Reproduction Abstracts

Introduction: The large, compact oocyte nucleoli, sometimes referred to as nucleolus precursor bodies (NPBs), are essential for embryonic development in mammals. It has been convincingly documented that zygotes inherit the oocyte nucleolar material and form NPBs again in pronuclei. During early embryonic development, the compact zygote NPBs gradually transform into reticulated nucleoli of somatic cells type. Here we show that zygote NPBs are not required for embryonic and full-term development in the mouse.

Materials and methods: We microsurgically aspirated NPBs from both female and male pronuclei (enucleolation) at 10 h after ICSI. Zygotes from which a small amount of nucleoplasm was aspirated and removed were served as controls (sham-operated). After enucleolation, cleavage, and morulae/blastocysts formation rates were recorded at 24 h and 3.5 days after ICSI respectively. Moreover, after transfer of two-cell stage embryos, we examined full-term development of embryos originating from enucleolated zygotes. To examine the nucleolus formation in developing embryos originating from enucleolated zygotes, live-cell imaging, and immunostaining were performed.

Results and discussion: When NPBs were removed from late-stage zygotes by micromanipulation, the enucleolated zygotes developed to the blastocyst stage, and after transfer to recipients, live pups were obtained. We also presented de novo formation of nucleoli in developing embryos. After removal of NPBs from zygotes, they formed new nucleoli at after several divisions. These results indicate that zygote NPBs are not essential for embryonic development and not required for the formation of nucleoli in developing embryos.