FERTILIZATION OF PORCINE OOCYTES FOLLOWING INTRACYTOPLASMIC SPERMATOZOON OR ISOLATED SPERM HEAD INJECTION

We demonstrated normal fertilization processes las determined by pronu clear formation, pronuclear apposition and syngamy) in porcine oocytes either following intracytoplasmic spermatozoon (ICSI) or isolated spe rm head injection. Microtubule organization and chromatin configuratio n were investigated in these oocytes during the first cell cycle. Foll owing ICSI, the microtubular aster was organized from the neck of the spermatozoon and filled the whole cytoplasm. These male-derived microt ubules appear to move both pronuclei to the center of oocytes. These c ytoskeletal changes are analogous to those seen following conventional fertilization. In contrast, following isolated sperm head injection, the sperm aster was not seen. Instead, the microtubule matrix was orga nized from the cortex and then filled the whole cytoplasm in all cases in normally fertilized oocytes following injection (n = 35). This org anization is similar to what has been shown in the parthenogenetically activated oocytes. Chromosome analysis revealed that the oocytes inje cted with isolated sperm heads were fertilized normally At 7 days foll owing injection, the incidence of blastocoele formation following ICSI (38%) and isolated sperm head injection (22%) was higher than that fo llowing sham injection (2%). These results suggested that successful f ertilization and preimplantation development occurred in porcine oocyt es following either ICSI or isolated sperm head injection. Our results also indicated that fertilization processes can occur by self-assembl ed microtubules within cytoplasm in the absence of a sperm centrosome. Mol. Reprod. Dev. 51 :436-444, 1998. (C) 1998 Wiley-Liss, Inc.