The oocyte GV/GVs (germinal vesicle/germinal vesicles) and zygot PN/PNs (pronucleus/pronuclei) of some mammals contain clearly visible nucleoli which exhibit an atypical morphological structure. These nucleoli (NCLs) can be relatively easily manipulated, i.e. removed from GVs/PNs or eventually transferred into another oocyte/zygote. Thus, with the help of micromanipulation techniques it was possible to uncover the real function(s) they play in processes of oocyte maturation and early embryonic development. The purpose of our review is to describe briefly the micromanipulation techniques that can be used for oocyte/zygote nucleoli manipulation. Moreover, we present some examples of results that were obtained in nucleolus manipulation experiments.
- MeSH
- Cell Nucleolus metabolism transplantation MeSH
- Micromanipulation methods MeSH
- Mice MeSH
- Oocytes cytology drug effects MeSH
- Parthenogenesis MeSH
- Swine MeSH
- Animals MeSH
- Zygote cytology MeSH
- Check Tag
- Mice MeSH
- Animals MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
- Review MeSH
Mammalian oocytes/zygotes contain atypical nucleoli that are composed exclusively of a dense fibrillar material. It has been commonly accepted that these nucleoli serve as a repository of components that are used later on, as the embryo develops, for the construction of typical tripartite nucleoli. Indeed, when nucleoli were removed from immature oocytes (enucleolation) and these oocytes were then matured, fertilized or parthenogenetically activated, development of the produced embryos ceased after one or two cleavages with no detectable nucleoli in nuclei. This indicated that zygotic nucleoli originate exclusively from oocytes, i.e. are maternally inherited. Recently published results, however, do not support this developmental biology dogma and demonstrate that maternal nucleoli in one-cell stage embryos are necessary only during a very short time period after fertilization when they serve as a major heterochromatin organizing structures. Nevertheless, it still remains to be determined, which other functions/roles the atypical oocyte/zygote nucleoli eventually have.
- MeSH
- Cell Nucleolus physiology MeSH
- Time Factors MeSH
- Embryo, Mammalian MeSH
- Embryonic Development MeSH
- Fertilization MeSH
- Heterochromatin physiology MeSH
- Humans MeSH
- Maternal Inheritance MeSH
- Mice MeSH
- Nucleoplasmins genetics MeSH
- Oocytes physiology ultrastructure MeSH
- Animals MeSH
- Zygote physiology MeSH
- Check Tag
- Humans MeSH
- Mice MeSH
- Female MeSH
- Animals MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
- Review MeSH
It is well known that nucleoli of fully grown mammalian oocytes are indispensable for embryonic development. Therefore, the embryos originated from previously enucleolated (ENL) oocytes undergo only one or two cleavages and then their development ceases. In our study the interspecies (mouse/pig) nucleolus transferred embryos (NuTE) were produced and their embryonic development was analyzed by autoradiography, transmission electron microscopy (TEM) and immunofluorescence (C23 and upstream binding factor (UBF)). Our results show that the re-injection of isolated oocyte nucleoli, either from the pig (P + P) or mouse (P + M), into previously enucleolated and subsequently matured porcine oocytes rescues their development after parthenogenetic activation and some of these develop up to the blastocyst stage (P + P, 11.8%; P + M, 13.5%). In nucleolus re-injected 8-cell and blastocyst stage embryos the number of nucleoli labeled with C23 in P + P and P + M groups was lower than in control (non-manipulated) group. UBF was localized in small foci within the nucleoli of blastocysts in control and P + P embryos, however, in P + M embryos the labeling was evenly distributed in the nucleoplasm. The TEM and autoradiographic evaluations showed the formation of functional nucleoli and de novo rRNA synthesis at the 8-cell stage in both, control and P + P group. In the P + M group the formation of comparable nucleoli was delayed. In conclusion, our results indicate that the mouse nucleolus can rescue embryonic development of enucleolated porcine oocytes, but the localization of selected nucleolar proteins, the timing of transcription activation and the formation of the functional nucleoli in NuTE compared with control group show evident aberrations.
- MeSH
- Blastocyst cytology metabolism MeSH
- Cell Nucleolus physiology transplantation MeSH
- Embryo, Mammalian cytology metabolism MeSH
- Embryonic Development physiology MeSH
- Cloning, Organism MeSH
- Mice MeSH
- Oocytes cytology physiology MeSH
- Oogenesis physiology MeSH
- Swine MeSH
- Embryo Transfer MeSH
- Pregnancy MeSH
- Animals MeSH
- Check Tag
- Mice MeSH
- Pregnancy MeSH
- Female MeSH
- Animals MeSH
- Publication type
- Journal Article MeSH
The large, compact oocyte nucleoli, sometimes referred to as nucleolus precursor bodies (NPBs), are essential for embryonic development in mammals; in their absence, the oocytes complete maturation and can be fertilized, but no nucleoli are formed in the zygote or embryo, leading to developmental failure. It has been convincingly documented that zygotes inherit the oocyte nucleolar material and form NPBs again in pronuclei. It is commonly accepted that during early embryonic development, the original compact zygote NPBs gradually transform into reticulated nucleoli of somatic cells. Here, we show that zygote NPBs are not required for embryonic and full-term development in the mouse. 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 describe de novo formation of nucleoli in developing embryos. After removal of NPBs from zygotes, they formed new nucleoli after several divisions. These results indicate that the zygote NPBs are not used in embryonic development and that the nucleoli in developing embryos originate from de novo synthesized materials.
- MeSH
- Blastocyst cytology MeSH
- Cell Division MeSH
- Cell Nucleolus physiology MeSH
- NIH 3T3 Cells MeSH
- Embryo Culture Techniques MeSH
- Cumulus Cells cytology MeSH
- Micromanipulation MeSH
- Mice, Inbred C57BL MeSH
- Mice, Inbred DBA MeSH
- Mice, Inbred ICR MeSH
- Mice MeSH
- Oocytes cytology MeSH
- Embryo Transfer MeSH
- Pregnancy MeSH
- Animals MeSH
- Zygote growth & development MeSH
- Check Tag
- Male MeSH
- Mice MeSH
- Pregnancy MeSH
- Female MeSH
- Animals MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
The oocyte (maternal) nucleolus is essential for early embryonic development and embryos originating from enucleolated oocytes arrest at the 2-cell stage. The reason for this is unclear. Surprisingly, RNA polymerase I activity in nucleolus-less mouse embryos, as manifested by pre-rRNA synthesis, and pre-rRNA processing are not affected, indicating an unusual role of the nucleolus. We report here that the maternal nucleolus is indispensable for the regulation of major and minor satellite repeats soon after fertilisation. During the first embryonic cell cycle, absence of the nucleolus causes a significant reduction in major and minor satellite DNA by 12% and 18%, respectively. The expression of satellite transcripts is also affected, being reduced by more than half. Moreover, extensive chromosome bridging of the major and minor satellite sequences was observed during the first mitosis. Finally, we show that the absence of the maternal nucleolus alters S-phase dynamics and causes abnormal deposition of the H3.3 histone chaperone DAXX in pronuclei of nucleolus-less zygotes.
- MeSH
- Blastocyst cytology metabolism MeSH
- Cell Nucleolus metabolism MeSH
- Centromere metabolism MeSH
- Embryo, Mammalian cytology metabolism MeSH
- Transcription, Genetic MeSH
- Genome genetics MeSH
- Heterochromatin genetics MeSH
- RNA, Messenger genetics metabolism MeSH
- Microsatellite Repeats genetics MeSH
- Minisatellite Repeats genetics MeSH
- Mice MeSH
- Oocytes cytology metabolism MeSH
- RNA Processing, Post-Transcriptional genetics MeSH
- RNA Precursors genetics MeSH
- Recombination, Genetic genetics MeSH
- DNA Replication genetics MeSH
- Chromatin Assembly and Disassembly genetics MeSH
- RNA, Ribosomal biosynthesis genetics MeSH
- S Phase genetics MeSH
- Chromosomes, Mammalian metabolism MeSH
- Animals MeSH
- Check Tag
- Male MeSH
- Mice MeSH
- Female MeSH
- Animals MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
