-
Current Topics in Developmental Biology 2015In Xenopus, the germline is specified by the inheritance of germ-plasm components synthesized at the beginning of oogenesis. Only the cells in the early embryo that... (Review)
Review
In Xenopus, the germline is specified by the inheritance of germ-plasm components synthesized at the beginning of oogenesis. Only the cells in the early embryo that receive germ plasm, the primordial germ cells (PGCs), are competent to give rise to the gametes. Thus, germ-plasm components continue the totipotent potential exhibited by the oocyte into the developing embryo at a time when most cells are preprogrammed for somatic differentiation as dictated by localized maternal determinants. When zygotic transcription begins at the mid-blastula transition, the maternally set program for somatic differentiation is realized. At this time, genetic control is ceded to the zygotic genome, and developmental potential gradually becomes more restricted within the primary germ layers. PGCs are a notable exception to this paradigm and remain transcriptionally silent until the late gastrula. How the germ-cell lineage retains full potential while somatic cells become fate restricted is a tale of translational repression, selective degradation of somatic maternal determinants, and delayed activation of zygotic transcription.
Topics: Animals; Cell Lineage; Cytoskeleton; Female; Germ Cells; RNA Stability; Xenopus; Zygote
PubMed: 26358876
DOI: 10.1016/bs.ctdb.2015.07.021 -
Plant Physiology Jan 2017A comparison of eudicot and monocot model plants explores recent advances and open questions on gene regulatory networks during zygote development, parental influences... (Review)
Review
A comparison of eudicot and monocot model plants explores recent advances and open questions on gene regulatory networks during zygote development, parental influences on early embryogenesis, zygotic genome activation, and cell fate determination.
Topics: Cell Communication; Cell Differentiation; Cell Division; Cell Lineage; Gene Regulatory Networks; Genome, Plant; Genomic Imprinting; Indoleacetic Acids; Magnoliopsida; Plant Growth Regulators; Zygote
PubMed: 27909044
DOI: 10.1104/pp.16.01406 -
The International Journal of... Nov 1998Leech and ascidian embryos are well suited for the study of certain developmental processes. Although leeches and ascidians belong to different bilateralia groups... (Review)
Review
Leech and ascidian embryos are well suited for the study of certain developmental processes. Although leeches and ascidians belong to different bilateralia groups (protostomes and deuterostomes, respectively) they share important developmental features and, in particular, the determinate character of their embryogenesis. In both types of embryos this property is related to the presence of specific cytoplasmic domains that are selectively allocated to different blastomeres during cleavage. In this review leech and ascidian eggs and zygotes are compared in terms of the structure of these cytoplasmic domains and of the cellular mechanisms involved in their formation and localization. During meiosis the zygote of leeches and ascidians undergo stereotypic actin-dependent contraction movements related to both the emission of the polar bodies and the formation and relocalization of cytoplasmic domains. After completion of meiosis, during first interphase, monaster microtubules nucleated from the sperm-derived centrosome play a key role in pronuclear migration. In addition, these astral microtubules direct the relocalization of cytoplasmic domains and the translocation and accumulation of organelles in the interior of the zygote. Microtubules and microfilaments, on the other hand, are involved in cortical reorganizations and organelle translocations in both zygote species during interphase and cleavage divisions. In the case of leech zygotes, this process leads to formation of characteristic polar cytoplasmic domains called teloplasms. These domains are selectively inherited by teloblasts, precursor stem cells of ectodermal and mesodermal tissues in the leech embryo. In the ascidian zygote, the cytoplasmic movements observed during interphase and mitosis lead to relocalization of the bulk of a mitochondria-rich domain, called the myoplasm, along with an endoplasmic reticulum-rich domain towards the future posterior pole of the embryo. The myoplasm is inherited by a subset of posterior blastomeres committed to become the primary muscle cells of the ascidian tadpole.
Topics: Animals; Cytoplasm; Fertilization; Interphase; Leeches; Meiosis; Mitosis; Urochordata; Zygote
PubMed: 9879704
DOI: No ID Found -
Journal of Assisted Reproduction and... Nov 2021
Topics: Animals; Embryonic Development; Humans; Mammals; Zygote
PubMed: 34796415
DOI: 10.1007/s10815-021-02360-5 -
International Journal of Molecular... Aug 2022Maternal-to-zygotic transition (MZT) of the control of early post-fertilization development is a key-event conditioning the fate of the future embryo, fetus and newborn.... (Review)
Review
Maternal-to-zygotic transition (MZT) of the control of early post-fertilization development is a key-event conditioning the fate of the future embryo, fetus and newborn. Because of the relative paucity of data concerning human embryos, due to ethical concerns and the poor availability of human embryos donated for research, most data have to be derived from animal models, among which those obtained using mouse embryos are most prevalent. However, data obtained by studies performed in non-mammalian specie can also provide useful information. For this reason, this review focuses on similarities and differences of MZT control mechanisms in humans and other species, with particular attention to the mouse. A number of molecular pathways controlling MZT in mice and humans are compared, pointing out those that could be at the origin of further focused experimental studies and the development of new diagnostic tools based on the translational medicine principles. Data concerning possible candidate molecules to be included in these studies are identified.
Topics: Animals; Embryo, Mammalian; Embryonic Development; Gene Expression Regulation, Developmental; Humans; Mice; Zygote
PubMed: 35955697
DOI: 10.3390/ijms23158562 -
Nucleus (Austin, Tex.) 2014Nucleoli in mammalian oocytes and zygotes, sometimes referred to as nucleolus precursor bodies (NPBs), are compact and morphologically different from nucleoli in somatic... (Review)
Review
Nucleoli in mammalian oocytes and zygotes, sometimes referred to as nucleolus precursor bodies (NPBs), are compact and morphologically different from nucleoli in somatic cells. We applied a unique NPB analyzing method "enucleolation" technique to zygotes to remove the NPBs. It has been reported that oocyte NPBs are essential for embryonic development; in their absence, the oocytes complete maturation and can be fertilized, but no nucleoli are formed in the zygotes and embryos, leading to developmental failure. However, we found that when NPBs were removed from zygotes, the zygotes developed successfully to live-born pups. These results indicated that oocyte NPBs are essential for embryonic development, but zygote NPBs are not. In addition, the enucleolated zygotes formed somatic-type nucleoli during early embryonic development, demonstrating that somatic-type nucleoli do not originate from zygote NPBs. We summarize our recent investigation on NPBs, and provide additional comments and findings.
Topics: Animals; Blastocyst; Cell Nucleolus; Embryonic Development; Female; Intranuclear Inclusion Bodies; Mammals; Mice; Oocytes; Pregnancy; Zygote
PubMed: 25495074
DOI: 10.4161/19491034.2014.990858 -
The International Journal of... 2010Nuclear reprogramming, the conversion of the epigenome of a differentiated cell to one that is similar to the undifferentiated embryonic state, can be facilitated by... (Review)
Review
Nuclear reprogramming, the conversion of the epigenome of a differentiated cell to one that is similar to the undifferentiated embryonic state, can be facilitated by several methods, such as nuclear transfer, cell fusion, use of embryonic stem cell extracts, and more recently, by the introduction of exogenous transcription factors. Amongst these various strategies, somatic cell nuclear transfer (SCNT) is, by far, the most effective method of nuclear reprogramming. The majority of SCNT studies have been carried out using enucleated mature oocytes, as reprogramming is efficient and can be completed within hours following the introduction of the somatic cell nuclei into the recipient oocyte. Fertilized eggs, on the other hand, were regarded as poor recipients for nuclear transfer, as previous studies showed that embryonic blastomeres transferred into enucleated zygotes were unable to develop to blastocysts. However, more recent studies have demonstrated that the method of enucleation and the cell cycle phase of the embryos can impact the success of somatic cell reprogramming when zygotes were used as nuclear recipients. It is, therefore, timely to revisit and further explore the nuclear reprogramming capacity of zygotes as recipients for SCNT. Assessment of the various factors that influence the reprogramming capacity of zygotes in SCNT also provide hints of the mechanistic nature of nuclear reprogramming.
Topics: Animals; Cell Dedifferentiation; Cell Nucleus; Cellular Reprogramming; Gene Expression Regulation, Developmental; Humans; Nuclear Transfer Techniques; Zygote
PubMed: 21404184
DOI: 10.1387/ijdb.103201cl -
Plant Signaling & Behavior Sep 2016Polyploidization is a common phenomenon in angiosperms, and polyploidy has played a major role in the long-term diversification and evolutionary success of plants....
Polyploidization is a common phenomenon in angiosperms, and polyploidy has played a major role in the long-term diversification and evolutionary success of plants. Triploid plants are considered as the intermediate stage in the formation of stable autotetraploid plants, and this pathway of tetraploid formation is known as the triploid bridge. As for the mechanism of triploid formation among diploid populations, fusion of an unreduced gamete with a reduced gamete is generally accepted. In addition, the possibility of polyspermy has been proposed for maize, wheat and some orchids, although it has been regarded as an uncommon mechanism of polyploid formation. One of the reasons why polyspermy is regarded as uncommon is because it is difficult to reproduce the polyspermy situation in zygotes and to analyze the developmental profiles of polyspermic zygotes. In the study, we produced polyspermic rice zygotes by electric fusion of an egg cell with two sperm cells and monitored their developmental profiles. The two sperm nuclei and the egg nucleus fused into a zygotic nucleus in the polyspermic zygote, and the triploid zygote divided into a two-celled embryo via mitotic division with a typical bipolar microtubule spindle. The two-celled proembryos developed and regenerated into triploid plants. These results suggest that polyspermic plant zygotes have the potential to form triploid embryos, and that polyspermy in angiosperms might be a pathway for the formation of triploid plants.
Topics: Fertilization; Polyploidy; Seeds; Triploidy; Zea mays; Zygote
PubMed: 27617495
DOI: 10.1080/15592324.2016.1218107 -
Proceedings of the National Academy of... Feb 2019In most flowering plants, the asymmetric cell division of the zygote is the initial step in establishing the apical-basal axis of the mature plant. The zygote is...
In most flowering plants, the asymmetric cell division of the zygote is the initial step in establishing the apical-basal axis of the mature plant. The zygote is polarized, possessing the nucleus at the apical tip and large vacuoles at the basal end. Despite their known polar localization, whether the positioning of the vacuoles and the nucleus is coordinated and what the role of the vacuole is in the asymmetric zygotic division remain elusive. In the present study, we utilized a live-cell imaging system to visualize the dynamics of vacuoles during the entire process of zygote polarization in Image analysis revealed that the vacuoles formed tubular strands around the apically migrating nucleus. They gradually accumulated at the basal region and filled the space, resulting in asymmetric distribution in the mature zygote. To assess the role of vacuoles in the zygote, we screened various vacuole mutants and identified that (), in which the vacuolar structural change was impaired, failed to form tubular vacuoles and to polarly distribute the vacuole. In , large vacuoles occupied the apical tip and thus nuclear migration was blocked, resulting in a more symmetric zygotic division. We further observed that tubular vacuole formation and asymmetric vacuolar distribution both depended on the longitudinal array of actin filaments. Overall, our results show that vacuolar dynamics is crucial not only for the polar distribution along actin filaments but also for adequate nuclear positioning, and consequently zygote-division asymmetry.
Topics: Actin Cytoskeleton; Arabidopsis; Arabidopsis Proteins; Asymmetric Cell Division; Cell Nucleus; Cell Polarity; Chloroplast Proteins; Fluorescent Antibody Technique; Mutation; Vacuoles; Zygote
PubMed: 30651313
DOI: 10.1073/pnas.1814160116 -
EMBO Reports Aug 2010RNA silencing is a complex of mechanisms that regulate gene expression through small RNA molecules. The microRNA (miRNA) pathway is the most common of these in mammals.... (Review)
Review
RNA silencing is a complex of mechanisms that regulate gene expression through small RNA molecules. The microRNA (miRNA) pathway is the most common of these in mammals. Genome-encoded miRNAs suppress translation in a sequence-specific manner and facilitate shifts in gene expression during developmental transitions. Here, we discuss the role of miRNAs in oocyte-to-zygote transition and in the control of pluripotency. Existing data suggest a common principle involving miRNAs in defining pluripotent and differentiated cells. RNA silencing pathways also rapidly evolve, resulting in many unique features of RNA silencing in different taxonomic groups. This is exemplified in the mouse model of oocyte-to-zygote transition, in which the endogenous RNA interference pathway has acquired a novel role in regulating protein-coding genes, while the miRNA pathway has become transiently suppressed.
Topics: Animals; Base Sequence; Humans; MicroRNAs; Molecular Sequence Data; Oocytes; Phylogeny; Pluripotent Stem Cells; RNA Interference; RNA, Small Interfering; Sequence Alignment; Zygote
PubMed: 20651740
DOI: 10.1038/embor.2010.102