Dual spindles assemble in bovine zygotes despite the presence of paternal centrosomes

The first mitosis of the mammalian embryo must partition the parental genomes contained in two pronuclei. In rodent zygotes, sperm centrosomes are degraded, and instead, acentriolar microtubule organizing centers and microtubule self-organization guide the assembly of two separate spindles around the genomes. In nonrodent mammals, including human or bovine, centrosomes are inherited from the sperm and have been widely assumed to be active. Whether nonrodent zygotes assemble a single centrosomal spindle around both genomes or follow the dual spindle self-assembly pathway is unclear. To address this, we investigated spindle assembly in bovine zygotes by systematic immunofluorescence and real-time light-sheet microscopy. We show that two independent spindles form despite the presence of centrosomes, which had little effect on spindle structure and were only loosely connected to the two spindles. We conclude that the dual spindle assembly pathway is conserved in nonrodent mammals. This could explain whole parental genome loss frequently observed in blastomeres of human IVF embryos.

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Non-rodent mammalian zygotes assemble dual spindles despite the presence of paternal centrosomes

10.1101/2020.10.16.342154 ◽

2020 ◽

Cited By ~ 1

Author(s):

Isabell Schneider ◽

Marta de Ruijter-Villani ◽

M. Julius Hossain ◽

Tom A. E. Stout ◽

Jan Ellenberg

Keyword(s):

Self Assembly ◽

Spindle Assembly ◽

Light Sheet ◽

Self Organization ◽

Parental Genome ◽

Mammalian Embryo ◽

Light Sheet Microscopy ◽

Assembly Pathway ◽

Spindle Structure ◽

Human Ivf

AbstractThe first mitosis of the mammalian embryo must partition the parental genomes contained in two pronuclei. In rodent zygotes, sperm centrosomes are degraded and, instead, acentriolar microtubule organizing centers and microtubule self-organization guide the assembly of two separate spindles around the genomes. In non-rodent mammals, including human or bovine, centrosomes are inherited from the sperm and have been widely assumed to be active. Whether non-rodent zygotes assemble a single centrosomal spindle around both genomes, or follow the dual spindle self-assembly pathway is unclear. To address this, we investigated spindle assembly in bovine zygotes by systematic immunofluorescence and real-time light-sheet microscopy. We show that two independent spindles form around the parental genomes despite the presence of centrosomes, which had little effect on spindle structure and were only loosely connected to the two spindles. We conclude that the dual spindle assembly pathway is conserved in non-rodent mammals. This could explain whole parental genome loss frequently observed in blastomeres of human IVF embryos.SummaryThis study investigates spindle assembly during the first embryonic division in bovine zygotes that, like human, inherit centrosomes from the sperm. It shows that two independent microtubule arrays form by self-organization around parental genomes with only loosely connected centrosomes.

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Augmin accumulation on long-lived microtubules drives amplification and kinetochore-directed growth

The Journal of Cell Biology ◽

10.1083/jcb.201805044 ◽

2019 ◽

Vol 218 (7) ◽

pp. 2150-2168 ◽

Cited By ~ 23

Author(s):

Ana F. David ◽

Philippe Roudot ◽

Wesley R. Legant ◽

Eric Betzig ◽

Gaudenz Danuser ◽

...

Keyword(s):

Spindle Assembly ◽

Light Sheet ◽

Spindle Pole ◽

Directional Bias ◽

Fiber Assembly ◽

Light Sheet Microscopy ◽

Sister Chromatids ◽

Spindle Dynamics ◽

Dividing Cells ◽

Microtubule Growth

Dividing cells reorganize their microtubule cytoskeleton into a bipolar spindle, which moves one set of sister chromatids to each nascent daughter cell. Early spindle assembly models postulated that spindle pole–derived microtubules search the cytoplasmic space until they randomly encounter a kinetochore to form a stable attachment. More recent work uncovered several additional, centrosome-independent microtubule generation pathways, but the contributions of each pathway to spindle assembly have remained unclear. Here, we combined live microscopy and mathematical modeling to show that most microtubules nucleate at noncentrosomal regions in dividing human cells. Using a live-cell probe that selectively labels aged microtubule lattices, we demonstrate that the distribution of growing microtubule plus ends can be almost entirely explained by Augmin-dependent amplification of long-lived microtubule lattices. By ultrafast 3D lattice light-sheet microscopy, we observed that this mechanism results in a strong directional bias of microtubule growth toward individual kinetochores. Our systematic quantification of spindle dynamics reveals highly coordinated microtubule growth during kinetochore fiber assembly.

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Dual spindle formation in zygotes keeps parental genomes apart in early mammalian embryos

10.1101/198275 ◽

2017 ◽

Cited By ~ 1

Author(s):

Judith Reichmann ◽

Bianca Nijmeijer ◽

M. Julius Hossain ◽

Manuel Eguren ◽

Isabell Schneider ◽

...

Keyword(s):

Genetic Material ◽

Spindle Assembly ◽

Light Sheet ◽

Light Sheet Microscopy ◽

Nuclear Compartments ◽

Assembly Mechanism ◽

Mammalian Embryos ◽

Cell Embryo ◽

Bipolar Spindles ◽

Fertilized Egg

AbstractAt the beginning of mammalian life the genetic material from each parent meets when the fertilized egg divides. It was previously thought that a single microtubule spindle is responsible to spatially combine the two genomes and then segregate them to create the two-cell embryo. Utilizing light-sheet microscopy, we showed that two bipolar spindles form in the zygote, that independently congress the maternal and paternal genomes. These two spindles aligned their poles prior to anaphase but kept the parental genomes apart during the first cleavage. This spindle assembly mechanism provides a rationale for erroneous divisions into more than two blastomeric nuclei observed in mammalian zygotes and reveals the mechanism behind the observation that parental genomes occupy separate nuclear compartments in the two-cell embryo.One Sentence Summary: After fertilization, two spindles form around pro-nuclei in mammalian zygotes and keep the parental genomes apart during the first division.

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Augmin-mediated amplification of long-lived spindle microtubules directs plus-ends to kinetochores

10.1101/501445 ◽

2018 ◽

Cited By ~ 1

Author(s):

Ana F. David ◽

Philippe Roudot ◽

Wesley R. Legant ◽

Eric Betzig ◽

Gaudenz Danuser ◽

...

Keyword(s):

Spindle Assembly ◽

Light Sheet ◽

Spindle Pole ◽

Directional Bias ◽

Fiber Assembly ◽

Light Sheet Microscopy ◽

Sister Chromatids ◽

Spindle Dynamics ◽

Dividing Cells ◽

Microtubule Growth

AbstractDividing cells reorganize their microtubule cytoskeleton into a bipolar spindle, which moves one set of sister chromatids to each nascent daughter cell. Early spindle assembly models postulated that spindle-pole-derived microtubules search the cytoplasmic space until they randomly encounter a kinetochore to form a stable attachment. More recent work uncovered several additional, centrosome-independent microtubule generation pathways, but the contributions of each pathway to spindle assembly have remained unclear. Here, we combined live microscopy and mathematical modeling to show that most microtubules nucleate at non-centrosomal regions in dividing human cells. Using a live-cell probe that selectively labels aged microtubule lattices, we demonstrate that the distribution of growing microtubule plus-ends can be almost entirely explained by Augmin-dependent amplification of long-lived microtubules. By ultra-fast 3D lattice light-sheet microscopy, we observed that this mechanism results in a strong directional bias of microtubule growth towards individual kinetochores. Our systematic quantification of spindle dynamics reveals highly coordinated microtubule growth during kinetochore-fiber assembly.

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Spindle scaling mechanisms

Essays in Biochemistry ◽

10.1042/ebc20190064 ◽

2020 ◽

Vol 64 (2) ◽

pp. 383-396

Author(s):

Lara K. Krüger ◽

Phong T. Tran

Keyword(s):

Cell Size ◽

Spindle Assembly ◽

Dependent Manner ◽

Post Translational Modification ◽

Size Dependent ◽

A Cell ◽

Chromosome Separation ◽

Spindle Elongation ◽

Protein Gradients ◽

Spindle Structure

Abstract The mitotic spindle robustly scales with cell size in a plethora of different organisms. During development and throughout evolution, the spindle adjusts to cell size in metazoans and yeast in order to ensure faithful chromosome separation. Spindle adjustment to cell size occurs by the scaling of spindle length, spindle shape and the velocity of spindle assembly and elongation. Different mechanisms, depending on spindle structure and organism, account for these scaling relationships. The limited availability of critical spindle components, protein gradients, sequestration of spindle components, or post-translational modification and differential expression levels have been implicated in the regulation of spindle length and the spindle assembly/elongation velocity in a cell size-dependent manner. In this review, we will discuss the phenomenon and mechanisms of spindle length, spindle shape and spindle elongation velocity scaling with cell size.

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Faculty Opinions recommendation of Reconstruction of zebrafish early embryonic development by scanned light sheet microscopy.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.1123365.584346 ◽

2008 ◽

Author(s):

Kees Jalink

Keyword(s):

Embryonic Development ◽

Light Sheet ◽

Early Embryonic Development ◽

Light Sheet Microscopy

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Achromatic terahertz Airy beam generation with dielectric metasurfaces

Nanophotonics ◽

10.1515/nanoph-2020-0536 ◽

2020 ◽

Vol 0 (0) ◽

Author(s):

Qingqing Cheng ◽

Juncheng Wang ◽

Ling Ma ◽

Zhixiong Shen ◽

Jing Zhang ◽

...

Keyword(s):

Biomedical Imaging ◽

Frequency Dispersion ◽

Light Sheet ◽

Photonic Devices ◽

Self Healing ◽

Beam Focusing ◽

Light Sheet Microscopy ◽

Airy Beam ◽

Potential Applications ◽

Airy Beams

AbstractAiry beams exhibit intriguing properties such as nonspreading, self-bending, and self-healing and have attracted considerable recent interest because of their many potential applications in photonics, such as to beam focusing, light-sheet microscopy, and biomedical imaging. However, previous approaches to generate Airy beams using photonic structures have suffered from severe chromatic problems arising from strong frequency dispersion of the scatterers. Here, we design and fabricate a metasurface composed of silicon posts for the frequency range 0.4–0.8 THz in transmission mode, and we experimentally demonstrate achromatic Airy beams exhibiting autofocusing properties. We further show numerically that a generated achromatic Airy-beam-based metalens exhibits self-healing properties that are immune to scattering by particles and that it also possesses a larger depth of focus than a traditional metalens. Our results pave the way to the realization of flat photonic devices for applications to noninvasive biomedical imaging and light-sheet microscopy, and we provide a numerical demonstration of a device protocol.

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