[Dynamic changes of microtubule in parthenogenetic and in vitro fertilized preimplantation embryos in mouse.]

In this study we detected dynamic changes and function of beta-tubulin, a subtype of microtubule, during the first cleavage period in mouse parthenogenetic and in vitro fertilized embryos. Firstly, we compared the developmental potential of in vitro fertilized, parthenogenetic, and in vivo fertilized embryos in culture. Then, the dynamic changes of beta-tubulin and nucleus in parthenogenetic and in vitro fertilized preimplantation embryos were detected by immunofluorescence and confocal microscopy to analyze the role of microtubules in meiotic division and embryonic development. The results indicated that the development rate of in vivo fertilized embryos was significantly higher than that of in vitro fertilized or parthenogenetic embryos (P<0.05). However, there was no significant difference in developmental potential between in vitro fertilized and parthenogenetic embryos. During in vitro fertilization, oocyte was activated when sperm entered it. Oocyte resumed the second meiotic division. Condensed maternal chromosomes aligning at the equator of the spindle were pulled to the spindle poles by kinetochore microtubules in anaphase. Furthermore, in telophase, there were microtubules between the two sets of decondensed maternal chromosomes. One set formed the second polar body (Pb(2)), which was extruded to the perivitelline space. The other set formed female pronucleus. Meanwhile, 5-8 h after fertilization, sperm chromatin condensed and decondensed to form male pronucleus. Microtubule composed mesosome and cytaster remodeling around male and female pronuclei to form long microtubules, which pull the pronuclei to get close. During 4-6 h parthenogenetic activation, SrCl(2) activated oocytes to resume meiosis. As a consequence, sister chromatids were pulled to spindle poles. Cytochalasin B, which was applied in the medium, inhibited the extrusion of Pb(2). Two haploid pronuclei in the cytoplasm were connected by microtubules. Compared with that in in vitro fertilization, oocyte is easier to be activated in parthenogenetic activation. Chemical activation is more efficient than sperm penetration in in vitro fertilization as indicated by earlier and better remodeling of the microtubules.