Biology subjects

Schleiffer, A.

Publications and source records attributed to Schleiffer, A..

At least 19 recordsLinked to original sources

bioRxiv2026

Dbf4-dependent kinase promotes meiotic DNA end resection through cyclin-dependent kinase 12 and DNA-2 in Caenorhabditis elegans

Meiotic crossovers depend on the accurate processing of programmed DNA double-strand breaks by homologous recombination, which involves generating by resection the single-stranded DNA ends required for the subsequent strand invasion step. How regulatory kinases control DNA end resection in animal meiosis remains poorly understood. Here, we identify the Caenorhabditis elegans Dbf4-dependent kinase (DDK) complex, composed of CDC-7 and DBF-4, and identify CDK-12 as a candidate substrate. DDK promotes efficient meiotic DNA end resection, while crossover formation remains largely preserved in its absence. Loss of DDK function leads to SPO-11-dependent chromosome bridges at diakinesis that arise from recombination intermediates formed early in recombination. In addition to chromosome bridges, we observed elevated heterologous recombination that occurs independently of the canonical or alternative end-joining pathways. Interestingly, CDC-7 and DBF-4 localize dynamically during prophase I and load onto DNA in a hierarchical manner that depends on the BRC-1-BRD-1 complex. Epistasis analysis placed CDC-7 and CDK-12 within the DNA-2-dependent branch of long-range DNA resection. Together, our findings reveal an unidentified DDK/CDK-12/DNA-2 signaling axis that promotes efficient meiotic DNA resection to avoid the generation of aberrant recombination outcomes.

cell biology↗

bioRxiv2026

The SPARK complex forms the molecular basis of vertebrate fertilization

Fertilization requires gamete recognition and membrane fusion, yet the molecular basis of this process in vertebrates remains unknown. Here we identify SPARK (sperm protein assembly and receptor-binding key), a conserved multi-protein complex that integrates all known sperm fertilization factors, including TMEM81-IZUMO1-SPACA6 and DCST1/2, together with two newly identified components, TMDD1 and FAM187A. SPARK subunits are mutually dependent for stability in mature sperm, and disruption of any single component causes male sterility in zebrafish and mice. Incubating zebrafish sperm with soluble egg receptor Bouncer partially rescues fertilization of Bouncer-deficient eggs in a SPARK-dependent manner, consistent with egg receptor binding priming the complex for fusion. Thus, we propose SPARK as a con-served molecular machine that couples gamete recognition to membrane fusion.

developmental biology↗

bioRxiv2025

Systematic Discovery of Pathogen Effector Functions across Human Pathogens and Pathways

Pathogens deploy effector proteins to exploit host cell biology, and most pathogen open reading frames (ORFs) are rapidly evolving and lack functional annotation. We developed the eORFeome, a scalable functional genomics platform encompassing 3,835 effector ORFs from diverse viruses, bacteria, and parasites. High-throughput barcoded screens across NF{kappa}B, apoptosis, p53, cGAS-STING and MHC-I pathways revealed functions for hundreds of uncharacterized eORFs, unexpected new activities for known effectors, and distinct pathway-specific functions encoded by single ORFs. Illustrating the power of the approach, we identify HHV6A U14 as a p53 antagonist, HHV7 U21 as a dual-function STING antagonist and MHC-I antigen display inhibitor, and adenoviral 13.6K/i-leader protein as a de novo evolved TAP inhibitor that suppresses MHC-I display. These results establish a general framework for systematic effector annotation, uncover new mechanisms of host-pathogen interaction across kingdoms, and highlight pathogen effectors as a versatile toolkit for rewiring and probing human cellular pathways.

systems biology↗

bioRxiv2024

Architecture of the UBR4 complex, a giant E4 ligase central to eukaryotic protein quality control

Eukaryotic cells have evolved sophisticated quality control mechanisms to eliminate aggregation-prone proteins that compromise cellular health. Central to this defense is the ubiquitin-proteasome system, where UBR4 acts as essential E4 ubiquitin ligase, amplifying degradation marks on defective proteins. Our cryo-EM analysis of UBR4 in complex with its cofactors KCMF1 and CALM1 reveals a massive 1.3 MDa ring structure, featuring a central substrate-binding arena and flexibly attached catalytic units. Structural data illustrate how UBR4 binds substrate and extends K48-specific ubiquitin chains. Importantly, efficient substrate targeting depends on both pre-ubiquitination and specific N-degrons, with KCMF1 acting as key substrate filter. Furthermore, we show that the architecture of the E4 megacomplex is conserved across eukaryotes but with species specific adaptations, allowing UBR4 to perform its precisely tuned quality-control function in diverse cellular environments.

biochemistry↗

bioRxiv2024

PITHD1: An Endogenous Inhibitor of the 26S Proteasome During Cellular Dormancy

Cellular dormancy represents a state of regulated growth arrest essential for diverse biological processes, from reproduction to cancer progression. While mechanisms controlling protein synthesis in dormant cells have been identified, how cells regulate protein degradation during dormancy remains unclear. Using zebrafish oocytes, eggs and embryos as a model system, we discovered PITHD1 as an endogenous inhibitor of the 26S proteasome. Our high-resolution cryoEM structure reveals that PITHD1 simultaneously blocks three crucial functional sites on the 19S regulatory particle which are required for ubiquitin recognition, processing, and substrate translocation. This triple-lock mechanism effectively prevents protein degradation in dormant cells. Given PITHD1s evolutionary conservation across species, this mechanism likely represents a general strategy for reversible proteasome regulation during cellular dormancy. Our findings establish a new paradigm for controlling proteostasis in quiescent states.

biochemistry↗

bioRxiv2024

CLEC18A interacts with sulfated GAGs and controls clear cell renal cell carcinoma progression

C-type lectins are a large family of proteins with essential functions in both health and disease. In cancer, some C-type lectins have been found to both promote and inhibit tumor growth, but many of the C-type lectins still remain uncharacterised in a tumor context. Therefore, there is growing interst in further elucidating the mechanisms with which C-type lectins control tumor growth. Here, we report a key role of the CLEC18 family of C-type lectins in the progression of clear cell renal cell carcinoma (ccRCC). The CLEC18 family is conserved across the entire Chordata phylum with recent gene duplication events in humans. We found that CLEC18A is exclusively expressed in the proximal tubule of the kidney and the medial habenula of the brain. We further identified sulfated glycosaminoglycans (GAGs) of proteoglycans as the main CLEC18A ligand, making them unique among C-type lectins. In ccRCC patients, high expression of the CLEC18 family lectins in the tumor are associated with improved survival. In mouse models of ccRCC, deletion of the mouse ortholog Clec18a resulted in enhanced tumor growth. Our results establishes CLEC18A as a novel and critical regulators of ccRCC tumor growth and highlights the potential benefit of modulating CLEC18 expression in the renal tumor microenvironment.

cancer biology↗

bioRxiv2023

Evolutionary adaptation of the chromodomain of the HP1-protein Rhino allows the integration of chromatin and DNA sequence signals

Members of the diverse heterochromatin protein 1 (HP1) family play crucial roles in heterochromatin formation and maintenance. Despite the similar affinities of their chromodomains for di- and tri-methylated histone H3 lysine 9 (H3K9me2/3), different HP1 proteins exhibit distinct chromatin binding patterns, likely due to interactions with various specificity factors. Here, we elucidate the molecular basis of the interaction between the HP1 protein Rhino, a crucial factor of the Drosophila piRNA pathway, and Kipferl, a DNA sequence-specific C2H2 zinc finger protein and Rhino guidance factor. Through phylogenetic analyses, structure prediction, and in vivo genetics, we identify a single amino acid change within Rhinos chromodomain, G31D, that does not affect H3K9me2/3 binding but disrupts the interaction between Rhino and Kipferl. Flies carrying the rhinoG31Dmutation phenocopy kipferl mutant flies, with Rhino redistributing from piRNA clusters to satellite repeats, causing pronounced changes in the ovarian piRNA profile of rhinoG31D flies. Thus, Rhinos chromodomain functions as a dual-specificity module, facilitating interactions with both a histone mark and a DNA-binding protein.

genetics↗

bioRxiv2023

A conserved fertilization complex of Izumo1, Spaca6, and Tmem81 mediates sperm-egg interaction in vertebrates

Fertilization, the fusion of sperm and egg, is essential for sexual reproduction. While several proteins have been demonstrated to be essential for the binding and fusion of gametes in vertebrates, the molecular mechanisms driving this key process are poorly understood. Here, we performed a protein interaction screen using AlphaFold-Multimer to uncover protein-protein interactions in fertilization. This screen resulted in the prediction of a trimeric complex composed of the essential fertilization factors Izumo1 and Spaca6, and Tmem81, a protein previously not implicated in fertilization. We show that Tmem81 is a conserved, testis-expressed transmembrane protein that is evolutionarily related to Izumo1 and Spaca6 and is essential for male fertility in fish and mice. Consistent with trimer formation in vivo, zebrafish izumo1-/-, spaca6-/-, and tmem81-/- mutants exhibit the same sperm-egg binding defect and show co-depletion of all three proteins in sperm. Moreover, we provide experimental evidence that Izumo1, Spaca6, and Tmem81 interact in zebrafish sperm. Strikingly, the Izumo1-Spaca6 interaction is predicted to form a cleft that serves as a binding site for Bouncer, the only identified egg protein essential for fertilization in zebrafish. Together, these results provide compelling evidence for a conserved sperm factor complex in vertebrates that forms a specific interface for the sperm-egg interaction required for successful fertilization.

developmental biology↗

bioRxiv2022

A Phylogenetic Profiling Approach Identifies Novel Ciliogenesis Genes In Drosophila And C. elegans

Cilia are cellular projections that perform sensory and motile functions in eukaryotic cells. A defining feature of cilia is that they are evolutionarily ancient yet not universally conserved. In this study we have used the resulting presence and absence pattern in the genomes of diverse eukaryotes to identify a set of 386 human genes associated with cilium assembly or motility. Comprehensive tissue-specific RNAi in Drosophila and mutant analysis in C. elegans revealed signature ciliary defects for 70-80% of novel genes, a percentage similar to that for known genes within the cluster. Further characterization identified different phenotypic classes, including a set of genes related to the cartwheel component Bld10/Cep135 and two highly conserved regulators of cilium biogenesis. We believe this dataset to define the core set of genes required for cilium assembly and motility across eukaryotes, an invaluable resource for future studies of cilium biology and associated disorders.

cell biology↗

bioRxiv2022

Cryo-EM structure of the chain-elongating E3 ligase UBR5

UBR5 is a nuclear E3 ligase that ubiquitinates a vast range of substrates for proteasomal degradation. This HECT E3 ligase has recently been identified as an important regulator of oncogenes, e.g., MYC, but little is known about its structure or mechanisms of substrate engagement and ubiquitination. Here, we present the cryo-EM structure of the human UBR5, revealing a building block of an antiparallel dimer which can further assemble into larger oligomers. The large helical scaffold of the dimer is decorated with numerous protein-interacting motifs for substrate engagement. Using cryo-EM processing tools, we observe the dynamic nature of the domain movements of UBR5, which allows the catalytic HECT domain to reach engaged substrates. We characterise the proteasomal nuclear import factor AKIRIN2 as an interacting protein and propose UBR5 as an efficient ubiquitin chain elongator. This preference for ubiquitinated substrates permits UBR5 to function in several different signalling pathways and cancers. Together, our data expand on the limited knowledge of the structure and function of HECT E3s.

biochemistry↗

bioRxiv2022

SORORIN is an evolutionary conserved antagonist of WAPL

Cohesin mediates sister chromatid cohesion to enable chromosome segregation and DNA damage repair. To perform these functions, cohesin needs to be protected from WAPL, which otherwise releases cohesin from DNA. It has been proposed that cohesin is protected from WAPL by SORORIN. However, in vivo evidence for this antagonism is missing and SORORIN is only known to exist in vertebrates and insects. It is therefore unknown how important and widespread SORORINs functions are. Here we report the identification of SORORIN orthologs in Schizosaccharomyces pombe (Sor1) and Arabidopsis thaliana (AtSORORIN). sor1{Delta} mutants display cohesion defects, which are partially alleviated by wpl1{Delta}. Atsororin mutant plants display dwarfism, tissue specific cohesion defects and chromosome mis-segregation. Furthermore, Atsororin mutant plants are sterile and separate sister chromatids prematurely at anaphase I. The somatic, but not the meiotic deficiencies can be alleviated by loss of WAPL. These results provide in vivo evidence for SORORIN antagonizing WAPL, reveal that SORORIN is present in organisms beyond the animal kingdom and indicate that it has acquired tissue specific functions in plants.

cell biology↗

bioRxiv2022

Cohesin mediates DNA loop extrusion and sister chromatid cohesion by distinct mechanisms

Cohesin connects CTCF binding sites and other genomic loci in cis to form chromatin loops, and replicated DNA molecules in trans to mediate sister chromatid cohesion. Whether cohesin uses distinct or related mechanisms to perform these functions is unknown. Here we describe a cohesin hinge mutant, which can extrude DNA into loops but is unable to mediate cohesion. Our results suggest that the latter defect arises during cohesion establishment. The observation that cohesins cohesion and loop extrusion activities can be separated indicates that cohesin uses distinct mechanisms to perform these two functions. Unexpectedly, the same hinge mutant can also not be stopped by CTCF boundaries as well as wildtype cohesin. This suggests that cohesion establishment and cohesins interaction with CTCF boundaries depend on related mechanisms and raises the possibility that both require transient hinge opening to entrap DNA inside the cohesin ring.

cell biology↗

bioRxiv2022

Distinct features in fish Bouncer proteins determine sperm-egg compatibility

All sexually reproducing organisms depend on fertilization to survive as species. Despite the importance of fertilization, the mechanisms that drive sperm-egg compatibility are poorly understood. In fish, the egg protein Bouncer is necessary for fertilization and is species-specific between medaka and zebrafish. Here, we investigate whether Bouncer is generally species-specific in fish and identify features mediating its medaka/zebrafish specificity. In vitro fertilization experiments using zebrafish and medaka show that Bouncer is not a general specificity factor. Instead, its homologs exhibit wide compatibility with sperm, in line with the pervasive purifying selection that dominates Bouncers evolution. We further uncover specific features of Bouncer-- distinct amino acid residues and N-glycosylation patterns--that differentially influence the function of medaka and zebrafish Bouncer homologs and contribute to medaka/zebrafish specificity. This work reveals important themes central to understanding Bouncers function in sperm binding and clarifying the molecular requirements for Bouncers sperm interaction partner.

developmental biology↗

bioRxiv2022

Identification and characterization of repressive domains in Drosophila transcription factors

All multicellular life relies on differential gene expression, determined by regulatory DNA elements and DNA-binding transcription factors that mediate activation and repression via cofactor recruitment. While activators have been extensively characterized, repressors are less well studied and their repressive domains (RDs) are typically unknown, as are the RDs properties and the co-repressors (CoRs) they recruit. Here, we develop the high-throughput next-generation-sequencing-based method Repressive-Domain (RD)-seq to systematically identify RDs in complex libraries. Screening more than 200,000 fragments covering the coding sequences of all transcription-related proteins in Drosophila melanogaster, we identify 195 RDs in known repressors and in proteins not previously associated with repression. Many RDs contain recurrent short peptide motifs that are required for RD function, as demonstrated by motif mutagenesis, and are conserved between fly and human. Moreover, we show that RDs which contain one of five distinct repressive motifs interact with and depend on different CoRs, including Groucho, CtBP, Sin3A or Smrter. Overall, our work constitutes an invaluable resource and advances our understanding of repressors, their sequences, and the functional impact of sequence-altering mutations.

molecular biology↗

bioRxiv2021

The sperm protein Spaca6 is essential for fertilization in zebrafish

Fertilization is a key process in all sexually reproducing species, yet the molecular mechanisms that underlie this event remain unclear. To date, only a few proteins have been shown to be essential for sperm-egg binding and fusion in mice, and only some are conserved across vertebrates. One of these conserved, testis-expressed factors is SPACA6, yet its function has not been investigated outside of mammals. Here we show that zebrafish spaca6 encodes for a sperm membrane protein which is essential for fertilization. Zebrafish spaca6 knockout males are sterile. Furthermore, Spaca6-deficient sperm have normal morphology, are motile, and can approach the egg, but fail to bind to the egg and therefore cannot complete fertilization. Interestingly, sperm lacking Spaca6 have decreased levels of another essential and conserved sperm fertility factor, Dcst2, revealing a previously unknown dependence of Dcst2 expression on Spaca6. Together, our results show that zebrafish Spaca6 regulates Dcst2 levels and is required for binding between the sperm membrane and the oolemma. This is in contrast to murine SPACA6, which was reported not to be required for sperm-egg membrane binding but necessary for fusion. These findings demonstrate that Spaca6 is essential for zebrafish fertilization and is a conserved sperm factor in vertebrate reproduction.

developmental biology↗

bioRxiv2020

Zebrafish Ski7 tunes RNA levels during the oocyte-to-embryo transition

Post-transcriptional mechanisms are crucial for the regulation of gene expression. These mechanisms are particularly important during rapid developmental transitions such as the oocyte-to-embryo transition, which is characterized by dramatic changes to the developmental program in the absence of nuclear transcription. Under these conditions, changes to the RNA content are solely dependent on RNA degradation. Although several mechanisms that promote RNA decay during embryogenesis have been identified, it remains unclear which cellular machineries contribute to remodeling the maternal transcriptome during the oocyte-to-embryo transition. Here, we focused on the auxiliary 3-to-5 degradation factor Ski7 in zebrafish as its mRNA peaks during this time frame. Homozygous ski7 mutant fish were viable and developed into morphologically normal adults, yet they had decreased fertility. Consistent with the idea that Ski7 participates in remodeling the transcriptome during the oocyte-to-embryo transition, transcriptome profiling identified stage-specific mRNA targets of Ski7. Genes upregulated in ski7 mutants were generally lowly expressed in wild type, suggesting that Ski7 maintains low transcript levels for this subset of genes. GO enrichment analyses of genes mis-regulated in ski7 mutants implicated Ski7 in the regulation of redox processes. This was confirmed experimentally by an increased resistance of ski7 mutant embryos to reductive stress. Overall, our results provide first insights into the physiological role of vertebrate Ski7 as an important post-transcriptional regulator during the oocyte-to-embryo transition.

developmental biology↗

bioRxiv2019

Site-specific ubiquitination of the E3 ligase HOIP regulates cell death and immune signaling

HOIP, the catalytic component of the Linear Ubiquitin chain Assembly Complex (LUBAC), is a critical regulator of inflammation. However, how HOIP itself is regulated to control inflammatory responses is unclear. Here, we discover that site-specific ubiquitination of K784 within HOIP promotes Tumour Necrosis Factor (TNF)-induced inflammatory signalling by controlling TNF Receptor complex I (TNFR1) formation. A HOIP K784R mutant is catalytically active but shows reduced induction of an NF-{kappa}B reporter relative to wild type HOIP. HOIP K784 is evolutionarily conserved, equivalent to HOIP K778 in mice. We generated HoipK778R/K778R knockin mice, which show no overt developmental phenotypes; however, in response to TNF, HoipK778R/K778R mouse embryonic fibroblasts display suppressed NF-{kappa}B activation and increased sensitivity to apoptosis. On the other hand, HOIP K778R enhances the TNF-induced formation of TNFR complex II, and an interaction between TNFR complex II and LUBAC. Loss of the LUBAC component SHARPIN leads to embryonic lethality in HoipK778R/K778R mice, which is rescued by knockout of TNFR1. We propose that site-specific ubiquitination of HOIP regulates a LUBAC-dependent switch between survival and apoptosis in TNF-signalling.

cell biology↗

bioRxiv2018

ANKRD31 regulates spatiotemporal patterning of meiotic recombination initiation and ensures recombination between heterologous sex chromosomes in mice

Orderly segregation of chromosomes during meiosis requires that crossovers form between homologous chromosomes by recombination. Programmed DNA double-strand breaks (DSBs) initiate meiotic recombination. We identify ANKRD31 as a critical component of complexes of DSB-promoting proteins which assemble on meiotic chromosome axes. Genome-wide, ANKRD31 deficiency causes delayed recombination initiation. In addition, loss of ANKRD31 alters DSB distribution owing to reduced selectivity for sites that normally attract DSBs. Strikingly, ANKRD31 deficiency also abolishes uniquely high rates of recombination that normally characterize pseudoautosomal regions (PARs) of X and Y chromosomes. Consequently, sex chromosomes do not form crossovers leading to chromosome segregation failure in ANKRD31-deficient spermatocytes. These defects are accompanied by a genome-wide delay in assembling DSB-promoting proteins on axes and a loss of a specialized PAR-axis domain that is highly enriched for DSB-promoting proteins. Thus, we propose a model for spatiotemporal patterning of recombination by ANKRD31-dependent control of axis-associated complexes of DSB-promoting proteins.

cell biology↗