Biology subjects

Mogessie, B.

Publications and source records attributed to Mogessie, B..

6 recordsLinked to original sources

bioRxiv2026

A cohesion optimum underlies chromosome segregation fidelity in oocytes

Chromosome segregation is compromised in eggs from women of both early and advanced reproductive ages. Deteriorating cohesion causes premature separation of sister-chromatids in eggs from older females. We show that the converse is true for oocytes of adolescents, with excessive cohesion impeding segregation. Oocytes from juvenile mice show severe chromosome lagging in anaphase I, leading to nondisjunction or, in extreme cases, failure of the first meiotic division. These defects are suppressed by experimentally weakening cohesion or enhancing its resolution during anaphase I. By contrast, lagging and nondisjunction are rare in the oocytes of young adults because cohesion is inherently weaker. Thus, relative cohesion strength underlies both the frequency and type of segregation errors observed in eggs throughout the female reproductive lifespan. One-Sentence SummaryIn eggs, errors in chromosome segregation arise from age-dependent imbalances in how tightly chromosomes are held together.

cell biology↗

bioRxiv2026

The cytoplasmic lattice in mammalian eggs sequesters ubiquitination machinery and tubulin in reserve

The cytoplasmic lattice (CPL) in mammalian eggs is essential for early embryonic development, but its molecular components, structural organization, and functional capacity have remained elusive. Here, using cryo-electron microscopy, we show that the CPL filament in mouse eggs contains repeating units with a periodicity of [~]37 nm, and determine its high-resolution, native structure and complete subunit composition. The CPL architecture organizes maternal-effect proteins, ubiquitination machinery, and tubulin into a highly structured reservoir. Maternal-effect proteins form the scaffold of the CPL to sequester a UBE2D-UHRF1 E2-E3 ubiquitination module and three distinct FBXW E3 ubiquitin ligases, notably all in activity-excluded states. The CPL further contains an {beta}-tubulin heterodimer in a GTP-bound state with a calcium ion coordinated to -tubulin, suggesting microtubule assembly-competent tubulin held in reserve. The CPL structure is capped at each end by a terminal unit that lacks a PADI6 dimer, a scaffold component, thereby preventing further oligomerization. Interactions between maternal-effect proteins in adjacent CPL units promote the assembly of a three-dimensional lattice in the egg cytoplasm. Taken together, our work defines how CPL assembly and architecture prime mammalian eggs for ubiquitin-mediated protein degradation and cytoskeletal remodeling during the egg-to-embryo transition.

biophysics↗

bioRxiv2025

A versatile cohesion manipulation system reveals CENP-A dysfunction accelerates female reproductive age-related egg aneuploidy.

Female reproductive aging is accompanied by a dramatic rise in the incidence of egg aneuploidy. Premature loss of chromosome cohesion proteins and untimely separation of chromosomes is thought to underly high rates egg aneuploidy during maternal aging. However, because chromosome cohesion loss occurs gradually over female reproductive lifespan and cytoskeletal defects alone can predispose eggs to chromosomal abnormalities, the root causes of exponential rise in egg aneuploidy at advanced reproductive ages remain a mystery. Here, we applied high-resolution live imaging to visualize for the first time cohesion protein dynamics underpinning meiotic chromosome segregation. To discover proteins whose dysfunction accelerates aneuploidies associated with female reproductive aging, we innovated the first experimental system in which chemically induced cohesion reduction rapidly triggers aging-like chromosomal abnormalities in young eggs. By integrating this direct cohesion manipulation system with quantitative high-resolution microscopy and targeted protein degradation tools, we identified the centromeric protein CENP-A as a new factor whose aging-like depletion causes a dramatic rise in premature separation of sister chromatids. Our work illuminates cohesion loss-independent origins of age-related egg aneuploidy and provides new avenues to discover therapeutic targets for extending the female reproductive lifespan.

cell biology↗

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↗

bioRxiv2022

Actin limits egg aneuploidies associated with female reproductive aging.

Aging-related centromeric cohesion loss underlies premature separation of sister chromatids (PSSC) and egg aneuploidy in reproductively older females. Here we show that F-actin maintains chromatid association after cohesion deterioration in aged eggs. F-actin disruption in aged mouse eggs exacerbated PSSC, while its removal in young eggs induced extensive chromatid separation events generally only seen in advanced reproductive ages. In young eggs containing experimentally reduced cohesion, F-actin removal accelerated PSSC in a microtubule dynamics-dependent manner, suggesting that actin counteracts chromatid-pulling spindle forces. Consistently, F-actin stabilization restricted PSSC even when cohesion was acutely depleted by targeted protein degradation. We conclude that actin mitigates PSSCs arising from age-related cohesion depletion by limiting microtubule-driven chromatid separation. This is supported by a spindle-specific disruption of F-actin in aged mammalian eggs. One-Sentence SummaryActin counteracts microtubule-based pulling forces to reduce the effects of chromosome cohesion loss in aged mammalian eggs.

cell biology↗

bioRxiv2020

The prophase oocyte nucleus is a homeostatic G-actin buffer

Formation of healthy mammalian eggs from oocytes requires specialised F-actin structures. F-actin disruption produces aneuploid eggs, which are a leading cause of human embryo deaths, genetic disorders, and infertility. We found that oocytes regulate F-actin organisation and function by promptly transferring excess monomeric G-actin from the cytoplasm to the nucleus. Inside healthy oocyte nuclei, transferred monomers form dynamic F-actin structures, a conserved feature that significantly declines with maternal age. Monomer transfer must be controlled tightly. Blocked nuclear import of G-actin triggers assembly of a dense cytoplasmic F-actin network, while excess G-actin in the nucleus dramatically stabilises nuclear F-actin. Imbalances in either direction predispose oocytes to aneuploidy. The large oocyte nucleus is thus a homeostatic G-actin buffer that is used to maintain cytoplasmic F-actin form and function. One Sentence SummaryMammalian oocyte nuclei buffer cytosolic G-actin

cell biology↗