The development of novel quantification assay for mitochondrial DNA heteroplasmy aimed at preimplantation genetic diagnosis of Leigh encephalopathy

PURPOSE

To perform preimplantation genetic diagnosis (PGD) of Leigh encephalopathy, we developed a rapid and reliable quantification assay for the percentage of T8993G mtDNA mutation and analyzed various specimens.

METHODS

We prepared the standard curve by measuring serial proportion of 8993T/G cloned plasmid DNA using real-time PCR, and measured (1) mutant DNA (known proportions by PCR-RFLP), (2) single lymphocytes from 46% mutant carrier, (3) 123 blastomeres from 20 abnormal embryos.

RESULTS

(1) These were within -5 - +6% error range, (2) mean 44.3%(11-70%), (3) Five embryos harbored T8993G mutation (4-22%). Embryos from same person indicated different degrees of heteroplasmy, and blastomeres from same embryo demonstrated limited dispersion of heteroplasmy (2-11%).

CONCLUSIONS

(1) This method provides rapid and reliable PGD for Leigh encephalopathy. (2) The variable heteroplasmy with somatic mitosis was suggested. (3) T8993G mutation was existed in undeveloped embryo, and the bottleneck theory was supported. The limited heteroplasmy dispersion of blastomeres from same embryo also supported reliability of PGD for T8993G mutation.

Histone arginine methylation regulates pluripotency in the early mouse embryo

It has been generally accepted that the mammalian embryo starts its development with all cells identical, and only when inside and outside cells form do differences between cells first emerge. However, recent findings show that cells in the mouse embryo can differ in their developmental fate and potency as early as the four-cell stage. These differences depend on the orientation and order of the cleavage divisions that generated them. Because epigenetic marks are suggested to be involved in sustaining pluripotency, we considered that such developmental properties might be achieved through epigenetic mechanisms. Here we show that modification of histone H3, through the methylation of specific arginine residues, is correlated with cell fate and potency. Levels of H3 methylation at specific arginine residues are maximal in four-cell blastomeres that will contribute to the inner cell mass (ICM) and polar trophectoderm and undertake full development when combined together in chimaeras. Arginine methylation of H3 is minimal in cells whose progeny contributes more to the mural trophectoderm and that show compromised development when combined in chimaeras. This suggests that higher levels of H3 arginine methylation predispose blastomeres to contribute to the pluripotent cells of the ICM. We confirm this prediction by overexpressing the H3-specific arginine methyltransferase CARM1 in individual blastomeres and show that this directs their progeny to the ICM and results in a dramatic upregulation of Nanog and Sox2. Thus, our results identify specific histone modifications as the earliest known epigenetic marker contributing to development of ICM and show that manipulation of epigenetic information influences cell fate determination.

Obtaining metaphase spreads from single blastomeres for PGD of chromosomal rearrangements

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

Timing and Uniformity of Embryonic Gene Activation Affect Subsequent Pre-implantation Development of Cloned Bovine Embryos

In the present study, we examined the timing of onset, intensity, and mosaicism of embryonic gene expression in bovine nuclear transfer (NT) embryos. The relationship between gene expression and early embryonic development was also examined. To monitor the gene expression of NT embryos, we produced NT embryos with bovine transfected fibroblasts carrying a firefly luciferase gene under the control of a chicken beta-actin promoter, an expression system that has previously been shown to be representative of embryonic gene expression in mice. Photon count imaging showed that luciferase luminescence began in NT embryos with fibroblasts 48 hours post fusion (hpf) and reached a plateau at the 4- to 8-cell stage at 60 hpf. Only 4- to 8-cell NT embryos luminescent by 60 hpf developed to the blastocyst stage. At 60 hpf, strongly luminescent embryos developed to the blastocyst stage at a higher rate (P<0.05) than embryos with weak or absent luminescence. However, embryos with mosaic luminescence developed at a much lower rate (P<0.05) than those with whole-embryo luminescence, even if the embryos exhibited strong luminescence. Our results indicate that precise and uniform embryonic gene expression at the 4- to 8-cell stage at 60 hpf may be closely related to development of bovine NT embryos to the blastocyst stage.

PHA-4/FoxA cooperates with TAM-1/TRIM to regulate cell fate restriction in the C. elegans foregut

A key question in development is how pluripotent progenitors are progressively restricted to acquire specific cell fates. Here we investigate how embryonic blastomeres in C. elegans develop into foregut (pharynx) cells in response to the selector gene PHA-4/FoxA. When pha-4 is removed from pharyngeal precursors, they exhibit two alternative responses. Before late-gastrulation (8E stage), these cells lose their pharyngeal identity and acquire an alternative fate such as ectoderm (Specification stage). After the Specification stage, mutant cells develop into aberrant pharyngeal cells (Morphogenesis/Differentiation stage). Two lines of evidence suggest that the Specification stage depends on transcriptional repression of ectodermal genes by pha-4. First, pha-4 exhibits strong synthetic phenotypes with the B class synMuv gene tam-1 (Tandam Array expression Modifier 1) and with a mediator of transcriptional repression, the NuRD complex (NUcleosome Remodeling and histone Deacetylase). Second, pha-4 associates with the promoter of the ectodermal regulator lin-26 and is required to repress lin-26 expression. We propose that restriction of early blastomeres to the pharyngeal fate depends on both repression of ectodermal genes and activation of pharyngeal genes by PHA-4.

Defining the transcriptional redundancy of early bodywall muscle development in C. elegans: evidence for a unified theory of animal muscle development

Myogenic regulatory factors (MRFs) are required for mammalian skeletal myogenesis. In contrast, bodywall muscle is readily detectable in Caenorhabditis elegans embryos lacking activity of the lone MRF ortholog HLH-1, indicating that additional myogenic factors must function in the nematode. We find that two additional C. elegans proteins, UNC-120/SRF and HND-1/HAND, can convert naïve blastomeres to muscle when overproduced ectopically in the embryo. In addition, we have used genetic null mutants to demonstrate that both of these factors act in concert with HLH-1 to regulate myogenesis. Loss of all three factors results in embryos that lack detectable bodywall muscle differentiation, identifying this trio as a set that is both necessary and sufficient for bodywall myogenesis in C. elegans. In mammals, SRF and HAND play prominent roles in regulating smooth and cardiac muscle development. That C. elegans bodywall muscle development is dependent on transcription factors that are associated with all three types of mammalian muscle supports a theory that all animal muscle types are derived from a common ancestral contractile cell type.

The Emergence of Pattern in Embryogenesis: Regulation of beta-Catenin Localization During Early Sea Urchin Development

The accumulation of beta-catenin in the nuclei of blastomeres at one pole of the early embryo is a highly conserved and essential feature of animal development. In the sea urchin, beta-catenin accumulates in the nuclei of vegetal blastomeres during early cleavage and activates gene regulatory networks that drive mesoderm and endoderm formation. Measurements of beta-catenin half-life in vivo have demonstrated a gradient in stability along the animal-vegetal axis. Dishevelled (Dsh), a protein that regulates beta-catenin turnover, is localized in the vegetal cortex, where it has an essential role in stabilizing beta-catenin and activating endomesodermal gene networks. Two motifs of Dsh are required for targeting to the vegetal cortex. Overexpression of Dsh in animal blastomeres does not alter their fate, which suggests that a localized activator of Dsh may be missing in these cells. Wnt signaling may be localized in the early sea urchin embryo, as it is in Xenopus, but findings point to possible differences in the initial polarizing signal in amphibians and echinoderms. Further studies will be required to determine the extent to which mechanisms that control beta-catenin nuclearization in early embryogenesis have been conserved during animal evolution.

Mathematical model of morphogen electrophoresis through gap junctions

Gap junctional communication is important for embryonic morphogenesis. However, the factors regulating the spatial properties of small molecule signal flows through gap junctions remain poorly understood. Recent data on gap junctions, ion transporters, and serotonin during left-right patterning suggest a specific model: the net unidirectional transfer of small molecules through long-range gap junctional paths driven by an electrophoretic mechanism. However, this concept has only been discussed qualitatively, and it is not known whether such a mechanism can actually establish a gradient within physiological constraints. We review the existing functional data and develop a mathematical model of the flow of serotonin through the early Xenopus embryo under an electrophoretic force generated by ion pumps. Through computer simulation of this process using realistic parameters, we explored quantitatively the dynamics of morphogen movement through gap junctions, confirming the plausibility of the proposed electrophoretic mechanism, which generates a considerable gradient in the available time frame. The model made several testable predictions and revealed properties of robustness, cellular gradients of serotonin, and the dependence of the gradient on several developmental constants. This work quantitatively supports the plausibility of electrophoretic control of morphogen movement through gap junctions during early left-right patterning. This conceptual framework for modeling gap junctional signaling -- an epigenetic patterning mechanism of wide relevance in biological regulation -- suggests numerous experimental approaches in other patterning systems.

Analysis of protein expression (secretome) by human and mouse preimplantation embryos

OBJECTIVE

To analyze the protein production into the surrounding medium (secretome) of both human and mouse embryos and correlate these findings with ongoing blastocyst development. Along with improvements in culture systems, there is renewed focus on the development of noninvasive viability assays in human IVF. Because the majority of biologic functions are carried out by proteins, it is important to study the dynamics of the proteome during embryonic development and its response to both internal and external stimuli.

DESIGN

Experimental study.

SETTING

Research laboratory.

PATIENT(S)

Couples undergoing infertility treatment donated with consent spent culture media for research.

INTERVENTION(S)

Analysis by time-of-flight mass spectrometry.

MAIN OUTCOME MEASURE(S)

Protein profiles of spent culture media.

RESULT(S)

Distinctive and significantly different secretome profiles were observed at each embryonic developmental stage (P<0.05). Correlation of day 5 secretome data with ongoing blastocyst development revealed an 8.5-kDa protein biomarker that was significantly up-regulated (P<0.05). The best candidate for this protein biomarker was ubiquitin, which has been implicated in the implantation process of mammalian species.

CONCLUSION(S)

This approach to analyze the secretome should not only further our understanding of embryo physiology but provide the basis for the development of noninvasive assays of embryo viability in human IVF.

Voltage-dependent calcium influx mediates maturation of myofibril arrangement in ascidian larval muscle

Calcium signaling is important for multiple events during embryonic development. However, roles of calcium influx during embryogenesis have not been fully understood since routes of calcium influx are often redundant. To define roles of voltage-gated calcium channel (Cav) during embryogenesis, we have isolated an ascidian Cav beta subunit gene (TuCavbeta) and performed gene knockdown using the morpholino antisense oligonucleotide (MO). The suppression of Cav activity by TuCavbetaMO remarkably perturbed gastrulation and tail elongation. Further, larvae with normal morphology also failed to exhibit motility. Phalloidin-staining showed that arrangement of myofibrils was uncoordinated in muscle cells of TuCavbetaMO-injected larvae with normal tail. To further understand the roles of Cav activity in myofibrillogenesis, we tested pharmacological inhibitions with ryanodine, curare, and N-benzyl-p-toluensulphonamide (BTS). The treatment with ryanodine, an intracellular calcium release blocker, did not significantly affect the motility and establishment of the myofibril orientation. However, treatment with curare, an acetylcholine receptor blocker, and BTS, an actomyosin ATPase specific inhibitor, led to abnormal motility and irregular orientation of myofibrils that was similar to those of TuCavbetaMO-injected larvae. Our results suggest that contractile activation regulated by voltage-dependent calcium influx but not by intracellular calcium release is required for proper arrangement of myofibrils.

PRINS as an efficient tool for aneuploidy assessment in human oocytes and preimplantation embryos

An ultrarapid three- and four-color primed in situ (PRINS) procedure has been developed for rapid chromosome identification and aneuploidy assessment on isolated cells. Based on the direct in situ mixing of fluorochromes (fluorescein isothiocyanate, tetramethylrhodamine isothiocyanate, Cascade Blue), this multicolor PRINS procedure is described on unfertilized human oocytes and isolated human blastomeres.

Preimplantation genetic diagnosis for Marfan syndrome

OBJECTIVE

To develop and apply efficient and reliable protocols for preimplantation genetic diagnosis (PGD) for Marfan syndrome.

DESIGN

Two mutation-specific protocols were developed, and the markers D15S1028, D15S992, D15S196, D15S576, D15S123, and D15S143 were used to set up four multiplex polymerase chain reactions (PCRs).

SETTING

Research Center Reproduction and Genetics.

PATIENT(S)

Ten couples carrying mutations in the FBN1 gene.

INTERVENTION(S)

Six PGD protocols were developed for 10 couples, and 7 of them underwent a total of 16 clinical cycles.

MAIN OUTCOME MEASURE(S)

Amplification, allele drop-out (ADO), and contamination rates during the preclinical assays. DNA analyses of blastomeres from embryos biopsied during PGD cycles.

RESULT(S)

Six different protocols were set up, with the main objective being to to use one protocol for several couples. A total of 16 PGD cycles were performed, which resulted in the delivery of an unaffected boy and three ongoing pregnancies.

CONCLUSION(S)

The development of single-cell multiplex PCRs for linked markers and its use in PGD reduce the workload of the genetic diagnostic laboratory as well as the average waiting time for patients. This approach also allows for the simultaneous and accurate detection of recombination, contamination, and ADO, thereby increasing the reliability of the diagnosis.

Specification of the C. elegans MS blastomere by the T-box factor TBX-35

In C. elegans, many mesodermal cell types are made by descendants of the progenitor MS, born at the seven-cell stage of embryonic development. Descendants of MS contribute to body wall muscle and to the posterior half of the pharynx. We have previously shown that MS is specified by the activity of the divergent MED-1,2 GATA factors. We report that the MED-1,2 target gene tbx-35, which encodes a T-box transcription factor, specifies the MS fate. Embryos homozygous for a putative tbx-35-null mutation fail to generate MS-derived pharynx and body muscle, and instead generate ectopic PAL-1-dependent muscle and hypodermis, tissues normally made by the C blastomere. Conversely, overexpression of tbx-35 results in the generation of ectopic pharynx and muscle tissue. The MS and E sister cells are made different by transduction of a Wnt/MAPK/Src pathway signal through the nuclear effector TCF/POP-1. We show that in E, tbx-35 is repressed in a Wnt-dependent manner that does not require activity of TCF/POP-1, suggesting that an additional nuclear Wnt effector functions in E to repress MS development. Genes of the T-box family are known to function in protostomes and deuterostomes in the specification of mesodermal fates. Our results show that this role has been evolutionarily conserved in the early C. elegans embryo, and that a progenitor of multiple tissue types can be specified by a surprisingly simple gene cascade.

Wntless, a conserved membrane protein dedicated to the secretion of Wnt proteins from signaling cells

Cell-cell communication via Wnt signals represents a fundamental means by which animal development and homeostasis are controlled. The identification of components of the Wnt pathway is reaching saturation for the transduction process in receiving cells but is incomplete concerning the events occurring in Wnt-secreting cells. Here, we describe the discovery of a novel Wnt pathway component, Wntless (Wls/Evi), and show that it is required for Wingless-dependent patterning processes in Drosophila, for MOM-2-governed polarization of blastomeres in C. elegans, and for Wnt3a-mediated communication between cultured human cells. In each of these cases, Wls is acting in the Wnt-sending cells to promote the secretion of Wnt proteins. Since loss of Wls function has no effect on other signaling pathways yet appears to impede all the Wnt signals we analyzed, we propose that Wls represents an ancient partner for Wnts dedicated to promoting their secretion into the extracellular milieu.

A prospective randomized study to assess the benefit of partial zona pellucida digestion before frozen-thawed embryo transfers

BACKGROUND

Assisted hatching (AH) in fresh embryo transfer (ET) could be associated with increased implantation rates. However, very few prospective randomized studies have specifically addressed the issue of AH during frozen-thawed embryo transfers (FET) cycles, those that have reported controversial results. The aim of this study was to evaluate the benefit of an enzymatic zona pellucida treatment of frozen-thawed embryos before transfer.

METHODS

This was a prospective study including 125 non-donor FET cycles from 125 infertile couples. FETs were randomly allocated into AH group (n = 61, embryos pretreated with pronase 5 IU/ml for 1 min at 37 degrees C) or control group (n = 64, untreated embryos). Zona pellucida thickness was measured for each transferred embryo. The main outcome parameters were clinical pregnancy and implantation rates.

RESULTS

The two groups were comparable regarding mean women's age, duration and indications of infertility, IVF outcome after fresh ETs, numbers and quality of fresh and frozen embryos, frozen-thawed embryo survival rates and blastomeres survival indexes. Despite a statistically significant decrease of zona pellucida thickness after pronase treatment [(mean +/- SD) 18.5 +/- 2.25 versus 14.5 +/- 2.75 microm; P < 0.0001], implantation (9.6 versus 9.2%) and clinical pregnancy rates (18.0 versus 17.2%) were not statistically different after FETs, with a similar mean number of embryos transferred between AH and control groups, respectively.

CONCLUSION

Within the constraints of our protocol, partial enzymatic digestion of zona pellucida by pronase was not related with any benefit of the FET outcome especially concerning the implantation ability of frozen-thawed embryos.

The role of early lineage in GABAergic and glutamatergic cell fate determination in Xenopus laevis

Proper functioning of the adult nervous system is critically dependent on neurons adopting the correct neurotransmitter phenotype during early development. Whereas the importance of cell-cell communication in fate determination is well documented for a number of neurotransmitter phenotypes, the contributions made by early lineage to this process remain less clear. This is particularly true for gamma-aminobutyric acid (GABA)ergic and glutamatergic neurons, which are present as the most abundant inhibitory and excitatory neurons, respectively, in the central nervous system of all vertebrates. In the present study, we have investigated the role of early lineage in the determination of these two neurotransmitter phenotypes by constructing a fate map of GABAergic and glutamatergic neurons for the 32-cell stage Xenopus embryo with the goal of determining whether early lineage influences the acquisition of these two neurotransmitter phenotypes. To examine these phenotypes, we have cloned xGAT-1, a molecular marker for the GABAergic phenotype in Xenopus, and described its expression pattern over the course of development. Although we have identified isolated examples of a blastomere imparting a statistically significant bias, when taken together, our results suggest that blastomere lineage does not impart a widespread bias for subsequent GABAergic or glutamatergic fate determination. In addition, the fate map presented here suggests a general dorsal-anterior to ventral-posterior patterning progression of the nervous system for the 32-cell stage Xenopus embryo.

The analysis of one or two blastomeres for PGD using fluorescence in-situ hybridization

BACKGROUND

The analysis of one or two blastomeres for PGD using fluorescence in-situ hybridization (FISH) is debated. The proportion of analysable embryos, false negatives, false positives, sensitivity, specificity, negative predictive value (NPV), positive predictive value (PPV) and efficiency were evaluated when one or two blastomeres were analysed.

METHODS

Embryos of patients having PGD for aneuploidy screening were assigned non-randomly to two groups: group I (n = 413), more slow cleaving embryos with one nucleus for analysis, and group II (n = 1366), regularly cleaving embryos with two nuclei for analysis. A two-round FISH procedure was performed investigating seven chromosomes; 486 embryos were reanalysed.

RESULTS

The proportion of analysable embryos was significantly higher in group II (98.2 versus 95.9%) (P = 0.04). Despite the apparently increased false-positive rate (group I: 25.6% and group II: 13.6%) and the decreased PPV (group I: 91.9% and group II: 96.7%), specificity (group I: 74.4% and group II: 86.4%) and efficiency (group I: 93.5% and group II: 97.3%) in group I, no significance was reached (P = 0.11, P = 0.053, P = 0.11 and P = 0.06, respectively).

CONCLUSIONS

Although the analysis of one blastomere generates statistically significantly fewer embryos with a diagnosis than does the analysis of two blastomeres, the 2% difference may not be clinically relevant. The diagnostic accuracy is not significantly different between the two groups, hence not favouring the analysis of one or two blastomeres.

Early Lineage Segregation between Epiblast and Primitive Endoderm in Mouse Blastocysts through the Grb2-MAPK Pathway

It has been thought that early inner cell mass (ICM) is a homogeneous population and that cell position in the ICM leads to the formation of two lineages, epiblast (EPI) and primitive endoderm (PE), by E4.5. Here, however, we show that the ICM at E3.5 is already heterogeneous. The EPI- and PE-specific transcription factors, Nanog and Gata6, were expressed in the ICM in a random "salt and pepper" pattern, as early as E3.5, in a mutually exclusive manner. Lineage tracing showed predominant lineage restriction of single ICM cells at E3.5 to either lineage. In embryos lacking Grb2 where no PE forms, Gata6 expression was lost and all ICM cells were Nanog positive. We propose a model in which the ICM develops as a mosaic of EPI and PE progenitors at E3.5, dependent on Grb2-Ras-MAP kinase signaling, followed by later segregation of the progenitors into the appropriate cell layers.

Cell specification and the role of the polar lobe in the gastropod mollusc Crepidula fornicata

A small polar lobe forms at the first and second cleavage divisions in the gastropod mollusc Crepidula fornicata. These lobes normally fuse with the blastomeres that give rise to the D quadrant at the two- and four-cell stages (cells ultimately generating the 4d mesentoblast and D quadrant organizer). Significantly, removal of the small polar lobe had no noticeable effect on subsequent development of the veliger larva. The behavior of the polar lobe and characteristic early cell shape changes involving protrusion of the 3D macromere at the 24-cell suggest that the D quadrant is specified prior to the sixth cleavage division. On the other hand, blastomere deletion experiments indicate that the D quadrant is not determined until the time of formation of the 4d blastomere (mesentoblast). In fact, embryos can undergo regulation to form normal-appearing larvae if the prospective D blastomere or 3D macromere is removed. Removal of the 4d mesentoblast leads to highly disorganized, radial development. Removal of the first quartet micromeres at the 8-cell stage also leads to the development of radialized larvae. These findings indicate that the embryos of C. fornicata follow the mode of development exhibited by equal-cleaving spiralians, which involves conditional specification of the D quadrant organizer via inductive interactions, presumably from the first quartet micromeres.

Role of Fyn kinase in signaling associated with epiboly during zebrafish development

The function of Fyn kinase during zebrafish development through the blastula stage was investigated through the use of dominant-negative constructs designed to suppress the function of zebrafish c-Fyn. Microinjection of SH2 domain-containing fusion protein or mRNA encoding the mutated, catalytically inactive Fyn at 45 min post-insemination had no significant effect during cleavage and did not inhibit formation of the yolk syncitial layer. Smoothing of the enveloping cell layer at the midblastula transition occurred normally and expression of bon/mixer and mezzo, zygotic transcription factors indicated that activation of the zygotic genome did occur. Signaling pathways involved with axis determination such as beta-catenin, activin, and nodal appeared to function normally as evidenced by expression of boz, goosecoid, and mezzo. However, while formation of the yolk syncitial layer was normal, the marginal blastomeres failed to migrate toward the vegetal pole and epiboly did not occur, a phenotype similar but distinct from that resulting from suppression of c-Yes kinase. The block to development was prevented by co-injection of c-Fyn mRNA with the dominant-negative construct indicating that it was a specific effect. Injection of the dominant-negative mRNA into individual blastomeres indicated that the effect was exerted on the intrinsic ability of the individual blastomeres to respond to signals directing epiboly and not on the signals themselves. Analysis of the pattern of calcium signaling in experimental and control embryos demonstrated that the elevated [Ca2+]i characteristic of the marginal blastomeres was suppressed. Together, these observations indicate that Fyn kinase plays an important role in epiboly, possibly through its effects in calcium signaling.

PGD for dystrophin gene deletions using fluorescence in situ hybridization

Duchenne muscular dystrophy and Becker muscular dystrophy (DMD and BMD) are caused by mutations in the dystrophin gene (Xp21). In two-thirds of DMD/BMD cases, the mutation is a large deletion of one or several exons. We have established PGD for DMD/BMD using interphase fluorescence in situ hybridization (FISH) analysis on single nuclei from blastomeres for the detection of deletions of specific exons in the dystrophin gene. We performed PGD for two carrier females; one had a deletion of exons 45-50 (DMD), and the other had a deletion of exons 45-48 (BMD). An exon 45-specific probe was used in combination with probes for the X and Y centromeres. Using this straightforward approach, we can distinguish affected and unaffected male embryos as well as carrier female and normal female embryos. Three cycles were performed for each patient, which resulted in a pregnancy and the birth of a healthy girl. To the best of our knowledge, this approach for PGD has not been previously reported. The use of interphase FISH is an attractive alternative to sexing or PCR-based mutation detection for PGD patients with known deletions of the dystrophin gene.

Translational repression restricts expression of the C. elegans Nanos homolog NOS-2 to the embryonic germline

Members of the nanos gene family are evolutionarily conserved regulators of germ cell development. In several organisms, Nanos protein expression is restricted to the primordial germ cells (PGCs) during early embryogenesis. Here, we investigate the regulation of the Caenorhabditis elegans nanos homolog nos-2. We find that the nos-2 RNA is translationally repressed. In the adult germline, translation of the nos-2 RNA is inhibited in growing oocytes, and this inhibition depends on a short stem loop in the nos-2 3'UTR. In embryos, nos-2 translation is repressed in early blastomeres, and this inhibition depends on a second region in the nos-2 3'UTR. nos-2 RNA is also degraded in somatic blastomeres by a process that is independent of translational repression and requires the CCCH finger proteins MEX-5 and MEX-6. Finally, the germ plasm component POS-1 activates nos-2 translation in the PGCs. A combination of translational repression, RNA degradation, and activation by germ plasm has also been implicated in the regulation of nanos homologs in Drosophila and zebrafish, suggesting the existence of conserved mechanisms to restrict Nanos expression to the germline.

[HLA-A site genotyping on single blastomeres is studied by nest-PCR-SSP method]

OBJECTIVE

To assess the accuracy and reliability of the nest-PCR-sequence specific primer(SSP) method in HLA-A site genotyping of single blastomeres retrieved from human pre-implantation embryos.

METHODS

By nest PCR on HLA-A exon 2, the success rate of first-round amplification was estimated for single blastomeres. Based on the first-round amplification, the HLA-A genotype of every single blastomeres was analyzed by commercially available PCR-SSP kits.

RESULTS

The amplification of HLA-A exon 2 were performed to 120 blasotmeres retrieved from in vitro fertilization(IVF) surplus embryos donated by 10 couples. The average success rate of family 1-5 and 6-10 was 78.2%(43/55) and 93.8%(61/65), respectively. And 86.7%(104/120) in total. Eighty blastomeres were further tested by nest-PCR-SSP, among which 11 blastomeres failed to HLA-A exon 2 amplification and then failed to genotyping while the other 69 blastomeres succeed in HLA-A exon 2 amplification and succeed in genotyping. Except for 6 blastomeres that were uncertain for allele lost because of parents' homozygosity, the left 63 blastomeres had accurate HLA genotyping. Among these 63 blastomeres, 59 blastomeres had genotypes confirmed from their parents(93.6%), 3 blastomeres lost one of parents' alleles(4.8%), and only one blastomere had two more than parents' alleles(1.6%).

CONCLUSION

The above research results indicated that based on the successful first round amplification of single blastomeres, nest-PCR-SSP strategy offers a convenient and reliable option for HLA genotyping on single blastomeres, which is a key process in pre-selecting HLA-identical sibling for allogeneic cord blood cell transplantation.

The aPKC-PAR-6-PAR-3 cell polarity complex localizes to the centrosome attracting body, a macroscopic cortical structure responsible for asymmetric divisions in the early ascidian embryo

Posterior blastomeres of 8-cell stage ascidian embryos undergo a series of asymmetric divisions that generate cells of unequal sizes and segregate muscle from germ cell fates. These divisions are orchestrated by a macroscopic cortical structure, the ;centrosome attracting body' (CAB) which controls spindle positioning and distribution of mRNA determinants. The CAB is composed of a mass of cortical endoplasmic reticulum containing mRNAs (the cER-mRNA domain) and an electron dense matrix, but little is known about its precise structure and functions. We have examined the ascidian homologues of PAR proteins, known to regulate polarity in many cell types. We found that aPKC, PAR-6 and PAR-3 proteins, but not their mRNAs, localize to the CAB during the series of asymmetric divisions. Surface particles rich in aPKC concentrate in the CAB at the level of cortical actin microfilaments and form a localized patch sandwiched between the plasma membrane and the cER-mRNA domain. Localization of aPKC to the CAB is dependent on actin but not microtubules. Both the aPKC layer and cER-mRNA domain adhere to cortical fragments prepared from 8-cell stage embryos. Astral microtubules emanating from the proximal centrosome contact the aPKC-rich cortical domain. Our observations indicate that asymmetric division involves the accumulation of the aPKC-PAR-6-PAR-3 complex at the cortical position beneath the pre-existing cER-mRNA domain.