In vitro development of non-enucleated rat oocytes following microinjection of a cumulus nucleus and chemical activation

Synaptotagmin 1 regulates cortical granule exocytosis during mouse oocyte activation

Synaptotagmin 1 (Syt1) is an abundant and important presynaptic vesicle protein that binds Ca2+ for the regulation of synaptic vesicle exocytosis. Our previous study reported its localization and function on spindle assembly in mouse oocyte meiotic maturation. The present study was designed to investigate the function of Syt1 during mouse oocyte activation and subsequent cortical granule exocytosis (CGE) using confocal microscopy, morpholinol-based knockdown and time-lapse live cell imaging. By employing live cell imaging, we first studied the dynamic process of CGE and calculated the time interval between [Ca2+]i rise and CGE after oocyte activation. We further showed that Syt1 was co-localized to cortical granules (CGs) at the oocyte cortex. After oocyte activation with SrCl2, the Syt1 distribution pattern was altered significantly, similar to the changes seen for the CGs. Knockdown of Syt1 inhibited [Ca2+]i oscillations, disrupted the F-actin distribution pattern and delayed the time of cortical reaction. In summary, as a synaptic vesicle protein and calcium sensor for exocytosis, Syt1 acts as an essential regulator in mouse oocyte activation events including the generation of Ca2+ signals and CGE.

Blastocysts derivation from somatic cell fusion with premature oocytes (prematuration somatic cell fusion)

This study was undertaken to investigate the development of immature oocytes after their fusion with male somatic cells expressing red fluorescence protein (RFP). RFP-expressing cells were fused with immature oocytes, matured in vitro and then parthenogenetically activated. Somatic nuclei showed spindle formation, 1st polar body extrusion after in vitro maturation and protruded the 2nd polar body after parthenogenetic activation. RFP was expressed in the resultant embryos; two-cell stage and blastocysts. Chromosomal analysis showed aneuploidy in 81.82% of the resulting blastocysts while 18.18% of the resulting blastocysts were diploid. Among eight RFP-expressing blastocysts, Xist mRNAs was detected in six while Sry mRNA was detected in only one blastocyst. We propose "prematuration somatic cell fusion" as an approach to generate embryos using somatic cells instead of spermatozoa. The current approach, if improved, would assist production of embryos for couples where the male partner is sterile, however, genetic and chromosomal analysis of the resultant embryos are required before transfer to the mothers.

Glycosaminoglycans improves early development of zona-free 8-cell rat embryos to blastocysts in a chemically defined medium, but not the pregnancy rate following transfer of the blastocysts

The objective of the present study was to clarify the possible role of the zona pellucida (ZP) in early development of rat embryos and to determine the effect of glycosaminoglycans on the development of ZP-free 8-cell embryos before or after embryo transfer at the blastocyst stage. Eight-cell embryos were divided into three groups comprised of, 1) intact controls, 2) embryos with the ZP was removed with acidic solution and 3) pairs of ZP-free 8-cell embryos aggregated in a small hollow. These embryos were cultured in a chemically defined mR1ECM for 24 h. Developmental ability to the blastocyst stage and mean cell number in the blastocyst was lower in ZP-free embryos than in intact controls. When these blastocysts were transferred, the farrowing rate and efficiency of embryos developed to term were also lower in ZP-free embryos, but not in the aggregated ones. Supplementation with hyaluronan (HA; 63-250 µg/ml) or heparan sulfate proteoglycan (HS; 15 µg/ml) significantly improved blastocyst formation of ZP-free embryos and the cell number in the blastocyst by reducing the incidence of apoptosis. However, there were no beneficial effects of HA or HS on farrowing and newborn rates after transfer of the blastocysts. In conclusion, the ZP plays roles in maintaining successful development of early rat embryos at least from the 8-cell stage not only to the blastocyst stage but also to posttransfer stages. Glycosaminoglycans, such as HA or HS, appear to contribute to successful cleavage during early development to the blastocyst stage but may be insufficient to maintain the posttransfer survival of ZP-free embryos.

In vitro development and chromosomal configuration of bovine somatic cloned embryos with nonenucleated metaphase II oocytes

This study was designed to examine the effects of the presence of oocyte nuclei on the donor cell nuclear remodeling, including premature chromosome condensation (PCC) and DNA configuration, and subsequent embryo development. The results showed that: (1) the presence of oocyte MII spindles was more likely to induce donor cell PCC. (2) The positional relationship between the fused donor cell and the oocyte metaphase spindle had an effect on oocyte PB2 extrusion. When the fused donor cell was widely separated from the MII spindle, 94.4% of the reconstructed oocytes expelled a PB2. When the donor cell was fused adjacently to the MII spindle, almost all of the reconstructed oocytes did not expel the PB2; the majority (67.9%) formed a very large M-phase spindle in which the oocyte and the donor cell chromosomes merged. (3) After activation, the oocyte and donor nuclei exhibited a variety of pronuclear patterns and asynchronous development. (4) The embryos reconstituted with nonenucleated oocytes resulted in a similar cleavage rate as observed in the control embryos reconstituted with enucleated oocytes. Blastocyst developmental rates were no different between nonenucleated and enucleated cloned embryos; however, the development rates from early to hatching blastocysts significantly decreased in the nonenucleation group compared to enucleation controls (0 vs. 23.1%; 27.5 vs. 67.8%), regardless with either cumulus cells or fibroblasts as donor cells. (5) All nonenucleated oocyte-derived blastocysts contained mixed polyploidy with a variety of compositions that included 2n/4n, 2n/6n, 2n/8n, and 2n/4n/8n. (6) Nuclear transfer preceding the oocyte enucleation experiment indicated that prolonged presence of oocyte nuclei induced abnormal DNA configuration and reduced in vitro development of transferred somatic nuclei, but short time presence of oocyte nuclei did not affect the in vitro development of cloned embryos. We conclude that oocyte MII spindles induce donor cell PCC, the developmental capacity of cloned embryos reconstituted with nonenucleated oocytes is inferior to those with enucleated oocytes, and that all such derived blastocysts are polyploidy.