Biology subjects

Heim, A.

Publications and source records attributed to Heim, A..

6 recordsLinked to original sources

bioRxiv2026

SAS-1 and SSNA-1 form dynamic centriolar satellites in C. elegans

Centriolar satellites are dynamic pericentrosomal assemblies that regulate centrosomal protein homeostasis and ciliogenesis. While extensively characterized in vertebrates, their existence and assembly principles in other systems are less well understood. Here, we identify SAS-1 and its interaction partner SSNA-1 as core components of centriolar satellite-like structures in C. elegans. We show that SAS-1 satellites occupy a previously unrecognized centrosomal layer positioned between the pericentriolar material and a specialized endoplasmic reticulum. SAS-1 satellites exhibit many features of biomolecular condensates, such as dose-dependent formation, rapid dynamics, and sensitivity to disruption of weak hydrophobic interactions, while their organization depends on the microtubule cytoskeleton. Mechanistically we identify the unstructured and so far, uncharacterized N-terminal region of SAS-1 being functionally important for embryonic viability, satellite formation and binding to microtubules. Our findings demonstrate that C. elegans possesses bona fide centriolar satellites that share many features with vertebrate satellites, highlighting their evolutionary conservation and importance across species. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=156 SRC="FIGDIR/small/708307v2_ufig1.gif" ALT="Figure 1"> View larger version (64K): org.highwire.dtl.DTLVardef@4ca11org.highwire.dtl.DTLVardef@6e4a1borg.highwire.dtl.DTLVardef@c34132org.highwire.dtl.DTLVardef@ed4029_HPS_FORMAT_FIGEXP M_FIG C_FIG

cell biology↗

bioRxiv2024

PCMD-1 stabilizes the PCM scaffold and facilitates centriole separation

Centrosomes are highly dynamic organelles, and maintaining their stability is crucial for spindle pole integrity and bipolar spindle formation. Centrosomes consist of a pair of centrioles surrounded by the pericentriolar material (PCM). In Caenorhabditis elegans, interactions between the PCM scaffold protein SPD-5 and the regulatory kinase PLK-1 are essential for PCM formation and disassembly. However, how PCM stability is established and maintained remains an open question. Here, we address this question by analyzing the function of PCMD-1, a protein that predominantly localizes to centrioles. Mutations in the predicted PLK-1 binding sites of PCMD-1 result in a reduction of centrosomal PLK-1 and PCMD-1 levels, leading to severe distortion of the PCM scaffold. The disorganization of the PCM is already evident during its formation and results in the assembly of a structurally unstable mitotic centrosome, which is unable to resist the microtubule pulling forces exerted on the spindle pole. As a consequence of a weakened PCM scaffold, the pulling forces are not effectively relayed to the entrapped centriole pair, resulting in delayed centriole separation in late anaphase. Together, these findings show that PCMD-1, which predominantly localizes to centrioles and tethers the PCM scaffold to them, is essential for stabilizing the entire PCM scaffold and ensuring timely centriole separation during PCM disassembly. We propose a model in which PCMD-1 initiates the ordered assembly of the PCM scaffold by biasing the PCM core to a certain intrinsic order around the centrioles. This intrinsic order acts as a seed that propagates throughout the surrounding micron-scale PCM scaffold, providing the necessary strength and structural integrity for the centrosome.

cell biology↗

bioRxiv2024

A phosphate-binding pocket in cyclin B3 is essential for XErp1/Emi2 degradation in meiosis I

To ensure the correct euploid state of embryos, it is essential that vertebrate oocytes await fertilization arrested at metaphase of meiosis II. This MII arrest is mediated by XErp1/Emi2, which inhibits the ubiquitin ligase APC/C (anaphase-promoting complex/cyclosome). Cyclin B3 in complex with Cdk1 (cyclin-dependent kinase 1) is essential to prevent an untimely arrest of vertebrate oocytes in meiosis I by targeting XErp1/Emi2 for degradation. Yet, the molecular mechanism of XErp1/Emi2 degradation in MI is not well understood. Here, by combining TRIM-Away in oocytes with egg extract and in vitro studies, we demonstrate that a hitherto unknown phosphate-binding pocket in cyclin B3 is essential for efficient XErp1/Emi2 degradation in meiosis I. This pocket enables Cdk1/cyclin B3 to bind pre-phosphorylated XErp1/Emi2 facilitating further phosphorylation events, which ultimately target XErp1/Emi2 for degradation in a Plk1 (Polo-like kinase 1) dependent manner. Key elements of this degradative mechanism are conserved in frog and mouse. Our studies identify a novel, evolutionarily conserved determinant of Cdk/cyclin substrate specificity essential to prevent an untimely oocyte arrest at meiosis I with catastrophic consequences upon fertilization.

molecular biology↗

bioRxiv2022

Cyclin B3 implements timely vertebrate oocyte arrest for fertilization

To ensure successful offspring ploidy, vertebrate oocytes must halt the cell cycle in meiosis II until sperm entry. Emi2 is essential to keep oocytes arrested until fertilization. Yet, how this arrest is implemented exclusively in meiosis II and not prematurely in meiosis I remained enigmatic. Using mouse and frog oocytes, we show here that cyclin B3, an understudied B- type cyclin, is essential to keep Emi2 levels low in meiosis I. Direct phosphorylation of Emi2 at an evolutionarily highly conserved site by Cdk1/cyclin B3 targets Emi2 for degradation. In contrast, Cdk1/cyclin B1 is inefficient in Emi2 phosphorylation providing a molecular explanation for the requirement of different B-type cyclins for oocyte maturation. Cyclin B3 degradation at exit from meiosis I enables Emi2 accumulation and thus, timely arrest in meiosis II. Our findings illuminate the evolutionarily conserved mechanisms controlling oocyte arrest for fertilization at the correct cell cycle stage, essential for embryo viability.

cell biology↗

bioRxiv2022

Molecular Phylogeny of human adenovirus type 41 lineages

Type 41 of human adenovirus species F (HAdV-F41) is a frequent aetiology of gastroenteritis in children, and nosocomial as well as kindergarten outbreaks have been frequently described. In contrast to other HAdV types, HAdV-F41 was not associated with life-threatening disseminated disease in allogeneic haematopoietic stem cell transplant (HSCT) recipients or any severe organ infections so far. Due to the limited clinical significance, the evolution of HAdV-F41 has not been studied in detail. Recently, HAdV-F41 has been associated with severe hepatitis in young children, and interest in HAdV-F41 has skyrocketed, although the aetiology of the hepatitis has not been resolved. Complete genomic HAdV-F41 sequences from 32 diagnostic specimens of the past 11 years (2011-2022) were generated, all originating from gastroenteritis patients. Additionally, 33 complete HAdV-F41 genomes from GenBank were added to our phylogenetic analysis. Phylogenetic analysis of 65 genomes indicated that HAdV-F41 evolved with three lineages co-circulating. Lineage 1 included the prototype Tak from 1973 and six isolates from 2007 to 2017 with an average nucleotide identity of 99.3 %. Lineage 2 included 53 isolates from 2000 to 2022, had an average nucleotide identity of 99.8 %, and split into two sublineages. Lineage 3, probably described for the first time in 2009, had a 45nt deletion in the long fiber gene and had evolved significantly in the short fiber and E3 region. Moreover, a recent lineage 3 isolate from 2022 had a recombinant phylogeny of the short fiber gene. Fibers interact with cellular receptors and determine cellular tropism, whereas E3 gene products interfere with the immune recognition of HAdV infected cells. This in-depth study on the phylogeny of HAdV-F41 discovered significant evolution of recently described lineage 3 of HAdV-F41, possibly resulting in altered cellular tropism, virulence and pathophysiology.

microbiology↗

bioRxiv2020

The zinc finger antiviral protein ZAP destabilises viral transcripts and restricts cytomegalovirus

Interferon-stimulated gene products (ISGs) play a crucial role in early infection control. The ISG zinc finger CCCH-type antiviral protein 1 (ZAP/ZC3HAV1) antagonises several RNA viruses by binding to CG-rich RNA sequences, whereas its effect on DNA viruses is largely unknown. Here, we decipher the role of ZAP in the context of human cytomegalovirus (HCMV) infection, a {beta}-herpesvirus that is associated with high morbidity in immunosuppressed individuals and newborns. We show that expression of the two major isoforms of ZAP, the long (ZAP-L) and short (ZAP-S), is induced during HCMV infection and that both negatively affect HCMV replication. Transcriptome and proteome analyses demonstrated that the expression of ZAP decelerates the progression of HCMV infection. SLAM-sequencing revealed that ZAP restricts HCMV at early stages of infection by destabilising a distinct subset of viral transcripts with low CG content. In summary, this report provides evidence of an important antiviral role for ZAP in host defense against HCMV infection and highlights its differentiated function during DNA virus infection.

molecular biology↗