Cytoplasmic volume of recipient oocytes affects the nucleus reprogramming and the developmental competence of HMC buffalo (Bubalus bubalis) embryos

Dynamic and aberrant patterns of H3K4me3, H3K9me3, and H3K27me3 during early zygotic genome activation in cloned mouse embryos

Somatic cell nuclear transfer (NT) is associated with aberrant changes in epigenetic reprogramming that impede the development of embryos, particularly during zygotic genome activation. Here, we characterized epigenetic patterns of H3K4me3, H3K9me3, and H3K27me3 in mouse NT embryos up to the second cell cycle (i.e. four-celled stage) during zygotic genome activation. In vivo fertilized and parthenogenetically activated (PA) embryos served as controls. In fertilized embryos, maternal and paternal pronuclei exhibited asymmetric H3K4me3, H3K9me3, and H3K27me3 modifications, with the paternal pronucleus showing delayed epigenetic modifications. Higher levels of H3K4me3 and H3K9me3 were observed in NT and PA embryos than in fertilized embryos. However, NT embryos exhibited a lower level of H3K27me3 than PA and fertilized embryos from pronuclear stage 3 to the four-celled stage. Our finding that NT embryos exhibited aberrant H3K4me3, H3K9me3, and H3K27me3 modifications in comparison with fertilized embryos during early zygotic genome activation help to unravel the epigenetic mechanisms of methylation changes in early NT reprogramming and provide an insight into the role of histone H3 in the regulation of cell plasticity during natural reproduction and somatic cell NT.

Exploration of the Cytoplasmic Function of Abnormally Fertilized Embryos via Novel Pronuclear-Stage Cytoplasmic Transfer

In regular IVF, a portion of oocytes exhibit abnormal numbers of pronuclei (PN) that is considered as abnormal fertilization, and they are routinely discarded. However, it is known that abnormal ploidy still does not completely abandon embryo development and implantation. To explore the potential of cytoplasm from those abnormally fertilized oocytes, we developed a novel technique for the transfer of large cytoplasm between pronuclear-stage mouse embryos, and assessed its impact. A large volume of cytoplast could be efficiently transferred in the PN stage using a novel two-step method of pronuclear-stage cytoplasmic transfer (PNCT). PNCT revealed the difference in the cytoplasmic function among abnormally fertilized embryos where the cytoplasm of 3PN was developmentally more competent than 1PN, and the supplementing of fresh 3PN cytoplasm restored the impaired developmental potential of postovulatory “aged” oocytes. PNCT-derived embryos harbored significantly higher mitochondrial DNA copies, ATP content, oxygen consumption rate, and total cells. The difference in cytoplasmic function between 3PN and 1PN mouse oocytes probably attributed to the proper activation via sperm and may impact subsequent epigenetic events. These results imply that PNCT may serve as a potential alternative treatment to whole egg donation for patients with age-related recurrent IVF failure.

Morphometric, subcellular, in vitro fertilisation and embryonic developmental assessment of mouse oocytes produced by anti-inhibin serum or pregnant mare serum gonadotrophin superovulation

This study compared the morphometric, subcellular characteristics, in vitro fertilisation (IVF) and embryonic developmental potential of metaphase II (MII) mouse oocytes obtained from females superovulated with either anti-inhibin serum-human chorionic gonadotrophin (AIS-hCG) or pregnant mare serum gonadotrophin (PMSG)-hCG. The oocyte's quantity, quality, zona pellucida (ZP) thickness, perivitelline space (PVS), diameter, microtubules, F-actin, cortical granules (CGs) and mitochondrial distribution were determined. Superovulation using AIS-hCG resulted in a higher numbers of oocyte/donor compared with PMSG-hCG (P=0.002). There was no difference in morphologically normal and abnormal oocytes between AIS-hCG and PMSG-hCG (P=0.425 and P=0.194, respectively). The morphometric measurements showed no difference in oocyte diameter between AIS-hCG and PMSG-hCG (P=0.289). However, the thickness of the ZP of oocytes from AIS-hCG females was decreased compared with PMSG-hCG (P<0.001). The PVS of oocytes from the AIS-hCG was larger than with PMSG-hCG (P<0.001). The microtubules of oocytes from both AIS-hCG and PMSG-hCG were normal, although there was an increased fluorescence intensity in the AIS-hCG oocytes (P<0.001). The F-actin and CGs distribution in oocytes from both AIS-hCG and PMSG-hCG were similar (P=0.330 and P=0.13, respectively). Although the oocytes from PMSG-hCG females had homogenously distributed mitochondria, AIS-hCG oocytes showed more peripheral distribution with no differences in fluorescence intensity (P=0.137). The blastocyst development rates after IVF with fresh sperm showed no difference between AIS-hCG and PMSG-hCG (P=0.235). These data suggested that AIS-hCG superovulation produces high numbers of morphologically normal oocytes that also possess normal subcellular structures, good morphological characteristics and had high invitro embryonic developmental potential.

Effect of Additional Cytoplasm of Cloned Embryo on In Vitro Developmental Competence and Reprogramming Efficiency in Mice

Somatic cell nuclear transfer (SCNT) is an important technique for biological science research. Cytoplasm injection cloning technology (CICT) was developed to improve the reprogramming efficiency as well as to overcome the limitations of SCNT. CICT uses an additional cytoplasm fused with an enucleated oocyte to restore the cytoplasmic volume of the cloned embryo, and this method could improve the reprogramming efficiency of the cloned embryo. In this study, we show that CICT can be adapted to mouse species to overcome the inefficiency of the SCNT method. In this study, results indicate that the two-cell embryo and blastocyst rates of cloned embryos with the use of the CICT method were significantly higher (p < 0.05) than that of the SCNT method (96.6% ± 1.1% vs. 86.7% ± 6.0%, 29.5% ± 2.6% vs. 22.1% ± 3.0%, respectively). Furthermore, the apoptotic cell number per blastocyst was significantly lower in the CICT group than that in the SCNT group (1.7 ± 0.2 vs. 2.9 ± 0.3, p < 0.05). Moreover, the acH3K9/K14 expression level in the CICT group was greater than that of the SCNT group (p < 0.05), and the relative acH3K56 level in the CICT group was significantly (p < 0.05) higher than that in the SCNT group. These results indicate that CICT helps improve the in vitro developmental competence and quality of cloned embryos.

Production of cloned cats using additional complimentary cytoplasm

Somatic cell nuclear transfer (SCNT) is an important technique for producing cloned animals. It, however, is inefficient when there is use of SCNT for cloned animal production. Cytoplasm injection cloning technology (CICT) was developed to overcome the inefficiencies of SCNT use of this purpose. The use of CICT involves additional cytoplasm fusing with enucleated oocytes to restore the cytoplasmic volume, thus improving the in vitro developmental competence and quality of cloned embryos. In this study, there was application of CICT in cats to improve the in vitro developmental competence of cloned embryos, as well as the production of the offspring. The results of this study were that fusion rate of the cloned embryos with use of the CICT method was greater than that with SCNT (80.0 ± 4.8% compared with 67.8 ± 11.3%, respectively), and more blastocysts developed with use of CICT than SCNT (20.0 ± 2.0% compared with 13.5 ± 5.0%, respectively). The 62 cloned embryos that were produced with use of CICT were transferred into five estrous synchronized recipients, and 151 cloned embryos produced using SCNT were transferred to 13 estrous-synchronized recipients. After the embryo transfer, there was birth from surrogate mothers of one live-born kitten that resulted using SCNT compared with three live-born kittens using CICT. The number of CICT-cloned embryos born was greater than that of SCNT-cloned embryos (4.8 ± 2.3% compared with 0.7 ± 1.3%, P <  0.05). These results indicate that the CICT technique can be used to produce cloned kittens, including endangered feline species.