Genetic analysis of embryo in a human case of spontaneous oocyte activation: a case report

Parthenogenesis, a unique form of reproduction, is normally inhibited in mammals and a human embryo with parthenogenetic origin is not considered capable of producing offspring. The aim of this report is to analyze a parthenogenetic oocyte retrieved from a patient so as to have a better understanding on parthenogenesis and causes of infertility. A 38-year-old woman presented at our center with a history of primary infertility for 10 years and underwent an IVF-ICSI cycle. Three MII oocytes retrieved and one of which presented with 1 pronucleus before conducting ICSI and developed into an embryo 30 h post-retrieval. Blastomere biopsy, genome amplification, copy number variation (CNV) analysis and MultiSNPs analysis was performed on the embryo. The results showed that only one blastomere contains DNA and CNV analysis indicated a genotype of 48, XX, +17, +17 and the genetic contribution of biopsied embryo was of exclusively maternal origin. Such analysis might be beneficial for patients with a history of oocyte spontaneous activation in diagnosing case-specific aberrations and providing individualized therapeutic strategies such as preimplantation genetic diagnosis to choose a genetic normal embryo to transplant.

Single Cell Restriction Enzyme-Based Analysis of Methylation at Genomic Imprinted Regions in Preimplantation Mouse Embryos

The methylation of cytosines in DNA is a fundamental epigenetic regulatory mechanism. During preimplantation development, mammalian embryos undergo extensive epigenetic reprogramming, including the global erasure of germ cell-specific DNA methylation marks, to allow for the establishment of the pluripotent state of the epiblast. However, DNA methylation marks at specific regions, such as imprinted gene regions, escape this reprogramming process, as their inheritance from germline to soma is paramount for proper development. To study the dynamics of DNA methylation marks in single blastomeres of mouse preimplantation embryos, we devised a new approach-single cell restriction enzyme analysis of methylation (SCRAM). SCRAM allows for reliable, fast, and high-throughput analysis of DNA methylation states of multiple regions of interest from single cells. In the method described below, SCRAM is specifically used to address loss of DNA methylation at genomic imprints or other highly methylated regions of interest.

Pronuclear transfer in human embryos to prevent transmission of mitochondrial DNA disease

Mutations in mitochondrial DNA (mtDNA) are a common cause of genetic disease. Pathogenic mutations in mtDNA are detected in approximately 1 in 250 live births and at least 1 in 10,000 adults in the UK are affected by mtDNA disease. Treatment options for patients with mtDNA disease are extremely limited and are predominantly supportive in nature. Mitochondrial DNA is transmitted maternally and it has been proposed that nuclear transfer techniques may be an approach for the prevention of transmission of human mtDNA disease. Here we show that transfer of pronuclei between abnormally fertilized human zygotes results in minimal carry-over of donor zygote mtDNA and is compatible with onward development to the blastocyst stage in vitro. By optimizing the procedure we found the average level of carry-over after transfer of two pronuclei is less than 2.0%, with many of the embryos containing no detectable donor mtDNA. We believe that pronuclear transfer between zygotes, as well as the recently described metaphase II spindle transfer, has the potential to prevent the transmission of mtDNA disease in humans.

[Distribution of foreign mitochondrial DNA during the first splittings of the transmitochondrial mouse embryos]

Distribution of human mitochondrial DNA (mtDNA) among separate murine blastomeres was analyzed during the splitting of embryos in which the suspension of human mitochondria had been injected at the one- or two-cell stage. Human mtDNA was detected by PCR with species specific primers. The total amount of the two- and four-cell murine embryos analyzed in the study was 339. In all embryos examined the copies of human mitochondrial genome were revealed along with murine mtDNA, which indicated the phenomenon of an artificially modeled heteroplasmy. The foreign mtDNA was not ubiquitous among the blastomeres of transmitochondrial embryos. Mathematical analysis of the results showed that in the period between the injection of human mitochondria and the subsequent splitting no equal distribution of the human mtDNA occurred in the cytoplasm. These results also point at the presence of more than 2-3 segregation units of mtDNA in the entire pool of mitochondria (about 5 x 10(2)) introduced into an embryo by microinjection.

Single Cell Polymerase Chain Reaction for Preimplantation Genetic Diagnosis

We provide an overview of the methodology involved in single cell polymerase chain reaction (PCR), especially for single lymphocytes or cultured lymphoblasts and blastomeres. The first step toward single cell PCR is isolation of single cells; the protocols given can be carried out using basic instruments such as a stereomicroscope. We also describe the alkaline lysis method for cell lysis as well as the design and execution of single cell PCR, either in simplex or in multiplex. Finally, we briefly discuss the different methods for analyzing PCR products and obtaining an accurate diagnosis. Special attention is given to measures that avoid contamination with extraneous DNA and reduce allele dropout.

Fluorescence In Situ Hybridization on Single Cells

Fluorescence in situ hybridization (FISH) is the technique of choice for preimplantation genetic diagnosis (PGD) selection of female embryos in families with X-linked disease, for which there is no mutation-specific test. FISH with target-specific DNA probes is also the primary technique used for PGD detection of chromosome imbalance associated with Robertsonian translocations, reciprocal translocations, inversions, and other chromosome rearrangements, because the DNA probes, labeled with different fluorochromes or haptens, detect the copy number of their target loci. The methods described outline strategies for PGD for sex determination and chromosome rearrangements. These methods are assessment of reproductive risks, the selection of suitable probes for interphase FISH, spreading techniques for blastomere nuclei, and in situ hybridization and signal scoring using directly labeled and indirectly labeled probes.

Single-cell chromosomal imbalances detection by array CGH

Genomic imbalances are a major cause of constitutional and acquired disorders. Therefore, aneuploidy screening has become the cornerstone of preimplantation, prenatal and postnatal genetic diagnosis, as well as a routine aspect of the diagnostic workup of many acquired disorders. Recently, array comparative genomic hybridization (array CGH) has been introduced as a rapid and high-resolution method for the detection of both benign and disease-causing genomic copy-number variations. Until now, array CGH has been performed using a significant quantity of DNA derived from a pool of cells. Here, we present an array CGH method that accurately detects chromosomal imbalances from a single lymphoblast, fibroblast and blastomere within a single day. Trisomy 13, 18, 21 and monosomy X, as well as normal ploidy levels of all other chromosomes, were accurately determined from single fibroblasts. Moreover, we showed that a segmental deletion as small as 34 Mb could be detected. Finally, we demonstrated the possibility to detect aneuploidies in single blastomeres derived from preimplantation embryos. This technique offers new possibilities for genetic analysis of single cells in general and opens the route towards aneuploidy screening and detection of unbalanced translocations in preimplantation embryos in particular.

The "spanning protocol": a new DNA extraction method for efficient single-cell genetic diagnosis

PURPOSE

We evaluated methods of preparation of DNA from single cells for amplification and preimplantation genetic diagnosis (PGD), including our "spanning protocol."

METHODS

Dystrophin gene exons 45 and 51 were amplified by nested polymerase chain reaction (PCR) from a single lymphocyte or blastomere. Amplification efficiencies were compared between DNA extraction by (A) lysis in distilled water with freeze-thawing and boiling; (B) two-step lysis involving potassium hydroxide and dithiothreitol; and (C) the spanning protocol, using N-lauroylsarcosine.

RESULTS

With method A, amplification efficiency was 66/120 (55%) and false-positive such as amplification failure or allele drop out was 42/120 (35%); with B, 96/120 (80%) and 21/120 (17.5%); and with C, 111/120 (92%) and 5/120 (4.2%), using single blastomeres and unaffected lymphocytes from male. Occurrence of false-negative such as contamination of another DNA with method A was 4/120 (3.3%); with B, 10/120 (8.3%); and with C, 2/120 (1.7%) from using single lymphocytes from affected males.

CONCLUSION

The spanning protocol was most efficient for extracting DNA from a single cell and should be particularly useful for preimplantation genetic diagnosis.

Body composition, dietary carbohydrates and fatty acids determine post-fertilisation development of bovine oocytes in vitro

This study assessed the interactive effects of carbohydrate type (fibre vs starch) and fatty acid (FA) supplementation (0% vs 6% calcium soaps of palm oil FA) on the post-fertilisation development of oocytes recovered from low and moderate body condition score (BCS) heifers. A secondary objective was to compare the FA composition of plasma to that of granulosa cells (GCs) and cumulus–oocyte complexes (COCs) from these animals, and to relate these findings to the developmental potential of oocytes. Plasma, GCs and COCs were recovered from 32 heifers on day 5 of a synchronised oestrous cycle for FA analyses. Oocytes were also recovered on days 10 and 15 of the same cycle after short-term ovarian stimulation (FSH + GnRH), and matured, fertilised and cultured to the blastocyst stagein vitro. High levels of dietary starch increased (P< 0.01) plasma insulin but, together with dietary FA, reduced (P< 0.05) blastocyst yields in low, but not in moderate, BCS heifers. Diet-induced alterations to the FA content of plasma were less apparent in GCs and COCs. In summary, although dietary lipids increased the FA content of COCs, the selective uptake of saturated FAs at the expense of mainly polyunsaturated FAs within the follicular compartment ensured that the FA composition of COCs was largely unaffected by diet. However, the concentration of saturated FAs within COCs was inherently high, and so further increases in FA content may have impaired post-fertilisation development. The data establish a robust nutritional framework for more detailed studies into the mechanistic effects of dietary composition on the post-fertilisation developmental potential of oocytes.

Microarray analysis of localization of maternal transcripts in eggs and early embryos of the ascidian, Ciona intestinalis

The establishment of body axes and specification of early embryonic cells depend on maternally supplied transcripts and/or proteins, several of which are localized at specific regions of fertilized eggs and early embryos. The ascidian is known to exhibit a mosaic mode of development, and this mode is largely dependent on localized maternal factors. Using blastomere isolation, microarray and whole-mount in situ hybridization, the present study of Ciona intestinalis demonstrates that maternal transcripts of a total of 17 genes are localized at the posterior-most region of fertilized eggs and early embryos. Ten of them are newly identified in the present study, while the remaining seven genes have already been characterized in previous studies. In addition, maternal transcripts of two genes, in addition to 14 genes encoded by the mitochondrial genome, showed a mitochondria-like distribution. Despite the present comprehensive approach, we could not identify maternal transcripts that are clearly localized to the animal-pole side, the vegetal-pole side, the anterior-side or other specific regions of the early embryo. Therefore, we concluded that the posterior-most localization and mitochondria-like distribution appear to be major specialized patterns of maternal transcripts in early Ciona embryos.

Sexing using single blastomere derived from IVF bovine embryos by fluorescence in situ hybridization (FISH)

Fluorescence in situ hybridization (FISH) is a sensitive technique for molecular diagnosis of chromosomes on single cells and can be applied to sex determination of embryos. The objective has been to develop an accurate and reliable bovine Y chromosome-specific DNA probe in order to sex biopsed blastomeres derived from IVF bovine embryos by FISH. Bovine Y chromosome-specific PCR product derived from BtY2 sequences was labeled with biotin-16-dUTP (BtY2-L1 probe), and FISH was performed on karyoplasts of biopsed blastomeres and matched demi-embryos. Our FISH signal was clearly detected in nuclei of blastomeres of male embryos. FISH analysis of bovine embryos gave high reliability (96%) between biopsied blastomeres and matched demi-embryos. These results indicated that the BtY2-L1 bovine Y chromosome-specific FISH probe was an effective probe for bovine embryo sexing, and the FISH technique of probe detection could improve the efficiency and reliability.

Rapid sexing of bovine preimplantation embryos using loop-mediated isothermal amplification

Loop-mediated isothermal amplification (LAMP) is a novel DNA amplification method that amplifies a target sequence specifically under isothermal conditions. The product of LAMP is detected by the turbidity of the reaction mixture without electrophoresis. The objective of this study was to develop a rapid sexing method for bovine preimplantation embryos using LAMP. The first experiment was conducted to optimize the DNA extraction method for LAMP-based embryo sexing. The DNA of single blastomeres was extracted using three methods: heat, NaOH, and proteinase K-Tween 20 (PK-TW) treatments. Sexing was performed with two LAMP reactions, male-specific and male-female common reaction, after DNA extraction. The rates of correct determination of sex were 88.9-94.4%, with no difference among methods. The sensitivity and accuracy of LAMP-based embryo sexing were evaluated in the next experiment. The proportion of samples in which the sex was correctly determined was 75-100% for one to five biopsied cells. Lastly, in vivo-derived embryos were examined to verify the usefulness of LAMP-based embryo sexing, and some of these fresh, sexed embryos were transferred into recipient animals. The time needed for sexing was <1 h. The pregnancy rate was 57.4% and all calves born were of the predicted sex (12 male and 21 female). Therefore, LAMP-based embryo sexing accurately determined gender and is suitable for field application.

Real-time PCR for single-cell genotyping in sickle cell and thalassemia syndromes as a rapid, accurate, reliable, and widely applicable protocol for preimplantation genetic diagnosis

Sickle-cell and beta-thalassemia syndromes are priority genetic diseases for prevention programs involving population screening with the option of prenatal diagnosis for carrier couples. Preimplantation genetic diagnosis (PGD) represents a specialized alternative to prenatal diagnosis and is most appropriately used for couples with an unsuccessful reproductive history and/or undergoing assisted reproduction. However, clinical application of PGD has been hindered by difficulties in reliably transferring molecular diagnostic protocols to the single-cell level. We standardized and validated a protocol involving first-round multiplex PCR, amplifying the region of the beta-globin gene containing most of the common disease mutations world-wide and two unlinked microsatellite markers (GABRB3 and D13S314), followed by: 1) analysis of beta-globin genotypes with real-time PCR and 2) microsatellite sizing to exclude chance contamination. The protocol was standardized on 100 single lymphocytes from a beta-thalassemia heterozygote, including 15 artificially contaminated samples, the latter demonstrated through microsatellite analysis. PCR failure and allele drop-out (ADO) were observed in one (uncontaminated) sample each (1.2%). A pilot study in six clinical PGD cycles with five different beta-globin genotype interactions achieved results (in 5-6 hr) in 46 out of 50 single blastomeres (92%), all concordant with results from an established PGD method applied simultaneously; microsatellite analysis detected only parental alleles, excluding contamination. Beta-globin genotypes were also confirmed in two blastomeres through prenatal diagnosis (twin pregnancy), and in 11 out of 12 spare embryos, revealing one incident of ADO. Overall, the protocol proved to be sensitive, accurate, reliable, rapid, and applicable for many genotype interactions, with internal monitoring of contamination, thus fulfilling all requirements for clinical PGD application.

Single-cell sequencing and mini-sequencing for preimplantation genetic diagnosis

There is increasing interest in the use of preimplantation genetic diagnosis (PGD) as an alternative to routine prenatal diagnosis. However, the costs associated with development and testing of new PGD protocols have forced some PGD centres to limit the number of diseases for which PGD is offered. One of the main factors in the design of new protocols, which affects cost and accuracy, is the choice of the mutation-detection technique. We have assessed the reliability of DNA sequencing and mini-sequencing for clinical diagnosis at the single-cell level and have found them to be rapid and accurate. Extensive optimisation for individual mutations is not usually necessary when employing these versatile techniques and consequently a smaller investment of time and resources should be required during development of new protocols. Additionally, we report single-cell protocols for the diagnoses of cystic fibrosis, sickle cell anaemia and beta-thalassaemia, which utilise mini-sequencing. Unlike most mutation-detection techniques, mini-sequencing permits analysis of very small DNA fragments. Small amplicons experience low allele dropout (ADO) rates, and consequently this approach could potentially improve the reliability of PGD.

The fragilis interferon-inducible gene family of transmembrane proteins is associated with germ cell specification in mice

BACKGROUND

Specification of primordial germ cells in mice depends on instructive signalling events, which act first to confer germ cell competence on epiblast cells, and second, to impose a germ cell fate upon competent precursors. fragilis, an interferon-inducible gene coding for a transmembrane protein, is the first gene to be implicated in the acquisition of germ cell competence.

RESULTS

Here, we describe four additional fragilis-related genes, fragilis2-5, which are clustered within a 68 kb region in the vicinity of the fragilis locus on Chr 7. These genes exist in a number of mammalian species, which in the human are also clustered on the syntenic region on Chr 11. In the mouse, fragilis2 and fragilis3, which are proximate to fragilis, exhibit expression that overlaps with the latter in the region of specification of primordial germ cells. Using single cell analysis, we confirm that all these three fragilis-related genes are predominant in nascent primordial germ cells, as well as in gonadal germ cells.

CONCLUSION

The Fragilis family of interferon-inducible genes is tightly associated with germ cell specification in mice. Furthermore, its evolutionary conservation suggests that it probably plays a critical role in all mammals. Detailed analysis of these genes may also elucidate the role of interferons as signalling molecules during development.

Furrow-specific endocytosis during cytokinesis of zebrafish blastomeres

Mutations affecting endocytosis, such as those in clathrin and dynamin, unexpectedly cause defects in cytokinesis in a number of organisms. To explore the relationship between endocytosis and cytokinesis, we used the relatively large cells of the transparent zebrafish embryo. Using fluorescent markers for fluid-phase as well as plasma membrane uptake, we demonstrate that cytokinesis involves furrow-specific endocytosis. Clathrin-coated pits are visible near the furrow in ultrathin sections, while immunolabeling demonstrates that clathrin and caveolin are localized to the cleavage furrow. Hence, it is likely that both clathrin- and caveolae-mediated endocytosis occurs at the furrow during cytokinesis. Dynamin II is also localized to the furrow and may mediate furrow-specific endocytosis. Treatment of embryos with chlorpromazine or with methyl-beta-cyclodextrin, both of which inhibit endocytosis, prevents the normal completion of cytokinesis. These data suggest that furrow-specific endocytosis is an integral part of cytokinesis.

Sex determination of bovine embryo blastomeres by fluorogenic probes

One of the major challenges of using genetic information in marker assisted selection (MAS) is the detection of multiple marker loci from a small biopsy sample of a preimplantation stage embryo. The objective of this study was to develop a fast, nested, multiplex preamplification, polymerase chain reaction (PCR) method for the determination of sex in bovine embryo blastomeres. For this aim, ZFX/ZFY sequences were preamplified simultaneously with other genomic regions. The preamplification product was used as a template in an allelic discrimination assay, with nested primers and sex specific fluorogenic probes for ZFX and ZFY. Fluorogenic probes were used to eliminate the need for time consuming electrophoresis. Compared to sexing with Bovy/kappa-casein co-amplification method and other replicates from the same embryo, the accuracy of sexing with the use of fluorogenic probes after preamplification was 99% (112/113 blastomeres). The amplification efficiency was 96% (113/117 blastomeres).

Preimplantation genetic diagnosis for familial amyloidotic polyneuropathy (FAP)

Preimplantation genetic diagnosis (PGD) was developed more than a decade ago to offer an alternative to prenatal diagnosis for couples at risk of transmitting an inherited disease to their offspring. Portuguese-type familial amyloidotic polyneuropathy (FAP type I), is an autosomal dominant disease presenting an inherited mutation in the gene encoding the plasma protein transthyretin (TTR). We here report the first protocol for single-cell detection of the Met30 mutation in FAP type I and its application to PGD. A nested PCR reaction for exon 2 of the TTR gene was developed. The PCR product was then analysed by restriction enzyme analysis and SSCP allowing the detection of the point mutation. Ten clinical cycles were performed in seven couples. From the 93 metaphase II (MII) injected oocytes, 82 were normally fertilized and 78 were biopsied. A positive signal in the nested PCR reaction was obtained in 61 blastomeres, corresponding to a DNA amplification efficiency of 78.2%. No allele dropout (ADO) or contamination were detected. A biochemical pregnancy was obtained in three cases and a clinical pregnancy in one couple is actually in normal evolution.

Rapid sexing of preimplantation bovine embryo using consecutive and multiplex polymerase chain reaction (PCR) with biopsied single blastomere

The objective of this study was to establish a rapid and reliable PCR method for the sexing of 8- to 16-cell stage bovine embryos. The BOV97M and bovine 1.715 satellite DNA sequences were selected for amplification of male- and bovine-specific DNA, respectively. But the unequal number of copies of these two repetitive sequences required some modification of the multiplex PCR method. In consecutive and multiplex PCR, the first 10 PCR cycles were done with male-specific primer followed by an additional 23 cycles with bovine-specific primer. In this PCR method, the appearance of male- and bovine-specific bands was independent of the DNA concentration. This PCR method was applied successfully using groups of 8, 4, 2, and 1 blastomeres dissociated from the embryos, and the sexing efficiency was 100.0, 96.3, 94.3 and 92.1%, respectively. The coincident rate of sex determination between biopsied single blastomere and matched blastocyst was 90.0%. Therefore the developmental potential from 8- to 16-cell stage embryos to the blastocyst stage was not significantly different (P>0.2) for intact embryo (42.3%) than for demi-embryos (53.8%), suggesting that trauma to the demi-embryo caused by single-blastomere aspiration using a bevelled micropipette was very small. In conclusion, we developed a rapid (within 2 hours) and effective PCR method for the sexing of 8- to 16-cell stage bovine embryos using a single blastomere.

First unaffected pregnancy using preimplantation genetic diagnosis for sickle cell anemia

CONTEXT

Sickle cell anemia is a common autosomal recessive disorder. However, preimplantation genetic diagnosis (PGD) for this severe genetic disorder previously has not been successful.

OBJECTIVE

To achieve pregnancy with an unaffected embryo using in vitro fertilization (IVF) and PGD.

DESIGN

Laboratory analysis of DNA from single cells obtained by biopsy from embryos in 2 IVF attempts, 1 in 1996 and 1 in 1997, to determine the genetic status of each embryo before intrauterine transfer.

SETTING

University hospital in a large metropolitan area.

PATIENTS

A couple, both carriers of the recessive mutation for sickle cell disease.

INTERVENTIONS

Standard IVF treatment, intracytoplasmic sperm injection, embryo biopsy, single-cell polymerase chain reaction and DNA analyses, embryo transfer to uterus, pregnancy confirmation, and prenatal diagnosis by amniocentesis at 16.5 weeks' gestation.

MAIN OUTCOME MEASURE

DNA analysis of single blastomeres indicating whether embryos carried the sickle cell mutation, allowing only unaffected or carrier embryos to be transferred.

RESULTS

The first IVF attempt failed to produce a pregnancy. Of the 7 embryos analyzed in the second attempt, PGD indicated that 4 were normal and 2 were carriers; diagnosis was not possible in 1. Three embryos were transferred to the uterus on the fourth day after oocyte retrieval. A twin pregnancy was confirmed by ultrasonography, and subsequent amniocentesis revealed that both fetuses were unaffected and were not carriers of the sickle cell mutation. The patient delivered healthy twins at 39 weeks' gestation.

CONCLUSION

This first unaffected pregnancy resulting from PGD for sickle cell anemia demonstrates that the technique can be a powerful diagnostic tool for carrier couples who desire a healthy child but wish to avoid the difficult decision of whether to abort an affected fetus.

Requirement of Cdk2-cyclin E activity for repeated centrosome reproduction in Xenopus egg extracts

The abnormally high number of centrosomes found in many human tumor cells can lead directly to aneuploidy and genomic instability through the formation of multipolar mitotic spindles. To facilitate investigation of the mechanisms that control centrosome reproduction, a frog egg extract arrested in S phase of the cell cycle that supported repeated assembly of daughter centrosomes was developed. Multiple rounds of centrosome reproduction were blocked by selective inactivation of cyclin-dependent kinase 2-cyclin E (Cdk2-E) and were restored by addition of purified Cdk2-E. Confocal immunomicroscopy revealed that cyclin E was localized at the centrosome. These results demonstrate that Cdk2-E activity is required for centrosome duplication during S phase and suggest a mechanism that could coordinate centrosome reproduction with cycles of DNA synthesis and mitosis.

Detection of benzo[a]pyrene diol epoxide-DNA adducts in embryos from smoking couples: evidence for transmission by spermatozoa

Tobacco smoking is deleterious to reproduction. Benzo[a]pyrene (B[a]P) is a potent carcinogen in cigarette smoke. Its reactive metabolite induces DNA-adducts, which can cause mutations. We investigated whether B[a]P diol epoxide (BPDE) DNA adducts are detectable in preimplantation embryos in relation to parental smoking. A total of 17 couples were classified by their smoking habits: (i) both partners smoke; (ii) wife non-smoker, husband smokes; and (iii) both partners were non-smokers. Their 27 embryos were exposed to an anti-BPDE monoclonal antibody that recognizes BPDE-DNA adducts. Immunostaining was assessed in each embryo and an intensity score was calculated for embryos in each smoking group. The proportion of blastomeres which stained was higher for embryos of smokers than for non-smokers (0.723 versus 0.310). The mean intensity score was also higher for embryos of smokers (1.40+/-0.28) than for non-smokers (0.38+/-0.14; P = 0.015), but was similar for both types of smoking couples. The mean intensity score was positively correlated with the number of cigarettes smoked by fathers (P = 0.02). Increased mean immunostaining in embryos from smokers, relative to non-smokers, indicates a relationship with parental smoking. The similar levels of immunostaining in embryos from both types of smoking couples suggest that transmission of modified DNA is mainly through spermatozoa. We confirmed paternal transmission of modified DNA by detection of DNA adducts in spermatozoa of a smoker father and his embryo.

A role for Rho-like GTPases in the polarisation of mouse eight-cell blastomeres

Polarisation of cells during mouse preimplantation development first occurs within blastomeres at the eight-cell stage, as part of a process called compaction. Cell-cell contact mediated by the cell adhesion molecule uvomorulin (E-cadherin) and the activity of the microfilament cytoskeleton are important in the development of compaction, which is crucial for establishment of trophoblast and pluriblast (inner cell mass) lineages and for subsequent development. Members of the Rho family of p21 GTPases have been shown to regulate the organisation of the actin cytoskeleton and adhesion in other cell types. The potential role of these proteins in compaction was investigated. Inhibition of Rho with Clostridium botulinum C3-transferase disturbed intercellular flattening at compaction and prevented cytocortical microfilament polarisation of eight-cell blastomeres, in contrast to cytochalasin D which inhibited only adhesion. Microinjection of a constitutively activated recombinant Rho protein into four-cell blastomeres induced cortical microfilament disruption and apical displacement of nuclei associated with polarised clustering of microtubules. Interblastomere adhesion was reduced and E-cadherin was aberrently clustered at remaining cell-cell contacts. Similarly, activated Cdc42 protein induced nuclear displacement with additional cytoplasmic actin bundle formation between nucleus and cell-cell contacts. The effects produced by both of the activated GTPase proteins are indicative of prematurely induced but aberrently organised polarity. These results suggest that Rho family GTPases are involved in the polarisation of early mouse blastomeres.

Furrow-associated microtubule arrays are required for the cohesion of zebrafish blastomeres following cytokinesis

During the first few cleavages of the zebrafish embryo, daughter blastomeres are loosely associated immediately after furrow ingression, but then gradually cohere. Cohesion appears to be cadherin-dependent, as cadherin and beta-catenin are found at the membrane between cohering blastomeres, and blastomeres fail to cohere in calcium-free medium. Cadherin and beta-catenin are not initially found on the blastomere surface, but are deposited specifically at the furrow surface. An array of parallel microtubules is present on either side of the furrow tip during ingression, as seen by confocal microscopy of alpha-tubulin labelled embryos. Transient incubation of embryos in 1 microg/ml nocodazole at the start of furrowing, which causes a loss of the furrow array, inhibits the localization of beta-catenin to the furrow surface but does not prevent furrow ingression. During ingression, intracellular membranes are transported to the furrow, as shown by labelling with DiD or DiOC6(3). Concentration of these membranes near the furrow surface is microtubule-dependent. These findings suggest that microtubules are required for cohesion of blastomeres because they mediate trafficking of intracellular membranes to the furrow surface, where they are exocytosed and allow cohesion via cadherins.

Autonomous activation of histone H1 kinase, cortical activity and microtubule organization in one- and two-cell mouse embryos

The activation of M-phase promoting factor (MPF) in one-cell mouse embryo is independent from the nucleus. Other autonomous phenomena include the cortical activity observed at the end of the first cell cycle and the reorganization of the microtubule network. Here, we observed that the autonomous control of MPF activation is present also in two-cell mouse embryos (H1 kinase activity being higher in the first than in the second cell cycle). Moreover, the disappearance of the cortical activity in anucleated halves is observed when MPF activation takes place. The rounding up of the cytoplast and the mitotic reorganization of the microtubule network correlates with the maximum activity of H1 kinase in anucleated halves from one-cell embryos. In anucleated halves of two-cell stage blastomeres neither the cortical activity nor the microtubule reorganization were observed. The degree of activation of histone H1 kinase, and, as a consequence, the cortical activity and the microtubule reorganization, does not depend on the distribution of cyclin B. Finally, the level of cyclin B synthesis is similar in anucleated and nucleated halves derived from both one- and two-cell embryos.

Medial cell mixing during axial morphogenesis of the amphibian embryo requires cadherin function

A truncated form of Xenopus E-cadherin (deltaE-cad) comprising the cytoplasmic and transmembrane domains was overexpressed generating a dominant negative mutation in the urodelan amphibian embryo Pleurodeles waltl. deltaE-cad mRNA and rhodamine-lysinated-dextran (RLDx) cell lineage tracer were microinjected into 32-cell stage blastomeres which contribute principally to the notochord and central nervous system. deltaE-cad expression causes defects in forebrain and hindbrain formation coupled with the development of supernumerary vesicles. Duplication of the notochord also occurs due to the retardation of medial cell intercalation with correlated duplications of spinal cord and somites. These results emphasize the role of cadherins in mediating cell-cell adhesion in early amphibian embryogenesis. They extend to Pleurodeles the observations made in Xenopus, illustrating that despite differences in morphogenetic processes, the molecular mechanisms are conserved in these two species.

Spectral imaging in preconception/preimplantation genetic diagnosis of aneuploidy: multicolor, multichromosome screening of single cells

PURPOSE

Our purpose was to evaluate the utility of spectral imaging for multicolor, multichromosome enumeration in human interphase cell nuclei.

METHODS

Chromosome-specific probes labeled with different fluorochromes or nonfluorescent haptens were obtained commercially or prepared in-house. Metaphase spreads, interphase lymphocytes, or blastomeres cells were hybridized with either 7 or 11 distinctly different probes. Following 46 hr of hybridization, slides were washed and detected using either a filter-based quantitative image processing system (QUIPS) developed in-house or a commercial spectral imaging system.

RESULTS

The filter-based fluorescence microscope system is preferred for simultaneous detection of up to seven chromosome targets because of its high sensitivity and speed. However, this approach may not be applicable to interphase cells when 11 or more targets need to be discriminated. Interferometer-based spectral imaging with a spectral resolution of approximately 10 nm allows labeling of chromosome-specific DNA probes with fluorochromes having greatly overlapping emission spectra. This leads to increases in the number of fluorochromes or fluorochrome combinations available to score unambiguously chromosomes in interphase nuclei.

CONCLUSIONS

Spectral imaging provides a significant improvement over conventional filter-based microscope systems for enumeration of multiple chromosomes in interphase nuclei, although further technical development is necessary in its application to embryonic blastomeres. When applied to preconception/preimplantation genetic diagnosis, presently available probes for spectral imaging are expected to detect abnormalities responsible for 70-80% of spontaneous abortions caused by chromosomal trisomies.

Do alterations in the sex ratio occur at fertilization? A case report using fluorescent in situ hybridization

PURPOSE

The mechanisms by which the sex ratio might be altered at fertilization were reviewed, following a case of preimplantation gender analysis revealing a significantly skewed proportion of male-to-female embryos.

METHODS

The case of a known carrier of X-linked hydrocephalus with a history of three affected male pregnancies is presented. Her husband's family history consisted of a strong increase in the number of males relative to females. She had four cycles of stimulated in vitro fertilization, with sex chromosome analysis using fluorescent in situ hybridization (FISH) on suitable cleavage-stage embryos. The difference in the sex ratio of normal male-to-female embryos was compared using a significance probabilities test for sex ratio. The sex ratio of sperm from a semen sample from the male partner was determined by FISH.

RESULTS

Fifty embryos were suitable for analysis. A significantly higher number of normal male (n = 20) than normal female (n = 8) embryos was obtained (P < 0.05). The FISH assessment of the husband's semen analysis revealed no alteration in the normal X:Y ratio.

CONCLUSIONS

As the sperm analysis revealed a normal X:Y ratio, an alteration in the embryo sex ratio might be explained by the preferential binding of Y-bearing sperm to the oocyte, an oocyte-related "discouragement" of binding of X-bearing sperm, or a postfertilization event.

HrWnt-5: a maternally expressed ascidian Wnt gene with posterior localization in early embryos

Ascidians show a highly determinate mode of development. In particular, components of the posterior-vegetal cytoplasm of fertilized eggs are responsible for the establishment of the embryonic axis. Recent studies have, however, also revealed significant roles of cell-cell interactions during embryogenesis. Proteins encoded by the Wnt family of genes act as signals and have been shown to play important roles in a wide range of developmental processes. Here we have isolated and characterized an ascidian Wnt gene, HrWnt-5, from Halocynthia roretzi. HrWnt-5 mRNA is present in the vegetal cortex in unfertilized eggs. After fertilization, HrWnt-5 mRNA moves to the equatorial region to form a crescent-like structure, after which the mRNA is concentrated in the posteriormost region of the embryo. This early pattern of HrWnt-5 mRNA localization coincides with another posterior-vegetally localized mRNA, pem, isolated from Ciona savignyi. In the gastrula, the zygotic HrWnt-5 mRNA is found in a variety of blastomeres, suggesting multiple roles of the gene.

Preimplantation genetic diagnosis of inherited cancer: familial adenomatous polyposis coli

PURPOSE

Our purpose was to achieve preimplantation genetic diagnosis (PGD) of the dominant cancer predisposition syndrome, familial adenomatous polyposis coli (FAPC), as an alternative to prenatal diagnosis.

METHODS

The affected patient was superovulated and oocytes were retrieved and fertilized by intracytoplasmic sperm injection (ICSI). Two cells were biopsied from each embryo and the whole genome was amplified by primer extension preamplification (PEP). Nested PCR was then used to amplify two APC fragments: one including the APC mutation site and the other an informative intragenic polymorphism. Both were detected by simultaneous single-strand conformation polymorphism and heteroduplex analysis.

RESULTS

Four normally fertilized embryos were biopsied on day 3 post ICSI, and two cells were successfully removed from each embryo. Following PEP the APC mutation was successfully amplified in 7 of 8 cells, and the polymorphism in 6 of 8 cells. The APC mutation was detected in three embryos. This result was confirmed by identification of the mutation associated polymorphism in two cases. A single embryo was diagnosed as homozygous normal for the mutation and the polymorphism in both cells sampled. This unaffected embryo was transferred to the mother, but no pregnancy resulted.

CONCLUSIONS

We report here the first diagnosis of a cancer predisposition syndrome in human preimplantation embryos. Our results indicate that difficulties associated with single-cell PCR, allele-specific amplification failure in particular, need not prevent preimplantation diagnosis of diseases with a dominant mode of inheritance, provided appropriate strategies are applied.

Preimplantation genetic diagnosis of chromosome balance in embryos from a patient with a balanced reciprocal translocation

Duplications or deletions are present in a high percentage of the gametes produced by individuals carrying balanced translocations. Preimplantation genetic diagnosis was used to examine chromosome balance in embryos from a patient having a reciprocal translocation within the short arms of chromosomes 5 and 8 (46,XX,t(5;8)(p13;p23)). This woman has two sisters with the translocation unbalanced, resulting in a partial trisomy for chromosome 5 and partial monosomy for chromosome 8 (46,XX,-8, +der(8)t(5;8)(p13;p23)) with associated mental retardation and physical abnormalities. The patient and her husband desired to have children without the abnormal chromosome balance and wished to reduce the likelihood of spontaneous abortion or need for therapeutic abortion. Fluorescence in-situ hybridization (FISH) probes for the alpha-satellite region of chromosome 8 and for a region on the short arm of chromosome 5 (5p15.2) were tested initially on lymphocytes from the patient and her sisters. The hybridization signal for chromosome 5 was detected in the expected two copies for the patient and three copies for the sisters in 87% of the cells. Two hybridization signals for chromosome 8 were detected in 96% of the cells from all individuals. Additional probe testing was done using blastomeres from polyspermic embryos. The couple then proceeded with a stimulated in-vitro fertilization (IVF) cycle and biopsies were done on 13 embryos at the 7-10-cell stage using a method of zona drilling and fluid displacement. Diagnosis was possible on at least one blastomere for nine embryos. Three embryos had nuclei with three hybridization signals for chromosome 5, three had fewer than two signals for one or both chromosomes, one was mosaic, and two had two signals for each chromosome. The latter were transferred to the patient, but pregnancy was not achieved. The results demonstrate that preimplantation genetic diagnosis for patients with reciprocal translocations can be used to identify embryos having normal chromosome balance. The potential advantages and limitations of this approach are discussed.

POP-1 and anterior-posterior fate decisions in C. elegans embryos

Blastomeres in C. elegans embryos execute lineage programs wherein the fate of a cell is correlated reproducibly with the division sequence by which that cell is born. We provide evidence that the pop-1 gene functions to link anterior-posterior cell divisions with cell fate decisions. Each anterior cell resulting from an anterior-posterior division appears to have a higher level of nuclear POP-1 protein than does its posterior sister. Genes in the C. elegans Wnt pathway are required for this inequality in POP-1 levels. We show that loss of pop-1(+) activity leads to several types of anterior cells adopting the fates of their posterior sisters. These results suggest a mechanism for the invariance of blastomere lineages.

Carrier-specific breakpoint-spanning DNA probes: an approach to preimplantation genetic diagnosis in interphase cells

Carriers of chromosomal inversions or other balanced rearrangements represent a significant fraction of patients in in-vitro fertilization (IVF) programmes due to recurrent reproductive problems. In most cases, chromosomal imbalance in fertilized oocytes is incompatible with embryo survival leading to increased rates of spontaneous abortions. Assuming that a fraction of the germ cells is karyotypically normal, these patients would greatly benefit from efficient procedures for generation and use of breakpoint-specific DNA hybridization probes in preconception and preimplantation genetic diagnosis (PGD). We describe the generation of such patient-specific probes to discriminate between normal and aberrant chromosomes in interphase cells. First, a large insert DNA library was screened for probes that bind adjacent to the chromosomal breakpoints or span them. Then, probe and hybridization parameters were optimized using white blood cells from the carrier to increase in hybridization signal intensity and contrast. Finally, the probes were tested on target cells (typically polar bodies or blastomeres) and a decision about the colour labelling scheme was made, before the probes can be used for preconception or preimplantation genetic analysis. Thus, it was demonstrated that cells with known structural abnormalities could be detected, based on hybridization of breakpoint spanning yeast artificial chromosome (YAC) DNA probes in interphase cells.

A C. elegans E/Daughterless bHLH protein marks neuronal but not striated muscle development

The E proteins of mammals, and the related Daughterless (DA) protein of Drosophila, are ubiquitously expressed helix-loop-helix (HLH) transcription factors that play a role in many developmental processes. We report here the characterization of a related C. elegans protein, CeE/DA, which has a dynamic and restricted distribution during development. CeE/DA is present embryonically in neuronal precursors, some of which are marked by promoter activity of a newly described Achaete-scute-like gene hlh-3. In contrast, we have been unable to detect CeE/DA in CeMyoD-positive striated muscle cells. In vitro gel mobility shift analysis detects dimerization of CeE/DA with HLH-3 while efficient interaction of CeE/DA with CeMyoD is not seen. These studies suggest multiple roles for CeE/DA in C. elegans development and provide evidence that both common and alternative strategies have evolved for the use of related HLH proteins in controlling cell fates in different species.

Preimplantation genetic diagnosis in Marfan syndrome

The in vitro fertilization technology coupled with the ability to amplify DNA from a single cell has been used for the preimplantation genetic diagnosis of Marfan syndrome. An intragenic FBN1 gene marker has been used to track the inheritance of this disorder in a family. Marker genotyping was established following two rounds of amplification. Whenever possible, two blastomeres were separately assayed per embryo. The transfer of five embryos resulted in a singleton pregnancy and the birth of a full-term male infant.

Three-dimensional labeling program for elucidation of the geometric properties of biological particles in three-dimensional space

For all biological particles such as cells or cellular organelles, there are three-dimensional coordinates representing the centroid or center of gravity. These coordinates and other numerical parameters such as volume, fluorescence intensity, surface area, and shape are referred to in this paper as geometric properties, which may provide critical information for the clarification of in situ mechanisms of molecular and cellular functions in living organisms. We have established a method for the elucidation of these properties, designated the three-dimensional labeling program (3DLP). Algorithms of 3DLP are so simple that this method can be carried out through the use of software combinations in image analysis on a personal computer. To evaluate 3DLP, it was applied to a 32-cell-stage sea urchin embryo, double stained with FITC for cellular protein of blastomeres and propidium iodide for nuclear DNA. A stack of optical serial section images was obtained by confocal laser scanning microscopy. The method was found effective for determining geometric properties and should prove applicable to the study of many different kinds of biological particles in three-dimensional space.

Sex determination by simultaneous application of polymerase chain reaction and fluorescent in situ hybridization on the same blastomere of a pre-embryo

OBJECTIVE

To describe an investigation of the feasibility of carrying out polymerase chain reaction (PCR) and fluorescent in situ hybridization on the same single human cell for sex determination.

DESIGN

To develop protocol for a clinical diagnostic test in preclinical trials.

SETTING

Infertile human volunteers in a clinical environment.

PATIENTS

Polyploid embryos were obtained from patients treated by IVF at the Advanced Institute of Fertility.

INTERVENTIONS

Seventeen blastomeres biopsied from human polyploid embryos were analyzed for sex determination by simultaneous application of PCR and fluorescent in situ hybridization.

MAIN OUTCOME MEASURE

Presence of an X- or X and Y-chromosome band after agarose gel electrophoresis of PCR products and presence of an X- or X and Y-chromosome fluorescent probe signal after fluorescent in situ hybridization following PCR analysis.

RESULTS

By PCR, all 17 blastomeres were amplified and, by fluorescent in situ hybridization, 12 (70.6%) blastomeres produced signals that were consistent with PCR results. Two blastomeres showed only X signals, although by PCR they had both X and Y-chromosome bands.

CONCLUSIONS

The sequential use of PCR and fluorescent in situ hybridization on the same blastomere can be applied to improve the accuracy of sex determination before fresh ET.

Tight junctions in early amphibian development: detection of junctional cingulin from the 2-cell stage and its localization at the boundary of distinct membrane domains in dividing blastomeres in low calcium

Although functional studies indicate that tight junctions (TJ) are present in Xenopus laevis embryos from the 2-cell stage onward, morphological studies have failed to identify typical TJ structures before the 32-cell stage. Nothing is known about the expression and localization of TJ proteins in early Xenopus development. Here we have investigated the formation and composition of TJ in developing Xenopus embryos by whole-mount immunoperoxidase staining of eggs/embryos and immunoblotting of extracts with an antiserum against the TJ protein cingulin. Immunoblot analysis of eggs and embryo extracts showed that the antiserum labeled a major polypeptide of apparent M(r) 160 kD. Maternal cingulin was distributed diffusely in the cytocortical region of eggs and early embryos. Intense cingulin labeling became localized in the junctional region starting from the first cell division (2-cell stage). During cytokinesis, cingulin labeling was accumulated into new junctions in a precise spatial/temporal relationship with the deepening of the cleavage furrow. In semithin sections of stained embryos, labeling was detected in the most apical portion of the region of cell-cell contact. In embryos incubated in low calcium medium for 30 min, newly divided blastomeres failed to completely adhere to each other. However, cingulin labeling was accumulated along a linear structure that was at the border between distinct membrane domains (apical and lateral). These observations provide the first description of assembly of a TJ protein at the earliest stages of Xenopus development and suggest that TJ occur from the 2-cell stage onward and are assembled with maternal stores of protein. The formation of cingulin-containing structures even when lateral cell-cell adhesion is greatly reduced suggests that the apical cytocortex may have a determinative influence on TJ assembly and establishment of cell polarity.

Aneuploidy 16 in human embryos increases significantly with maternal age

OBJECTIVE

To determine aneuploidy for chromosome 16 by recycling nuclei of cells already analyzed for chromosomes X, Y, 18, 13, and 21 using multiple fluorescence in situ hybridization in preimplantation human embryos in a time frame compatible with clinical IVF and to asssess the incidence of chromosome 16 aneuploidy in embryos related to maternal age.

DESIGN

Prospective experimental study.

SETTING

In vitro fertilization program in a tertiary center.

PATIENTS

One hundred four consenting patients undergoing IVF.

MAIN OUTCOME MEASURES

Chromosome 16 ploidy was analyzed in a total of 195 embryos. In 89 embryos, a standard multiple-probe fluorescence in situ hybridization was used for chromosomes X, Y, 18 and 16 (series 1). The remaining 106 embryos (series 2) were reanalyzed with a new procedure for chromosome 16, which involves rehybridization with a digoxigenin-labeled alpha satellite probe after the standard analysis for chromosomes X, Y, 18, 13, and 21 was completed. The embryos were assigned to one of three groups according to the women's age; group 1: </= 34 years (n = 34), group 2: 35 to 39 years (n = 47); group 3: >/= 40 years (n = 23).

RESULTS

Successful analysis, including biopsy, fixation, and fluorescence in situ hybridization was achieved in 86% of the blastomeres within approximately 10 hours. A significant relationship was found between the rate of aneuploidy for chromosome 16 and increasing maternal age: group 1: 0%, group 2: 6.3%, and group 3: 11.7%. Monosomy for chromosome 16 was found in 72.7% of the 11 embryos carrying chromosome 16 anomalies, with the remaining three embryos having two trisomies and one tetrasomy. This new protocol was applied clinically to five patients undergoing preimplantation aneuploidy assessment. Aneuploidy for chromosome 16 was found in five embryos from three of those patients.

CONCLUSIONS

This study demonstrates that preimplantation genetic diagnosis of the major human aneuploidies is achievable within a time frame compatible with IVF. In addition, this study confirms, for embryos, the existing data from spontaneous abortions suggesting that chromosome 16 aneuploidy increases with maternal age. The high prevalence of embryonic monosomy, which is rarely found in spontaneous abortions, suggests that monosomy 16 could be a factor associated with failure of implantation, as well as pointing to a different mechanism involved in the generation of chromosome 16 aneuploidy.

Detection of chromosomal abnormalities in human preimplantation embryos using FISH

PURPOSE

Multicolour FISH has been used for the preimplantation diagnosis of sex for X-linked disorders and to examine the chromosome constitution of early human embryos.

MATERIALS AND METHODS

Single blastomeres and whole embryos were spread using HCI and Tween 20. Multicolour FISH was performed using directly-labelled human DNA probes for chromosomes X, Y, and 1 in a two hour FISH procedure.

RESULTS

Four groups of chromosome arrangements have been found in human preimplantation embryos (i) normal, all nuclei uniformly diploid, (ii) diploid mosaics, majority of the nuclei diploid, with a small number of nuclei aneuploid (iii) chromosomally abnormal, all nuclei uniformly chromosomally abnormal, e.g. XO, XXY, XXX and (iv) chaotic, all nuclei showing different chromosome complements.

CONCLUSIONS

For the preimplantation diagnosis of sex, an XX nucleus has always been representative of a female embryo. However, for the diagnosis of dominant disorders or chromosome abnormalities, two cells should be analysed to reduce the chance of misdiagnosis which may arise from chromosomal mosaicism. Implantation and further embryo development may be possible from mosaic or chromosomally abnormal embryos, but those showing chaotic chromosome arrangements would be unlikely to implant.

Fluorescent PCR: a new technique for PGD of sex and single-gene defects

BACKGROUND

For single-cell diagnosis, particularly preimplantation genetic diagnosis to be successful four main criteria must be achieved: sensitivity, reliability, accuracy, and identification/elimination of contamination.

METHODS AND RESULTS

Fluorescent PCR achieves all four necessary criteria and, in addition, currently allows genes on up to nine chromosomes to be simultaneously investigated. Fluorescent PCR has high sensitivity (approximately 1000 x conventional analysis systems), high reliability (97%), and high accuracy (97%) rates for both sex and CF diagnosis in single somatic cells. The low detection threshold allows allelic dropout (one of the main causes of misdiagnosis) to be easily distinguished from PCR phenomena such as preferential amplification. High reliability (90%) and accuracy (97-100%) have been achieved in sex and CF diagnosis in human blastomeres. Fluorescent PCR can also be used to DNA fingerprint (STR profiling) single cells to identify the source/origin of the cell and determine if contamination has occurred.

CONCLUSIONS

Fluorescent PCR is therefore a suitable method for PGD.

Identifying the sex of human preimplantation embryos in X-linked disease: amplification efficiency of a Y-specific alphoid repeat from single blastomeres with two lysis protocols

INTRODUCTION

Preimplantation diagnosis involves detecting genetic defects in one or two blastomeres biopsied from cleavage stage embryos following a vitro fertilization (IVF). For X-linked recessive disease, identification of the sex of embryos allows transfer of only unaffected females. To examine how critical the preparation of the single blastomere is for amplification of a Y chromosome specific repeat sequence using the polymerase chain reaction (PCR), the incidence of amplification failure has been examined following two lysis protocols.

MATERIALS AND METHODS

Amplification of a Y alphoid repeat sequence from single blastomeres disaggregated from cleavage stage embryos was examined after either (1) lysis in distilled water and freeze-thawing twice or (2) a two-step lysis protocol involving an initial treatment in potassium hydroxide and dithiothreitol. Some of the embryos had been previously sexed by cleavage-stage biopsy and fluorescent in situ hybridization with X- and Y-specific probes.

RESULTS

Amplification failure occurred in 6 of 50 (12%) and 4 of 60 (7%) single blastomeres from male embryos following lysis in distilled water or using the two-step protocol, respectively. Conversely, amplification from contaminating DNA occurred in 5 of 63 (8%) single blastomeres from female embryos and 6 of 94 (6%) of control medium-blanks.

CONCLUSIONS

The incidence of amplification failure was improved but not eliminated using the two-step lysis protocol. At least two cells, therefore, would be necessary for accurate identification of males by amplification of Y-specific repeat sequences alone. Nevertheless, this protocol for preparing cleavage-stage blastomeres is likely to give more consistent amplification of any unique or repeat sequences.

Reduced allele dropout in single-cell analysis for preimplantation genetic diagnosis of cystic fibrosis

BACKGROUND

For couples at risk of transmitting a known single-gene defect, preimplantation genetic diagnosis (PGD) allows the identification and transfer of only unaffected embryos following in vitro fertilisation (IVF), single-cell biopsy at about the eight-cell stage, and genetic analysis by PCR. This technique therefore avoids the risk of terminating an affected pregnancy diagnosed later in gestation.

METHODS AND RESULTS

Using nested PCR, the delta F508 mutation causing cystic fibrosis can be detected in single cells and we previously reported successful PGD in a couple in whom both partners carry the delta F508 mutation. To date we have treated 12 couples in a total of 18 cycles. This resulted in five singleton births confirmed to be homozygous normal. Single blastomeres from disaggregated embryos which had not been transferred were analysed to confirm the original diagnosis and assess reliability in clinical practice. Amplification efficiency and accuracy were high, with blastomeres from embryos diagnosed as homozygous normal or affected. In a proportion of blastomeres from presumed carrier embryos, one of the parental alleles failed to amplify, apparently at random (allele dropout, ADO). A possible explanation is the relative inaccessibility of one of the target allele early in the PCR. To test this we have used single lymphocytes from delta F508 carriers and investigated the effects of various denaturation temperatures in the early cycles of amplification.

CONCLUSIONS

Increasing the denaturation temperature reduced the rate of ADO without affecting amplification efficiency.

Nuclear structural conditions and PCR amplification in human preimplantation diagnosis

An understanding of the relationship between nuclear morphology and DNA function is important in cytology and preimplantation diagnosis. In this study, direct polymerase chain reaction (PCR) amplification was used to diagnose the common delta F508 mutation of cystic fibrosis in 62 biopsied human embryo cells. The nuclei were photographed and classified into three categories depending on their microscopic appearance; these were further correlated with the results of PCR amplification. The normal nucleus group (42 embryo cells, with clear and regular nuclear membrane, transparent nucleoplasm and prominent nucleoli) showed 100% PCR amplification, with normal amplification results, i.e. bright DNA bands. These were considered to be the living cells. Only half of the cells (10 embryo cells) which contained abnormal nuclei (with abnormal nuclear membranes or nucleoplasm) showed PCR amplification, often with abnormal amplification results, i.e. weak DNA bands. These cells were considered to be either degenerate or to be undergoing degeneration. The anuclear cells (10 embryo cells) were composed of living (metaphase) and degenerated cells and showed about 30% PCR amplification. These results demonstrated that one of the important signs of early visible cell degeneration is the partial or total degeneration of the nucleus. Abnormal morphological changes of the nuclear membrane and nucleoplasm are usually accompanied with functional and structural DNA alteration. It is suggested that base degradation occurs earlier than the breakage of base-sugar bonds and phosphodlester bonds during the course of DNA degradation. The selection of optimal cells with a normal nucleus for single cell embryo biopsy is important for the precision and safety of preimplantation diagnosis.

Review: preimplantation diagnosis of inherited disease

Preimplantation diagnosis of inherited diseases has become possible with the techniques of in vitro fertilization, blastomere biopsy of the 6- to 10-cell embryo and DNA analysis of the single blastomeres. Disease-free embryos are selected for transfer to the uterus, thereby avoiding the need for termination of a fetus diagnosed as affected in prenatal diagnosis in the first or early-second trimester of pregnancy. The genetic indications for preimplantation diagnosis are theoretically the same as for prenatal diagnosis, but the defects must be detectable by the polymerase chain reaction. For X-linked recessive diseases, fluorescence in situ hybridization can be used as an alternative for the selection of female embryos. So far almost 40 healthy children have been born worldwide after preimplantation diagnosis for genetic disease. The possibilities and limitations of preimplantation diagnosis, especially in prevention of inherited disease, are discussed in this review.

Asymmetrically distributed PAR-3 protein contributes to cell polarity and spindle alignment in early C. elegans embryos

The par-3 gene is required for establishing polarity in early C. elegans embryos. Embryos from par-3 homozygous mothers show defects in segregation of cytoplasmic determinants and in positioning of the early cleavage spindles. We report here that the PAR-3 protein is asymmetrically distributed at the periphery of the zygote and asymmetrically dividing blastomeres of the germline lineage. The PAR-3 distribution is roughly the reciprocal of PAR-1, another protein required for establishing embryonic polarity in C. elegans. Analysis of the distribution of PAR-3 and PAR-1 in other par mutants reveals that par-2 activity is required for proper localization of PAR-3 and that PAR-3 is required for proper localization of PAR-1. In addition, the distribution of the PAR-3 protein correlates with differences in cleavage spindle orientation and suggests a mechanism by which PAR-3 contributes to control of cleavage pattern.

Strategies to respond to polymerase chain reaction deoxyribonucleic acid amplification failure in a preimplantation genetic diagnosis program

OBJECTIVES

Our purpose was to identify and evaluate practical methods within a preimplantation genetic diagnosis program that will increase the percentage of embryos for which a genetic diagnosis can be obtained, including clinical responses after failure of deoxyribonucleic acid amplification has occurred.

STUDY DESIGN

Known human lymphoblast cell lines and human embryo blastomeres were evaluated in a single-cell, nested primer polymerase chain reaction system with primer sequences for the specific locus surrounding the four base pair insertion mutation on exon 11 of beta-hexosaminidase A-Tay-Sachs disease, the delta F508 mutation of cystic fibrosis, and the sex-determining region on the Y chromosome. Reamplification polymerase chain reaction with standard polymerase chain reaction and primer extension preamplification was performed in deoxyribonucleic acid preparations after previous polymerase chain reaction amplification attempts had resulted in failure of amplification.

RESULTS

The amplification efficiency of Tay-Sachs disease, 51% (97/187), was significantly lower than that for cystic fibrosis, 85% (87/107), and for the sex-determining region on the Y chromosome, 85% (77/90). Tay-Sachs disease polymerase chain reaction amplification occurred in 51% of one-cell lymphoblasts, 89% of two-cell lymphoblasts, and 94% of samples when more than two cells were processed together. When previous amplification failure had occurred, standard Tay-Sachs disease polymerase chain reaction resulted in an amplification efficiency of 16% (three of 19), whereas primer extension preamplification polymerase chain reaction for Tay-Sachs disease resulted in amplification of 52% (31/59) lymphoblasts and 54% (13/24) of polyspermic human blastomeres. Four of six human blastomeres in which amplification failure occurred in a Tay-Sachs disease preimplantation genetic diagnosis cycle amplified by primer extension preamplification polymerase chain reaction, which increased the diagnostic information obtained from four to six of the seven embryos on which biopsy was performed.

CONCLUSIONS

We suggest that practical approaches for consideration within a clinical preimplantation genetic diagnosis program to limit the net effect of amplification failure (i.e., reduced embryo transfer number) include increasing the deoxyribonucleic acid content in the polymerase chain reaction tube by using more than one blastomere and by using primer extension preamplification when the initial attempt at amplification fails.

Developmental expression of D-galactoside-binding lectin in sea urchin (Anthocidaris crassispina) eggs

The spatial and temporal expression of a sea urchin (Anthocidaris crassispina) egg lectin (SUEL) during early embryogenesis was studied using antiserum raised against SUEL. Western blotting analysis revealed the presence of SUEL in all stages so far examined, from unfertilized eggs to gastrula stage embryos. Immunofluorescence and immunoelectron microscopic observation showed that SUEL was stored in small electron-dense granules which migrated to the cortex within 10 min after fertilization. SUEL was localized in the cortical cytoplasm of the blastomere during cleavage stages and subsequently migrated to the outer surface of the embryo, including the invaginated portion of the gastrula. Immunoelectron microscopic study indicated that SUEL was deposited in the hyaline layer at least at the mid gastrula stage. Migration of SUEL to the cortex was significantly reduced by treatment with cytochalasin B, suggesting that actin filaments play an important role in this translocation. Exogenously added SUEL was adsorbed at the surface of unfertilized eggs and hatched embryos, but not to embryos with fertilization membrane. Lactose inhibited this adsorption, suggesting the presence of an endogenous glycoligand(s) specific for SUEL on the surface of unfertilized eggs and in the hyaline layer. We conclude that SUEL is secreted at a certain stage of embryogenesis and specifically adsorbed to the hyaline layer. Temporal changes in extraembryonic matrices caused by SUEL seem to play an important role in developmental morphogenesis.

Production of chimeric pigs and the analysis of chimerism using mitochondrial deoxyribonucleic acid as a cell marker

Two injection methods were examined for making chimeras between Chinese pigs (Meishan) and European pigs (Landrace or Landrace x Large White). Furthermore, mitochondrial DNA (mtDNA) polymorphism was detected as a cell marker for the analysis of chimerism. In the first experiment, blastomeres were transplanted into embryos at the 4-16-cell stage. Of 41 transplanted embryos transferred into 3 females, 12 were single-colored, but no overt chimeras were obtained. Judging from coat color and mtDNA in white blood cells, 2 piglets in 2 litters were derived from injected blastomeres, and 10 piglets in 3 litters were derived from recipient blastomeres. In the second experiment, inner cell mass cells of Day 6 Landrace embryos were injected into blastocoels of Day 6 Meishan embryos. Of 35 injected embryos transferred into 3 females, 2 overt chimeras of each sex were obtained in a single litter. In the overt male chimera, mtDNA clearly showed chimerism in spleen, pancreas, brain, kidney, lung, liver, heart, testis, and small intestine. The overt female chimera showed chimerism not only in blood but also in germ line according to a progeny test. No chimerism was detected in any of the 21 single-colored piglets in the second experiment.