gamma-32P]ATP or the fluorescent molecule tetramethylrhodamine-5/-6. Hybridization sensitivity for each of the probes was determined by hybridization to heat-denatured RNA immobilized on blots or to formaldehyde fixed whole cells. All of the probes hybridized with equal efficiency to denatured RNA. However, the probes exhibited a wide range of sensitivity (from none to very strong) when hybridized with whole cells using a previously developed FISH procedure. Differential hybridization efficiencies against whole cells could not be attributed to cell wall type, since the relative probe efficiency was preserved when either Gram-negative or -positive cells were used. These studies represent one of the first attempts to systematically define criteria for 16S rRNA targeted probe design for use against whole cells and establish target site location as a critical parameter in probe design.

High resolution multicolor fluorescence in situ hybridization using cyanine and fluorescein dyes: rapid chromosome identification by directly fluorescently labeled alphoid DNA probes.

We tested DNA probes directly labeled by fluorescently labeled nucleotides (Cy3-dCTP, Cy5-dCTP, FluorX-dCTP) for high resolution uni- and multicolor detection of human chromosomes and analysis of centromeric DNA organization by in situ hybridization. Alpha-satellite DNA probes specific to chromosomes 1, 2, 3, 4 + 9, 5 + 19, 6, 7, 8, 10, 11, 13 + 21, 14 + 22, 15, 16, 17, 18, 20, 22, X and Y were suitable for the accurate identification of human chromosomes in metaphase and interphase cells. Cy3-labeled probes had several advantages: (1) a high level of fluorescence (5-10 times more compared with fluorescein-labeled probes); (2) a low level of fluorescence in solution, allowing the detection of target chromosomes in situ during hybridization without the washing of slides; and (3) high resistance to photobleaching during prolonged (1-2 h) exposure to strong light, thus allowing the use of a high energy mercury lamp or a long integration time during image acquisition in digital imaging microscopy for the determination of weak signals. For di- and multicolor fluorescence in situ hybridization (FISH), we successfully used different combinations of directly fluorophorated probes with preservation of images by conventional microscopy or by digital imaging microscopy. FluorX and Cy3 dyes allowed the use of cosmid probes for mapping in a one-step hybridization experiment. Cyanine-labeled fluorophorated DNA probes offer additional possibilities for rapid chromosome detection during a simple 15-min FISH procedure, and can be recommended for basic research and clinical studies, utilizing FISH.

Combination of lamin immunocytochemistry and in situ hybridization for the analysis of chromosome copy numbers in tumor cell areas with high nuclear density.

We describe the application of lamin immunocytochemistry (ICC) and single- or double-target fluorescence in situ hybridization (FISH) on 4 microm thick frozen tissue sections as a method to facilitate scoring of aberrant chromosome copy numbers in colonic tumors. Analysis of FISH signals in colon tissue sections is often hampered by overlap and truncation of epithelial nuclei, due to the density of the epithelial cells. Furthermore, on the basis of nuclear staining it is often difficult to determine whether or not nuclei are overlapping, or adjoining. Therefore, reliable evaluation of (F)ISH signals to screen for genomic changes was until now mainly restricted to isolated nuclei obtained from relatively thick tissue sections. In this study the applicability of lamin ICC, to stain the nuclear periphery and to distinguish individual nuclei, combined with the FISH procedure is explored to solve this problem for colon epithelium. For ICC we applied the alkaline phosphatase (APase)-Fast Red detection method, since the fluorescent precipitate of this reaction resists extensive proteolytic digestion as needed for efficient FISH on tissue sections. Chromosome copy numbers could easily be determined in 4 microm thick frozen tissue sections by combining lamin ICC and FISH. The ratio of the copy numbers of the chromosomes 7 and 17 could be determined in frozen tissue sections after combined lamin ICC and double-target FISH. It is concluded that the combination of lamin ICC and FISH improves chromosome copy number analysis and can be used to investigate genomic changes in different tumor compartments in thin frozen tissue sections.

Prenatal diagnosis of trisomy 21 using interphase fluorescence in situ hybridization of post‐replicated cells with site‐specific cosmid and cosmid contig probes

Interphase fluorescence in situ hybridization (FISH) with chromosome 21-specific cosmid clones was used to identify trisomy 21 in cultured and uncultured amniotic cells. Two novel site-specific cosmid clones (regions 21q22 and 21qtel) were compared with a cosmid contig (Zheng et al., 1992). Correct identification of chromosome 21 copy number was made in 65-75 per cent of trisomic cells and in 70-75 per cent of normal disomic cells by using all the tested probes. However, the chromosome 21-specific telomeric probe (cos 17F8) showed the best results due to more intense and clearly visible hybridization. Utilization of a directly fluorophorated telomeric probe using Cy3-dCTP and FluorX-dCTP allows accurate detection of chromosome 21 in a fast 'one-step' FISH procedure on uncultured interphase nuclei. In addition, we compared the efficacy of FISH analysis for the total population of interphase cells and cells in the post-replication (late S, G2) periods of the cell cycle. Selective scoring of cells in the post-replicative period (showing a pair of hybridization signals on each chromatid of the replicated interphase chromosome) increased the number of informative nuclei by up to 95-97 per cent. This approach allows cells with overlapping chromosomes, artificial double hybridization signals on separate chromatids in interphase chromosomes, background hybridization, and polyploid cells to be analysed. Application of directly labelled telomeric cosmid probes and integral analysis of hybridized nuclei in the pre- and post-replication periods of the cell cycle may help to further improve the prenatal detection of trisomy 21.

Genetic diagnosis using polymerase chain reaction and fluorescent in-situ hybridization analysis of biopsied cells from both the cleavage and blastocyst stages of individual cultured human preimplantation embryos

Cultured human preimplantation embryos have been used to develop methods which allow preimplantation genetic diagnosis (PGD) analyses by polymerase chain reaction (PCR) and fluorescent in-situ hybridization (FISH) on biopsied blastomeres and trophectoderm cells from the same embryo. An experimental design is described and experiments undertaken, which demonstrate the feasibility of extending biopsy and PGD procedures currently in use. We have shown that dual-stage biopsies are possible, and that the PCR and FISH analyses of the biopsied cell samples are effective. One to two blastomeres were biopsied from an 8- to 10-cell embryo and processed for the simultaneous PCR amplification of a beta-globin and a cytosine adenine (CA) repeat sequence, or a Y chromosome sequence. FISH procedures were also used to detect the presence of Y chromosome markers. The biopsied cleavage-stage embryo can be cultured to the blastocyst stage, where the serial biopsy of three to five mural trophectoderm cells provides two further cell samples. These can be used to repeat and/or undertake additional PGD analyses. The biopsied blastocyst is either used to confirm earlier diagnoses, or placed in culture for a further 4-24 h. Maintenance of a blastocoele cavity, hatching and formation of an outgrowth demonstrates continuing viability following the dual-stage biopsy procedures. The PCR DNA amplification procedures are effective at the cellular level for both biopsied blastomeres and mural trophectoderm cells. The FISH techniques have shown a definitive Y signal in 50% (one out of two) and 100% (two out of two) of the biopsied blastomeres and 72% (two out of three, four out of five and 7 out of 10) for the trophectoderm cell nuclei. Preliminary experiments have demonstrated that the FISH preparations can be re-amplified to improve the signal, and dual fluorescent procedures using the X and Y probes are effective. A retrospective PCR analysis has also been undertaken on preparations of biopsied cells which were previously used for PGD analysis by FISH.

Identification of the sex of human preimplantation embryos in two hours using an improved spreading method and fluorescent in-situ hybridization (FISH) using directly labelled probes

Dual fluorescent in-situ hybridization (FISH) using X and Y chromosome specific probes has been used to identify the sex of human embryos for preimplantation diagnosis of X-linked disease. With a modified spreading method and directly labelled fluorescent DNA probes, we have examined the possibility of reducing the time of the FISH procedure from 7 to 2 h. A total of 17 normally fertilized human embryos were disaggregated and 98 intact blastomeres obtained. The spreading efficiency was 96% and FISH signals were obtained from 97% of nuclei. In all cases, sibling blastomeres from the same embryo were the same sex. Mosaicism was observed in some embryos. Five cells which lysed during the disaggregation process were spread to determine whether FISH was possible in these cells, but in all cases the morphology of the nuclei was poor and multiple signals were observed so that reliable diagnosis of sex was not possible. The data reported here confirm that by using an improved spreading method in combination with directly labelled DNA probes, we have increased the efficiency and reduced the time required for sexing embryos for preimplantation diagnosis of X-linked disease.