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Cell Jul 2022Mouse germline cysts, on average, develop into six oocytes supported by 24 nurse cells that transfer cytoplasm and organelles to generate a Balbiani body. We showed that...
Mouse germline cysts, on average, develop into six oocytes supported by 24 nurse cells that transfer cytoplasm and organelles to generate a Balbiani body. We showed that between E14.5 and P5, cysts periodically activate some nurse cells to begin cytoplasmic transfer, which causes them to shrink and turnover within 2 days. Nurse cells die by a programmed cell death (PCD) pathway involving acidification, similar to Drosophila nurse cells, and only infrequently by apoptosis. Prior to initiating transfer, nurse cells co-cluster by scRNA-seq with their pro-oocyte sisters, but during their final 2 days, they cluster separately. The genes promoting oocyte development and nurse cell PCD are upregulated, whereas the genes that repress transfer, such as Tex14, and oocyte factors, such as Nobox and Lhx8, are under-expressed. The transferred nurse cell centrosomes build a cytocentrum that establishes a large microtubule aster in the primordial oocyte that organizes the Balbiani body, defining the earliest oocyte polarity.
Topics: Animals; Apoptosis; Cell Enlargement; Cell Lineage; Cysts; Cytoplasm; Drosophila melanogaster; Female; Gene Expression Regulation, Developmental; Mice; Oocytes; Ovary
PubMed: 35623357
DOI: 10.1016/j.cell.2022.05.001 -
Trends in Cell Biology Apr 2021Phase separation has emerged as a new key principle of intracellular organization. Phase-separated structures play diverse roles in various biological processes and... (Review)
Review
Phase separation has emerged as a new key principle of intracellular organization. Phase-separated structures play diverse roles in various biological processes and pathogenesis of protein aggregation diseases. Recent work has revealed crucial functions for phase separation during germline development. Phase separation controls the assembly and segregation of germ granules that determine which embryonic cells become germ cells. Phase separation promotes the formation of the Balbiani body, a structure that stores organelles and RNAs during the prolonged prophase arrest of oocytes. Phase separation also facilitates meiotic recombination that prepares homologous chromosomes for segregation, and drives the formation of a liquid-like spindle domain that promotes spindle assembly in mammalian oocytes. We review how phase separation drives these essential steps during germline development.
Topics: Animals; Germ Cell Ribonucleoprotein Granules; Germ Cells; Homologous Recombination; Meiosis; Oocytes
PubMed: 33455855
DOI: 10.1016/j.tcb.2020.12.004 -
ELife Nov 2022Recent studies show that pre-follicular mouse oogenesis takes place in germline cysts, highly conserved groups of oogonial cells connected by intercellular bridges that...
Recent studies show that pre-follicular mouse oogenesis takes place in germline cysts, highly conserved groups of oogonial cells connected by intercellular bridges that develop as nurse cells as well as an oocyte. Long studied in and insect gametogenesis, female germline cysts acquire cytoskeletal polarity and traffic centrosomes and organelles between nurse cells and the oocyte to form the Balbiani body, a conserved marker of polarity. Mouse oocyte development and nurse cell dumping are supported by dynamic, cell-specific programs of germline gene expression. High levels of perinatal germ cell death in this species primarily result from programmed nurse cell turnover after transfer rather than defective oocyte production. The striking evolutionary conservation of early oogenesis mechanisms between distant animal groups strongly suggests that gametogenesis and early embryonic development in vertebrates and invertebrates share even more in common than currently believed.
Topics: Female; Pregnancy; Mice; Animals; Drosophila; Oogenesis; Germ Cells; Oocytes; Gametogenesis
PubMed: 36445738
DOI: 10.7554/eLife.83230 -
Frontiers in Cell and Developmental... 2021Maternal factors which accumulate and establish oocyte polarity during the early stages of oogenesis play key roles in embryonic development, as well as germ cell... (Review)
Review
Maternal factors which accumulate and establish oocyte polarity during the early stages of oogenesis play key roles in embryonic development, as well as germ cell formation. However, vertebrate oogenesis, especially early stages of oogenesis, is not well understood due to the difficulty of accessing these oocytes and the lack of analytical methods. Here, we report on a microinjection method for analyzing zebrafish early-stage oocytes and some artifacts to be aware of when performing oocyte injections or analyzing oocytes. Using this method, we successfully injected mRNAs encoding fluorescent-tagged proteins into early-stage oocytes and observed subcellular localization in the live oocytes. This method is expected to advance the functional analysis of genes involved in oogenesis.
PubMed: 34820378
DOI: 10.3389/fcell.2021.753642 -
Developmental Biology Apr 2022The Balbiani body (Bb) is the first marker of polarity in vertebrate oocytes. The Bb is a conserved structure found in diverse animals including insects, fish,...
The Balbiani body (Bb) is the first marker of polarity in vertebrate oocytes. The Bb is a conserved structure found in diverse animals including insects, fish, amphibians, and mammals. During early zebrafish oogenesis, the Bb assembles as a transient aggregate of mRNA, proteins, and membrane-bound organelles at the presumptive vegetal side of the oocyte. As the early oocyte develops, the Bb appears to grow slowly, until at the end of stage I of oogenesis it disassembles and deposits its cargo of localized mRNAs and proteins. In fish and frogs, this cargo includes the germ plasm as well as gene products required to specify dorsal tissues of the future embryo. We demonstrate that the Bb is a stable, solid structure that forms a size exclusion barrier similar to other biological hydrogels. Despite its central role in oocyte polarity, little is known about the mechanism behind the Bb's action. Analysis of the few known protein components of the Bb is insufficient to explain how the Bb assembles, translocates, and disassembles. We isolated Bbs from zebrafish oocytes and performed mass spectrometry to define the Bb proteome. We successfully identified 77 proteins associated with the Bb sample, including known Bb proteins and novel RNA-binding proteins. In particular, we identified Cirbpa and Cirbpb, which have both an RNA-binding domain and a predicted self-aggregation domain. In stage I oocytes, Cirbpa and Cirbpb localize to the Bb rather than the nucleus (as in somatic cells), indicating that they may have a specialized function in the germ line. Both the RNA-binding domain and the self-aggregation domain are sufficient to localize to the Bb, suggesting that Cirbpa and Cirbpb interact with more than just their mRNA targets within the Bb. We propose that Cirbp proteins crosslink mRNA cargo and proteinaceous components of the Bb as it grows. Beyond Cirbpa and Cirbpb, our proteomics dataset presents many candidates for further study, making it a valuable resource for building a comprehensive mechanism for Bb function at a protein level.
Topics: Animals; Cell Polarity; Mammals; Oocytes; Oogenesis; Organelles; Proteomics; Zebrafish; Zebrafish Proteins
PubMed: 35065906
DOI: 10.1016/j.ydbio.2022.01.006 -
MicroPublication Biology 2023Dormant human oocytes contain a perinuclear super-organelle, called the Balbiani Body, which is not present in mature oocytes. Here, we use confocal imaging to visualize...
Dormant human oocytes contain a perinuclear super-organelle, called the Balbiani Body, which is not present in mature oocytes. Here, we use confocal imaging to visualize two Balbiani Body markers-mitochondria and the DEAD-box helicase DDX4-in preantral follicles isolated from a 20-year-old female patient. In primordial follicles, mitochondria were concentrated in a ring near the oocyte nucleus, while DDX4 formed adjacent micron-scale spherical condensates. In primary and secondary follicles, the mitochondria were dispersed throughout the oocyte cytoplasm, and large DDX4 condensates were not visible. Our data suggest that the Balbiani Body breaks down during the primordial to primary follicle transition, thus releasing mitochondria and soluble DDX4 protein into the oocyte cytoplasm.
PubMed: 37920272
DOI: 10.17912/micropub.biology.000989 -
Postepy Biochemii Dec 2021The Balbiani body is an organelle assemblage (termed sometimes a super-organelle) characteristic for the developing oocytes of almost all investigated animal species. In...
The Balbiani body is an organelle assemblage (termed sometimes a super-organelle) characteristic for the developing oocytes of almost all investigated animal species. In the vast majority of species, this complex resides next to the germinal vesicle and comprises such organelles as mitochondria, elements of endoplasmic reticulum, Golgi complexes as well as accumulations of nuage material. Comparative analyses have shown that the Balbiani bodies, even in closely related organisms, are often morphologically different. The differences concern not only the composition of this assemblage but also mutual relations between its components. So far, it has been found that the Balbiani body is implicated in several cellular processes undergoing in female germline cells. Most importantly this organelle complex is responsible for the delivery and localization of certain macromolecules and organelles to specific regions of the ooplasm (oocyte cytoplasm), as well as in the transfer of mitochondria to the zygote, i.e. to the next generation. Moreover, it has been shown recently that at least in some species the Balbiani body participates in the elimination of nonfunctional, damaged mitochondria from the developing oocytes and egg cells.
Topics: Animals; Endoplasmic Reticulum; Invertebrates; Morphogenesis; Oocytes; Vertebrates
PubMed: 35107964
DOI: 10.18388/pb.2021_410 -
Genes Jan 2020The most important role of mitochondria is to supply cells with metabolic energy in the form of adenosine triphosphate (ATP). As synthesis of ATP molecules is... (Review)
Review
The most important role of mitochondria is to supply cells with metabolic energy in the form of adenosine triphosphate (ATP). As synthesis of ATP molecules is accompanied by the generation of reactive oxygen species (ROS), mitochondrial DNA (mtDNA) is highly vulnerable to impairment and, consequently, accumulation of deleterious mutations. In most animals, mitochondria are transmitted to the next generation maternally, i.e., exclusively from female germline cells (oocytes and eggs). It has been suggested, in this context, that a specialized mechanism must operate in the developing oocytes enabling escape from the impairment and subsequent transmission of accurate (devoid of mutations) mtDNA from one generation to the next. Literature survey suggest that two distinct and irreplaceable pathways of mitochondria transmission may be operational in various animal lineages. In some taxa, the mitochondria are apparently selected: functional mitochondria with high inner membrane potential are transferred to the cells of the embryo, whereas those with low membrane potential (overloaded with mutations in mtDNA) are eliminated by mitophagy. In other species, the respiratory activity of germline mitochondria is suppressed and ROS production alleviated leading to the same final effect, i.e., transmission of undamaged mitochondria to offspring, via an entirely different route.
Topics: Animals; DNA, Mitochondrial; Female; Mitochondria; Mitophagy; Mutation; Oocytes; Oogenesis
PubMed: 31963356
DOI: 10.3390/genes11010104 -
ELife Jul 2021Selection against deleterious mitochondrial mutations is facilitated by germline processes, lowering the risk of genetic diseases. How selection works is disputed:...
Selection against deleterious mitochondrial mutations is facilitated by germline processes, lowering the risk of genetic diseases. How selection works is disputed: experimental data are conflicting and previous modeling work has not clarified the issues; here, we develop computational and evolutionary models that compare the outcome of selection at the level of individuals, cells and mitochondria. Using realistic mutation rates and germline development parameters from mouse and humans, the evolutionary model predicts the observed prevalence of mitochondrial mutations and diseases in human populations. We show the importance of organelle-level selection, seen in the selective pooling of mitochondria into the Balbiani body, in achieving high-quality mitochondria at extreme ploidy in mature oocytes. Alternative mechanisms debated in the literature, bottlenecks and follicular atresia, are unlikely to account for the clinical data, because neither process effectively eliminates mitochondrial mutations under realistic conditions. Our findings explain the major features of female germline architecture, notably the longstanding paradox of over-proliferation of primordial germ cells followed by massive loss. The near-universality of these processes across animal taxa makes sense in light of the need to maintain mitochondrial quality at extreme ploidy in mature oocytes, in the absence of sex and recombination.
Topics: Animals; Biological Evolution; Cell Death; Cell Proliferation; DNA, Mitochondrial; Female; Follicular Atresia; Germ Cells; Humans; Mammals; Mice; Mitochondria; Mutation; Oocytes; Oogenesis; Ploidies
PubMed: 34279226
DOI: 10.7554/eLife.69344 -
Scientific Reports Apr 2024Oocytes of both vertebrates and invertebrates often contain an intricate organelle assemblage, termed the Balbiani body (Bb). It has previously been suggested that this...
Oocytes of both vertebrates and invertebrates often contain an intricate organelle assemblage, termed the Balbiani body (Bb). It has previously been suggested that this assemblage is involved in the delivery of organelles and macromolecules to the germ plasm, formation of oocyte reserve materials, and transfer of mitochondria to the next generation. To gain further insight into the function of the Bb, we performed a series of analyses and experiments, including computer-aided 3-dimensional reconstructions, detection of DNA (mtDNA) synthesis as well as immunolocalization studies. We showed that in orthopteran Meconema meridionale, the Bb comprises a network of mitochondria and perinuclear nuage aggregations. As oogenesis progresses, the network expands filling almost entire ooplasm, then partitions into several smaller entities, termed micro-networks, and ultimately into individual mitochondria. As in somatic cells, this process involves microfilaments and elements of endoplasmic reticulum. We showed also that at least some of the individual mitochondria are surrounded by phagophores and eliminated via mitophagy. These findings support the idea that the Bb is implicated in the multiplication and selective elimination of (defective) mitochondria and therefore may participate in the transfer of undamaged (healthy) mitochondria to the next generation.
Topics: Animals; Oocytes; Oogenesis; Mitochondria; Insecta; Endoplasmic Reticulum; Orthoptera
PubMed: 38594333
DOI: 10.1038/s41598-024-58997-6