Ultrastructure in Porcine Oocytes following Intracytoplasmic Injection of Murine Spermatozoa

Although successful pronuclear formation and apposition were seen in porcine oocytes following mouse sperm injection, little is known on the morphology of male and female pronuclei following sperm injection. The objective of this study is to describe the ultrastructure of porcine zygote following murine sperm injection in relation to the chronology of pronuclear S phase. At 40h ~ 44h following in vitro maturation, Cumulus cells were removed in TCM-HEPES with 0.1% hyaluronidase. Then, spermatozoa was injected into the cytoplasm of oocytes. After. injection, all oocytes were transferred to NCSU23 medium and cultured at 39$^{\circ}C$ under 5% $CO_2$ in air. Oocytes were fixed in 2% glutaraldehyde in Dulbeccos phosphate-buffered saline and observed by Transmission Electron Microscopy. Nuclear precursor bodies were observed in each pronucleus. A cluster of large and small granules was attached in the nucleolus precursor body. After the apposition of male and female chromatin, chromatin condensation was observed throughout the nucleoplasm and nucleolus precursor bodies and condensed chromatin in contact with clusters of small and large granules and the nuclear envelope were found in apposed pronuclear regions. These results suggest that non-species specific nuclear cytoplasmic interactions take place during pronuclear formation and apposition following sperm injection.