Biology subjects

Reimer, R.

Publications and source records attributed to Reimer, R..

6 recordsLinked to original sources

bioRxiv2026

A PROPPIN links V-ATPase assembly to endocytic membrane dynamics in malaria parasites

Malaria parasites replicate inside red blood cells, degrading hemoglobin within a specialized digestive vacuole. Efficient hemoglobin processing is essential for parasite survival and influences antimalarial drug susceptibility. The vacuole constantly fuses with incoming hemoglobin-filled vesicles, yet the mechanisms that balance cargo influx with membrane homeostasis remain unclear. Here, using conditional reverse genetics, quantitative live-cell imaging, and 3D electron microscopy, we characterize the autophagy-related protein 18 of Plasmodium falciparum (PfATG18) as a key regulator of vacuolar membrane dynamics. Loss of PfATG18 caused vacuole fragmentation, accumulation of hemoglobin-filled vesicles, and parasite death. These defects were preceded by broad architectural destabilization of the parasites V-ATPase, a proton pump controlling organelle acidification and the vacuoles fusion-fission equilibrium. Direct interference with its membrane sector phenocopied PfATG18 deficiency. We found that PfATG18 does not interact directly with the proton pump but instead associates with a putative V-ATPase assembly factor and with complexes regulating phosphoinositide balance and vesicle trafficking. The breadth of these interactions indicates a multifaceted role at the vacuolar membrane and a regulatory influence on V-ATPase mediated through associated protein machinery. Although a point mutation in PfATG18 has been linked to artemisinin resistance, its complete knockout did not decrease sensitivity, but rather hypersensitized ring-stage parasites to dihydroartemisinin. Together, these findings establish PfATG18 as a central regulator of endocytic membrane homeostasis, essential for V-ATPase function and asexual parasite proliferation in the human blood.

microbiology↗

bioRxiv2025

The nuclear egress complex of MHV-68 is not essential for nuclear egress but mediates C-capsid specificity

Herpesvirus capsids must exit the nucleus to undergo additional maturation steps in the cytoplasm, such as secondary envelopment. This process is orchestrated by the nuclear egress complex (NEC), a conserved heterodimer that deforms the inner nuclear membrane and facilitates capsid egress. While NEC proteins are critical for the release of capsids into the cytoplasm and, therefore, efficient replication in [a]-, {beta}-, and {gamma}-herpesviruses, residual infectivity has been observed in NEC-deficient mutants of certain herpesviruses, including the [a]-herpesvirus Pseudorabies virus (PrV). To investigate the role of the NEC in murine gammaherpesvirus 68 (MHV-68), a mutant virus lacking most of the nucleoplasmic NEC component ORF69 ({Delta}ORF69) was generated. Unlike previous studies relying on transfection-based systems, this study demonstrates that NEC-deficient MHV-68 remains replication-competent, albeit with a significant replication defect. Despite the absence of ORF69, the mutant virus produced infectious progeny in non-complementing cells. Quantitative electron microscopy revealed regular nuclear capsid assembly and DNA packaging. However, while the parental virus primarily exported mature, genome-filled C-capsids, the {Delta}ORF69 mutant exhibited cytoplasmic and extracellular emergence of all capsid forms. These findings indicate that the MHV-68 NEC functions as a quality control checkpoint, selectively facilitating the nuclear egress of mature capsids. In the absence of ORF69, some capsids still egress, likely through alternative, less efficient pathways. Inhibition of cyclin-dependent kinases reduced parental and mutant virus spread, suggesting that {gamma}-herpesviruses exploit host-dependent mechanisms for an alternative nuclear egress route. ImportanceGammaherpesviruses, such as Epstein-Barr virus and Kaposis sarcoma-associated herpesvirus, establish lifelong infections and can contribute to cancer. A crucial step in the viral life cycle depends on the nuclear egress of capsids, a process mediated by the viral nuclear egress complex (NEC). Surprisingly, murine gammaherpesvirus 68 (MHV-68) can translocate capsids from the nucleus to the cytoplasm even when a key NEC component, nucleoplasmic ORF69, is disrupted. Deleting most of ORF69 reduced viral replication but did not entirely block nuclear egress. Instead, the mutant virus allowed both mature and immature capsids to leave the nucleus, suggesting that the NEC functions as a quality control checkpoint for mature capsids. Furthermore, host cell kinases seem to enable alternative routes for egress that do not rely on the NEC. These findings further support the notion that NEC is not strictly necessary and suggest the potential exploitation of host-virus interactions for antiviral approaches.

microbiology↗

bioRxiv2025

Merkel cell polyomavirus infection and persistence modelled in skin organoids

Merkel cell polyomavirus (MCPyV) causes most Merkel cell carcinomas (MCC). The virus is one of the few known human tumor viruses, and due to its direct role in this skin cancer development, it is a bona fide model for viral tumorigenesis and tumorigenesis in general. Chronic viruses in humans such as MCPyV are highly adapted to their host and current models to study infection, persistence and pathogenesis are highly limited. We here use an induced pluripotent stem cell (iPSC)-derived hair-bearing skin organoid (SkO) system to demonstrate efficient viral infection, progression and spread of MCPyV. Using bulk-, single cell - and spatial-transcriptomics, combined with immunostaining and nucleic acid hybridization technologies, we show that MCPyV ensures persistence due to a quasi-latency state within the majority of dermal fibroblasts carry the viral genome. Further, we identify the cell type of productive infection with papillary fibroblasts and dermal sheath fibroblasts supporting viral replication and progeny production. Our high-resolution methods demonstrate that the virus in these cells evades the innate immune response, as evidenced by the efficacy of interferon-beta treatment or ruxolitinib, a JAK/STAT inhibitor, in suppressing or stimulating viral replication. We show that iPSC-derived SkOs are able to support infection and long-term persistence of the virus under conditions very similar to those found in humans. Thus, this infection model provides a robust platform for understanding and characterizing the interaction of this virus with the immune system in infection, testing treatment strategies to control reactivation and map processes involved in tumor development.

molecular biology↗

bioRxiv2022

Glial control of sphingolipid levels sculpts diurnal remodeling of sleep circuitry

Structural plasticity in the brain often necessitates dramatic remodeling of neuronal processes and attendant reorganization of the cytoskeleton and membranes. While cytoskeletal restructuring has been studied extensively, how lipids might orchestrate structural plasticity remains unclear. We show that specific glial cells in Drosophila produce Glucocerebrosidase (GBA) to locally catabolize sphingolipids. Sphingolipid accumulation drives lysosomal dysfunction, causing gba1b mutants to harbor protein aggregates that cycle across circadian time and are regulated by neural activity, the circadian clock, and sleep. While the vast majority of membrane lipids are stable across the day, a specific subset, highly enriched in sphingolipids, cycles daily in a gba1b-dependant fashion. In parallel, circadian clock neurons remodel their neurites, growing and shrinking across the day to shape circadian behavior. Remarkably, this neuronal remodeling relies on a cycle of temporally offset sphingolipid biosynthesis and catabolism. Thus, dynamic sphingolipid regulation by glia enables diurnal circuit remodeling and proper circadian behavior.

neuroscience↗

bioRxiv2021

Intermittent bulk release of human cytomegalovirus through multivesicular bodies

Human Cytomegalovirus (HCMV) can infect a variety of cell types by using virions of varying glycoprotein compositions. It is still unclear how this diversity is generated, but spatio-temporally separated envelopment and egress pathways might play a role. So far, one egress pathway has been described in which HCMV particles are individually enveloped into small vesicles and are subsequently exocytosed continuously. However, some studies have also found enveloped virus particles inside multivesicular structures but could not link them to productive egress or degradation pathways. We used a novel 3D-CLEM workflow allowing us to investigate these structures in HCMV morphogenesis and egress at high spatio-temporal resolution. We found that multiple envelopment events occurred at individual vesicles leading to multiviral bodies (MViBs), which subsequently traversed the cytoplasm to release virions as intermittent bulk pulses at the plasma membrane to form extracellular virus accumulations (EVAs). Our data support the existence of a novel bona fide HCMV egress pathway, which opens the gate to evaluate divergent egress pathways in generating virion diversity.

microbiology↗

bioRxiv2019

Human cytomegalovirus nuclear capsid motility is non-directed and independent of nuclear actin bundles

Herpesvirus genome replication, capsid assembly and packaging take place in the host cell nucleus. Matured capsids leave the nucleus through a unique envelopment-de-envelopment process at the nuclear membranes called nuclear egress. How assembled and DNA-containing herpesvirus capsids reach the sites of nuclear egress is however still controversially discussed, as host chromatin that marginalizes during infection might constitute a major barrier. For alphaherpesviruses, previous work has suggested that nuclear capsids use active transport mediated by nuclear filamentous actin (F-actin). However, direct evidence for nuclear capsid motility on nuclear F-actin was missing. Our subsequent work did not detect nuclear F-actin associated with motile capsids, but instead found evidence for chromatin remodeling to facilitate passive capsid diffusion. A recent report described that human cyto-megalovirus, a betaherpesvirus, induces nuclear F-actin and that the motor protein myosin V localizes to these structures. Direct evidence of capsid recruitment to these structures and motility on them was however missing. In this study, we tested the functional role of HCMV-induced, nuclear actin assemblies for capsid transport. We did not observe transport events along nuclear F-actin. Instead, reproduction of nuclear F-actin was only possible using strong overexpression of the fluorescent marker LifeAct-mCherry-NLS. Also, two alternative fluo-rescent F-actin markers did not detect F-actin in HCMV-infected cells. Furthermore, single particle tracking of nuclear HCMV capsids showed no indication for active transport, which is in line with previous work on alphaherpesviruses.

microbiology↗