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Developmental Cell Aug 2018Parental genomes are initially separate in the zygote following fertilization. A recent study in Science by Reichmann et al. (2018) reveals that dual spindles assemble...
Parental genomes are initially separate in the zygote following fertilization. A recent study in Science by Reichmann et al. (2018) reveals that dual spindles assemble around the two pronuclei in mouse embryos to maintain separation of the two parental genomes through the first zygotic division.
Topics: Animals; Cell Nucleus; Fertilization; Genome; Mice; Zygote
PubMed: 30086299
DOI: 10.1016/j.devcel.2018.07.019 -
Cellular and Molecular Life Sciences :... Jan 2020Zygosis is the generation of new biological individuals by the sexual fusion of gamete cells. Our current understanding of eukaryotic phylogeny indicates that sex is... (Review)
Review
Zygosis is the generation of new biological individuals by the sexual fusion of gamete cells. Our current understanding of eukaryotic phylogeny indicates that sex is ancestral to all extant eukaryotes. Although sexual development is extremely diverse, common molecular elements have been retained. HAP2-GCS1, a protein that promotes the fusion of gamete cell membranes that is related in structure to certain viral fusogens, is conserved in many eukaryotic lineages, even though gametes vary considerably in form and behaviour between species. Similarly, although zygotes have dramatically different forms and fates in different organisms, diverse eukaryotes share a common developmental programme in which homeodomain-containing transcription factors play a central role. These common mechanistic elements suggest possible common evolutionary histories that, if correct, would have profound implications for our understanding of eukaryogenesis.
Topics: Animals; Biological Evolution; Cell Membrane; Eukaryota; Germ Cells; Phylogeny; Transcription Factors; Zygote
PubMed: 31203379
DOI: 10.1007/s00018-019-03187-1 -
Cold Spring Harbor Perspectives in... Nov 2015Epigenetic mechanisms play an essential role in the germline and imprinting cycle. Germ cells show extensive epigenetic programming in preparation for the generation of... (Review)
Review
Epigenetic mechanisms play an essential role in the germline and imprinting cycle. Germ cells show extensive epigenetic programming in preparation for the generation of the totipotent state, which in turn leads to the establishment of pluripotent cells in blastocysts. The latter are the cells from which pluripotent embryonic stem cells are derived and maintained in culture. Following blastocyst implantation, postimplantation epiblast cells develop, which give rise to all somatic cells as well as primordial germ cells, the precursors of sperm and eggs. Pluripotent stem cells in culture can be induced to undergo differentiation into somatic cells and germ cells in culture. Understanding the natural cycles of epigenetic reprogramming that occur in the germline will allow the generation of better and more versatile stem cells for both therapeutic and research purposes.
Topics: Adult Stem Cells; Animals; Blastocyst; Cell Communication; Cell Differentiation; DNA Methylation; Embryonic Development; Epigenomics; Genomic Imprinting; Histones; Oocytes; Pluripotent Stem Cells; Zygote
PubMed: 26525151
DOI: 10.1101/cshperspect.a019422 -
Methods in Molecular Biology (Clifton,... 2019Programmable nucleases like CRISPR/Cas9 enable to edit the mouse genome directly in the zygote. Several methods have been successfully used for this. Here we describe...
Programmable nucleases like CRISPR/Cas9 enable to edit the mouse genome directly in the zygote. Several methods have been successfully used for this. Here we describe injection into one of the pronuclei of the zygote and electroporation of zygotes. Alternative methods will be mentioned.
Topics: Animals; CRISPR-Cas Systems; Electroporation; Gene Editing; Mice; RNA, Guide, CRISPR-Cas Systems; Zygote
PubMed: 30912050
DOI: 10.1007/978-1-4939-9170-9_15 -
Biology Open Dec 2021Mouse zygote morphokinetics were measured during interphase, the mitotic period, cytokinesis, and two-cell stage. Sequences of rounder-distorted-rounder shapes were...
Mouse zygote morphokinetics were measured during interphase, the mitotic period, cytokinesis, and two-cell stage. Sequences of rounder-distorted-rounder shapes were revealed, as were changing patterns of cross section area. A calcium chelator and an actin-disrupting agent inhibited the area changes that occurred between pronuclear envelope breakdown and cytokinesis. During cell division, two vortices developed in each nascent cell and they rotated in opposite directions at each end of the cell, a pattern that sometimes persisted for up to 10 h. Exchange with the environment may have been promoted by these shape and area cycles and persisting circulation in the cytoplasm may have a similar function between a cell's interior and periphery. Some of these movements were sporadically also seen in human zygotes with abnormal numbers of pronuclei and the two-cell stages that developed from these compromised human zygotes.
Topics: Animals; Cell Nucleus; Cytoplasm; Humans; Mice; Zygote
PubMed: 34935907
DOI: 10.1242/bio.059013 -
Current Topics in Developmental Biology 2020Mammalian embryogenesis depends on maternal factors accumulated in eggs prior to fertilization and on placental transfers later in gestation. In this review, we focus on... (Review)
Review
Mammalian embryogenesis depends on maternal factors accumulated in eggs prior to fertilization and on placental transfers later in gestation. In this review, we focus on initial events when the organism has insufficient newly synthesized embryonic factors to sustain development. These maternal factors regulate preimplantation embryogenesis both uniquely in pronuclear formation, genome reprogramming and cell fate determination and more universally in regulating cell division, transcription and RNA metabolism. Depletion, disruption or inappropriate persistence of maternal factors can result in developmental defects in early embryos. To better understand the origins of these maternal effects, we include oocyte maturation processes that are responsible for their production. We focus on recent publications and reference comprehensive reviews that include earlier scientific literature of early mouse development.
Topics: Animals; Embryo, Mammalian; Embryonic Development; Female; Gene Expression Regulation, Developmental; Genome; Maternal Inheritance; Mice; Oocytes; Zygote
PubMed: 32591079
DOI: 10.1016/bs.ctdb.2019.10.006 -
Current Opinion in Cell Biology Feb 2022The genome of an early embryo undergoes significant remodelling at the epigenetic, transcriptional, and structural levels. New technological developments have made it... (Review)
Review
The genome of an early embryo undergoes significant remodelling at the epigenetic, transcriptional, and structural levels. New technological developments have made it possible to study 3D genome organisation in the zygote and early embryo of many different species. Recent studies in human embryos, zebrafish, medaka, and Xenopus have revealed that, similar to previous results in mouse and Drosophila, the zygotic genome is unstructured prior to zygotic genome activation. While these studies show that topologically associating domains are established coincident with zygotic genome activation across species, other 3D genome structures have more varied timing. Here, we review recent studies examining the timing and mechanisms of establishment of 3D genome organisation in the early embryo, and discuss similarities and differences between species. Investigating the establishment of 3D chromatin conformation in early embryos has the potential to reveal novel mechanisms of 3D genome organisation.
Topics: Animals; Chromatin; Drosophila; Drosophila Proteins; Gene Expression Regulation, Developmental; Genome; Mice; Zebrafish; Zygote
PubMed: 35065445
DOI: 10.1016/j.ceb.2021.12.004 -
Results and Problems in Cell... 2017Proteins and RNA molecules are deposited into the developing egg by the mother. These gene products will drive the first stages of development and are coded by maternal... (Review)
Review
Proteins and RNA molecules are deposited into the developing egg by the mother. These gene products will drive the first stages of development and are coded by maternal genes. Maternal genes are essential, yet, despite their importance, their evolutionary dynamics is largely unknown. Here I review the current knowledge of maternal gene evolution. The evolutionary origin of maternal genes tends to be more recent than that of zygotic genes. Some studies support the theoretical prediction that maternal genes evolve faster than zygotic genes. However, most studies were done on a limited set of species and genes. I also discuss the way forward to understand the evolution of maternal genes by combining high-throughput genomics and theoretical evolutionary approaches.
Topics: Animals; Evolution, Molecular; Gene Expression Regulation, Developmental; Maternal Inheritance; Zygote
PubMed: 28779330
DOI: 10.1007/978-3-319-60855-6_20 -
Current Topics in Developmental Biology 2021The fertilized frog egg contains all the materials needed to initiate development of a new organism, including stored RNAs and proteins deposited during oogenesis, thus... (Review)
Review
The fertilized frog egg contains all the materials needed to initiate development of a new organism, including stored RNAs and proteins deposited during oogenesis, thus the earliest stages of development do not require transcription. The onset of transcription from the zygotic genome marks the first genetic switch activating the gene regulatory network that programs embryonic development. Zygotic genome activation occurs after an initial phase of transcriptional quiescence that continues until the midblastula stage, a period called the midblastula transition, which was first identified in Xenopus. Activation of transcription is programmed by maternally supplied factors and is regulated at multiple levels. A similar switch exists in most animals and is of great interest both to developmental biologists and to those interested in understanding nuclear reprogramming. Here we review in detail our knowledge on this major switch in transcription in Xenopus and place recent discoveries in the context of a decades old problem.
Topics: Animals; Genome; Oogenesis; Xenopus laevis; Zygote
PubMed: 34074529
DOI: 10.1016/bs.ctdb.2021.03.003 -
Cells Sep 2021Recently, it was pointed out that classic models for the evolution of anisogamy do not take into account the possibility of parthenogenetic reproduction, even though sex...
Recently, it was pointed out that classic models for the evolution of anisogamy do not take into account the possibility of parthenogenetic reproduction, even though sex is facultative in many relevant taxa (e.g., algae) that harbour both anisogamous and isogamous species. Here, we complement this recent analysis with an approach where we assume that the relationship between progeny size and its survival may differ between parthenogenetically and sexually produced progeny, favouring either the former or the latter. We show that previous findings that parthenogenesis can stabilise isogamy relative to the obligate sex case, extend to our scenarios. We additionally investigate two different ways for one mating type to take over the entire population. First, parthenogenesis can lead to biased sex ratios that are sufficiently extreme that one type can displace the other, leading to de facto asexuality for the remaining type that now lacks partners to fuse with. This process involves positive feedback: microgametes, being numerous, lack opportunities for syngamy, and should they proliferate parthenogenetically, the next generation makes this asexual route even more prominent for microgametes. Second, we consider mutations to strict asexuality in producers of micro- or macrogametes, and show that the prospects of asexual invasion depend strongly on the mating type in which the mutation arises. Perhaps most interestingly, we also find scenarios in which parthenogens have an intrinsic survival advantage yet facultatively sexual isogamous populations are robust to the invasion of asexuals, despite us assuming no genetic benefits of recombination. Here, equal contribution from both mating types to zygotes that are sufficiently well provisioned can outweigh the additional costs associated with syngamy.
Topics: Biological Evolution; Gametogenesis; Germ Cells; Models, Biological; Mutation; Parthenogenesis; Phaeophyceae; Zygote
PubMed: 34572116
DOI: 10.3390/cells10092467