The Experts below are selected from a list of 6033 Experts worldwide ranked by ideXlab platform
Qing-yuan Sun - One of the best experts on this subject based on the ideXlab platform.
-
Cytoplasmic Determination of Meiotic Spindle Size Revealed by a Unique Inter-Species Germinal Vesicle Transfer Model.
Scientific reports, 2016Co-Authors: Zhong-wei Wang, Guang-li Zhang, Heide Schatten, John L. Carroll, Qing-yuan SunAbstract:Spindle sizes are different in diverse species and cell types. In frogs, the Meiotic Spindle size is positively correlated with the egg cell volume. Across species, relatively small mouse oocytes (70-80 μm) have a relatively large Spindle while larger pig oocytes (about 120 μm) have a considerably smaller Spindle. In this study we investigated whether species-specific oocyte Spindle size was determined by cytoplasmic or nuclear factors. By exchanging the germinal vesicle between mouse and pig oocytes, we obtained two kinds of reconstructed oocytes: one with mouse ooplasm and pig GV (mCy-pGV oocyte), and the other with pig ooplasm and mouse GV (pCy-mGV oocyte). We show that the MII Spindle size of the mCy-pGV oocyte is similar to that of the mouse Meiotic Spindle and significantly larger than that of the pig Meiotic Spindle. The timing of oocyte maturation also followed that of the species from which the oocyte cytoplasm arose, although some impact of the origin of the GV was observed. These data suggest that Spindle size and the timing of Meiotic progression are governed by cytoplasmic components rather than cytoplasmic volume and GV materials.
-
astrin regulates Meiotic Spindle organization Spindle pole tethering and cell cycle progression in mouse oocytes
Cell Cycle, 2009Co-Authors: Ju Yuan, Heide Schatten, Liang Wei, Shen Yin, Bo Xiong, Lin Shengli, Qing-yuan SunAbstract:Astrin has been described as a microtubule and kinetochore protein required for the maintenance of sister chromatid cohesion and centrosome integrity in human mitosis. However, its role in mammalian oocyte meiosis is unclear. In this study, we find that Astrin is mainly associated with the Meiotic Spindle microtubules and concentrated on Spindle poles at metaphase I and metaphase II stages. Taxol treatment and immunoprecipitation show that Astrin may interact with the centrosomal proteins Aurora-A or Plk1 to regulate microtubule organization and Spindle pole integrity. Loss-of-function of Astrin by RNAi and overexpression of Tof the coiled-coil domain results in Spindle disorganization, chromosome misalignment and meiosis progression arrestT. Thr24, Ser66 or Ser447 may be the potential phosphorylated sites of Astrin by Plk1, as site-directed mutation of these sites causes oocyte Meiotic arrest at HTmetaphaseTH I with highly disordered Spindles and disorganized chromosomes, although mutant Astrin localizes...
-
brca1 is required for Meiotic Spindle assembly and Spindle assembly checkpoint activation in mouse oocytes
Biology of Reproduction, 2008Co-Authors: Bo Xiong, Shen Yin, Yingchun Ouyang, Shaochen Sun, Dayuan Chen, Qing-yuan SunAbstract:BRCA1 as a tumor suppressor has been widely investigated in mitosis, but its functions in meiosis are unclear. In the present study, we examined the expression, localization, and function of BRCA1 during mouse oocyte Meiotic maturation. We found that expression level of BRCA1 was increased progressively from germinal vesicle to metaphase I stage, and then remained stable until metaphase II stage. Immunofluorescent analysis showed that BRCA1 was localized to the Spindle poles at metaphase I and metaphase II stages, colocalizing with centrosomal protein gamma-tubulin. Taxol treatment resulted in the presence of BRCA1 onto the Spindle microtubule fibers, whereas nocodazole treatment induced the localization of BRCA1 onto the chromosomes. Depletion of BRCA1 by both antibody injection and siRNA injection caused severely impaired Spindles and misaligned chromosomes. Furthermore, BRCA1-depleted oocytes could not arrest at the metaphase I in the presence of low-dose nocodazole, suggesting that the Spindle checkpoint is defective. Also, in BRCA1-depleted oocytes, gamma-tubulin dissociated from Spindle poles and MAD2L1 failed to rebind to the kinetochores when exposed to nocodazole at metaphase I stage. Collectively, these data indicate that BRCA1 regulates not only Meiotic Spindle assembly, but also Spindle assembly checkpoint, implying a link between BRCA1 deficiency and aneuploid embryos.
-
Effects of cooling on Meiotic Spindle structure and chromosome alignment within in vitro matured porcine oocytes.
Molecular reproduction and development, 2003Co-Authors: Rui-hua Liu, Qing-yuan Sun, Li-hong Jiao, Wei-hua WangAbstract:Meiotic Spindle structure and chromosome alignment were examined after porcine oocytes were cooled at metaphase II (M II) stage. Cumulus–oocyte complexes (COCs) collected from medium size follicles were cultured in an oocyte maturation medium at 39°C, 5% CO2 in air for 44 hr. At the end of culture, oocytes were removed from cumulus cells and cooled to 24 or 4°C for 5, 30, or 120 min in a solution with or without 1.5 M dimethyl sulfoxide (DMSO). After being cooled, oocytes were either fixed immediately for examination of the Meiotic Spindle and chromosome alignment or returned to maturation medium at 39°C for 2 hr for examination of Spindle recovery. Most oocytes (65–71%) cooled to 24°C showed partially depolymerized Spindles but 81–92% of oocytes cooled at 4°C did not have a Spindle after cooling for 120 min. Quicker disassembly of Spindles in the oocytes was observed at 4°C than at 24°C. Cooling also induced chromosome abnormality, which was indicated by dispersed chromosomes in the cytoplasm. Limited Spindle recovery was observed in the oocytes cooled to both 4 and 24°C regardless of cooling time. The effect of cooling on the Spindle organization and chromosome alignment was not influenced by the presence of DMSO. These results indicate that the Meiotic Spindles in porcine M II oocytes are very sensitive to a drop in the temperature. Both Spindle and chromosomes were damaged during cooling, and such damage was not reversible by incubating the oocytes after they had been cooled. Mol. Reprod. Dev. 65: 212–218, 2003. © 2003 Wiley-Liss, Inc.
-
Rotation of Meiotic Spindle Is Controlled by Microfilaments in Mouse Oocytes
Biology of reproduction, 2003Co-Authors: Zi Yu Zhu, Da Yuan Chen, Li Lian, Lei Lei, Zhiming Han, Qing-yuan SunAbstract:The completion of meiosis requires the spatial and temporal coordination of cytokinesis and karyokinesis. During Meiotic maturation, many events, such as formation, location, and rotation of the Meiotic Spindle as well as chromosomal movement, polar body extrusion, and pronuclear migration, are dependent on regulation of the cytoskeleton system. To study functions of microfilaments in meiosis, we induced metaphase II (MII) mouse oocytes to resume meiosis by in vitro fertilization or parthenogenetic activation, and we treated such oocytes with cytochalasin B (CB). The changes of the Meiotic Spindle, as visualized in preparations stained for β-tubulin and chromatin, were observed by fluorescent confocal microscopy. The Meiotic Spindle of MII oocytes was observed to be parallel to the plasmalemma. After meiosis had resumed, the Spindle rotated to the vertical position so that the second polar body could be extruded into the perivitelline space. When meiosis resumed and oocytes were treated with 10 μg/ml of CB, the Spindle rotation was inhibited. Consequently, the oocyte formed an extra pronucleus instead of extruding a second polar body. These results indicate that Spindle rotation is essential for polar body extrusion; it is the microfilaments that play a crucial role in regulating rotation of the Meiotic Spindle.
Francis J Mcnally - One of the best experts on this subject based on the ideXlab platform.
-
Mechanisms that prevent catastrophic interactions between paternal chromosomes and the oocyte Meiotic Spindle.
Cell cycle (Georgetown Tex.), 2018Co-Authors: Michelle T. Panzica, Francis J McnallyAbstract:Meiosis produces haploid gametes by accurately reducing chromosome ploidy through one round of DNA replication and two subsequent rounds of chromosome segregation and cell division. The cell divisions of female meiosis are highly asymmetric and give rise to a large egg and two very small polar bodies that do not contribute to development. These asymmetric divisions are driven by Meiotic Spindles that are small relative to the size of the egg and have one pole juxtaposed against the cell cortex to promote polar body extrusion. An additional unique feature of female meiosis is that fertilization occurs before extrusion of the second polar body in nearly all animal species. Thus sperm-derived chromosomes are present in the egg during female meiosis. Here, we explore the idea that the asymmetry of female meiosis spatially separates the sperm from the Meiotic Spindle to prevent detrimental interactions between the Spindle and the paternal chromosomes.
-
F-actin prevents interaction between sperm DNA and the oocyte Meiotic Spindle in C. elegans
Journal of Cell Biology, 2017Co-Authors: Michelle T. Panzica, Harold C. Marin, Anne-cécile Reymann, Francis J McnallyAbstract:Fertilization occurs during female meiosis in most animals, which raises the question of what prevents the sperm DNA from interacting with the Meiotic Spindle. In this study, we find that Caenorhabditis elegans sperm DNA stays in a fixed position at the opposite end of the embryo from the Meiotic Spindle while yolk granules are transported throughout the embryo by kinesin-1. In the absence of F-actin, the sperm DNA, centrioles, and organelles were transported as a unit with the yolk granules, resulting in sperm DNA within 2 µm of the Meiotic Spindle. F-actin imaging revealed a cytoplas- mic meshwork that might restrict transport in a size-dependent manner. However, increasing yolk granule size did not slow their velocity, and the F-actin moved with the yolk granules. Instead, sperm contents connect to the cortical F-actin to prevent interaction with the Meiotic Spindle.
-
Kinesin-1 prevents capture of the oocyte Meiotic Spindle by the sperm aster.
Developmental cell, 2012Co-Authors: Karen Mcnally, Amy S. Fabritius, Marina L. Ellefson, Jonathan R. Flynn, Jennifer A. Milan, Francis J McnallyAbstract:Centrioles are lost during oogenesis and inherited from the sperm at fertilization. In the zygote, the centrioles recruit pericentriolar proteins from the egg to form a mature centrosome that nucleates a sperm aster. The sperm aster then captures the female pronucleus to join the maternal and paternal genomes. Because fertilization occurs before completion of female meiosis, some mechanism must prevent capture of the Meiotic Spindle by the sperm aster. Here we show that in wild-type Caenorhabditis elegans zygotes, maternal pericentriolar proteins are not recruited to the sperm centrioles until after completion of meiosis. Depletion of kinesin-1 heavy chain or its binding partner resulted in premature centrosome maturation during meiosis and growth of a sperm aster that could capture the oocyte Meiotic Spindle. Kinesin prevents recruitment of pericentriolar proteins by coating the sperm DNA and centrioles and thus prevents triploidy by a nonmotor mechanism.
-
CDK-1 inhibits Meiotic Spindle shortening and dynein-dependent Spindle rotation in C. elegans
The Journal of cell biology, 2011Co-Authors: Marina L. Ellefson, Francis J McnallyAbstract:In animals, the female Meiotic Spindle is positioned at the egg cortex in a perpendicular orientation to facilitate the disposal of half of the chromosomes into a polar body. In Caenorhabditis elegans, the metaphase Spindle lies parallel to the cortex, dynein is dispersed on the Spindle, and the dynein activators ASPM-1 and LIN-5 are concentrated at Spindle poles. Anaphase-promoting complex (APC) activation results in dynein accumulation at Spindle poles and dynein-dependent rotation of one Spindle pole to the cortex, resulting in perpendicular orientation. To test whether the APC initiates Spindle rotation through cyclin B-CDK-1 inactivation, separase activation, or degradation of an unknown dynein inhibitor, CDK-1 was inhibited with purvalanol A in metaphase-I-arrested, APC-depleted embryos. CDK-1 inhibition resulted in the accumulation of dynein at Spindle poles and dynein-dependent Spindle rotation without chromosome separation. These results suggest that CDK-1 blocks rotation by inhibiting dynein association with microtubules and with LIN-5-ASPM-1 at Meiotic Spindle poles and that the APC promotes Spindle rotation by inhibiting CDK-1.
-
katanin controls mitotic and Meiotic Spindle length
Journal of Cell Biology, 2006Co-Authors: Karen Mcnally, Anjon Audhya, Karen Oegema, Francis J McnallyAbstract:Accurate control of Spindle length is a conserved feature of eukaryotic cell division. Lengthening of mitotic Spindles contributes to chromosome segregation and cytokinesis during mitosis in animals and fungi. In contrast, Spindle shortening may contribute to conservation of egg cytoplasm during female meiosis. Katanin is a microtubule-severing enzyme that is concentrated at mitotic and Meiotic Spindle poles in animals. We show that inhibition of katanin slows the rate of Spindle shortening in nocodazole-treated mammalian fibroblasts and in untreated Caenorhabditis elegans Meiotic embryos. Wild-type C. elegans Meiotic Spindle shortening proceeds through an early katanin-independent phase marked by increasing microtubule density and a second, katanin-dependent phase that occurs after microtubule density stops increasing. In addition, double-mutant analysis indicated that gamma-tubulin-dependent nucleation and microtubule severing may provide redundant mechanisms for increasing microtubule number during the early stages of Meiotic Spindle assembly.
K Madan - One of the best experts on this subject based on the ideXlab platform.
-
Meiotic Spindle and zona pellucida characteristics as predictors of embryonic development a preliminary study using polscope imaging
Reproductive Biomedicine Online, 2007Co-Authors: G Rama A Raju, Gomedhikam J Prakash, K M Krishna, K MadanAbstract:This study assesses Meiotic Spindle and zona pellucida characteristics using the PolScope, and analyses their relationship to embryonic development potential. A total of 205 matured oocytes retrieved from 25 patients undergoing ovarian stimulation were imaged for Meiotic Spindle and zona pellucida characteristics using the PolScope. After intracytoplasmic sperm injection, the oocytes were cultured and assessed for progression to blastocysts. Meiotic Spindles were visualized in 78.0% of oocytes. Significantly more oocytes with visible Spindles fertilized and progressed to blastocysts compared with oocytes without visible Spindles. Oocytes with Spindle retardance of >3 nm showed a greater progression to blastocysts compared with those with a retardance of 2-3 nm or 12 nm than from oocytes with Spindle lengths 10-12 nm or 3 nm compared with oocytes with retardance of 2-3 nm or <2 nm. Oocytes with an inner layer zona of 10-12 nm thickness showed better progression compared with those with a thickness of 8-10 nm or <8 nm. Quantitative measurement of length and retardance of the Meiotic Spindle and zona pellucida has a positive predictive value in relation to embryonic development.
-
Meiotic Spindle and zona pellucida characteristics as predictors of embryonic development: a preliminary study using PolScope imaging.
Reproductive biomedicine online, 2007Co-Authors: Ga Rama Raju, Gomedhikam J Prakash, K M Krishna, K MadanAbstract:This study assesses Meiotic Spindle and zona pellucida characteristics using the PolScope, and analyses their relationship to embryonic development potential. A total of 205 matured oocytes retrieved from 25 patients undergoing ovarian stimulation were imaged for Meiotic Spindle and zona pellucida characteristics using the PolScope. After intracytoplasmic sperm injection, the oocytes were cultured and assessed for progression to blastocysts. Meiotic Spindles were visualized in 78.0% of oocytes. Significantly more oocytes with visible Spindles fertilized and progressed to blastocysts compared with oocytes without visible Spindles. Oocytes with Spindle retardance of >3 nm showed a greater progression to blastocysts compared with those with a retardance of 2-3 nm or 12 nm than from oocytes with Spindle lengths 10-12 nm or 3 nm compared with oocytes with retardance of 2-3 nm or
Shin'ichi Ishiwata - One of the best experts on this subject based on the ideXlab platform.
-
micromechanics of the vertebrate Meiotic Spindle examined by stretching along the pole to pole axis
Biophysical Journal, 2014Co-Authors: Jun Takagi, Takeshi Itabashi, Yuta Shimamoto, Tarun M. Kapoor, Kazuya Suzuki, Shin'ichi IshiwataAbstract:The Meiotic Spindle is a bipolar molecular machine that is designed to segregate duplicated chromosomes toward the opposite poles of the cell. The size and shape of the Spindle are considered to be maintained by a balance of forces produced by molecular motors and microtubule assembly dynamics. Several studies have probed how mechanical perturbations of the force balance affect the Spindle structure. However, the Spindle’s response to a stretching force acting at the Spindle pole and along its long axis, i.e., the direction in which chromosomes are segregated, has not been examined. Here, we describe a method to apply a stretching force to the metaphase Spindle assembled in Xenopus egg extracts and measure the relationship between the force and the three-dimensional deformation of the Spindle. We found that the Spindle behaves as a Zener-type viscoelastic body when forces are applied at the Spindle pole, generating a restoring force for several minutes. In addition, both the volume of the Spindle and the tubulin density are conserved under the stretching force. These results provide insight into how the Spindle size is maintained at metaphase.
-
Probing the Force-Balancing Mechanism of the Meiotic Spindle in Xenopus Egg Extracts
Biophysical Journal, 2010Co-Authors: Jun Takagi, Takeshi Itabashi, Yuta Shimamoto, Tarun M. Kapoor, Shin'ichi IshiwataAbstract:During cell division, the Meiotic Spindle equally segregates replicated genomes into two daughter cells. Errors in this process cause birth defect and cancer.Spindles are mainly composed of microtubules (MTs) and molecular motors. Various studies have revealed key regulators, such as Kinesin-5 (plus-end directed kinesin tetramer), depolymerizing kinesins and microtubule-associated proteins (MAPs). These exert forces for sliding MTs or regulating MT dynamics in the Spindle, so that the Spindle maintains a rugby ball-like structure at metaphase. These forces are also known to generate a poleward flux of Spindle MTs. At metaphase, size and shape of the Spindle are maintained constant in spite of the dynamic nature of Spindle MTs. This indicates forces exerted by molecular motors and MTs are well balanced in the Spindle.In this study, we developed micromanipulation techniques for changing Spindle shape to disrupt steady state force balance of the Spindle without any changes in molecular components of the Spindle. Spindles spontaneously assembled in Xenopus egg extracts were stretched along their pole-to-pole axis using two glass micro-needles. When the Spindles were briefly stretched, they recovered their original size and shape after a while. In contrast, when Spindles were kept stretched, they gradually recovered their original shape with the increase in the Spindle width, resulting in the enlargement in size. This result indicates that the Meiotic Spindle has an ability to adjust its size and shape to the externally applied force. Our findings provide new insights into the force-balancing mechanism of the Spindle.
-
Probing the mechanical architecture of the vertebrate Meiotic Spindle.
Nature methods, 2009Co-Authors: Takeshi Itabashi, Jun Takagi, Yuta Shimamoto, Hiroaki Onoe, Kenta Kuwana, Isao Shimoyama, Jedidiah Gaetz, Tarun M. Kapoor, Shin'ichi IshiwataAbstract:A piezo-resistive dual-cantilever system is combined with fluorescence imaging to examine the mechanical features of the in vitro–assembled vertebrate Meiotic Spindle. Accurate chromosome segregation during meiosis depends on the assembly of a microtubule-based Spindle of proper shape and size. Current models for Spindle-size control focus on reaction diffusion–based chemical regulation and balance in activities of motor proteins. Although several molecular perturbations have been used to test these models, controlled mechanical perturbations have not been possible. Here we report a piezoresistive dual cantilever–based system to test models for Spindle-size control and examine the mechanical features, such as deformability and stiffness, of the vertebrate Meiotic Spindle. We found that Meiotic Spindles prepared in Xenopus laevis egg extracts were viscoelastic and recovered their original shape in response to small compression. Larger compression resulted in plastic deformation, but the Spindle adapted to this change, establishing a stable mechanical architecture at different sizes. The technique we describe here may also be useful for examining the micromechanics of other cellular organelles.
Yuta Shimamoto - One of the best experts on this subject based on the ideXlab platform.
-
mechanically distinct microtubule arrays determine the length and force response of the Meiotic Spindle
Developmental Cell, 2019Co-Authors: Jun Takagi, Ryota Sakamoto, Gen Shiratsuchi, Yusuke T Maeda, Yuta ShimamotoAbstract:Summary The microtubule-based Spindle is subjected to various mechanical forces during cell division. How the structure generates and responds to forces while maintaining overall integrity is unknown because we have a poor understanding of the relationship between filament architecture and mechanics. Here, to fill this gap, we combine microneedle-based quantitative micromanipulation with high-resolution imaging, simultaneously analyzing forces and local filament motility in the Xenopus Meiotic Spindle. We find that microtubules exhibit a compliant, fluid-like mechanical response at the middle of the Spindle half, being distinct from those near the pole and the equator. A force altering Spindle length induces filament sliding at this compliant array, where parallel microtubules predominate, without influencing equatorial antiparallel filament dynamics. Molecular perturbations suggest that kinesin-5 and dynein contribute to the Spindle’s local mechanical difference. Together, our data establish a link between Spindle architecture and mechanics and uncover the mechanical design of this essential cytoskeletal assembly.
-
micromechanics of the vertebrate Meiotic Spindle examined by stretching along the pole to pole axis
Biophysical Journal, 2014Co-Authors: Jun Takagi, Takeshi Itabashi, Yuta Shimamoto, Tarun M. Kapoor, Kazuya Suzuki, Shin'ichi IshiwataAbstract:The Meiotic Spindle is a bipolar molecular machine that is designed to segregate duplicated chromosomes toward the opposite poles of the cell. The size and shape of the Spindle are considered to be maintained by a balance of forces produced by molecular motors and microtubule assembly dynamics. Several studies have probed how mechanical perturbations of the force balance affect the Spindle structure. However, the Spindle’s response to a stretching force acting at the Spindle pole and along its long axis, i.e., the direction in which chromosomes are segregated, has not been examined. Here, we describe a method to apply a stretching force to the metaphase Spindle assembled in Xenopus egg extracts and measure the relationship between the force and the three-dimensional deformation of the Spindle. We found that the Spindle behaves as a Zener-type viscoelastic body when forces are applied at the Spindle pole, generating a restoring force for several minutes. In addition, both the volume of the Spindle and the tubulin density are conserved under the stretching force. These results provide insight into how the Spindle size is maintained at metaphase.
-
Probing the Force-Balancing Mechanism of the Meiotic Spindle in Xenopus Egg Extracts
Biophysical Journal, 2010Co-Authors: Jun Takagi, Takeshi Itabashi, Yuta Shimamoto, Tarun M. Kapoor, Shin'ichi IshiwataAbstract:During cell division, the Meiotic Spindle equally segregates replicated genomes into two daughter cells. Errors in this process cause birth defect and cancer.Spindles are mainly composed of microtubules (MTs) and molecular motors. Various studies have revealed key regulators, such as Kinesin-5 (plus-end directed kinesin tetramer), depolymerizing kinesins and microtubule-associated proteins (MAPs). These exert forces for sliding MTs or regulating MT dynamics in the Spindle, so that the Spindle maintains a rugby ball-like structure at metaphase. These forces are also known to generate a poleward flux of Spindle MTs. At metaphase, size and shape of the Spindle are maintained constant in spite of the dynamic nature of Spindle MTs. This indicates forces exerted by molecular motors and MTs are well balanced in the Spindle.In this study, we developed micromanipulation techniques for changing Spindle shape to disrupt steady state force balance of the Spindle without any changes in molecular components of the Spindle. Spindles spontaneously assembled in Xenopus egg extracts were stretched along their pole-to-pole axis using two glass micro-needles. When the Spindles were briefly stretched, they recovered their original size and shape after a while. In contrast, when Spindles were kept stretched, they gradually recovered their original shape with the increase in the Spindle width, resulting in the enlargement in size. This result indicates that the Meiotic Spindle has an ability to adjust its size and shape to the externally applied force. Our findings provide new insights into the force-balancing mechanism of the Spindle.
-
Probing the mechanical architecture of the vertebrate Meiotic Spindle.
Nature methods, 2009Co-Authors: Takeshi Itabashi, Jun Takagi, Yuta Shimamoto, Hiroaki Onoe, Kenta Kuwana, Isao Shimoyama, Jedidiah Gaetz, Tarun M. Kapoor, Shin'ichi IshiwataAbstract:A piezo-resistive dual-cantilever system is combined with fluorescence imaging to examine the mechanical features of the in vitro–assembled vertebrate Meiotic Spindle. Accurate chromosome segregation during meiosis depends on the assembly of a microtubule-based Spindle of proper shape and size. Current models for Spindle-size control focus on reaction diffusion–based chemical regulation and balance in activities of motor proteins. Although several molecular perturbations have been used to test these models, controlled mechanical perturbations have not been possible. Here we report a piezoresistive dual cantilever–based system to test models for Spindle-size control and examine the mechanical features, such as deformability and stiffness, of the vertebrate Meiotic Spindle. We found that Meiotic Spindles prepared in Xenopus laevis egg extracts were viscoelastic and recovered their original shape in response to small compression. Larger compression resulted in plastic deformation, but the Spindle adapted to this change, establishing a stable mechanical architecture at different sizes. The technique we describe here may also be useful for examining the micromechanics of other cellular organelles.