The COP9 signalosome subunit 3 is necessary for early embryo survival by way of a stable protein deposit in mouse oocytes.

Investigations of genes required in early mammalian development are complicated by protein deposits of maternal products, which continue to operate after the gene locus has been disrupted. This leads to delayed phenotypic manifestations and underestimation of the number of genes known to be needed during the embryonic phase of cellular totipotency. Here we expose a critical role of the gene Cops3 by showing that it protects genome integrity during the 2-cell stage of mouse development, in contrast to the previous functional assignment at postimplantation. This new role is mediated by a substantial deposit of protein (94th percentile of the proteome), divided between an exceptionally stable cortical rim, which is prevalent in oocytes, and an ancillary deposit in the embryonic nuclei. Since protein abundance and stability defeat prospects of DNA- or RNA-based gene inactivation in oocytes, we harnessed a classical method next to an emerging method for protein inactivation: antigen masking (for functional inhibition) versus TRIM21-mediated proteasomal degradation, also known as 'Trim away' (for physical removal). Both resulted in 2-cell embryo lethality, unlike the embryos receiving anti-green fluorescent protein. Comparisons between COPS3 protein-targeted and non-targeted embryos revealed large-scale transcriptome differences, which were most evident for genes associated with biological functions critical for RNA metabolism and for the preservation of genome integrity. The gene expression abnormalities associated with COPS3 inactivation were confirmed in situ by the occurrence of DNA endoreduplication and DNA strand breaks in 2-cell embryos. These results recruit Cops3 to the small family of genes that are necessary for early embryo survival. Overall, assigning genes with roles in embryogenesis may be less safe than assumed, if the protein products of these genes accumulate in oocytes: the inactivation of a gene at the protein level can expose an earlier phenotype than that identified by genetic techniques such as conventional gene silencing.

Chromosomal analysis for embryos from balanced chromosomal rearrangement carriers using next generation sequencing.

We aimed to use next generation sequencing (NGS) to investigate chromosomal abnormalities in blastocyst trophectoderm (TE) samples, and reproductive outcomes with the different types of chromosomal rearrangements (CR) and for each sex of CR carrier. A total of 1189 blastocyst TE samples were evaluated using NGS to detect chromosomal unbalanced translocations as well as aneuploidy, including blastocytes from 637 blastocysts from carriers of balanced CR and 552 blastocysts from carriers of normal chromosomes. The optimal embryos had lower chromosomal abnormality rates compared to the poor-quality embryos. The experimental group had significantly reduced rates of normal embryos and euploidy, and higher rates of total abnormalities, aneuploidy and unbalanced chromosomal aberrations. Carriers of reciprocal translocations had a reduced rate of normal embryos and an increased percentage of embryos with total abnormalities and unbalanced chromosomal aberrations compared with carriers of Robertsonian translocations. Couples with female carriers of chromosomal abnormalities had significantly reduced rates of normal embryos and euploidy, and a higher percentage of embryos with total abnormalities, aneuploidy, and unbalanced chromosomal aberrations compared with couples of male carriers. Our preimplantation genetic testing (PGT) study identified higher rates of chromosomal abnormalities, including chromosomal unbalanced translocations and aneuploidy, in blastocysts from CR carriers, especially from the female carriers, in a Chinese population. The PGT cycles successfully improved clinical outcomes by increasing the fertilization rate and reducing the early spontaneous abortion rate compared with the in vitro fertilization and intracytoplasmic sperm injection cycles, especially for CR carriers.

Assessing equine embryo developmental competency by time-lapse image analysis.

The timing of early mitotic events during preimplantation embryo development is important for subsequent embryogenesis in many mammalian species, including mouse and human, but, to date, no study has closely examined mitotic timing in equine embryos from oocytes obtained by ovum pick-up. Here, cumulus-oocyte complexes were collected by transvaginal follicular aspiration, matured invitro and fertilised via intracytoplasmic sperm injection. Each fertilised oocyte was cultured up to the blastocyst stage and monitored by time-lapse imaging for the measurement of cell cycle intervals and identification of morphological criteria indicative of developmental potential. Of the 56 fertilised oocytes, 35 initiated mitosis and 11 progressed to the blastocyst stage. Analysis of the first three mitotic divisions in embryos that formed blastocysts determined that typical blastocyst timing (median±IQR) is 30.0±17.5min, 8.8±1.7h and 0.6±1.4h respectively. Frequent cellular fragmentation, multipolar divisions and blastomere exclusion suggested that equine embryos likely contend with a high incidence of chromosomal missegregation. Indeed, chromosome-containing micronuclei and multinuclei with extensive DNA damage were observed throughout preimplantation embryogenesis. This indicates that time-lapse image analysis may be used as a non-invasive method to assess equine embryo quality in future studies.

Preimplantation genetic testing in assisted reproductive technology.

Preimplantation genetic testing is a methodology aimed at the assessment of the genetic composition of an embryo. This diagnostic approach has been used in assisted reproduction for almost thirty years. During these years, the technologies used for embryo's genetic analysis have been continuously improved allowing the development of more precise, comprehensive and robust strategies that are clinically employed nowadays. In this review, the main diagnostic approaches used for embryo genetic and chromosomal assessment are described and discussed both from an embryological and genetic standpoint.

Blastomere nucleation: Predictive factors and influence of blastomere with no apparent nuclei on blastocyst development and implantation.

OBJECTIVE: To investigate whether embryos presenting blastomere(s) with no apparent nucleus (BNAN) on days 2 and 3 are more likely to fail to develop into blastocysts, hatch and implant. METHODS: A total of 5705 zygotes obtained from 743 intracytoplasmic sperm injection (ICSI) cycles were analyzed. The presence and incidence of BNAN on days 2 and 3 of embryo development were recorded and then associated with ICSI outcomes. RESULTS: The occurrence of BNAN on day 2 of embryo development was determinant to the decreased odds of blastocyst formation (OR: 0.57, CI: 0.50-0.65), quality (OR: 0.56, CI: 0.43-0.73) and hatching status (OR: 0.66, CI: 0.50-0.87). The presence of BNAN on day 3 of embryo development was determinant to the decreased odds of blastocyst formation (OR: 0.67, CI: 0.58-0.78) and hatching status (OR: 0.61, CI: 0.45-0.83). The occurrence of BNAN on day 2 of embryo development was determinant to the decreased odds of blastocyst implantation (OR: 0.50, CI: 0.27-0.94). CONCLUSION: The presence of BNAN on day 2 or day 3 reduces development to blastocyst stage, hatching and implantation. Careful nuclear observation, taking into account the absence of blastomere nucleus, should be part of the strategies used for embryo selection.

Myosin-1 inhibition by PClP affects membrane shape, cortical actin distribution and lipid droplet dynamics in early Zebrafish embryos.

Myosin-1 (Myo1) represents a mechanical link between the membrane and actin-cytoskeleton in animal cells. We have studied the effect of Myo1 inhibitor PClP in 1-8 cell Zebrafish embryos. Our results indicate a unique involvement of Myo1 in early development of Zebrafish embryos. Inhibition of Myo1 (by PClP) and Myo2 (by Blebbistatin) lead to arrest in cell division. While Myo1 isoforms appears to be important for both the formation and the maintenance of cleavage furrows, Myo2 is required only for the formation of furrows. We found that the blastodisc of the embryo, which contains a thick actin cortex (~13 µm), is loaded with cortical Myo1. Myo1 appears to be crucial for maintaining the blastodisc morphology and the actin cortex thickness. In addition to cell division and furrow formation, inhibition of Myo1 has a drastic effect on the dynamics and distribution of lipid droplets (LDs) in the blastodisc near the cleavage furrow. All these results above are effects of Myo1 inhibition exclusively; Myo2 inhibition by blebbistatin does not show such phenotypes. Therefore, our results demonstrate a potential role for Myo1 in the maintenance and formation of furrow, blastodisc morphology, cell-division and LD organization within the blastodisc during early embryogenesis.

Imaging early embryonic calcium activity with GCaMP6s transgenic zebrafish.

Intracellular Ca2+ signaling regulates cellular activities during embryogenesis and in adult organisms. We generated stable Tg[ßactin2:GCaMP6s]stl351 and Tg[ubi:GCaMP6s]stl352 transgenic lines that combine the ubiquitously-expressed Ca2+ indicator GCaMP6s with the transparent characteristics of zebrafish embryos to achieve superior in vivo Ca2+ imaging. Using the Tg[ßactin2:GCaMP6s]stl351 line featuring strong GCaMP6s expression from cleavage through gastrula stages, we detected higher frequency of Ca2+ transients in the superficial blastomeres during the blastula stages preceding the midblastula transition. Additionally, GCaMP6s also revealed that dorsal-biased Ca2+ signaling that follows the midblastula transition persisted longer during gastrulation, compared with earlier studies. We observed that dorsal-biased Ca2+ signaling is diminished in ventralized ichabod/ß-catenin2 mutant embryos and ectopically induced in embryos dorsalized by excess ß-catenin. During gastrulation, we directly visualized Ca2+ signaling in the dorsal forerunner cells, which form in a Nodal signaling dependent manner and later give rise to the laterality organ. We found that excess Nodal increases the number and the duration of Ca2+ transients specifically in the dorsal forerunner cells. The GCaMP6s transgenic lines described here enable unprecedented visualization of dynamic Ca2+ events from embryogenesis through adulthood, augmenting the zebrafish toolbox.

Quantitative approaches for the study of microtubule aster motion in large eggs.

The proper positioning of microtubule (MT) asters underlies fundamental processes such as nuclear centration, cell polarity, division positioning, and embryogenesis. In large eggs and early blastomeres, MT asters may exhibit long range motions with atypical speed and precision to target their functional position. The biophysical mechanisms regulating such motions remain however largely unknown. The centration of sperm asters in sea urchin embryos is a stereotypical example of such aster long range motion. In this chapter, we describe methods developed in this system to (1) quantify sperm aster 3-D motion with confocal microscopy and automated image analysis and (2) severe a portion of astral MTs with a UV laser. These methods may serve as a template to dissect the generic mechanisms of aster motion and force production in other embryos and cell types.

Blastomere biopsy for PGD delays embryo compaction and blastulation: a time-lapse microscopic analysis.

PURPOSE: The purpose of the study was to explore the effect of blastomere biopsy for preimplantation genetic diagnosis (PGD) on the embryos' dynamics, further cleavage, development, and implantation. METHODS: The study group included 366 embryos from all PGD treatments (September 2012 to June 2014) cultured in the EmbryoScope™ time-lapse monitoring system. The control group included all intracytoplasmic sperm injection (ICSI) embryos cultured in EmbryoScope™ until day 5 during the same time period (385 embryos). Time points of key embryonic events were analyzed with an EmbryoViewer™. RESULTS: Most (88 %) of the embryos were biopsied at ≥8 cells. These results summarize the further dynamic development of the largest cohort of biopsied embryos and demonstrate that blastomere biopsy of cleavage-stage embryos significantly delayed compaction and blastulation compared to the control non-biopsied embryos. This delay in preimplanation developmental events also affected postimplantation development as observed when the dynamics of non-implanted embryos (known implantation data (KID) negative) were compared to those of implanted embryos (KID positive). CONCLUSION: Analysis of morphokinetic parameters enabled us to explore how blastomere biopsy interferes with the dynamic sequence of developmental events. Our results show that biopsy delays the compaction and the blastulation of the embryos, leading to a decrease in implantation.

Application of hollow fiber vitrification for cryopreservation of bovine early cleavage stage embryos and porcine morula-blastomeres.

A novel hollow fiber vitrification (HFV) method was applied to materials that have previously been difficult to cryopreserve, thereby expanding the potential application of this method. The results showed that zona-free porcine morulae and their isolated blastomeres remained viable even after vitrification. The rate of development to blastocysts after vitrification was similar for zona-free and zona-intact morulae (21/23, 91.3% for both). Vitrified blastomeres had a developmental potential equal to that of non-vitrified blastomeres (blastocyst formation rate after reaggregation: 16/17, 94.1% for both). The HFV method was also effective for the cryopreservation of in vitro matured/fertilized bovine embryos at the 2- to 4-cell, 8- to 16-cell and morula stages. The blastocyst formation rates of vitrified embryos (66.1-82.5%) were similar to those of non-vitrified embryos (74.5-82.5%). These results indicate that this novel HFV method is an effective tool for embryo cryopreservation that can enhance current practices in reproductive biology.

The Dynamin 2 inhibitor Dynasore affects the actin filament distribution during mouse early embryo development.

Dynamin 2 is a large GTPase notably involved in clathrin-mediated endocytosis, cell migration and cytokinesis in mitosis. Our previous study identified that Dynamin 2 regulated polar body extrusion in mammalian oocytes, but its roles in early embryo development, remain elusive. Here, we report the critical roles of Dynamin 2 in mouse early embryo development. Dynamin 2 accumulated at the periphery of the blastomere during embryonic development. When Dynamin 2 activity was inhibited by Dynasore, embryos failed to cleave to the 2-cell or 4-cell stage. Moreover, the actin filament distribution and relative amount were aberrant in the treatment group. Similar results were observed when embryos were cultured with Dynasore at the 8-cell stage; the embryos failed to undergo compaction and develop to the morula stage, indicating a role of Dynamin 2 in embryo cytokinesis. Therefore, our data indicate that Dynamin 2 might participate in the early embryonic development through an actin-based cytokinesis.

The conserved barH-like homeobox-2 gene barhl2 acts downstream of orthodentricle-2 and together with iroquois-3 in establishment of the caudal forebrain signaling center induced by Sonic Hedgehog.

In this study, we investigated the gene regulatory network that governs formation of the Zona limitans intrathalamica (ZLI), a signaling center that secretes Sonic Hedgehog (Shh) to control the growth and regionalization of the caudal forebrain. Using loss- and gain-of-function, explants and grafting experiments in amphibians, we demonstrate that barhl2 acts downstream of otx2 and together with the iroquois (irx)-3 gene in establishment of the ZLI compartment initiated by Shh influence. We find that the presumptive (pre)-ZLI domain expresses barhl2, otx2 and irx3, whereas the thalamus territory caudally bordering the pre-ZLI expresses barhl2, otx2 and irx1/2 and early on irx3. We demonstrate that Barhl2 activity is required for determination of the ZLI and thalamus fates and that within the p2 alar plate the ratio of Irx3 to Irx1/2 contributes to ZLI specification and size determination. We show that when continuously exposed to Shh, neuroepithelial cells coexpressing barhl2, otx2 and irx3 acquire two characteristics of the ZLI compartment-the competence to express shh and the ability to segregate from anterior neural plate cells. In contrast, neuroepithelial cells expressing barhl2, otx2 and irx1/2, are not competent to express shh. Noteworthy in explants, under Shh influence, ZLI-like cells segregate from thalamic-like cells. Our study establishes that Barhl2 activity plays a key role in p2 alar plate patterning, specifically ZLI formation, and provides new insights on establishment of the signaling center of the caudal forebrain.

Blastocentesis: a source of DNA for preimplantation genetic testing. Results from a pilot study.

OBJECTIVE: To investigate the presence of DNA in blastocyst fluids (BFs) and to estimate whether the chromosomal status predicted by its analysis corresponds with the ploidy condition in trophectoderm (TE) cells, the whole embryo, and that predicted by polar bodies (PBs) or blastomeres. DESIGN: Prospective study. SETTING: In vitro fertilization unit. PATIENT(S): Seventeen couples undergoing preimplantation genetic screening with the use of array comparative genomic hybridization on PBs (n = 12) or blastomeres (n = 5). INTERVENTION(S): BFs and TE cells were retrieved from 51 blastocysts for separate chromosomal analysis. MAIN OUTCOME MEASURE(S): Presence of DNA in BFs and assessment of the corresponding chromosome condition; correlation with the results in TE cells and those predicted by the analysis done at earlier stages. RESULT(S): DNA was detected in 39 BFs (76.5%). In 38 of 39 cases (97.4%) the ploidy condition of BFs was confirmed in TE cells, and the rate of concordance per single chromosome was 96.6% (904/936). In relation to the whole embryo, the ploidy condition corresponded in all cases with a per-chromosome concordance of 98.1%. The testing of PBs and blastomeres had 93.3% and 100% prediction of BF ploidy condition with a concordance per chromosome of 93.5% and 94%, respectively. CONCLUSION(S): Blastocentesis could represent an alternative source of material for chromosomal testing, because the BF is highly predictive of the embryo ploidy condition and chromosome content. Our data confirm the relevance of the oocyte and of the early-cleavage embryo in determining the ploidy condition of the resulting blastocyst.

Developmental capacity and pregnancy rate of tetrahedral- versus non-tetrahedral-shaped 4-cell stage human embryos.

PURPOSE: The arrangement of the blastomeres within the 4-cell stage embryo reflects the orientation of the cleavage planes during the second division. To examine their relevance, the developmental capacity and the pregnancy rate were compared between tetrahedral-shaped and non-tetrahedral-shaped 4-cell stage human embryos. METHODS: The study included 3,546 4-cell stage embryos. The arrangement of the blastomeres at the 4-cell stage was annotated as being tetrahedral or non-tetrahedral on day 2 of preimplantation development. Embryo quality was compared on day 3 and day 5. Pregnancy rates were calculated per single embryo transfer on day 3 or day 5. RESULTS: In total, 2,803 4-cell stage embryos (79 %) displayed a tetrahedral arrangement and 743 (21 %) displayed a non-tetrahedral arrangement. Tetrahedral-shaped embryos developed more into high-quality embryos on day 3 (p < 0.001) and day 5 (p = 0.036) and had a higher blastulation rate (p = 0.009). Though, the number of high-quality embryos selected for transfer did not differ between both groups on day 3 (p = 0.167) and day 5 (p ~ 1). Three hundred thirty single embryo transfers were analysed. No significant difference in clinical pregnancy was found between both groups after transfer on day 3 (p = 0.209) and day 5 (p = 0.653). CONCLUSIONS: The arrangement of the blastomeres according to their previous cleavage planes was correlated to the developmental potential of the 4-cell stage embryo up to the blastocyst stage. If embryo transfers are performed on day 3 and day 5 of development using embryos of adequate quality, the blastomere arrangement at the 4-cell stage had no predictable value regarding pregnancy success.

Chromosomal complement and clinical relevance of multinucleated embryos in PGD and PGS cycles.

The objective of this retrospective study was to investigate the incidence and clinical implications of multinucleation in blastomeres biopsied from cleavage-stage embryos obtained from patients undergoing preimplantation genetic screening (PGS) for aneuploidies or preimplantation genetic diagnosis (PGD) for translocations or single-gene defects (SGD). A total of 3515 embryos were obtained from 306 couples in 380 PGD or PGS cycles. Incidence of multinucleation, chromosomal complement in multinucleated (MN) and sibling embryos and the characteristics of MN embryos resulting in healthy births were investigated. Of all cycles, 41.3% involved at least one MN embryo. There were more uniformly diploid than uniformly haploid nuclei (22.0% versus 7.9%, P<0.01). The most common form of abnormality was chaotic chromosomal complement (39.9%, 147/368). Transfer of embryos that had MN blastomeres free of the genetic abnormalities tested resulted in three healthy deliveries. It is concluded that, although the majority of MN blastomeres are chromosomally abnormal, healthy births are possible after transfer of embryos containing these blastomeres subjected to genetic analysis. As far as is known, this is the first report of healthy births after transfer of embryos with MN blastomeres tested for translocations or SGD in PGD cycles. Preimplantation genetic diagnosis (PGD) is an established method for selecting genetically healthy embryos for transfer. A blastomere sampled from the developing embryo is subjected to genetic analysis. Some of these blastomeres may contain multiple nuclei, complicating the genetic diagnosis. We investigated clinical implications of multinucleation in PGD cycles. Our results indicate that majority of the multinucleated blastomeres, and consequently embryos, are genetically abnormal. However, healthy births are possible after transfer of multinucleated embryos that are free of the genetic abnormalities screened.

Correlative light and electron microscopic analyses of mitochondrial distribution in blastomeres of early fish embryos.

Early embryos of vertebrates undergo remarkable dynamic molecular events, such as embryonic gradient, cellular polarity, and asymmetry necessary for cell fate decisions. Correlative light and electron microscopy (CLEM) is a powerful tool to investigate rare or dynamic molecular events and has been developed for relatively small cells in culture and tissues but is not yet available for large cells of early development stage embryos. Here we report the capability of CLEM in blastomeres of medaka fish by using the mitochondria detection system. A short N-terminal signal peptide of the mitochondrial protein Tom20 was linked to green fluorescent protein (GFP), resulting in a fusion protein termed Tom20:GFP. The subcellular location of Tom20:GFP in medaka blastomeres reveals the lack of mitochondrial distribution in pseudopodia as well as inconspicuous redistribution during divisions. Blastomeres, after sample preparation procedures including high-pressure freezing and freeze substitution, are able to preserve fluorescence, antigenicity, and fine structures, which allows for precise correlation between the Tom20:GFP fluorescence and mitochondria on merged light and electron micrographs. Furthermore, nanogold immunostaining for Tom20:GFP and endogenous Tom20 revealed their specific localization on the mitochondrial outer membrane. Our results extend the CLEM approach to early development stage embryos of a vertebrate.

Early intrauterine embryonic development of the bothriocephalidean cestode Clestobothrium crassiceps (Rudolphi, 1819), a parasite of the teleost Merluccius merluccius (L., 1758) (Gadiformes: Merlucciidae).

The early intrauterine embryonic development of the bothriocephalidean cestode Clestobothrium crassiceps (Rudolphi, 1819), a parasite of the teleost Merluccius merluccius (L., 1758), was studied by means of light (LM) and transmission electron microscopy (TEM). Contrary to the generic diagnosis given in the CABI Keys to the cestode parasites of vertebrates, the eggs of C. crassiceps, the type of species of Clestobothrium Lühe, 1899, are operculate and embryonated. Our LM and TEM results provide direct evidence that an operculum is present and that the eggs exhibit various stages of intrauterine embryonic development, and in fact represent a good example of early ovoviviparity. The intrauterine eggs of this species are polylecithal and contain numerous vitellocytes, generally ∼30, which are pushed to the periphery and remain close to the eggshell, whereas the dividing zygote and later the early embryo remain in the egg centre. During early intrauterine embryonic development, several cleavage divisions take place, which result in the formation of three types of blastomeres, i.e. macro-, meso- and micromeres. These can be readily differentiated at the TEM level, not only by their size, but also by the ultrastructural characteristics of their nuclei and cytoplasmic organelles. The total number of blastomeres in these early embryos, enclosed within the electron-dense eggshells, can be up to ∼20 cells of various sizes and characteristics. Mitotic divisions of early blastomeres were frequently observed at both LM and TEM levels. Simultaneously with the mitotic cleavage divisions leading to blastomere multiplication and their rapid differentiation, there is also a deterioration of some blastomeres, mainly micromeres. A similar degeneration of vitellocytes begins even earlier. Both processes show a progressive degeneration of both vitellocytes and micromeres, and are good examples of apoptosis, a process that provides nutritive substances, including lipids, for the developing embryo.

Human preimplantation embryo development in vitro: a morphological assessment of sibling zygotes cultured in a single medium or in sequential media.

A comparison was made of the development of human zygotes in either a one-step (Global® medium) or two-step culture system (Quinn's Advantage®). A total of 257 normally fertilized 2PN zygotes from 28 patients were used in the study. The study was broken down into two parts: the first concerned the development of embryos from Days 1 to 3 in Global® medium and Quinn's Advantage® cleavage medium; the second consisted of a comparison of the development of embryos from Day 3 to 5/6 in Global® medium and Quinn's Advantage® blastocyst medium. There were no significant differences between the two culture media with respect to embryo quality throughout the preimplantation phase of human embryo development as determined by the extent and variability of the cell counts, fragmentation, and nucleation. A difference was noted in the blastomere symmetry of Day 2 embryos in the two media, but was no longer apparent on examination of Day 3 embryos. No differences were noted in the rates of blastocyst development, inner cell mass (ICM), and trophectoderm (TE) scores in the two culture media. Finally, no significant differences were noted with either the proportion of blastocysts chosen for transfer or cryopreservation (vitrification). The findings support the view that two-step sequential media protocols are sufficient but not necessary to support the complete in vitro development of human preimplantation embryos.

Analysis of localization and reorganization of germ plasm in Xenopus transgenic line with fluorescence-labeled mitochondria.

Germ plasm is found in germ-line cells of Xenopus and thought to include the determinant of primordial germ cells (PGCs). As mitochondria is abundant in germ plasm, vital staining of mitochondria was used to analyze the movement and function of germ plasm; however, its application was limited in early cleavage embryos. We made transgenic Xenopus, harboring enhanced green fluorescent protein (EGFP) fused to the mitochondria transport signal (Dria-line). Germ plasm with EGFP-labeled mitochondria was clearly distinguishable from the other cytoplasm, and retained mostly during one generation of germ-line cells in Dria-line females. Using the Dria-line, we show that germ plasm is reorganized from near the cell membrane to the perinuclear space at St. 9, dependent on the microtubule system.

Nucleoli from two-cell embryos support the development of enucleolated germinal vesicle oocytes in the pig.

Recent research has shown that nucleoli of oocytes at the germinal vesicle (GV) stage (GV nucleoli) are not necessary for oocyte maturation but are essential for early embryonic development. Nucleoli of 2-cell embryos (2-cell nucleoli) have morphology similar to that of nucleoli in oocytes at the GV stage. In this study, we examined the ability of 2-cell nucleoli to substitute for GV nucleoli in terms of supporting early embryonic development by nucleolus aspiration (enucleolation) and transfer into metaphase II (MII) oocytes or 2-cell embryos that were derived from enucleolated oocytes at the GV stage in the pig. When 2-cell embryos were centrifuged to move the lipid droplets to one side of the blastomere, multiple nucleoli in the nucleus fused into a single nucleolus. The nucleoli were then aspirated from the 2-cell embryos by micromanipulation. The injection of 2-cell nucleoli to GV enucleolated oocytes at the MII stage rescued the embryos from the early embryonic arrest, and the resulting oocytes developed to blastocysts. However, the injection of 2-cell and GV nucleoli to 2-cell embryos derived from GV enucleolated oocytes rarely restored the development to blastocysts. These results indicate that 2-cell nucleoli support early embryonic development as GV nucleoli and that the presence of nucleoli is essential for pig embryos before the 2-cell stage.