D quadrant specification in the leech Helobdella: actomyosin contractility controls the unequal cleavage of the CD blastomere

The unequal division of the CD blastomere at second cleavage is critical in establishing the second embryonic axis in the leech Helobdella, as in other unequally cleaving spiralians. When CD divides, the larger D and smaller C blastomeres arise invariantly on the left and right sides of the embryo, respectively. Here we show that stereotyped cellular dynamics, including the formation of an intercellular blastocoel, culminate in a morphological left-right asymmetry in the 2-cell embryo, which precedes cytokinesis and predicts the chirality of the second cleavage. In contrast to the unequal first cleavage, the unequal second cleavage does not result from down-regulation of one centrosome, nor from an asymmetry within the spindle itself. Instead, the unequal cleavage of the CD cell entails a symmetric mitotic apparatus moving and anisotropically growing rightward in an actomyosin-dependent process. Our data reveal that mechanisms controlling the establishment of the D quadrant differ fundamentally even among the monophyletic clitellate annelids. Thus, while the homologous spiral cleavage pattern is highly conserved in this clade, it has diverged significantly at the level of cell biological mechanisms. This combination of operational conservation and mechanistic divergence begins to explain how the spiral cleavage program has remained so refractory to change while, paradoxically, accommodating numerous modifications throughout evolution.

[Green fluorescent protein has no effect on blastocyst development in C57BL/6-Tg(ACTB-EGFP)1Osb/J mice]

The changes in the state of long-term culture of blastocysts derived from female C57BL/6 mice after crossing with C57BL/6-Tg(ACTB-EGFP)1Osb/J males with a green fluorescent protein transgene EGFP on chromosome 15 were studied. Possible causes of different culture results were analyzed: the preservation of undifferentiated cells as dense clusters in the inner cell mass or their differentiation into extraembryonic endoderm. Comparison of the events going in blastocysts with the -/- or -/EGFP genotypes demonstrated that the GFP presence has no effect on cell processes. This allows us to use embryonic material from this mouse line in experiments that require long-term vital observation of embryonic cells.

Differential cytotoxic effects of mono-(2-ethylhexyl) phthalate on blastomere-derived embryonic stem cells and differentiating neurons

Potential applications of embryonic stem (ES) cells are not limited to regenerative medicine but can also include in vitro screening of various toxicants. In this study, we established mouse ES cell lines from isolated blastomeres of two-cell stage embryos and examined their potential use as an in vitro system for the study of developmental toxicity. Two ES cell lines were established from 69 blastomere-derived blastocysts (2.9%). The blastomere-derived ES (bm-ES) cells were treated with mono-(2-ethylhexyl) phthalate (MEHP) in an undifferentiated state or after directed differentiation into early neural cell types. We observed significantly decreased cell viability when undifferentiated bm-ES cells were exposed to a high dose of MEHP (1000 microM). The cytotoxic effects of MEHP were accompanied by increased DNA fragmentation, nuclear condensation, and activation of Caspase-3, which are biochemical and morphological features of apoptosis. Compared to undifferentiated bm-ES cells, considerably lower doses of MEHP (50 and 100 microM) were sufficient to induce cell death in early neurons differentiated from bm-ES cells. At the lower doses, the number of neural cells positive for the active form of Caspase-3 was greater than that for undifferentiated bm-ES cells. Thus, our data indicate that differentiating neurons are more sensitive to MEHP than undifferentiated ES cells, and that undifferentiated ES cells may have more efficient defense systems against cytotoxic stresses. These findings might contribute to the development of a new predictive screening method for assessment of hazards for developmental toxicity.

Ectopic expression of prelamin A in early Xenopus embryos induces apoptosis

Lamin proteins are components of metazoan cell nuclei. During evolution, two classes of lamin proteins evolved, A- and B-type lamins. B-type lamins are expressed in nearly all cell types and in all developmental stages and are thought to be indispensable for cellular survival. In contrast, A-type lamins have a more restricted expression pattern. They are expressed in differentiated cells and appear late in embryogenesis. In the earliest steps of mammalian development, A-type lamins are present in oocytes, pronuclei and during the first cleavage stages of the developing embryo. But latest after the 16-cell stage, A-type lamin proteins are not any longer detectable in embryonic cells. Amphibian oocytes and early embryos do not express lamin A. Moreover, extracts of Xenopus oocytes and eggs have the ability to selectively remove A-type lamins from somatic nuclei. This observation and the restricted expression pattern suggest that the presence of lamin A might interfere with developmental processes in the early phase of embryogenesis. To test this, we ectopically expressed lamin A during early embryonic development of Xenopus laevis by microinjection of synthetic mRNA. Here, we show that introducing mature lamin A does not interfere with normal development. However, expression of prelamin A or lamin A variants that cannot be fully processed cause severe disturbances and lead to apoptosis during gastrulation. The toxic effect is due to lack of the conversion of prenylated prelamin A to its mature form. Remarkably, even a cytoplasmic prelamin A variant that is excluded from the nucleus drives embryos into apoptosis.

Changes in localization and expression levels of Shroom2 and spectrin contribute to variation in amphibian egg pigmentation patterns

One contributing factor in the worldwide decline in amphibian populations is thought to be the exposure of eggs to UV light. Enrichment of pigment in the animal hemisphere of eggs laid in the sunlight defends against UV damage, but little is known about the cell biological mechanisms controlling such polarized pigment patterns. Even less is known about how such mechanisms were modified during evolution to achieve the array of amphibian egg pigment patterns. Here, we show that ectopic expression of the gamma-tubulin regulator, Shroom2, is sufficient to induce co-accumulation of pigment granules, spectrin, and dynactin in Xenopus blastomeres. Shroom2 and spectrin are enriched and co-localize specifically in the pigmented animal hemisphere of Xenopus eggs and blastulae. Moreover, Shroom2 messenger RNA (mRNA) is expressed maternally at high levels in Xenopus. In contrast to Xenopus, eggs and blastulae of Physalaemus pustulosus have very little surface pigmentation. Rather, we find that pigment is enriched in the perinuclear region of these embryos, where it co-localizes with spectrin. Moreover, maternal Shroom2 mRNA was barely detectable in Physaleamus, though zygotic levels were comparable to Xenopus. We therefore suggest that a Shroom2/spectrin/dynactin-based mechanism controls pigment localization in amphibian eggs and that variation in maternal Shroom2 mRNA levels accounts in part for variation in amphibian egg pigment patterns during evolution.

[Osmotic behavior of mouse embryonic cells subjected to hypotonic shock]

Osmotic adaptation in a blastomere of mouse embryo has been studied by the direct measurement of the cell volume using laser scanning microscopy microtomography followed by quantitative 3D reconstruction. Embryonic cells subjected to hypotonic shock first swelled and then returned to the initial size. At the beginning of osmotic stress, the swelling occurred by the van't Hoff equation with the water permeability coefficient (L(p)) of 0.4 micro x min(-1) atm(-1). The phase of the regulatory volume decrease was not abolished by Na+/K(+)-ATPase inhibition.

Cell polarity emerges at first cleavage in sea urchin embryos

In protostomes, cell polarity is present after fertilization whereas most deuterostome embryos show minimal polarity during the early cleavages. We now show establishment of cell polarity as early as the first cleavage division in sea urchin embryos. We find, using the apical markers G(M1), integrins, and the aPKC-PAR6 complex, that cells are polarized upon insertion of distinct basolateral membrane at the first division. This early apical-basolateral polarity, similar to that found in much larger cleaving amphibian zygotes, reflects precocious functional epithelial cell polarity. Isolated cleavage blastomeres exhibit polarized actin-dependent fluid phase endocytosis only on the G(M1), integrin, microvillus-containing apical surface. A role for a functional PAR complex in cleavage plane determination was shown with experiments interfering with aPKC activity, which results in several spindle defects and compromised blastula development. These studies suggest that cell and embryonic polarity is established at the first cleavage, mediated in part by the Par complex of proteins, and is achieved by directed insertion of basolateral membrane in the cleavage furrow.

Housekeeping genes for cryopreservation studies on zebrafish embryos and blastomeres

Cryopreservation success is usually analysed in terms of cell survival, although there are other potential effects that do not necessarily result in cell death. These include DNA damage, which could result in altered gene expression. Real-time reverse transcriptase PCR allows quantitative analysis of gene expression but usually requires analysis of a 'housekeeping' gene as an internal reference. As the stability of housekeeping genes varies significantly among different groups of samples, it is recommended that those chosen are validated for each different type of sample group. This study aimed to validate housekeeping genes for use in cryopreservation studies of zebrafish embryos. Seven potential housekeeping genes were analysed across fresh and chilled intact embryos and across fresh and frozen isolated blastomeres using the GeNorm and NormFinder software packages. Results suggest that combined use of beta-actin and EF1alpha as housekeeping genes would be suitable for cryopreservation studies on zebrafish embryos and blastomeres.

Global transcriptional repression in C. elegans germline precursors by regulated sequestration of TAF-4

In C. elegans, four asymmetric divisions, beginning with the zygote (P0), generate transcriptionally repressed germline blastomeres (P1-P4) and somatic sisters that become transcriptionally active. The protein PIE-1 represses transcription in the later germline blastomeres but not in the earlier germline blastomeres P0 and P1. We show here that OMA-1 and OMA-2, previously shown to regulate oocyte maturation, repress transcription in P0 and P1 by binding to and sequestering in the cytoplasm TAF-4, a component critical for assembly of TFIID and the pol II preinitiation complex. OMA-1/2 binding to TAF-4 is developmentally regulated, requiring phosphorylation by the DYRK kinase MBK-2, which is activated at meiosis II after fertilization. OMA-1/2 are normally degraded after the first mitosis, but ectopic expression of wild-type OMA-1 is sufficient to repress transcription in both somatic and later germline blastomeres. We propose that phosphorylation by MBK-2 serves as a developmental switch, converting OMA-1/2 from oocyte to embryo regulators.

[Production of reconstructed two-cell rat embryos after chemical inactivation of chromosomes in MII oocytes by etoposide]

The application of etoposide for chemical enucleation of rat oocytes was tested. The reconstruction efficiency after chemical and mechanical enucleation was comparatively analyzed. The obtained data indicate similar viability of reconstructed rat embryos irrespective of the enucleation technique.

Live visualization of protein synthesis in axonal growth cones by microinjection of photoconvertible Kaede into Xenopus embryos

Photoconvertible fluorescent proteins, such as Kaede, can be switched irreversibly from their native color to a new one. This property can be exploited to visualize de novo mRNA translation, because newly synthesized proteins can be distinguished from preexisting ones by their color. In this protocol, Kaede cDNA linked to the 3' untranslated region (UTR) of beta-actin is delivered into cells fated to become the retina by injection into Xenopus blastomeres. Brief exposure (6-10 s) to UV light (350-410 nm) of Kaede-positive retinal axons/growth cones efficiently converts Kaede from its native green fluorescence to red. The reappearance of the green signal reports the synthesis of new Kaede protein. This approach can be used to investigate the spatiotemporal control of translation of specific mRNAs in response to external stimuli and to test the efficiency of full-length versus mutant UTRs. The 3-d protocol can be adapted for broad use with other photoactivatable fluorescent proteins.

[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.

The Xenopus Nieuwkoop center and Spemann-Mangold organizer share molecular components and a requirement for maternal Wnt activity

In Xenopus embryos, the dorso-ventral and antero-posterior axes are established by the Spemann-Mangold organizer. According to the prevalent model of early development, the organizer is induced by the dorsalizing Nieuwkoop signal, which is secreted by the Nieuwkoop center. Formation of the center requires the maternal Wnt pathway, which is active on the dorsal side of embryos. Nevertheless, the molecular nature of the Nieuwkoop signal remains unclear. Since the Nieuwkoop center and the organizer both produce dorsalizing signals in vitro, we asked if they might share molecular components. We find that vegetal explants, the source of Nieuwkoop signal in recombination assays, express a number of organizer genes. The product of one of these genes, chordin, is required for signaling, suggesting that the organizer and the center share at least some molecular components. Furthermore, experiments with whole embryos show that maternal Wnt activity is required in the organizer just as it is needed in the Nieuwkoop center in vitro. We conclude that the maternal Wnt pathway generates the Nieuwkoop center in vitro and the organizer in vivo by activating a common set of genes, without the need of an intermediary signaling step.

Delayed and stage specific phosphorylation of H2AX during preimplantation development of gamma-irradiated mouse embryos

Within minutes of the induction of DNA double-strand breaks in somatic cells, histone H2AX becomes phosphorylated in the serine 139 residue at the damage site. The phosphorylated H2AX, designated as gamma-H2AX, is visible as nuclear foci in the irradiated cells which are thought to serve as a platform for the assembly of proteins involved in checkpoint response and DNA repair. It is known that early stage mammalian embryos are highly sensitive to radiation but the mechanism of radiosensitivity is not well understood. Thus, we investigated the damage response of the preimplantation stage development by analyzing focus formation of gamma-H2AX in mouse embryos gamma-irradiated in utero. Our analysis revealed that although H2AX is present in early preimplantation embryos, its phosphorylation after 3 Gy gamma-irradiation is hindered up to the two cell stage of development. When left in utero for another 24-64 h, however, these irradiated embryos showed delayed phosphorylation of H2AX. In contrast, phosphorylation of H2AX was readily induced by radiation in post-compaction stage embryos. It is possible that phosphorylation of H2AX is inefficient in early stage embryos. It is also possible that the phosphorylated H2AX exists in the dispersed chromatin structure of early stage embryonic pronuclei, so that it cannot readily be detected by conventional immunostaining method. In either case, this phenomenon is likely to correlate with the lack of cell cycle arrest, apoptosis and high radiosensitivity of these developmental stages.

Murine fertilized ovum, blastomere and morula cells lacking SP phenotype

In the field of stem cell research, SP (side population) phenotype is used to define the property that cells maintain a high efflux capability for some fluorescent dye, such as Hoechst 33342. Recently, many researches proposed that SP phenotype is a phenotype shared by some stem cells and some progenitor cells, and that SP phenotype is regarded as a candidate purification marker for stem cells. In this research, murine fertilized ova (including conjugate and single nucleus fertilized ova), 2-cell stage and 8-cell stage blastomeres, morulas and blastocysts were isolated and directly stained by Hoechst 33342 dye. The results show that fertilized ovum, blastomere and morula cells do not demonstrate any ability to efflux the dye. However, the inner cell mass (ICM) cells of blastocyst exhibit SP phenotype, which is consistent with the result of embryonic stem cells (ESCs) in vitro. These results indicate that the SP phenotype of ICM-derived ESCs is an intrinsic property and independent of the culture condition in vitro, and that SP phenotype is one of the characteristics of at least some pluripotent stem cells, but is not shared by totipotent stem cells. In addition, the result that the SP phenotype of ICM cells disappeared when the inhibitor verapamil was added into medium implies that the SP phenotype is directly associated with ABCG2. These results suggest that not all the stem cells demonstrate SP phenotype, and that SP phenotype might act as a purification marker for partial stem cells such as some pluripotent embryonic stem cells and multipotent adult stem cells, but not for all stem cells exampled by the totipotent stem cells in the very early stage of mouse embryos.

Transient occurrence of vasa-expressing cells in nongenital segments during embryonic development in the oligochaete annelid Tubifex tubifex

The primordial germ cells (PGCs) in the oligochaete annelid Tubifex tubifex are mesodermal in origin and are located in the two midbody segments X and XI in which the testis and the ovary are formed, respectively. To identify a molecular marker for the Tubifex PGCs, we isolated the Tubifex homologue (Ttu-vas) of the Drosophila vasa gene. Using whole-mount in situ hybridization, we examined the spatial expression patterns of Ttu-vas from one-cell stage through juvenile stage. Ttu-vas messenger ribonucleic acid (RNA) is present as a maternal transcript distributed broadly throughout the early stages. Ttu-vas is expressed in all of the early cleavage blastomeres, in which Ttu-vas RNA associates with mitotic spindles and pole plasms. Expression of Ttu-vas gradually becomes restricted, first to teloblasts, then to their blast cell progeny comprising the germ bands (GBs), and finally to a set of large ventral cells (termed VE cells) in a variable set of midbody segments including the genital segments (X and XI). At the end of embryogenesis, VE cells are confined to genital segments where they are presumably germline precursors in the juvenile. Staining with a cross-reacting anti-Vasa antibody suggested that VE cells express Ttu-vas protein to the same extent irrespective of their positions along the anteroposterior axis. A set of cell ablation experiments suggested that VE cells are derived from the mesodermal teloblast lineage and that the emergence of VE cells takes place independently of the presence of the ectodermal GBs that normally overlay the mesoderm. These results suggest that T. tubifex generates supernumerary presumptive PGCs during embryogenesis whose number is variable among embryos.

BMP gradients steer nerve growth cones by a balancing act of LIM kinase and Slingshot phosphatase on ADF/cofilin

Bone morphogenic proteins (BMPs) are involved in axon pathfinding, but how they guide growth cones remains elusive. In this study, we report that a BMP7 gradient elicits bidirectional turning responses from nerve growth cones by acting through LIM kinase (LIMK) and Slingshot (SSH) phosphatase to regulate actin-depolymerizing factor (ADF)/cofilin-mediated actin dynamics. Xenopus laevis growth cones from 4–8-h cultured neurons are attracted to BMP7 gradients but become repelled by BMP7 after overnight culture. The attraction and repulsion are mediated by LIMK and SSH, respectively, which oppositely regulate the phosphorylation-dependent asymmetric activity of ADF/cofilin to control the actin dynamics and growth cone steering. The attraction to repulsion switching requires the expression of a transient receptor potential (TRP) channel TRPC1 and involves Ca²⁺ signaling through calcineurin phosphatase for SSH activation and growth cone repulsion. Together, we show that spatial regulation of ADF/cofilin activity controls the directional responses of the growth cone to BMP7, and Ca²⁺ influx through TRPC tilts the LIMK-SSH balance toward SSH-mediated repulsion.

Galphai generates multiple Pins activation states to link cortical polarity and spindle orientation in Drosophila neuroblasts

Drosophila neuroblasts divide asymmetrically by aligning their mitotic spindle with cortical cell polarity to generate distinct sibling cell types. Neuroblasts asymmetrically localize Galphai, Pins, and Mud proteins; Pins/Galphai direct cortical polarity, whereas Mud is required for spindle orientation. It is currently unknown how Galphai-Pins-Mud binding is regulated to link cortical polarity with spindle orientation. Here, we show that Pins forms a "closed" state via intramolecular GoLoco-tetratricopeptide repeat (TPR) interactions, which regulate Mud binding. Biochemical, genetic, and live imaging experiments show that Galphai binds to the first of three Pins GoLoco motifs to recruit Pins to the apical cortex without "opening" Pins or recruiting Mud. However, Galphai and Mud bind cooperatively to the Pins GoLocos 2/3 and tetratricopeptide repeat domains, respectively, thereby restricting Pins-Mud interaction to the apical cortex and fixing spindle orientation. We conclude that Pins has multiple activity states that generate cortical polarity and link it with mitotic spindle orientation.

Ankyrin-G is a molecular partner of E-cadherin in epithelial cells and early embryos

E-cadherin is a ubiquitous component of lateral membranes in epithelial tissues and is required to form the first lateral membrane domains in development. Here, we identify ankyrin-G as a molecular partner of E-cadherin and demonstrate that ankyrin-G and beta-2-spectrin are required for accumulation of E-cadherin at the lateral membrane in both epithelial cells and early embryos. Ankyrin-G binds to the cytoplasmic domain of E-cadherin at a conserved site distinct from that of beta-catenin. Ankyrin-G also recruits beta-2-spectrin to E-cadherin-beta-catenin complexes, thus providing a direct connection between E-cadherin and the spectrin/actin skeleton. In addition to restricting the membrane mobility of E-cadherin, ankyrin-G and beta-2-spectrin also are required for exit of E-cadherin from the trans-Golgi network in a microtubule-dependent pathway. Ankyrin-G and beta-2-spectrin co-localize with E-cadherin in preimplantation mouse embryos. Moreover, knockdown of either ankyrin-G or beta-2-spectrin in one cell of a two-cell embryo blocks accumulation of E-cadherin at sites of cell-cell contact. E-cadherin thus requires both ankyrin-G and beta-2-spectrin for its cellular localization in early embryos as well as cultured epithelial cells. We have recently reported that ankyrin-G and beta-2-spectrin collaborate in biogenesis of the lateral membrane ( Kizhatil, K., Yoon, W., Mohler, P. J., Davis, L. H., Hoffman, J. A., and Bennett, V. (2007) J. Biol. Chem. 282, 2029-2037 ). Together with the current findings, these data suggest a ankyrin/spectrin-based mechanism for coordinating membrane assembly with extracellular interactions of E-cadherin at sites of cell-cell contact.

[Effect of local microapplication of serotoninergic drugs on membrane currents of Paracentrotus lividus early embryos]

It was shown that local application of agonists of the 3rd type receptors SR57277A and quipazine into the interblastomere cleft of Paracentrotus lividus embryos evoked specific membrane currents. At the same time, ligands of 5-HT3-receptors specifically affected the cleavage patterns of half-embryos, i.e., imitated or avoided the interblastomere signal. In the view of the data obtained, we discuss a more precise concept of protosynapse, where the distribution of membrane serotonin receptors is restricted to the period of blastomere formation during cleavage and localized in the area of interblastomere contact.

Nuclear accumulation of β-catenin and transcription of downstream genes are regulated by zygotic Wnt5α and maternal Dsh in ascidian embryos

Nuclear beta-catenin plays crucial roles in the establishment of the embryonic axis and formation of mesendoderm tissues in ascidians and other animals. However, the cue responsible for nuclear accumulation of beta-catenin in the vegetal hemisphere is still unknown in ascidians. Here, we investigated the roles of Wnt5alpha and Dsh in the nuclear accumulation of beta-catenin and activation of its downstream genes in the ascidian Halocynthia roretzi. Wnt5alpha knockdown embryos lost nuclear accumulation of beta-catenin at the 64-cell stage but not at the 32-cell stage, and expression of Hr-lim, one of the targets of beta-catenin, was impaired in the anterior region of the embryo. Zygotic Wnt5alpha expression in the anterior-vegetal blastomeres was primarily responsible for these defects. Dsh knockdown showed no effect on nuclear localization of beta-catenin, but inhibited Hr-lim expression in the posterior region. These results suggest that maintenance of nuclear Hr-beta-catenin after the 64-cell stage is regulated by zygotic Hr-Wnt5alpha, and that expression of its target genes is modulated by both Hr-Wnt5alpha and Hr-Dsh. Our results also highlight the importance of nuclear accumulation of beta-catenin up to the 32-cell stage through a still unclarified mechanism.

[Preimplantation genetic diagnosis of Duchenne muscular dystrophy by single cell triplex PCR]

OBJECTIVE

To detect two exons of Duchenne muscular dystrophy (DMD) gene and a gender discrimination locus amelogenin gene by single cell triplex PCR, and to evaluate the possibility of this technique for preimplantation genetic diagnosis (PGD) in DMD family with DMD deletion mutation.

METHODS

Single lymphocytes from a normal male, a normal female, two DMD patients (exon 8 and 47 deleted, respectively) and single blastomeres from the couples treated by the in vitro fertilization pre-embryo transfer (IVF-ET) and without family history of DMD were obtained. Exons 8 and 47 of DMD gene were amplified by a triplex PCR assay, the amelogenin gene on X and Y chromosomes were co-amplified to analyze the correlation between embryo gender and deletion status.

RESULTS

In the normal single lymphocytes, the amplification rate of exons 8 and 47 of DMD and amelogenin gene were 93.8%, 93.8%, and 95.3% respectively. The false positive rate was 3.3%. In the exon 8 deleted DMD patient, the amplification rate of exon 47 of DMD and amelogenin gene was 95.8%, and the false positive rate was 3.3%. In the exon 47 deleted DMD patient, the amplification rate of exon 8 of DMD and amelogenin gene was 95.8%, and the false positive rate was 0. In the single blastomeres, the amplification rate of exons 8 and 47 of DMD and amelogenin gene was 82.5%, 80.0% and 77.5%, respectively, and the false positive rate was 0.

CONCLUSION

The single cell triplex PCR protocol for the detection of DMD and amelogenin gene is highly sensitive, specific and reliable, and can be used for PGD in those DMD families with DMD deletion mutation.

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.