Biology subjects

Vihinen-Ranta, M.

Publications and source records attributed to Vihinen-Ranta, M..

5 recordsLinked to original sources

bioRxiv2023

Progression of herpesvirus infection remodels mitochondrial organization and metabolism

Viruses target mitochondria to promote their replication, and infection-induced stress during the progression of infection leads to the regulation of antiviral defenses and mitochondrial metabolism which are opposed by counteracting viral factors. The precise structural and functional changes that underlie how mitochondria react to the infection remain largely unclear. Here we show extensive transcriptional remodeling of protein-encoding host genes involved in the respiratory chain, apoptosis, and structural organization of mitochondria as herpes simplex virus type 1 lytic infection proceeds from early to late stages of infection. High-resolution microscopy and interaction analyses unveiled infection-induced emergence of rough, thin, and elongated mitochondria relocalized at the perinuclear area, a significant increase in the number and clustering of ER-mitochondria contact sites, and thickening and shortening of mitochondrial cristae. Finally, metabolic analyses demonstrated that reactivation of ATP production is accompanied by increased mitochondrial Ca2+ content and proton leakage as the infection proceeds. Overall, the significant structural and functional changes in the mitochondria triggered by the viral invasion are tightly connected to the progression of the virus infection.

microbiology↗

bioRxiv2023

Alternative cell entry mechanisms for SARS-CoV-2 and multiple animal viruses

The cell entry mechanism of SARS-CoV-2, the causative agent of the COVID-19 pandemic, is not fully understood. Most animal viruses hijack cellular endocytic pathways as an entry route into the cell. Here, we show that in cells that do not express serine proteases such as TMPRSS2, genetic depletion of all dynamin isoforms blocked the uptake and strongly reduced infection with SARS-CoV-2 and its variant Delta. However, increasing the viral loads partially and dose-dependently restored infection via a thus far uncharacterized entry mechanism. Ultrastructural analysis by electron microscopy showed that this dynamin-independent endocytic processes appeared as 150-200 nm non-coated invaginations and was efficiently used by numerous mammalian viruses, including alphaviruses, influenza, vesicular stomatitis, bunya, adeno, vaccinia, and rhinovirus. Both the dynamin-dependent and dynamin-independent infection of SARS-CoV-2 required a functional actin cytoskeleton. In contrast, the alphavirus Semliki Forest virus, which is smaller in diameter, required actin only for the dynamin-independent entry. The presence of TMPRSS2 protease rescued SARS-CoV-2 infection in the absence of dynamins. Collectively, these results indicate that some viruses such as canine parvovirus and SARS-CoV-2 mainly rely on dynamin for endocytosis-dependent infection, while other viruses can efficiently bypass this requirement harnessing an alternative infection entry route dependent on actin.

microbiology↗

bioRxiv2023

CDK5 activity in retinal pigment epithelium contributes to gap junction dynamics during phagocytosis

Retinal pigment epithelium (RPE) at the back of the eye is a monolayer of cells with an extensive network of gap junctions that contributes to retinal health in a multitude of ways. One of those roles is the phagocytosis of photoreceptor outer segments. This renewal is under circadian regulation and peaks after light onset. Connexin 43 (Cx43) is the most predominantly expressed gap junction protein in RPE. In this study, we examine how gap junctions and specifically, Cx43 phosphorylation, contribute to phagocytosis in both human embryonic stem cell derived RPE and mouse RPE monolayers. We show that both Rac1 and CDK5 have differences in protein localization at different points in phagocytosis, and that by using their effectors, the capability of RPE for phagocytosis changes. CDK5 has not yet been reported in RPE tissue, and here we show that it likely regulates Cx43 localization and resulting electrical coupling. We find that gap junctions in RPE are temporally highly dynamic during phagocytosis and that regulation of gap junctions via phosphorylation is likely critical for maintaining eye health.

cell biology↗

bioRxiv2022

Iterative immunostaining combined with expansion microscopy and image processing reveals nanoscopic network organization of nuclear lamina

Investigation of nuclear lamina architecture relies on super-resolved microscopy. However, epitope accessibility, labeling density, and detection precision of individual molecules pose challenges within the molecularly crowded nucleus. We developed iterative indirect immunofluorescence (IT-IF) staining approach combined with expansion microscopy (ExM) and structured illumination microscopy to improve super-resolution microscopy of subnuclear nanostructures like lamins. We prove that ExM is applicable in analyzing highly compacted nuclear multiprotein complexes such as viral capsids and provide technical improvements to ExM method including 3D-printed gel casting equipment. We show that in comparison to conventional immunostaining, IT-IF results in a higher signal-to-background -ratio and a mean fluorescence intensity by improving the labeling density. Moreover, we present a signal processing pipeline for noise estimation, denoising, and deblurring to aid in quantitative image analyses and provide this platform for the microscopy imaging community. Finally, we show the potential of signal-resolved IT-IF in quantitative super-resolution ExM imaging of nuclear lamina and reveal nanoscopic details of the lamin network organization - a prerequisite for studying intranuclear structural co-regulation of cell function and fate. (Words: 175)

molecular biology↗

bioRxiv2022

Parvovirus infection alters the nucleolar structure

The nucleolus is a biomolecular condensate essential for ribosome biogenesis and cellular stress response, and it is a key target for many DNA viruses. However, little is known about how autonomous parvovirus infection impacts nucleolar structure and function. Here, we used advanced imaging techniques, including ten-fold robust expansion microscopy (TREx), cryo soft X-ray tomography (Cryo-SXT), and interactomics and biochemical approaches, to study nucleolar remodeling during canine parvovirus infection. Infection led to redistribution of nucleolar upstream binding transcription factor 1 (inner core), fibrillarin (middle layer), and Ki-67 (outer rim). In contrast, peripheral nucleolar proteins (nucleolin and nucleophosmin) and precursor ribosomal RNAs (pre-rRNAs) remain in circularized structures. TREx and Cryo-SXT microscopy revealed profound nucleolar structural changes, including thickened perinucleolar chromatin and enlarged nucleolar low-protein density channels. BioID identified interactions between viral NS2 and nucleolar proteins in ribosome biogenesis. Northern blotting demonstrated a slowdown in ribosome biogenesis during infection. Collectively, these findings provide novel insights into how parvoviruses remodel nucleolar structure and function.

cell biology↗