Polymerization of nonfilamentous actin into microfilaments is an importantprocess for porcine oocyte maturation and early embryo development

Actin is one of the major proteins in mammalian oocytes, Most developmental events are dependent on the normal distribution of filamentous (F-) actin, Polymerization of nonfilamentous (G-) actin into F-actin is important for both meiosis and mitosis, This study examined G- and F-actin distribution i n pig oocytes and embryos by immunocytochemical staining and confocal micro scopy, Actin protein was quantified by electrophoresis and immunoblotting, C-Actin was distributed in the whole cytoplasm of oocytes and embryos irres pective of their stages. F-Actin was distributed at the cortex of oocytes a nd embryos at all stages, at the joint of blastomeres in the embryos, in th e cytoplasm around the germinal vesicle (CV), and in the perinuclear area o f 2- to 4-cell-stage embryos, No differences in the amount of actin protein were found among oocytes and embryos, Oocytes cultured in medium with cyto chalasin D (CD), an inhibitor of microfilament polymerization, underwent GV breakdown and reached metaphase I but did not proceed to metaphase II, Two - to 4-cell-stage embryos cultured in medium with CD did not develop to bla stocysts, When GV-stage oocytes or 2- to 4-cell-stage embryos treated with CD for 6 h were recultured in media without CD, oocytes or embryos re-assem bled actin filaments and underwent a meiotic maturation or blastocyst forma tion similar to that of controls, These results indicate that it is the pol ymerization of C-actin into F-actin, not actin protein synthesis, that is i mportant for both meiosis and mitosis in pig oocytes and embryos.