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Current Opinion in Plant Biology Feb 2019Plant embryogenesis initiates with the fusion of sperm and egg cell, and completes the generation of the basic outline of the future plant. Here, we summarize the recent... (Review)
Review
Plant embryogenesis initiates with the fusion of sperm and egg cell, and completes the generation of the basic outline of the future plant. Here, we summarize the recent findings about the signaling cascade triggering the zygotic transcription, and the intracellular events and regulatory factors involved in the formation of the two major body axes. We highlight the lack of systematic de novo transcriptional activation in the zygote, and emphasize the importance of cytoskeletal reorganization to polarize the zygote and control the first asymmetric division that establishes the apical-basal axis. Finally, the limited knowledge of mechanisms that control the cell divisions separating the inner and outer cell layers is summarized and we propose approaches to enhance our understanding of basic principles of plant embryogenesis.
Topics: Body Patterning; Gene Expression Regulation, Plant; Models, Biological; Seeds; Transcription, Genetic; Zygote
PubMed: 30223185
DOI: 10.1016/j.pbi.2018.08.005 -
Journal of Integrative Plant Biology Sep 2012During early embryogenesis in mammals and higher plants, the maternal-to-zygotic transition (MZT) marks the turnover of developmental control from maternal products to... (Review)
Review
During early embryogenesis in mammals and higher plants, the maternal-to-zygotic transition (MZT) marks the turnover of developmental control from maternal products to de novo zygotic genome transcripts. Intensive studies in animals indicate that early embryonic development is largely maternally controlled. In recent years, the MZT has drawn the attention of botanists, as it is important for understanding the mechanism of embryogenesis and hybrid vigor. In this study, we present a brief overview of some aspects of the MZT in flowering plants. Based on what we have learned from Nicotiana tabacum, we hypothesize that the MZT occurs before zygotic cell division and that the development of the fertilized egg cell in flowering plants can be divided into two phases: the zygote stage, which is mainly controlled maternally, and the one-celled proembryo stage, in which zygotic genome activation (ZGA) occurs and is required for zygote division.
Topics: Models, Biological; Plants; RNA, Messenger; Time Factors; Zygote
PubMed: 22731521
DOI: 10.1111/j.1744-7909.2012.01138.x -
Cell Reports Jun 2020After fertilization, sperm and oocyte nuclei are rapidly remodeled to form swollen pronuclei (PN) in mammalian zygotes, and the proper formation and function of PN are...
After fertilization, sperm and oocyte nuclei are rapidly remodeled to form swollen pronuclei (PN) in mammalian zygotes, and the proper formation and function of PN are key to producing totipotent zygotes. However, how mature PN are formed has been unclear. We find that filamentous actin (F-actin) assembles in the PN of mouse zygotes and is required for fully functional PN. The perturbation of nuclear actin dynamics in zygotes results in the misregulation of genes related to genome integrity and abnormal development of mouse embryos. We show that nuclear F-actin ensures DNA damage repair, thus preventing the activation of a zygotic checkpoint. Furthermore, optogenetic control of cofilin nuclear localization reveals the dynamically regulated F-actin nucleoskeleton in zygotes, and its timely disassembly is needed for developmental progression. Nuclear F-actin is a hallmark of totipotent zygotic PN, and the temporal regulation of its polymerized state is necessary for normal embryonic development.
Topics: Actin Cytoskeleton; Actin Depolymerizing Factors; Actins; Animals; Cell Cycle Checkpoints; Cell Nucleus; Cell Survival; Checkpoint Kinase 1; DNA Damage; Embryo, Mammalian; Embryonic Development; Gene Expression Regulation, Developmental; Imaging, Three-Dimensional; Light; Mice, Inbred ICR; Mitosis; Polymerization; Up-Regulation; Zygote
PubMed: 32610125
DOI: 10.1016/j.celrep.2020.107824 -
The New Phytologist Sep 2016Contents 1170 I. 1170 II. 1172 III. 1175 IV. 1180 V. 1183 1184 References 1184 SUMMARY: An unintended consequence of global change is an increase in opportunities for... (Review)
Review
Contents 1170 I. 1170 II. 1172 III. 1175 IV. 1180 V. 1183 1184 References 1184 SUMMARY: An unintended consequence of global change is an increase in opportunities for hybridization among previously isolated lineages. Here we illustrate how global change can facilitate the breakdown of reproductive barriers and the formation of hybrids, drawing on the flora of the British Isles for insight. Although global change may ameliorate some of the barriers preventing hybrid establishment, for example by providing new ecological niches for hybrids, it will have limited effects on environment-independent post-zygotic barriers. For example, genic incompatibilities and differences in chromosome numbers and structure within hybrid genomes are unlikely to be affected by global change. We thus speculate that global change will have a larger effect on eroding pre-zygotic barriers (eco-geographical isolation and phenology) than post-zygotic barriers, shifting the relative importance of these two classes of reproductive barriers from what is usually seen in naturally produced hybrids where pre-zygotic barriers are the largest contributors to reproductive isolation. Although the long-term fate of neo-hybrids is still to be determined, the massive impact of global change on the dynamics and distribution of biodiversity generates an unprecedented opportunity to study large numbers of unpredicted, and often replicated, hybridization 'experiments', allowing us to peer into the birth and death of evolutionary lineages.
Topics: Climate Change; Ecosystem; Genetic Speciation; Hybridization, Genetic; Plant Infertility; Zygote
PubMed: 27214560
DOI: 10.1111/nph.14004 -
Journal of Assisted Reproduction and... Nov 2021
Topics: Animals; Embryonic Development; Humans; Mammals; Zygote
PubMed: 34796415
DOI: 10.1007/s10815-021-02360-5 -
Cytoskeleton (Hoboken, N.J.) Dec 2012Positioning of the cleavage plane is regulated to ensure proper animal development. Most animal cells rely on the astral microtubules to position the mitotic spindle,...
Positioning of the cleavage plane is regulated to ensure proper animal development. Most animal cells rely on the astral microtubules to position the mitotic spindle, which in turn specifies the cleavage plane. The mouse zygote lacks discernible astral microtubules but still divides symmetrically. Here, we demonstrate a cloud-like accumulation of F-actin surrounds the spindle in zygotes and when this actin network is disassembled, the spindle assumes an off-center position, and the resulting zygote divides asymmetrically into two unequal size blastomeres. Interestingly, when the spindle is micromanipulated to the subcortical region, the zygote without the actin network is unable to reposition the spindle and cleavage plane at the cell center. This study reveals that an actin network maintains the central spindle position in anastral mitosis, and ensures the first embryonic mitosis is symmetrical. © 2012 Wiley Periodicals, Inc.
Topics: Actin Cytoskeleton; Actins; Animals; Cell Division; Female; Male; Mice; Mice, Inbred C57BL; Mice, Inbred DBA; Pregnancy; Spindle Apparatus; Zygote
PubMed: 22887777
DOI: 10.1002/cm.21062 -
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 -
Reproduction, Fertility, and Development 1999Recently, several authors have proposed strategies for correction of triploidy based on the removal of the extra pronucleus at the zygote stage. In the present bioassay,... (Review)
Review
Recently, several authors have proposed strategies for correction of triploidy based on the removal of the extra pronucleus at the zygote stage. In the present bioassay, the following were analysed: (1) the different factors that can induce the formation of multipronuclear zygotes in mammals; (2) the different morphological patterns established according to the number of pronuclei and polar bodies that can be observed at the zygote stage and used to distinguish the origin of multipronuclear zygotes; and (3) the pattern of chromosomal segregation during the first mitotic division and ploidy status of the resulting preimplantation embryos. Such an analysis shows that the morphological criterion of counting the number of pronuclei and polar bodies can be misleading and should not be used for ascertaining the origin of tripronuclear zygotes. In addition, although monospermic digynic zygotes have a single sperm centromere, which likely organizes a single bipolar spindle during the first mitotic division, more data on chromosomal distribution and segregation of digynic tripronuclear zygotes should be collected before strategies for correction of triploidy are implemented in humans.
Topics: Age Factors; Animals; Cell Nucleus; Cryopreservation; Female; Humans; Male; Meiosis; Oocytes; Polyploidy; Sperm Injections, Intracytoplasmic; Sperm-Ovum Interactions; Spermatozoa; Zygote
PubMed: 10898292
DOI: 10.1071/rd99057 -
Current Topics in Developmental Biology 2020In animals, the early embryo is mostly transcriptionally silent and development is fueled by maternally supplied mRNAs and proteins. These maternal products are... (Review)
Review
In animals, the early embryo is mostly transcriptionally silent and development is fueled by maternally supplied mRNAs and proteins. These maternal products are important not only for survival, but also to gear up the zygote's genome for activation. Over the last three decades, research with different model organisms and experimental approaches has identified molecular factors and proposed mechanisms for how the embryo transitions from being transcriptionally silent to transcriptionally competent. In this chapter, we discuss the molecular players that shape the molecular landscape of ZGA and provide insights into their mode of action in activating the transcription program in the developing embryo.
Topics: Animals; Embryonic Development; Female; Gene Expression Regulation, Developmental; Genome; Maternal Inheritance; Models, Genetic; RNA, Messenger, Stored; Transcription, Genetic; Zygote
PubMed: 32591075
DOI: 10.1016/bs.ctdb.2020.02.002 -
PloS One 2017Many factors from the oocyte/sperm or the process of fertilization may affect the zygote formation. The zygote score (Z-score) describes the quality of a human zygote... (Comparative Study)
Comparative Study
BACKGROUND
Many factors from the oocyte/sperm or the process of fertilization may affect the zygote formation. The zygote score (Z-score) describes the quality of a human zygote based on its pronuclear morphology, nucleolar precursor bodies, and alignment of polar bodies, and it can be used in the selection process at the zygote stage for embryo transfer or cryopreservation.
OBJECTIVE
The aim of this retrospective cohort study was to investigate the relationship between different controlled ovarian stimulation (COS) protocols and the zygote score (Z-score) and to assess the feasibility of the Z-score for predicting embryo survival in the GnRH-antagonist (GnRH-ant) protocol.
METHODS
It is a retrospective, single-center cohort study. A total of 3,826 zygotes with normal fertilization were analyzed from 744 in vitro fertilization /intra-cytoplasmic sperm injection (IVF/ICSI) cycles (long protocol n = 392; GnRH-ant n = 352) between Jan 2010 and April 2014 in the IVF unit of Chang-Gung Memorial Hospital Kaohsiung Medical Center.
RESULTS
The Z-score distribution differed significantly between these two protocols. The overall Z-score was poorer for zygotes from GnRH-ant cycles (p<0.05). Univariate and multivariate analyses indicated the type of COS protocol is one of the main determinants of Z-score grading. Our study found good-quality day 3 embryo/blastocyst formation and the cumulative embryo survival rate were correlated with the Z-score but not the COS protocol. With the GnRH-ant protocol, the number of Z1 in the transferred cohort embryos was significantly correlated with the clinical pregnancy rate (r = 0.976; p = 0.024) and live birth rate (r = 0.971; p = 0.029). This correlation was not seen with the long protocol.
CONCLUSIONS
The Z-score distribution for the GnRH antagonist cycles was poorer than that of the long protocol, but the Z-score system is a valuable parameter for predicting embryo viability in the GnRH-ant protocol, providing a strong correlation with the clinical pregnancy rate and live birth rate.
Topics: Clinical Protocols; Embryo, Mammalian; Female; Fertilization in Vitro; Gonadotropin-Releasing Hormone; Humans; Male; Oocyte Retrieval; Ovulation Induction; Retrospective Studies; Sperm Injections, Intracytoplasmic; Zygote
PubMed: 28152037
DOI: 10.1371/journal.pone.0171465