Reproduction Abstracts

To determine whether chromosomes in porcine first polar body (PB1) can complete the second meiotic division and participate in subsequent normal embryo development, we examined developed competence of chromosome in PB1 that had been injected into enucleated MII stage oocytes by nuclear transfer method (chromosomes replacement group, CR group). After parthenogenetic activation (PA) and in vitro fertilization (IVF), the cleavage rate of reconstructed oocytes in IVF group (CR-IVF group, 34.2±3.5%) was significantly lower than in PA group (CR-PA group, 54.7±8.2%). The blastocyst formation rate was 7.0% in CR-PA group, but there was no blastocyst formation in the CR-IVF group. For producing tetraploid parthenogenetic embryos, intact MII stage oocytes injected with chromosomes in PB1 were electrically stimulated, treated with 7.5 μg/ml cytochalasin B for 3 h (MII oocyte+PB1+CB group), and then cultured without cytochalasin B. The average cleavage rate of reconstructed oocytes was 72.5% (48 of 66), and blastocyst formation rate was 18.7% (nine of 48). Chromosome analysis was shown that the similar proportion of chromosome status (haploid and diploid) were found between control (normal MII oocyte) and CR groups after PA. Overall 23.6% of blastocysts were tetraploid in MII oocyte+PB1+CB group. Our results demonstrated that chromosomes in porcine first polar body can participate in normal embryo development when injected into enucleated MII stage oocyte; Tetraploid PA blastocyst were produced when PB1 chromosomes were injected into intact MII stage oocyte, although the proportion of tetraploid was low. This result indicates that chromosomes within the first polar bodies can participate in embryonic development in intact MII stage oocyte.