Biology subjects

Vjestica, A.

Publications and source records attributed to Vjestica, A..

8 recordsLinked to original sources

bioRxiv2026

Meiotic cohesin Rec8 imposes fitness costs on fission yeast gametesfavoring the evolution of parental bias in gene expression

Differences between partner gametes, which evolved repeatedly in eukaryotes, can contribute to the evolution of the sexes, sexual selection and non-Mendelian inheritance1- 4. Yet, the empirical evidence for how functional asymmetries arise between initially equivalent gametes is limited. Here, we combine theoretical and experimental approaches in the fission yeast Schizosaccharomyces pombe to show how selective pressures acting concurrently on gametes and zygotes drive the evolution of gamete differences. We find that despite being morphologically identical, P- and M-type partner gametes invest asymmetrically in zygotic development by contributing different amounts of conserved meiotic cohesins. P-gametes preferentially produce thve Rec85 cohesin that increases zygotic fitness but reduces gamete viability, revealing a trade-off between reproductive success and gamete survival. We demonstrate that this asymmetry is mediated by partner-specific communication and model its evolutionary dynamics using empirically determined parameters. Our results support classical theoretical predictions for the evolution of gamete differences and provide a mechanistic understanding of how molecular asymmetries between partners can originate from opposing selection pressures acting in species that lack morphologically distinct gametes.

evolutionary biology↗

bioRxiv2024

Fertilization triggers cytosolic functions and P-body recruitment of the RNA-binding protein Mei2 to drive fission yeast zygotic development

Compartmentalized regulation of RNAs is emerging as a key driver of developmental transitions, with RNA-binding proteins performing specialized functions in different subcellular compartments. The RNA-binding protein Mei2, which arrests mitotic proliferation and drives zygotic development in fission yeast, was shown to function in the nucleus to trigger meiotic divisions. Here, using compartment-restricted alleles, we report that Mei2 functions in the cytosol to arrest mitotic growth and initiate development. We find that Mei2 is a zygote-specific component of P-bodies that inhibits the translation of tethered mRNAs. Importantly, we show that P-bodies are necessary for Mei2-driven development. Phosphorylation of Mei2 by the inhibitory Pat1 kinase impedes P-body recruitment of both Mei2 and its target RNA. Finally, we establish that Mei2 recruitment to P-bodies and its cytosolic functions, including translational repression of tethered RNAs, depend on the RNA-binding domain of Mei2 that is dispensable for nuclear Mei2 roles. Collectively, our results dissect how distinct pools of an RNA-binding protein control developmental stages and implicate P-bodies as key regulators of gamete-to-zygote transition.

cell biology↗

bioRxiv2022

Community review: a robust and scalable selection system for resource allocation within open science and innovation communities

Resource allocation is essential to the selection and implementation of innovative projects in science and technology. With large stakes involved in concentrating large fundings over a few promising projects, current "winner-take-all" models for grant applications are time-intensive endeavours that mobilise significant researcher time in writing extensive project proposals, and rely on the availability of a few time-saturated volunteer experts. Such processes usually carry over several months, resulting in high effective costs compared to expected benefits. Faced with the need for a rapid response to the Covid19 pandemic in 2020, we devised an agile "community review" system to allocate micro-grants for the fast prototyping of innovative solutions. Here we describe and evaluate the implementation of this community review across 147 projects from the "Just One Giant Labs OpenCOVID19 initiative" and "Helpful Engineering" open research communities. The community review process uses granular review forms and requires the participation of grant applicants in the review process. Within a year, we organised 7 rounds of review, resulting in 614 reviews from 201 reviewers, and the attribution of 48 micro-grants of up to 4,000 euros. We show that this system is fast, with a median process duration of 10 days, scalable, with a median of 4 reviewers per project independent of the total number of projects, and fair, with project rankings highly preserved after the synthetic removal of reviewers. We investigate the potential bias introduced by involving applicants in the process, and find that review scores from both applicants and non-applicants have a similar correlation of r=0.28 with other reviews within a project, matching previous observations using traditional approaches. Finally, we find that the ability of projects to apply to several rounds allows to both foster the further implementation of successful early prototypes, as well as provide a pathway to constructively improve an initially failing proposal in an agile manner. Overall, this study quantitatively highlights the benefits of a frugal, community review system acting as a due diligence for rapid and agile resource allocation in open research and innovation programs, with particular implications for decentralised communities.

scientific communication and education↗

bioRxiv2020

Cell patterning by secretion-induced plasma membrane flows

Cells self-organize using reaction-diffusion and fluid-flow principles. Whether bulk membrane flows contribute to cell patterning has not been established. Here, using mathematical modelling, optogenetics and synthetic probes, we show that polarized exocytosis causes lateral membrane flows away from regions of membrane insertion. Plasma membrane-associated proteins with sufficiently low diffusion and/or detachment rates couple to the flows and deplete from areas of exocytosis. In rod-shaped fission yeast cells, zones of Cdc42 GTPase activity driving polarized exocytosis are limited by GTPase activating proteins (GAPs). We show that membrane flows pattern the GAP Rga4 distribution and coupling of a synthetic GAP to membrane flows is sufficient to establish the rod shape. Thus, membrane flows induced by Cdc42-dependent exocytosis form a negative feedback restricting the zone of Cdc42 activity. One Sentence SummaryExocytosis causes bulk membrane flows that drag associated proteins and form a negative feedback restricting the exocytic site.

cell biology↗

bioRxiv2020

Fungal zygote survival and ploidy maintenance rely on cell cycle-dependent and independent mating blocks

To ensure genome stability, sexually reproducing organisms require that mating brings together exactly two haploid gametes and that meiosis occurs only in diploid zygotes. In the fission yeast Schizosaccharomyces pombe, fertilization triggers the Mei3-Pat1-Mei2 signaling cascade, which represses subsequent mating and initiates meiosis. Here, we establish a degron system to specifically degrade proteins post-fusion and demonstrate that mating blocks not only safeguard zygote ploidy but also prevent lysis caused by aberrant fusion attempts. Using long-term imaging and flow-cytometry approaches, we identify previously unrecognized and independent roles for Mei3 and Mei2 in zygotes. We show that Mei3 promotes premeiotic S-phase independently of Mei2 and that cell cycle progression is both necessary and sufficient to reduce zygotic mating behaviors. Mei2 imposes the meiotic program and promotes the meiotic cycle, but also blocks mating behaviors independently of Mei3 and cell cycle progression. Thus, we find that fungi preserve zygote ploidy and survival by at least two mechanisms where the zygotic fate imposed by Mei2 and the cell cycle re-entry triggered by Mei3 synergize to prevent zygotic mating.

cell biology↗

bioRxiv2019

A toolbox of Stable Integration Vectors (SIV) in the fission yeast Schizosaccharomyces pombe

Schizosaccharomyces pombe is a widely used model organism that resembles higher eukaryotes in many aspects of cell physiology. Its popularity as an experimental system partially stems from the ease of genetic manipulations, where the innate homology-targeted repair is exploited to precisely edit the genome. While vectors to incorporate exogenous sequences into the chromosomes are available, most are poorly characterized. Here we show that commonly used fission yeast vectors, which upon integration produce repetitive genomic regions, yield unstable genomic loci. We overcome this problem by designing a new series of Stable Integration Vectors (SIV) that target four different prototrophy genes. SIV produce non-repetitive, stable genomic loci and integrate predominantly as single copy. Additionally, we develop a set of complementary auxotrophic alleles that preclude false-positive integration events. We expand the vector series to include antibiotic resistance markers, promoters, fluorescent tags and terminators, and build a highly modular toolbox to introduce heterologous sequences. Finally, as proof of concept, we generate a large set of ready-to-use, fluorescent probes to mark organelles and cellular processes with a wide range of applications in fission yeast research.

cell biology↗

bioRxiv2019

Optogenetics reveals Cdc42 local activation by scaffold-mediated positive feedback and Ras GTPase

The small GTPase Cdc42 is critical for cell polarization. Scaffold-mediated positive feedback regulation was proposed to mediate symmetry-breaking to a single active zone in budding yeast cells. In rod-shaped fission yeast S. pombe cells, active Cdc42-GTP localizes to both cell poles, where it promotes bipolar growth. Here, we implement the CRY2-CIBN optogenetic system for acute light-dependent protein recruitment to the plasma membrane, which allowed to directly demonstrate positive feedback. Indeed, optogenetic recruitment of constitutively active Cdc42 leads to co-recruitment of the GEF Scd1, in a manner dependent on the scaffold protein Scd2. We show that Scd2 function is completely bypassed and positive feedback restored by an engineered interaction between the GEF and a Cdc42 effector, the Pak1 kinase. Remarkably, such re-wired cells are viable and grow in a bipolar manner even when lacking otherwise essential Cdc42 activators. Interestingly, these cells reveal that Ras1 GTPase plays a dual role in localizing and activating the GEF, thus potentiating the feedback. We conclude that scaffold-mediated positive feedback, gated by Ras activity, is minimally required for rod-shape formation.

cell biology↗

bioRxiv2018

Gamete fusion rapidly reconstitutes a bi-partite transcription factor to block re-fertilization

The ploidy cycle, integral to sexual reproduction, requires not only meiosis to halve the number of chromosomes, but also mechanisms that ensure zygotes are formed by exactly two partners1-5. During sexual reproduction of the fungal model organism Schizosaccharomyces pombe, haploid P- and M-cells normally fuse to form a diploid zygote that immediately enters meiosis6. Here, we reveal that fast post-fusion reconstitution of a bi-partite transcription factor actively blocks re-fertilization. We first identify mutants that undergo transient cell fusion involving cytosol exchange but not karyogamy, and show this drives distinct cell fates in the two gametes: The P-partner undergoes lethal, haploid meiosis while the M-cell persists in mating. Consistently, we find that the zygotic transcription that drives meiosis is initiated rapidly only from the P-parental genome, even in wild type cells. This asymmetric gene expression depends on a bi-partite complex formed post-fusion between the nuclear P-cell-specific homeobox protein Pi and a cytosolic M-specific peptide Mi7,8, which is captured by Pi in the P-nucleus. Zygotic transcription is thus poised to initiate in the P-nucleus as fast as Mi reaches it. The asymmetric nuclear accumulation is inherent to the transcription factor design, and is reconstituted by a pair of synthetic interactors, one localized to the nucleus of one gamete and the other in the cytosol of its partner. Strikingly, imposing a delay in zygotic transcription, by postponing Mi expression or deleting its transcriptional target in the P-genome, leads to zygotes fusing with additional gametes, thus forming polyploids and eventually aneuploid progeny. We further show that the signaling cascade to block re-fertilization shares components with, but bifurcates from, meiotic induction9-11. Thus, cytoplasmic connection upon gamete fusion leads to rapid reconstitution of a bi-partite transcription factor in one partner to block re-fertilization and induce meiosis, thus ensuring genome maintenance during sexual reproduction.

cell biology↗