-
Biochemical Society Transactions Nov 2021In somatic cells, RNA polymerase II (Pol II) transcription initiation starts by the binding of the general transcription factor TFIID, containing the TATA-binding... (Review)
Review
In somatic cells, RNA polymerase II (Pol II) transcription initiation starts by the binding of the general transcription factor TFIID, containing the TATA-binding protein (TBP) and 13 TBP-associated factors (TAFs), to core promoters. However, in growing oocytes active Pol II transcription is TFIID/TBP-independent, as during oocyte growth TBP is replaced by its vertebrate-specific paralog TBPL2. TBPL2 does not interact with TAFs, but stably associates with TFIIA. The maternal transcriptome is the population of mRNAs produced and stored in the cytoplasm of growing oocytes. After fertilization, maternal mRNAs are inherited by the zygote from the oocyte. As transcription becomes silent after oocyte growth, these mRNAs are the sole source for active protein translation. They will participate to complete the protein pool required for oocyte terminal differentiation, fertilization and initiation of early development, until reactivation of transcription in the embryo, called zygotic genome activation (ZGA). All these events are controlled by an important reshaping of the maternal transcriptome. This procedure combines cytoplasmic readenylation of stored transcripts, allowing their translation, and different waves of mRNA degradation by deadenylation coupled to decapping, to eliminate transcripts coding for proteins that are no longer required. The reshaping ends after ZGA with an almost total clearance of the maternal transcripts. In the past, the murine maternal transcriptome has received little attention but recent progresses have brought new insights into the regulation of maternal mRNA dynamics in the mouse. This review will address past and recent data on the mechanisms associated with maternal transcriptome dynamic in the mouse.
Topics: Animals; Embryonic Development; Female; Gene Expression Regulation, Developmental; Mice; Nuclear Proteins; Oocytes; Pregnancy; Promoter Regions, Genetic; RNA Polymerase II; RNA Stability; RNA, Messenger; TATA Box Binding Protein-Like Proteins; TATA-Box Binding Protein; Transcription, Genetic; Transcriptome; Zygote
PubMed: 34415300
DOI: 10.1042/BST20201125 -
Zygote (Cambridge, England) Feb 2021In higher plants, fertilization induces many structural and physiological changes in the fertilized egg that reflect the transition from the haploid female gamete to the... (Review)
Review
In higher plants, fertilization induces many structural and physiological changes in the fertilized egg that reflect the transition from the haploid female gamete to the diploid zygote - the first cell of the sporophyte. After fusion of the egg nucleus with the sperm nucleus, many molecular changes occur in the zygote during the process of zygote activation during embryogenesis. The zygote originates from the egg, from which some pre-stored translation initiation factors transfer into the zygote and function during zygote activation. This indicates that the control of zygote activation is pre-set in the egg. After the egg and sperm nuclei fuse, gene expression is activated in the zygote, and paternal and maternal gene expression patterns are displayed. This highlights the diversity of zygotic genome activation in higher plants. In addition to new gene expression in the zygote, some genes show quantitative changes in expression. The asymmetrical division of the zygote produces an apical cell and a basal cell that have different destinies during plant reconstruction; these destinies are determined in the zygote. This review describes significant advances in research on the mechanisms controlling zygote activation in higher plants.
Topics: Diploidy; Haploidy; Oryza; Seeds; Zygote
PubMed: 33054867
DOI: 10.1017/S0967199420000568 -
Current Topics in Developmental Biology 2020Gastrulation is a critical early morphogenetic process of animal development, during which the three germ layers; mesoderm, endoderm and ectoderm, are rearranged by... (Review)
Review
Gastrulation is a critical early morphogenetic process of animal development, during which the three germ layers; mesoderm, endoderm and ectoderm, are rearranged by internalization movements. Concurrent epiboly movements spread and thin the germ layers while convergence and extension movements shape them into an anteroposteriorly elongated body with head, trunk, tail and organ rudiments. In zebrafish, gastrulation follows the proliferative and inductive events that establish the embryonic and extraembryonic tissues and the embryonic axis. Specification of these tissues and embryonic axes are controlled by the maternal gene products deposited in the egg. These early maternally controlled processes need to generate sufficient cell numbers and establish the embryonic polarity to ensure normal gastrulation. Subsequently, after activation of the zygotic genome, the zygotic gene products govern mesoderm and endoderm induction and germ layer patterning. Gastrulation is initiated during the maternal-to-zygotic transition, a process that entails both activation of the zygotic genome and downregulation of the maternal transcripts. Genomic studies indicate that gastrulation is largely controlled by the zygotic genome. Nonetheless, genetic studies that investigate the relative contributions of maternal and zygotic gene function by comparing zygotic, maternal and maternal zygotic mutant phenotypes, reveal significant contribution of maternal gene products, transcripts and/or proteins, that persist through gastrulation, to the control of gastrulation movements. Therefore, in zebrafish, the maternally expressed gene products not only set the stage for, but they also actively participate in gastrulation morphogenesis.
Topics: Animals; Blastoderm; Blastula; Embryo, Nonmammalian; Gastrulation; Gene Expression Regulation, Developmental; Maternal Inheritance; Morphogenesis; Zebrafish; Zygote
PubMed: 32591082
DOI: 10.1016/bs.ctdb.2020.05.001 -
Methods in Molecular Biology (Clifton,... 2020A transgenic mouse carries within its genome an artificial DNA construct (transgene) that is deliberately introduced by an experimentalist. These animals are widely used...
A transgenic mouse carries within its genome an artificial DNA construct (transgene) that is deliberately introduced by an experimentalist. These animals are widely used to understand gene function and protein function. When addressing the history of transgenic mouse technology, it is apparent that a number of basic science research areas laid the groundwork for success. These include reproductive science, genetics and molecular biology, and micromanipulation and microscopy equipment. From reproductive physiology came applications on how to optimize mouse breeding, how to superovulate mice to produce zygotes for DNA microinjection or preimplantation embryos for combination with embryonic stem (ES) cells, and how to return zygotes and embryos to a pseudopregnant surrogate dam for gestation and birth. From developmental biology, it was learned how to micromanipulate embryos for morula aggregation and blastocyst microinjection and how to establish germline competent ES cells. From genetics came the foundational principles governing the inheritance of genes, the interactions of gene products, and an understanding of the phenotypic consequences of genetic mutations. From molecular biology came a panoply of tools and reagents that are used to clone DNA transgenes, to detect the presence of transgenes, to assess gene expression by measuring transcription, and to detect proteins in cells and tissues. Technical advances in light microscopes, micromanipulators, micropipette pullers, and ancillary equipment made it possible for experimentalists to insert thin glass needles into zygotes or embryos under controlled conditions to inject DNA solutions or ES cells. To fully discuss the breadth of contributions of these numerous scientific disciplines to a comprehensive history of transgenic science is beyond the scope of this work. Examples will be used to illustrate scientific developments central to the foundation of transgenic technology and that are in use today.
Topics: Animals; Embryo Transfer; Embryonic Stem Cells; Gene Transfer Techniques; History, 20th Century; History, 21st Century; Mice; Mice, Transgenic; Microinjections; Transgenes; Zygote
PubMed: 31512203
DOI: 10.1007/978-1-4939-9837-1_1 -
Nature Communications Feb 2021A new life begins with the unification of the maternal and paternal chromosomes upon fertilization. The parental chromosomes first become enclosed in two separate...
A new life begins with the unification of the maternal and paternal chromosomes upon fertilization. The parental chromosomes first become enclosed in two separate pronuclei near the surface of the fertilized egg. The mechanisms that then move the pronuclei inwards for their unification are only poorly understood in mammals. Here, we report two mechanisms that act in concert to unite the parental genomes in fertilized mouse eggs. The male pronucleus assembles within the fertilization cone and is rapidly moved inwards by the flattening cone. Rab11a recruits the actin nucleation factors Spire and Formin-2 into the fertilization cone, where they locally nucleate actin and further accelerate the pronucleus inwards. In parallel, a dynamic network of microtubules assembles that slowly moves the male and female pronuclei towards the cell centre in a dynein-dependent manner. Both mechanisms are partially redundant and act in concert to unite the parental pronuclei in the zygote's centre.
Topics: Actins; Animals; Cell Nucleus; Female; Fertilization; Formins; Gene Expression Regulation, Developmental; Genes, Reporter; Green Fluorescent Proteins; Luminescent Proteins; Male; Mice; Mice, Inbred C57BL; Mice, Inbred CBA; Microfilament Proteins; Microtubules; Movement; Nerve Tissue Proteins; Oocytes; Spermatozoa; Zygote; rab GTP-Binding Proteins; Red Fluorescent Protein
PubMed: 33547291
DOI: 10.1038/s41467-021-21020-x -
JBRA Assisted Reproduction May 2020The mitochondria are intracellular organelles, and just like the cell nucleus they have their own genome. They are extremely important for normal body functioning and... (Review)
Review
The mitochondria are intracellular organelles, and just like the cell nucleus they have their own genome. They are extremely important for normal body functioning and are responsible for ATP production - the main energy source for the cell. Mitochondrial diseases are associated with mutations in mitochondrial DNA and are inherited exclusively from the mother. They can affect organs that depend on energy metabolism, such as skeletal muscles, the cardiac system, the central nervous system, the endocrine system, the retina and liver, causing various incurable diseases. Mitochondrial replacement techniques provide women with mitochondrial defects a chance to have normal biological children. The goal of such treatment is to reconstruct functional oocytes and zygotes, in order to avoid the inheritance of mutated genes; for this the nuclear genome is withdrawn from an oocyte or zygotes, which carries mitochondrial mutations, and is implanted in a normal anucleated cell donor. Currently, the options of a couple to prevent the transmission of mitochondrial diseases are limited, and mitochondrial donation techniques provide women with mitochondrial defects a chance to have normal children. The nuclear genome can be transferred from oocytes or zygotes using techniques such as pronuclear transfer, spindle transfer, polar body transfer and germinal vesicle transfer. This study presents a review of developed mitochondrial substitution techniques, and its ability to prevent hereditary diseases.
Topics: Adult; DNA, Mitochondrial; Female; Genome, Mitochondrial; Humans; Male; Mitochondrial Diseases; Mitochondrial Replacement Therapy; Mutation; Oocytes; Parents; Zygote
PubMed: 32073245
DOI: 10.5935/1518-0557.20190086 -
The International Journal of... 2020Sexually reproducing organisms generate male and female haploid gametes, which meet and fuse at fertilization to produce a diploid zygote. The evolutionary process of... (Review)
Review
Sexually reproducing organisms generate male and female haploid gametes, which meet and fuse at fertilization to produce a diploid zygote. The evolutionary process of speciation is achieved and maintained by ensuring that gametes undergo productive fusion only within a species. In animals, hybrids from cross-species fertilization events may develop normally, but are usually sterile (Fitzpatrick, 2004). Metazoan sperm and eggs have several features to ensure that the gametes, which have evolved independently and also in conflict with each other, are competent to undergo fertilization (Firman, 2018). Fertilization is a specific process that is ideally supposed to result in randomized fusion of compatible egg and sperm. Here, I will discuss key processes driven by maternal factors in the egg that dictate earliest stages of gamete recognition, gamete choice and fusion in metazoans.
Topics: Animals; Biological Evolution; Female; Germ Cells; Male; Maternal Inheritance; Reproduction; Sperm-Ovum Interactions; Zygote
PubMed: 32659006
DOI: 10.1387/ijdb.190156sn -
Current Topics in Developmental Biology 2020In birds as in all amniotes, the site of gastrulation is a midline structure, the primitive streak. This appears as cells in the one cell-thick epiblast undergo... (Review)
Review
In birds as in all amniotes, the site of gastrulation is a midline structure, the primitive streak. This appears as cells in the one cell-thick epiblast undergo epithelial-to-mesenchymal transition to ingress and form definitive mesoderm and endoderm. Global movements involving tens of thousands of cells in the embryonic epiblast precede gastrulation. They position the primitive streak precursors from a marginal position (equivalent to the situation in anamniotes) along the future antero-posterior axis (typical for amniotes). These epithelial movements continue in modified form during gastrulation, when they are accompanied by collective movements of different class in the forming mesoderm and endoderm. Here I discuss the nature of these collective cell movements shaping the embryo, their interplay with signaling events controlling fate specification and significance in an evolutionary perspective.
Topics: Animals; Cell Movement; Chick Embryo; Chickens; Endoderm; Gastrula; Gastrulation; Gene Expression Regulation, Developmental; Mesoderm; Signal Transduction; Zebrafish Proteins; Zygote
PubMed: 31959297
DOI: 10.1016/bs.ctdb.2019.11.015 -
Current Opinion in Cell Biology Apr 2022The nuclear environment changes dramatically over the course of early development. Histones are core chromatin components that play critical roles in regulating gene... (Review)
Review
The nuclear environment changes dramatically over the course of early development. Histones are core chromatin components that play critical roles in regulating gene expression and nuclear architecture. Additionally, the embryos of many species, including Drosophila, Zebrafish, and Xenopus use the availability of maternally deposited histones to time critical early embryonic events including cell cycle slowing and zygotic genome activation. Here, we review recent insights into how histones control early development. We first discuss the regulation of chromatin functions through interaction of histones and transcription factors, incorporation of variant histones, and histone post-translational modifications. We also highlight emerging roles for histones as developmental regulators independent of chromatin association.
Topics: Animals; Cell Nucleus; Chromatin; Drosophila; Gene Expression Regulation, Developmental; Histones; Zebrafish; Zygote
PubMed: 35279563
DOI: 10.1016/j.ceb.2022.02.003 -
Current Opinion in Genetics &... Aug 2023The totipotent embryo initiates transcription during zygotic or embryonic genome activation (EGA, ZGA). ZGA occurs at the 8-cell stage in humans and its failure leads to... (Review)
Review
The totipotent embryo initiates transcription during zygotic or embryonic genome activation (EGA, ZGA). ZGA occurs at the 8-cell stage in humans and its failure leads to developmental arrest. Understanding the molecular pathways underlying ZGA and totipotency is essential to comprehend human development. Recently, human 8-cell-like cells (8CLCs) have been discovered in vitro that resemble the 8-cell embryo. 8CLCs exist among naive pluripotent stem cells and can be induced genetically or chemically. Their ZGA-like transcriptome, transposable element activation, 8-cell embryo-specific protein expression, and developmental properties make them an exceptional model system to study early embryonic cell-state transitions and human totipotency programs in vitro.
Topics: Humans; Pluripotent Stem Cells; Human Embryonic Stem Cells; Zygote; Genome, Human
PubMed: 37356343
DOI: 10.1016/j.gde.2023.102066