Histone phosphorylation and pericentromeric histone modifications in oocyte meiosis

Epigenetic regulation of pericentromeric heterochromatin is crucial for proper interactions between kinetochores and spindle microtubules governing accurate chromosome segregation. Here, we first examined the dynamic distribution of phosphorylated serine 10 and 28 on H3 during mouse oocyte maturation and early embryo development using immunofluorescent staining and confocal microscopy. Our results revealed strong signals of phosphorylated H3/ser10 and 28 in the pericentromeric heterochromatin area and continuous persistent staining of the chromosome periphery, respectively. A panel of specific antibodies against various acetylated lysine, dimethylated lysine or phosphorylated serine residues on histone H3 or H4 were used to investigate the effects of Trichostatin A (TSA), a general inhibitor of histone deacetylases (HDACs), on histone modifications of pericentromeric heterochromatin. Unexpectedly, TSA treatment was unable to alter the acetylation and methylation status of pericentromeric heterochromatin, however, it resulted in significant dephosphorylation of H3/ser10 at this site during mouse oocyte meiosis, which is likely to play a role in the TSA-induced defective chromosome segregation. Furthermore, by using ZM447439, an inhibitor of Aurora kinases, we revealed that Aurora kinases may participate in the regulation of histone phosphorylation during mouse oocyte maturation.

Histone deacetylation is required for orderly meiosis

Histone acetylation is associated with a diversity of chromatin-related processes in mitosis. However, its roles in mammalian oocyte meiosis are largely unknown. In the present study, we first investigated in detail the acetylation changes during porcine oocyte maturation using a panel of antibodies specific for the critical acetylated forms of histone H3 and H4, and showed meiosis stage-dependent and lysine residue-specific patterns of histone acetylation. By using trichostatin A (TSA), a general inhibitor of histone deacetylases (HDACs), we further determined that selective inhibition of histone deacetylation (thereby maintaining hyperacetylation) delayed the onset of germinal vesicle breakdown and produced a high frequency of lagging chromosomes or chromatin bridges at anaphase and telophase I (AT-I), suggesting that histone deacetylation is required for orderly meiotic resumption and accurate chromosome segregation in porcine oocytes. In addition, we examined the localization and expression of HDAC1 by performing immunofluorescence and immunoblotting analysis. The results showed that subcellular translocation, expression level and phosphorylated modification of HDAC1 were temporally regulated and likely to coparticipate in the establishment of histone acetylation profiles in oocyte meiosis.

Interspecies nuclear transfer reveals that demethylation of specific repetitive sequences is determined by recipient ooplasm but not by donor intrinsic property in cloned embryos

DNA methylation/demethylation of donor genomes in recipient ooplasm after nuclear transfer occurs in a species-specific way. In cloned rabbit and bovine embryos, repetitive sequences maintain the donor-type methylation status, but typical demethylation of repetitive sequences takes place in cloned porcine embryos. To clarify whether the demethylation is controlled by donor nucleus intrinsic property or by recipient ooplasm, we used interspecies somatic cell nuclear transfer (iSCNT) model to examine the methylation status of repetitive sequences in pig-to-rabbit and rabbit-to-pig interspecies embryos. We found that no demethylation of pig repetitive sequences was observed in pig-to-rabbit iSCNT embryos, while the examined rabbit repetitive sequence Rsat IIE was demethylated in rabbit-to-pig iSCNT embryos. These results indicate that demethylation of donor repetitive sequences is determined by ooplasm but not by donor intrinsic property and that ooplasm from different species have different capabilities to demethylate genes.

Cloning of Asian yellow goat (C. hircus) by somatic cell nuclear transfer: Telophase enucleation combined with whole cell intracytoplasmic injection

Our and other previous studies have shown that telophase enucleation is an efficient method for preparing recipient cytoplasts in nuclear transfer. Conventional methods of somatic cell nuclear transfer either by electro-fusion or direct nucleus injection have very low efficiency in animal somatic cell cloning. To simplify the manipulation procedure and increase the efficiency of somatic cell nuclear transfer, this study was designed to study in vitro and in vivo development of Asian yellow goat cloned embryos reconstructed by direct whole cell intracytoplasmic injection (WCICI) into in vitro matured oocytes enucleated at telophase II stage. Our results demonstrated that the rates of cleavage and blastocyst development of embryos reconstructed by WCICI were slightly higher than in conventional subzonal injection (SUZI) group, but no statistic difference (P > 0.05) existed between these two methods. However, the percentage of successful embryonic reconstruction in WCICI group was significantly higher than that in SUZI group (P < 0.05). After embryo transfer at 4-cell stage, the foster in both groups gave birth to offspring. Therefore, the present study suggests that the telophase ooplasm could properly reprogram the genome of somatic cells, produce Asian yellow goat cloned embryos and viable kids, and whole cell intracytoplasmic injection is an efficient protocol for goat somatic cell nuclear transfer.

Different fates of donor mitochondrial DNA in bovine-rabbit and cloned bovine-rabbit reconstructed embryos during preimplantation development

The functions of mitochondria depend on precise interaction between nuclear and cytoplasmic genomes. Non-balance of mtDNA has been reported in most nuclear transfer embryos and offspring. The reason of the degradation of donor mtDNA is still not clear. To further investigate the mechanism, in this study, we designed an experiment as follows. Two fibroblast cell lines sharing same nuclear genome but different mitochondria genome backgrounds, namely cells from ear tissues of cloned bovine and its donor, were choose as donor cells and introduced into enucleated rabbit oocytes. Similar developmental potential was observed in cloned bovine-rabbit (clone group) and bovine-rabbit (non-clone group) embryos. Real-time PCR assay showed that, in non-clone group, bovine mtDNA decreased during the development of reconstructed embryo, and that a sharp decrease was detected at the blastocyst stage. In clone group, bovine mtDNA decreased slightly, and the abrupt reduction of donor mtDNA did not occur during preimplantation development. In addition, an obvious increase in rabbit mtDNA was observed in both groups at the blastocyst stage. Our results demonstrate that: 1) the fates of donor mtDNAs in bovine-rabbit and cloned bovine-rabbit reconstructed embryos were different; and 2) recipient mtDNAs replicate at blastocyst regardless of the difference of donor cells.

Rabbit Oocyte Cytoplasm Supports Development of Nuclear Transfer Embryos Derived from the Somatic Cells of the Camel and Tibetan Antelope

This study was designed to examine the ability of rabbit metaphase II oocyte cytoplasm to support the development of interspecies nuclear transfer embryos reconstructed using donor nuclei from different species. Skin fibroblast cells from a camel and Tibetan antelope were used as donor nuclei. As a first step, we investigated the efficiency of different activation protocols by comparing the parthenogenetic development of rabbit oocytes. The protocol that yielded the highest blastocyst rate was used to activate the reconstructed embryos in nuclear transfer experiments. In addition, the effect of donor cell serum starvation on the development of the reconstructed embryo was also examined. More than half of the karyoplast-cytoplast couplets could be fused, and about one third of the reconstructed embryos were capable of completing first cleavage, regardless of the species of donor nuclei. Some of the cleaving reconstructed embryos were even capable of progressing further and developing to the blastocyst stage (1.4-8.7% for the Tibetan antelope and 0-7.5% for the camel, respectively). Our results suggest that the mechanisms regulating early embryo development may be conserved among mammalian species and some factors existing in rabbit oocyte cytoplasm for somatic nucleus reprogramming and dedifferentiation may not be species-specific. Rabbit oocyte cytoplasm can reprogram donor nuclei regardless of the origin of the nucleus and support in vitro development to an advanced stage.

Degradation of securin in mouse and pig oocytes is dependent on ubiquitin-proteasome pathway and is required for proteolysis of the cohesion subunit, Rec8, at the metaphase-to-anaphase transition

Although securin/separase/cohesion pathway was reported to regulate chromosome segregation during meiotic metaphase-to-anaphase transition, little biochemical evidence was provided. We recently found that oocytes could not progress beyond meiotic metaphase when ubiquitin-proteasome pathway was inhibited, but the mechanisms remain unclear. In the present study, we investigated the quantity of securin and Rec8 protein and the localization of securin, a cohesion subunit, during oocyte meiosis providing data in support of the hypothesis that the effect of ubiquitin-proteasome pathway on metaphase-to-anaphase transition was mediated by regulating securin and Rec8 degradation in mouse and pig oocytes. In germinal vesicle-stage oocytes, immunostaining of securin was mainly localized in the germinal vesicle. Shortly after germinal vesicle breakdown, immunoreactive securin accumulated around the condensed chromosomes at prometaphase I. At metaphase I and metaphase II, when chromosomes were organized at the equatorial plate, immunoreactive securin was concentrated around the aligned chromosomes, putatively associated with the position of the metaphase spindle. The accumulation of securin could not be detected at anaphase I and anaphase II. In both mouse and pig oocytes, Western blot analysis showed that securin protein was low at germinal vesicle stage, reached the highest level at metaphase I, while decreased at anaphase I. Securin was increased again at metaphase II, while it was decreased at anaphase II. Rec8 protein was present in germinal vesicle-stage oocytes and remained until metaphase I, while it was decreased at anaphase I. Like securin, Rec8 was increased at metaphase II, while it was decreased again at anaphase II. The inhibition of the ubiquitin-proteasome pathway inhibited the decrease in securin and Rec8 at metaphase-to-anaphase transitions in both mouse and pig oocytes. Microinjection of securin antibody into MII-arrested oocytes leads to the degradation of Rec8. In conclusion, these results suggest that the proteolysis of securin is dependent on ubiquitin-proteasome pathway and is necessary for the degradation of Rec8 during meiotic metaphase-to-anaphase transitions in mouse and pig oocytes.

Dynamic changes in NuMA and microtubules in monkey-rabbit nuclear transfer embryos

Previous reports have indicated that failure in cloning monkey is attributed to the removal of nuclear mitotic apparatus (NuMA) during enucleation and subsequent abnormal organization of mitotic apparatus. This study investigated the transformation and assembly of tubulin and NuMA protein during the first cell cycle of cloned monkey embryos reconstructed by using enucleated rabbit oocytes as recipients. After the oocyte fused with a fibroblast, extensive microtubule organization was observed around the introduced nucleus in most reconstructed embryos, suggesting the introduction of a somatic cell centrosome. A high proportion of fibroblast nuclei transferred into non-activated oocytes underwent premature chromosome condensation (PCC), transient spindle organization and chromosomes separation, followed by the formation of two pronucleus-like structures. In contrast, fibroblast nuclei in pre-activated ooplasm rarely underwent PCC, but formed a swollen pronucleus-like structure. Normal spindles were observed in about one third of the cloned embryos reconstructed by both methods. After transferring monkey fibroblasts into NuMA-removed enucleated rabbit oocytes, NuMA was localized in pseudo-pronuclei and gradually moved to mitotic spindle poles at the first mitotic spindle poles. NuMA antibody microinjection resulted in spindle disorganization and chromosome misalignment, but did not significantly affect early cleavage. Our findings indicate that: 1. NuMA in donor monkey fibroblast may contribute to form a normal spindle in enucleated rabbit oocyte; 2. when non-activated cytoplasts and pre-activated cytoplasts are used as recipients, the donor nuclei undergo different morphological changes, but yield similar early embryo development; 3. although abnormal spindle organization and chromosome alignment may cause low efficiency of animal cloning, these abnormalities do not significantly affect early cleavage.

Active demethylation of individual genes in intracytoplasmic sperm injection rabbit embryos

Intracytoplasmic sperm injection (ICSI), as an assisted reproduction technique, has been widely used in animal and human. However, its possible effect on epigenetic changes has not been well studied. To investigate whether ICSI can induce aberrant DNA methylation changes in rabbit preimplantation embryos, we examined the methylation status of the SP-A promoter region and the satellite sequence Rsat IIE by bisulfite-sequencing technology. The SP-A promoter region was extensively demethylated before the first round of DNA replication commences, and the unmethylated status was maintained until morula when dynamic remethylation occurred. A similar but more moderate demethylation process was observed in satellite sequence Rsat IIE. These results are in contrast with the previous reports of no active demethylation in normal rabbit embryos, suggesting that the active demethylation we observed may be induced by ICSI.

Effects of cooling, cryopreservation and heating on sperm proteins, nuclear DNA, and fertilization capability in mouse

In the present study, we used confocal microscopy and electrophoresis to study the effects of heating to 5 or 100 degrees C or cooling to 4 degrees C or -- 196 degrees C on the stability of sperm proteins and DNA. We used intracytoplasmic sperm injection (ICSI) to determine the fertilizing capability of treated spermatoza. It was shown that sperm cryopreservation at - 196 degrees C or cooling at 4 degrees C altered neither protein and DNA profiles nor the sperm fertilization capability, while the protein and DNA profiles of sperm heated at 100 degrees C were irreversibly degraded and inactivated. The proteins of sperm were severely damaged while the nuclear DNA still maintained its integrity when heated to 58 degrees C. Observation by laser confocal microscopy showed that after being heated to 58 degrees C and 100 degrees C, the nuclear of mouse sperm lost their ability to activate oocytes and they could not transform to male pronuclei though the membrane of some sperm could degrade and induce the formation of sperm asters in ICSI oocytes. The results indicate that the use of 58 degrees C heating only causes the degradation of sperm proteins, while the 100 degrees C heating elicits the irreversible degradation of both sperm proteins and nuclear DNA, and the damage of sperm proteins is primarily responsible for the observed decrease in sperm fertilizing capability.

Cyclic adenosine 3',5'-monophosphate-dependent activation of mitogen-activated protein kinase in cumulus cells is essential for germinal vesicle breakdown of porcine cumulus-enclosed oocytes

MAPK plays an important role during meiotic maturation in mammalian oocytes, whereas the necessity of MAPK during meiotic resumption in porcine oocytes is still controversial. Here, by applying the method of ultracentrifugation to move the opaque lipid droplets to the edge of the oocyte, therefore allowing clear visualization of porcine germinal vesicles, oocytes just before germinal vesicle breakdown (GVBD) and those that had just undergone GVBD were selected for the assay of MAPK activation. Our results showed that phosphorylation of MAPK in oocytes occurred after GVBD in all three different culture models: spontaneous maturation model, inhibition-induction maturation model, and normal maturation model. Moreover, we found that activation of MAPK in cumulus cells but not in oocytes was essential for GVBD in cumulus-enclosed oocytes. Then the cross-talk between cAMP and MAPK in cumulus cells was investigated by using cell-type-specific phosphodiesterase (PDE) isoenzyme inhibitors. Our results showed that PDE3 subtype existed in oocytes, whereas PDE4 subtype existed in cumulus cells. PDE3 inhibitor prevented meiotic resumption of oocytes, whereas PDE4 inhibitor enhanced the ability of FSH or forskolin to activate MAPK in cumulus cells. We propose that increased cAMP resulting from inhibition of PDE3 in oocytes blocks GVBD, whereas increased cAMP resulting from inhibition of PDE4 activates MAPK pathway in cumulus cells, which is essential for GVBD induction.

Cell cycle-dependent localization and possible roles of the small GTPase Ran in mouse oocyte maturation, fertilization and early cleavage

The small GTPase Ran controls numerous cellular processes of the mitotic cell cycle. In this experiment, we investigated the localization and possible roles of Ran during mouse oocyte meiotic maturation, fertilization and early cleavage by using confocal laser scanning microscopy, antibody microinjection and microtubule disturbance. The results showed that Ran was localized mainly in the nucleus (except for the nucleolus) in the oocyte, zygote and early embryo. At pro-metaphase of meiosis I, Ran distributed throughout the cell, but predominantly concentrated around the condensed chromosomes. During the completion of meiosis I and meiosis II, it concentrated to the meiotic spindle microtubules except for the midbody region. After sperm penetration, Ran dispersed with the extrusion of the second polar body and gradually concentrated in the male and female pronuclei thereafter. Ran was also observed to exist diffusely in the cytoplasm in prophase; it concentrated at the mitotic spindle, and migrated to the nucleus during early cleavage. Ran’s concentration around the spindle disappeared when microtubule assembly was inhibited by colchicine, while it was concentrated around the chromosomes after microtubule stabilization with taxol treatment. Ran did not display any role in cytokinesis during division when pseudo-cleavage of germinal vesicle-intact oocytes was induced. Anti-Ran antibody microinjection decreased the germinal vesicle breakdown and the first polar body extrusion, and distorted spindle organization and chromosome alignment. Our results indicate that Ran has a cell cycle-dependent localization and may have regulatory roles in cell cycle progression and microtubule organization in mouse oocytes, fertilized eggs and early embryos.

In vitro culture and mtDNA fate of ibex–rabbit nuclear transfer embryos

Rabbit oocyte can be used as the recipient in interspecies somatic cell nuclear transfer (iSCNT). This work was undertaken in order to study the developmental competence of Capra ibex somatic cells reprogrammed by rabbit oocytes and the fate of mitochondria in iSCNT embryos. Metaphase II (MII) oocytes from superovulated rabbit were used as nuclear recipients. The nuclear donors were Capra ibex somatic cells with different proliferative status: population doubling time (PDL)=15±2 (group 1), 35±2 (group 2), 55±2 (group 3) and 70±2 (group 4). Oocytes reconstructed with electrical pulses (2.1 kV/cm, 10 μs, 2 times) were activated (1.4 kV, 20 μs, 2 times) and then cultured in Medium199 containing 10% fetal bovine serum at 38.5 °C, 5% CO2 in air. In groups 1, 2, 3 and 4, the fusion rates were 35.83%, 66.03%, 65.40% and 35.35%, respectively. Similar cleavage rates were observed among the four groups. However, the developmental potential to morula/blastocyst from early nuclear donor embryos (16.42%/10.45%) was significantly higher (p < 0.05) than in terminal donor embryos (9.52%/3.81%). Polymerase chain reaction analysis of the mitochondrial (mt) DNA cytb gene demonstrated that mtDNAs from ibex and rabbit could be detected at various developmental stages before implantation. In conclusion, our results provide some original information about rescuing Capra ibex using the iSCNT technique. These results indicate that: (1) enucleated rabbit oocytes make Capra ibex fibroblast nuclei reprogramme; (2) the proliferative status of donor cells affects the efficiency of iSCNT; and (3) rabbit ooplasm rescues the donor-derived mtDNAs, resulting in mtDNA heteroplasmy before implantation.

Small GTPase RhoA is required for ooplasmic segregation and spindle rotation, but not for spindle organization and chromosome separation during mouse oocyte maturation, fertilization, and early cleavage

RhoA, a small GTPase, plays versatile roles in many aspects of cell function such as stress fiber formation, cytokinesis, and cell polarization. In this study, we investigated the subcellular localization of RhoA and its possible roles during oocyte maturation and fertilization. RhoA was localized in the cytoplasm of eggs from the germinal vesicle (GV) stage to 2-cell stage, especially concentrating in the midbody of telophase spindle when oocyte extruded PB1 and PB2. The RhoA kinases (ROCKs) specific inhibitor Y-27632 blocked GV breakdown (GVBD) and first polar body extrusion, but did not affect apparatus formation and anaphase/telophase I entry. Anti-RhoA antibody microinjection into the oocytes showed similar results. RhoA inhibitor caused abnormal organization of microfilaments, failure of spindle rotation, PB2 extrusion as well as cleavage furrow formation, while sister chromatid separation was not affected. Microinjection of RhoA antibody also blocked PB2 emission. Our findings indicate that RhoA, by regulating microfilament organization, regulates several important events including GVBD, polar body emission, spindle rotation, and cleavage.

Effects of oocyte collection time and injection position on pronucleus formation and blastocyst development in round spermatid injection in mouse

The injection of spermatozoa into mouse, human and rabbit oocytes at specific times and positions can result in different rates of viable embryo development. However, it is not clear how the timing and position of round spermatid injection (ROSI) affect pronucleus (PN) formation and blastocyst development of mice. First, we determined the changes in relative position of the first polar body and the spindle, carried out ROSI from 11.5 to 13 h post-hCG administration, then activated by Sr2+, and finally compared the development of ROSI zygotes, including the formation of pronuclei and development of blastocyst. Between 11.5 and 13 h post-hCG administration, the rate of 2PN formation by ROSI at 3 o'clock was the highest among all treated oocytes. Moreover, the blastocyst rate of zygotes with two pronuclei (2PN) was up to 27.41%. These results suggest that the time and position of ROSI can significantly influence the formation of 2PN, that the rates of 2PN formation are closely correlated with blastocyst formation and that the formation of 2PN is necessary for later embryo development.

Cell-cycle-dependent subcellular localization of cyclin B1, phosphorylated cyclin B1 and p34cdc2 during oocyte meiotic maturation and fertilization in mouse

M phase or maturation promoting factor (MPF), a kinase complex composed of the regulatory cyclin B and the catalytic p34cdc2 kinase, plays important roles in meiosis and mitosis. This study was designed to detect and compare the subcellular localization of cyclin B1, phosphorylated cyclin B1 and p34cdc2 during oocyte meiotic maturation and fertilization in mouse. We found that all these proteins were concentrated in the germinal vesicle of oocytes. Shortly after germinal vesicle breakdown, all these proteins were accumulated around the condensed chromosomes. With spindle formation at metaphase I, cyclin B1 and phosphorylated cyclin B1 were localized around the condensed chromosomes and concentrated at the spindle poles, while p34cdc2 was localized in the spindle region. At the anaphase/telophase transition, phosphorylated cyclin B1 was accumulated in the midbody between the separating chromosomes/chromatids, while p34cdc2 was accumulated in the entire spindle except for the midbody region. At metaphase II, both cyclin B1 and p34cdc2 were horizontally localized in the region with the aligned chromosomes and the two poles of the spindle, while phosphorylated cyclin B1 was localized in the two poles of spindle and the chromosomes. We could not detect a particular distribution of cyclin B1 in fertilized eggs when the pronuclei were initially formed, but in late pronuclei cyclin B1 was accumulated in the pronuclei. p34cdc2 and phosphorylated cyclin B1 were always concentrated in one pronucleus after parthenogenetic activation or in two pronuclei after fertilization. At metaphase of 1-cell embryos, cyclin B1 was accumulated around the condensed chromosomes. Cyclin B1 was accumulated in the nucleus of late 2-cell embryos but not in early 2-cell embryos. Furthermore, we also detected the accumulation of p34cdc2 in the nucleus of 2- and 4-cell embryos. All these results show that cyclin B1, phosphorylated cyclin B1 and p34cdc2 have similar distributions at some stages but different localizations at other stages during oocyte meiotic maturation and fertilization, suggesting that they may play a common role in some events but different roles in other events during oocyte maturation and fertilization.

Production of mouse by inter-strain inner cell mass replacement

The developmental ability of reconstructed blastocysts from C57BL/6 strain mouse inner cell masses (ICMs) and Kunming strain mouse trophoblasts was assessed. The procedure of ICM replacement was as follows: C57BL/6 ICMs were separated from the blastocysts using immunosurgery. A slit was made in the zona pellucida of a Kunming blastocyst to allow its ICM to extrude. The C57BL/6 ICM was injected into the Kunming blastocoele, and the extruded Kunming ICM was cut off. The reconstructed blastocysts were able to re-expand (77%) and hatch (27.3%) in vitro. A total of 64 reconstructed blastocysts and 124 Kunming blastocysts were co-transferred into the uteri of 11 pseudopregnant Kunming mice, and an ICM replacement offspring was born. The results indicate that reconstructed embryos obtained by inter-strain ICM replacement have the ability to develop to term. This technique may provide a method to solve the pregnancy failure in interspecific cloning.

Apoptosis in rabbit embryos produced by fertilization or nuclear transfer with fibroblasts and cumulus cells

In this study, we investigated the development, the cell number of the blastocyst, and apoptosis in rabbit nuclear transfer (NT) embryos derived from adult fibroblasts and cumulus cells as compared with embryos derived fromin vivofertilization andin vitroculture. The developmental rate and the total cell number of the blastocyst were significantly lower in NT embryos than in fertilized embryos (FEs). The type of donor cells did not affect the embryonic developmental rate and the total cell number of blastocysts in NT groups. The present study investigated the onset and the frequency of apoptosis in NT embryos and FEs by using a terminal deoxynucleotidyl transferase-mediated dUTP nick and labeling (TUNEL) assay. The earliest positive TUNEL signals were detected at the eight-cell stage in NT embryos and at the morula stage in FEs. The apoptotic index of the total blastocysts, the inner cell mass and the trophoderm was greatly higher in the NT embryos than in FEs. Moreover, the apoptotic index of the blastocyst from fibroblasts was significantly higher than that of the blastocyst from cumulus cells.

DNA hypomethylation of individual sequences in aborted cloned bovine fetuses

Cloned bovines have a much higher abortion rate than those derived in vivo. Available evidence indicates that inappropriate epigenetic reprogramming of donor nuclei is the primary cause of cloning failure. To gain a better understanding of the DNA methylation changes associated with the high abortion rate of cloned bovines, we examined the DNA methylation status of a repeated sequence (satellite I) and the promoter regions of two single-copy genes (interleukin 3/cytokeratin) in aborted cloned fetuses, aborted fetuses derived from artificial insemination (AI), cloned adults and AI adults by bisulfite sequencing and restriction enzyme analysis. Two of four aborted cloned fetuses show very low methylation levels in the two single-copy gene promoter regions. One of the two fetuses also showed undermethylated status in the satellite I sequence. The other two aborted cloned fetuses have similar methylation levels to those of aborted AI fetuses. However, no difference in methylation was observed between cloned adults and AI adults. Our results demonstrate for the first time the undermethylated status of individual sequences in aborted cloned fetuses. These findings suggest that aberrant DNA methylation may contribute to the developmental failure of cloned bovine fetuses.

Transplantation of somatic nuclei into oocyte cytoplasm reveals that the chromosome properties determine the chromosome separation fate in rabbit

G2/M somatic nuclei were introduced into enucleated meiotically competent oocytes and subsequently cultured in TCM199 plus 10% fetal calf serum (FCS). Pseudo-first polar bodies could be extruded, but the chromosomes failed to arrange normally. Kinetochores were traced with immunofluorescent microscopy using autoimmune sera from patients with CREST (Calcinosis, Raynaud's phenomenon, Esophageal dysmotility, Sclerodactyly, Telangiectasia) scleroderma. In vitro matured oocytes arrested at second meiotic metaphase and kinetochores were detectable as paired structures aligned at the spindle equator. At meiotic anaphase, present or past the kinetochores separated and remained aligned at the distal sides of the chromosomes until telophase, when their alignment perpendicular to the spindle axis was lost. Kinetochores failed to arrange normally after transferring somatic nuclei into oocytes. Our results suggest that somatic cell nuclei are unable to proceed normally through meiosis when introduced into oocyte meiotic cytoplasm.

The effects of chemical enucleation combined with whole cell intracytoplasmic injection on panda-rabbit interspecies nuclear transfer

Conventional methods of somatic cell nuclear transfer either by electrofusion or direct nucleus injection have very low efficiency in animal cloning, especially interspecies cloning. To increase the efficiency of interspecies somatic cell nuclear transfer, in the present study we introduced a method of whole cell intracytoplasmic injection (WCICI) combined with chemical enucleation into panda-rabbit nuclear transfer and assessed the effects of this method on the enucleation rate of rabbit oocytes and the in vitro development and spindle structures of giant panda-rabbit reconstructed embryos. Our results demonstrated that chemical enucleation can be used in rabbit oocytes and the optimal enucleation result can be obtained. When we compared the rates of cleavage and blastocyst formation of subzonal injection (SUZI) and WCICI using chemically enucleated rabbit oocytes as cytoplasm recipients, the rates in the WCICI group were higher than those in the SUZI group, but there was no statistically siginificant difference (p > 0.05) between the two methods. The microtubule structures of rabbit oocytes enucleated by chemicals and giant panda-rabbit embryos reconstructed by WCICI combined with chemical enucleation were normal. Therefore the present study suggests that WCICI combined with chemical enucleation can provide an efficient and less labor-intensive protocol of interspecies somatic cell nuclear transfer for producing giant panda cloned embryos.

Transplantation of male pronucleus derived from in vitro fertilization of enucleated oocyte into parthenogenetically activated oocyte results in live offspring in mouse

In this study, inter-strain reconstructed embryos were produced by combining the female pronucleus of Kunming mouse (white) with male pronucleus of C57BL/6 strain (black). Metaphase II (MII) oocytes of Kunming mouse were enucleated and the zona pellucida was removed. Then, the enucleated oocytes were inseminated by capacitated sperm of C57BL/6 mouse in vitro. At the same time, MII oocytes of Kunming mouse were artificially activated using strontium chloride solution, which did not contain cytochalasin B. Finally, we removed the male pronucleus derived from C57BL/6 sperm and injected it into a parthenogenetically activated one-pronucleus oocyte by micromanipulation. The reconstructed 2-cell embryos were transplanted into the oviducts of 22 foster mother mice, each receiving about 20 embryos. In the end, seven healthy and live pups were born from one recipient.

Full-term development of mouse eggs transplanted with male pronuclei derived from round spermatids: The effect of synchronization between male and female pronucleus on embryonic development

Pronucleus transplanted mice have been produced, but their donor male pronuclei were derived from mature sperm and were completely synchronous with female pronuclei because both male and female pronuclei came from the same fertilized oocyte. The present study firstly produced male pronuclei by introducing round spermatids into enucleated mouse oocytes, then transferred the male pronuclei into mouse oocytes at three activation stages and finally compared the effect of three kinds of oocytes on the development of reconstructed embryos. Our results indicate that, in enucleated oocytes, mouse round spermatid nuclei can transform to male pronuclei in a higher proportion, and the synchronization between male and female pronucleus does not significantly influence the early cleavage but the later and full-term development of reconstructed embryos.

Inducible nitric oxide synthase-derived nitric oxide regulates germinal vesicle breakdown and first polar body emission in the mouse oocyte

The present study investigated the subcellular localization of inducible nitric oxide synthase (iNOS) during mouse oocyte meiotic maturation and fertilization using confocal microscopy, and further studied the roles of iNOS-derived NO in oocyte maturation by using an iNOS-specific inhibitor aminoguanidine (AG) and iNOS antibody microinjection. In germinal vesicle-stage oocytes, iNOS immunoreactivity was mainly localized in the germinal vesicle. Shortly after germinal vesicle breakdown, the iNOS immunoreactivity accumulated around the condensed chromosomes. At metaphase I and metaphase II, with the organization of chromosomes to the equatorial plate, iNOS immunoreactivity was concentrated around the aligned chromosomes, putatively the position of the metaphase spindle. The accumulation of iNOS immunoreactivity could not be detected at anaphase I and anaphase II. However, at telophase I and telophase II, the staining of iNOS was concentrated in the region between the separating chromosomes/chromatids. Furthermore, the staining of iNOS also accumulated in the male and female pronuclei in fertilized eggs. Germinal vesicle breakdown and the first polar body emission of the oocytes were significantly blocked by the iNOS-specific inhibitor AG in a dose-dependent manner. The germinal vesicle breakdown in oocytes injected with iNOS antibody was also inhibited. We found that the phosphorylation of mitogen-activated protein kinase in oocytes after germinal vesicle breakdown was inhibited by AG treatment. The control oocytes extruded a normal first polar body, while the AG-treated oocytes exhibited an elongated protrusion or no elongated protrusion. The results of confocal microscopy showed that the AG-treated oocytes were arrested at anaphase I–telophase I. Our results suggest that the iNOS-derived NO pathway plays important roles in mouse oocyte meiotic maturation, especially in germinal vesicle breakdown and the anaphase–telophase transition.