Biology subjects

Schindler, K.

Publications and source records attributed to Schindler, K..

At least 19 recordsLinked to original sources

bioRxiv2026

Declining ribosome function limits oocyte longevity

Protein synthesis declines with age across many tissues, but whether this decline actively contributes to physiological aging remains unclear. Oocytes may be particularly vulnerable because they rely on ribosomes synthesized during growth and maintained for prolonged periods without continual replacement. Here we show that declining translational capacity is a causal component of oocyte aging. An unbiased genetic screen identified ribosome dosage as a major determinant of oocyte longevity, and experimentally reducing ribosome abundance was sufficient to accelerate the loss of developmental competence and prematurely recapitulate meiotic defects that arise during natural aging, while also producing defects in early embryonic development. Ribosomes isolated from aged Drosophila oocytes exhibit ~50% lower translational activity despite only a modest reduction in ribosome abundance and preserved gross structure and composition, with both ribosomal subunits contributing to this functional decline. Protein synthesis also declines markedly in aged metaphase-I mouse oocytes. Together, these findings identify long-lived translational machinery as an intrinsic vulnerability of the oocyte and establish declining ribosome function as a mechanistic contributor to reproductive aging.

cell biology↗

bioRxiv2026

Age-associated changes to mouse oocyte meiotic spindle properties revealed through in situ measurements

Chromosome segregation errors in oocyte meiosis are a leading cause of early miscarriage and congenital disorders in mammals and these errors become more prevalent with advanced maternal age. Although the effects of aging on the functions of critical meiotic proteins and cytoskeletal filaments in oocytes are known, the influence of aging on the force generating capabilities of oocyte spindle components remains largely unexplored. Through the integration of a coarse-grained model and in situ experiments, we compare the long-axis mechanical properties of metaphase I (MI) and II (MII) oocyte spindles from reproductively young and old mice. Increased inter-kinetochore distance in aged MII oocytes agree with a model of age-associated cohesion loss, and kinetochore dynamics in these spindles following laser ablation suggest a similar reduction in inter-kinetochore bridge viscosity. Simultaneously, we find that both cohesive and poleward force generators lose stiffness with advanced age in MI spindles. In total, we quantify the extent to which structural spindle components lose their stiffness and viscosity during maternal aging, highlighting the multifaceted impacts of aging on mouse oocyte spindle mechanics. Significance StatementO_LIMaternal aging influences mammalian oocyte spindles in numerous ways, yet the impacts of aging on the balance of collective spindle forces remain poorly understood. C_LIO_LIIntegrating coarse-grained mechanical modeling with in situ measurements of spindle morphology and kinetochore dynamics, we quantify age-associated changes to the viscosities and elastic stiffnesses of oocyte spindle component parts. C_LIO_LIThis work provides both a characterization of the effects of aging on force production in mammalian oocyte spindles and a blueprint for future studies of spindle force generation in complex biological contexts. C_LI

cell biology↗

bioRxiv2026

Developmentally programmed nuclear pore complex replacement enables oocyte specification

Oocytes endow embryos with molecular machinery essential for development, but not all maternal components are inherited indiscriminately. In Drosophila, surveillance pathways eliminate defective mitochondria and aberrant RNAs from the maternal pool. Whether stable nuclear structures, like nuclear pore complexes (NPCs), are similarly curated remains unknown. Here, we uncover a developmentally programmed NPC turnover pathway that renews NPCs during oocyte specification. NPC levels decline through a combination of passive dilution, driven by deferred nucleoporin expression, and active degradation mediated by the ESCRT-III/Vps4 pathway. This clearance is counterbalanced by subsequent de novo NPC synthesis. Failure to turn over NPCs results in aberrantly persistent germ cell gene expression and defective oocyte specification. These findings establish NPC renewal as a critical step in oocyte identity establishment and maternal provisioning.

developmental biology↗

bioRxiv2025

Directed cortico-limbic dialogue in the human brain

How can one trace the brains orderly directed signals amid a tangle of nerve fibers? Because direct access to actual brain signaling is rare in humans, the precise wiring diagrams for cortico-limbic communication during sleep and wake remain essentially unmapped, hampering progress in neuroscience. Now, a unique neurosurgical window on the human brain allows for electrically mapping cortical connections at the hospital, but studies so far have relied on average signals, masking the dynamic nature of signal flow across brain regions. To causally estimate signaling dynamics, we repeatedly probed cortico-limbic networks with short-lived electrical pulses over days and assessed the variable fate of each transmitted signal on a single-trial basis. In the resulting openly available dataset, we characterized signaling probabilities and directionality across thousands local and long-range cortico-limbic connections over days. Challenging established views, we found that limbic structures send twice as many signals as they receive, in both wakefulness and sleep. Our findings provide a fundamental framework for causally interpreting signal flow in the brain and formulating therapeutic strategies for brain networks disorders.

neuroscience↗

bioRxiv2025

A persistent intracellular bridge and cell cycle misregulation enable polar body cell divisions and tumor formation in Mos-deficient eggs

Mammalian female meiosis is uniquely regulated to produce a developmentally competent egg capable of supporting embryogenesis. During meiosis I, homologous chromosomes segregate, with half extruded into the first polar body. The egg then arrests at metaphase II and only resumes meiosis and extrudes the second polar body following fertilization. The MOS/MAPK signaling pathway is important for maintaining the metaphase II arrest; in mos-/- mutants, a subset of eggs undergo spontaneous parthenogenetic activation and exhibit additional abnormal cell divisions. To further understand the cell cycle mis-regulation in activated mos-/- eggs, we used time-lapse microscopy to monitor the abnormal divisions. We discovered that, following parthenogenetic activation, the first polar body can assemble a spindle, segregate chromosomes, and divide with timings similar to anaphase II onset in the egg. This behavior contrasts with wildtype polar bodies, which do not divide and are typically degenerated. We demonstrate that mos-/- eggs and polar bodies can exchange cytoplasm at the time of meiosis II spindle assembly, likely allowing the transfer of cell cycle regulators between the two compartments. Further inspection revealed that mos-/- eggs have defective meiotic midbody assembly with most eggs lacking a cap structure, which is needed to separate the two compartments. We report that polar bodies of mos-/- eggs can re-enter the cell cycle and undergo additional aberrant divisions. These findings identify MOS as a critical regulator of meiotic midbody formation and uncover a novel consequence of disrupted MOS/MAPK signaling: the potential for polar bodies to become mitotically active and contribute to tumor formation.

cell biology↗

bioRxiv2025

Maternal CENP-C restores centromere symmetry in mammalian zygotes to ensure proper chromosome segregation

Across metazoan species, the centromere-specific histone variant CENP-A is essential for accurate chromosome segregation, yet its regulation at the parental-to-zygote transition in mammals is poorly understood. To address this, we developed a CENP-A-mScarlet knock-in mouse model, which revealed sex-specific dynamics: mature sperm retains 10% of the CENP-A levels present in MII-oocytes. However, in zygotes prior to the first mitosis, this difference is resolved, using maternally inherited cytoplasmic-CENP-A. Notably, the increase in CENP-A at paternal centromeres is independent of sensing CENP-A asymmetry or the presence of maternal chromosomes. Instead, CENP-A equalization relies on asymmetric recruitment of maternal CENP-C to paternal centromeres. Depletion of maternal CENP-A decreases total CENP-A in pronuclei without disrupting equalization. In contrast, reducing maternal CENP-C or disruption of its dimerization domains impairs CENP-A equalization and chromosome segregation. Therefore, maternal CENP-C acts a key epigenetic regulator that resets centromeric symmetry at fertilization to preserve genome integrity. Highlights[bullet] CENP-A asymmetry between sperm and oocyte centromeres is a conserved feature from flies to mammals including mice and humans. [bullet]CENP-A asymmetry between parental centromeres is resolved prior to the first zygotic division via maternally inherited, cytoplasmic CENP-A. [bullet]Zygotic CENP-A levels in zygotes are regulated in a pronucleus-autonomous manner. [bullet]CENP-A equalization relies on asymmetric CENP-C recruitment to the paternal pronucleus and requires CENP-C dimerization. Key TermsCentromere; CENP-A; CENP-C; sperm; oocyte; zygote; intergenerational; epigenetics; mouse

genetics↗

bioRxiv2025

SIRT7 links H3K36ac epigenetic regulation with genome maintenance in the aging mouse testis

ABSTRACT/SUMMARYReproductive aging is an increasing health concern affecting family planning and overall well-being. While extensively studied in females, the mechanisms driving male reproductive aging remain largely unexamined. Here we found that mammalian Sirtuin 7 (SIRT7) sustains spermatogenesis in an age-dependent manner through the control of histone 3 lysine 36 acetylation (H3K36ac). SIRT7 deficiency in mice resulted in increased levels of H3K36ac in spermatogonia and spermatocytes. In a germ cell line, SIRT7 deficiency disrupted nucleosome stability and increased vulnerability to genotoxic stress. Importantly, undifferentiated spermatogonia, which are required for continuous sperm production, decreased prematurely in Sirt7-/- mice and showed genome damage accumulation. These changes were concurrent with age-dependent defects in homologous chromosome synapsis and partial meiotic arrest. Taken together, our results indicate that SIRT7 connects H3K36ac epigenetic regulation to long-term genome stability in male germ cells, ensuring steady-state spermatogenesis during the lengthy male reproductive lifespan.

cell biology↗

bioRxiv2024

AURKA controls oocyte spindle assembly checkpoint and chromosome alignment by HEC1 phosphorylation

In human oocytes, meiosis I is error-prone, causing early miscarriages and developmental disorders. The Aurora protein kinases are key regulators of chromosome segregation in mitosis and meiosis and their dysfunction is associated with aneuploidy. Oocytes contain three Aurora kinase (AURK) proteins, but only AURKA is necessary and sufficient to support oocyte meiosis in mice. However, the unique molecular contributions of AURKA remain unclear. Here, using a combination of genetic and pharmacological approaches, we evaluated how AURKA phosphorylation regulates outer kinetochore function during oocyte meiosis. We found that the outer kinetochore protein Ndc80/HEC1 is constitutively phosphorylated at multiple residues by Aurora kinases during meiosis I, but that Serine 69 is specifically phosphorylated by AURKA in mouse and human oocytes. We further show that Serine 69 phosphorylation regulates spindle assembly checkpoint (SAC) activation and chromosome alignment during meiosis I. These results provide a fundamental mechanistic understanding of how AURKA regulates meiosis and kinetochore function to ensure meiosis I fidelity.

cell biology↗

bioRxiv2024

Sleep modulates neural timescales and spatiotemporal integration in the human cortex

Spontaneous neural dynamics manifest across multiple timescales, which are intrinsic to brain areas and exhibit hierarchical organization across the cortex. In wake, a hierarchy of timescales is thought to naturally emerge from microstructural properties, gene expression, and recurrent connections. A fundamental question is timescales organization and changes in sleep, where physiological needs are different. Here, we describe two coexisting but distinct measures of neural timescales, obtained from broadband activity and gamma power, which display complementary properties. We leveraged intracranial electroencephalography (iEEG) data to characterize timescale changes from wake to sleep across the cortical hierarchy. We show that both broadband and gamma timescales are globally longer in sleep than in wake. While broadband timescales increase along the sensorimotor-association axis, gamma ones decrease. During sleep, slow waves can explain the increase of broadband and gamma timescales, but only broadband ones show a positive association with slow-wave density across the cortex. Finally, we characterize spatial correlations and their relationship with timescales as a proxy for spatiotemporal integration, finding high integration at long distances in wake for broadband and at short distances in sleep for gamma timescales. Our results suggest that mesoscopic neural populations possess different timescales that are shaped by anatomy and are modulated by the sleep/wake cycle. Significance statementUnderstanding the organization of intrinsic neural dynamics is crucial for investigating brain functions in health and disease. A key question is: how do neural dynamics change in the sleeping brain? Here we focus on neural timescales, which measure temporal autocorrelation and are organized hierarchically across the cortex, and spatial correlations. We show that two types of timescales exist in neural populations recorded with intracranial electroencephalography in humans, corresponding to broadband (0.5-80 Hz) and gamma (40-80 Hz) frequency ranges. Both timescales increase in sleep, where slow waves have an important role, but follow opposite hierarchies: broadband timescales increase from sensory to associative areas, while gamma timescales show the reverse pattern. Finally, timescales covary with spatial correlations, suggesting higher spatiotemporal integration over long distances in wake compared to sleep.

neuroscience↗

bioRxiv2024

Two retrotransposon-derived capsid genes PNMA1 and PNMA4 maintain reproductive capacity

The human genome contains 24 gag-like capsid genes derived from deactivated retrotransposons conserved among eutherians. Although some of their encoded proteins retain the ability to form capsids and even transfer cargo, their fitness benefit has remained elusive. Here we show that the gag-like genes PNMA1 and PNMA4 support reproductive capacity. Six-week-old mice lacking either Pnma1 or Pnma4 are indistinguishable from wild-type littermates, but by six months the mutant mice become prematurely subfertile, with precipitous drops in sex hormone levels, gonadal atrophy, and abdominal obesity; overall they produce markedly fewer offspring than controls. Analysis of donated human ovaries shows that expression of both genes declines normally with aging, while several PNMA1 and PNMA4 variants identified in genome-wide association studies are causally associated with low testosterone, altered puberty onset, or obesity. These findings expand our understanding of factors that maintain human reproductive health and lend insight into the domestication of retrotransposon-derived genes.

genetics↗

bioRxiv2024

A conserved germline-specific Dsn1 alternative splice isoform supports oocyte and embryo development

Alternative mRNA splicing can generate distinct protein isoforms to allow for the differential control of cell processes across cell types. However, alternative splice isoforms that differentially modulate distinct cell division programs have remained elusive. Here, we demonstrate that mammalian germ cells express an alternate mRNA splice isoform for the kinetochore component, DSN1, a subunit of the MIS12 complex that links the centromeres to spindle microtubules during chromosome segregation. This germline DSN1 isoform bypasses the requirement for Aurora kinase phosphorylation for its centromere localization due to the absence of a key regulatory region allowing DSN1 to display persistent centromere localization. Expression of the germline DSN1 isoform in somatic cells results in constitutive kinetochore localization, chromosome segregation errors, and growth defects, providing an explanation for its tight cell type-specific expression. Reciprocally, precisely eliminating expression of the germline DSN1 splice isoform in mouse models disrupts oocyte maturation and early embryonic divisions coupled with a reduction in fertility. Together, this work identifies a germline-specific splice isoform for a chromosome segregation component and implicates its role in mammalian fertility.

cell biology↗

bioRxiv2024

Spatio-temporal requirements of Aurora kinase A in mouse oocytes meiotic spindle building

Meiotic spindles are critical to ensure proper chromosome segregation during gamete formation. Oocytes lack centrosomes and use alternative microtubule nucleation pathways for spindle building. However, how these mechanisms are regulated is still unknown. Aurora kinase A (AURKA) is necessary and sufficient for oocyte meiosis in mouse because Aurka KO oocytes arrest in meiosis I [1] and AURKA compensates for loss of Aurkb/Aurkc [2]. AURKA is required early in pro-metaphase I to trigger microtubule organizing center fragmentation, a step necessary to effectively build a bipolar spindle. Moreover, in double Aurkb/Aurkc knockouts, AURKA localizes to spindles and chromatin to support meiosis. Although these mouse models were useful for foundational studies, we were unable to resolve AURKA spatial and temporal functions. Here we provide high-resolution analyses of AURKA requirements during multiple steps of meiotic spindle building and identify the subcellular populations that carry out these functions. By combining mouse genetics and pharmacological approaches we show that AURKA is specifically required in early spindle building and later for spindle stability, whereas AURKC is specifically required in late pro-metaphase. Through expression of targeted AURKA constructs expressed in triple Aurora kinase knockout oocytes and high-resolution live imaging, we demonstrate that the spindle pole population of AURKA is the predominate pool that controls meiotic spindle building and stability.

cell biology↗

bioRxiv2024

Multiple intersecting pathways are involved in the phosphorylation of CPEB1 to activate translation during mouse oocyte meiosis

The RNA-binding protein cytoplasmic polyadenylation element binding 1 (CPEB1) plays a fundamental role in the regulation of mRNA translation in oocytes. However, the nature of protein kinase cascades modulating the activity of CPEB1 is still a matter of controversy. Using genetic and pharmacological tools and detailed time courses, here we have reevaluated the relationship between CPEB1 phosphorylation and the activation of translation during mouse oocyte maturation. We show that both the CDK1/MAPK and AURKA/PLK1 pathways converge on the phosphorylation of CPEB1 during prometaphase. Only inactivation of the CDK1/MAPK pathway disrupts translation, while inactivation of either pathway leads to CPEB1 stabilization. However, stabilization of CPEB1 induced by inactivation of the AURKA/PLK1 does not affect translation, indicating that destabilization/degradation can be dissociated from translational activation. The accumulation of the endogenous CCNB1 protein closely recapitulates the translation data. These findings support the overarching hypothesis that the activation of translation in prometaphase in mouse oocytes relies on a CDK1-dependent CPEB1 phosphorylation, and this translational activation precedes CPEB1 destabilization.

developmental biology↗

bioRxiv2023

Whole Transcriptome and Functional Analyses Identify Novel Genes Involved in Meiosis and Fertility in Drosophila melanogaster

Reproductive success requires the development of viable oocytes and the accurate segregation of chromosomes during meiosis. Failure to segregate chromosomes properly can lead to infertility, miscarriages, or developmental disorders. A variety of factors contribute to accurate chromosome segregation and oocyte development, such as spindle assembly and sister chromatid cohesion. However, many proteins required for meiosis remain unknown. In this study, we aimed to identify and characterize novel meiotic and fertility genes using the genome of Drosophila melanogaster. To accomplish this goal, genes upregulated within meiotically active tissues were identified. About 200 genes with no known function were silenced using RNA interference (RNAi), and the effects on meiosis and fertility were assessed. We identified 65 genes that when silenced caused infertility and/or high levels of chromosomal nondisjunction. The vast majority of these genes have human and mouse homologs that are also poorly studied. Through this screening process, we identified novel genes that are crucial for meiosis and oocyte development but have not been extensively studied in human or model organisms. Understanding the function of these genes will be an important step towards the understanding of their biological significance during reproduction. Author SummaryIn this study, we aimed to identify and characterize novel meiotic and fertility genes within the genome of Drosophila melanogaster. We identified 65 genes that when silenced caused infertility and/or high levels of chromosomal nondisjunction. The vast majority of these genes have human and mouse homologs that are also poorly studied. Through this screening process, we identified novel genes that are crucial for meiosis and oocyte development, making them strong candidates for future studies to characterize their functions.

genetics↗

bioRxiv2023

Distinct Aurora B pools at the inner centromere and kinetochore have different contributions to meiotic and mitotic chromosome segregation

Proper chromosome segregation depends on establishment of bioriented kinetochore-microtubule attachments, which often requires multiple rounds of release and reattachment. Aurora B and C kinases phosphorylate kinetochore proteins to release tensionless attachments. Multiple pathways recruit Aurora B/C to the centromere and kinetochore. We studied how these pathways contribute to anaphase onset timing and correction of kinetochore-microtubule attachments in budding yeast meiosis and mitosis. We find that the pool localized by the Bub1/Bub3 pathway sets the normal duration of meiosis and mitosis, in differing ways. Our meiosis data suggests that disruption of this pathway leads to PP1 kinetochore localization, which dephosphorylates Cdc20 for premature anaphase onset. For error correction, the Bub1/Bub3 and COMA pathways are individually important in meiosis but compensatory in mitosis. Finally, we find that the haspin and Bub1/3 pathways function together to ensure error correction in mouse oogenesis. Our results suggest that each recruitment pathway localizes spatially distinct kinetochore-localized Aurora B/C pools that function differently between meiosis and mitosis.

cell biology↗

bioRxiv2022

The E2 SUMO-conjugating enzyme UBE2I coordinates the oocyte and zygotic transcriptional programs

In mammals, meiotically competent oocytes develop cyclically during ovarian folliculogenesis. During folliculogenesis, prophase I arrested oocytes are transcriptionally active, producing and storing transcripts required for their growth and for early stages of embryogenesis prior to the maternal to zygotic transition. Defective oocyte development during folliculogenesis leads to meiotic defects, aneuploidy, follicular atresia, or non-viable embryos. Here we generated a novel oocyte-specific knockout of the SUMO E2 ligase, Ube2i, using Zp3-cre to test its function during folliculogenesis. Ube2i Zp3-cre+ female mice are sterile with oocytes that arrest in meiosis I with defective spindles and chromosome alignment. Fully grown mutant oocytes abnormally maintain transcription but downregulate maternal effect genes and prematurely activate the zygotic transcriptional program. Thus, this work uncovers UBE2i as a novel orchestrator of chromatin and transcriptional regulation in mouse oocytes. TeaserOocyte-specific deletion of Ube2i causes loss of transcriptional repression and premature activation of the zygotic genome.

cell biology↗

bioRxiv2022

A meiotic midbody structure in mouse oocytes acts as a barrier for nascent translation to ensure developmental competence

Successful embryo development is dependent upon maternally deposited components. During egg formation, developmental competence is acquired through regulated translation of maternal mRNA stores. In addition, egg precursors undergo two rounds of chromosome segregation, each coupled to an asymmetric cytokinesis that produces two non-functional polar bodies. In somatic cells, cytokinesis produces two daughter cells and one midbody remnant (MBR), a signaling organelle assembled from the midbody (MB), which first appears in Telophase. MBs contain transcription and translation factors, and epigenetic modifiers. Once MBs mature to MBRs by abscission, they can be subsequently phagocytosed by another cell and influence cellular function or fate. Although the significance of MBs is elucidated in several cell types like neurons, cancer cells and stem cells, the presence and function of MBs in gametes and their roles in reproductive fitness are unknown. Here, we examined the formation and regulation of meiotic midbodies (mMB) in mouse oocytes. We find that although mouse oocyte mMBs contain analogous structures to somatic MBs, they also have a unique cap-like structure composed of the centralspindlin complex, and that cap formation depends upon an asymmetric microtubule abundance in the egg compared to the polar body. Furthermore, our results show that mMBs are translationally active ribonucleoprotein granules, supported by detection of ribosomes, polyadenylated mRNAs and nascent translation. Finally, by pharmacological and laser ablation-based approaches, we demonstrate that the mMB cap is a barrier to prevent translated products from leaving the egg and escaping into the polar body. Crucially, this barrier is critical for successful early embryonic development. Here, we document an evolutionary adaptation to the highly conserved process of cytokinesis in mouse oocytes and describe a new structure and new mechanism by which egg quality and embryonic developmental competence are regulated.

cell biology↗

bioRxiv2022

Equalizing epigenetically imprinted centromeres in early mammalian embryos

The CENP-A histone variant epigenetically defines centromeres, where its levels and locations are precisely maintained through mitotic cell divisions. However, differences in centromere CENP-A propagation in soma versus female/male germline remains poorly understood. Here, we generated CenpamScarlet mice and followed CENP-A dynamics in gametes, zygotes, and embryos. We found that, unlike somatic cells, progenitor female and male germ cells carry high centromeric CENP-A levels that decrease upon terminal differentiation. The reduction in CENP-A is differentially regulated between sexes, resulting in a ten-fold higher level in oocytes compared to sperm. In the zygote, the parent-of-origin CENP-A asymmetry is equalized prior to initial S-phase by redistribution of nuclear CENP-A from maternal to paternal chromosomes. Redistribution of CENP-A requires both CDK1/2 and PLK1 centromeric machinery. These experiments provide direct evidence for resetting of epigenetically imprinted centromeres in early pronuclear stage embryos and imply a mechanism to sense the non-equivalency of parental chromosomes. HighlightsO_LIIncreased CENP-A density at centromeres is a conserved property of germline stem cells while CENP-A reduction is coincident with germ cell differentiation C_LIO_LIPaternal and maternal CENP-A containing nucleosomes are intergenerationally inherited C_LIO_LICENP-A density at centromeres differs between male and female mature gametes C_LIO_LIUpon fertilization, maternal nuclear CENP-A is redistributed to equalize with parental CENP-A C_LIO_LICENP-C and MIS18BP1 are asymmetrically enriched in the parental pronuclei in accordance with CENP-A asymmetry. C_LIO_LILicensing for centromere equalization begins before zygotic DNA replication C_LI

developmental biology↗