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At least 19 recordsLinked to original sources

Development of a rapid antiviral screening assay based on GFP reporter virus of bovine enterovirus.

In recent years, bovine enterovirus (BEV) has been increasingly associated with diarrhea in cattle in China, posing new challenges for disease control in the cattle industry. However, the mechanisms underlying BEV pathogenesis and virulence remain poorly understood. Infectious cDNA clones provide a powerful tool for dissecting viral replication and pathogenic mechanisms. In this study, we generated a full-length infectious cDNA clone of the BEV-F isolate HB19-1. Three overlapping fragments spanning the complete viral genome were amplified by RT-PCR and assembled downstream of a cytomegalovirus (CMV) promoter placed immediately upstream of the 5' untranslated region (5'UTR). To establish a reporter virus system, the green fluorescent protein (GFP) gene was inserted between the 5'UTR and the N terminus of VP4, followed by a 2A cleavage sequence (IKTAG) at the C terminus of GFP. The recombinant rHB19-GFP virus was successfully rescued. Growth curve analysis demonstrated that rHB19-GFP exhibited slower replication kinetics at early time points relative to the parental HB19-1 virus, with no significant difference in their peak viral titers. This GFP-expressing reporter virus enables convenient monitoring of BEV replication and provides a useful platform for antiviral screening. Using this system, we found that 5-(N-Ethyl-N-isopropyl)amiloride (EIPA) inhibited BEV replication, suggesting its potential as an antiviral candidate. Overall, the rHB19-GFP infectious clone developed here offers a practical tool for studying BEV biology and for identifying antiviral compounds against BEV.

Animals

Overexpression of GFP Fusions of Regulators of the SAC from Arabidopsis thaliana.

Cell division is a fundamental biological process, essential for sustaining life on Earth. Accurate replication followed by uniform segregation of the genome is required to ensure cell division is sustainable and reduces the likelihood of aneuploidy. The cell cycle has various checkpoints to safeguard proper replication, for example, the spindle assembly checkpoint (SAC) which ensures that all chromosomes are correctly aligned and attached to the spindle, before the transition to anaphase. The precise function of the SAC and SAC components in plants is so far unclear. First, the high level of polyploidy in plants raises concerns about the efficacy of the SAC. Second, many plant SAC components are implicated in other cellular processes, such as MAD1, which has been implicated in the reproductive transition of Arabidopsis thaliana. Overexpression of GFP fusions of core SAC components provides a key route to establish the functions of the different SAC components in plants. Here we describe two methods for agrobacterium-mediated transformation of plants.

Arabidopsis

Novel Mycoparasitic Mechanisms and Colonization Patterns on Poplar Revealed by GFP Tagging of the Biocontrol Fungus Clonostachys reniana.

Clonostachys rosea has long been the primary model for studying mycoparasitism within its genus; however, the potential of other species remains largely unexplored. In this study, we established a PEG-CaCl2-mediated protoplast transformation system for Clonostachys reniana. Our results demonstrate for the first time that this species is amenable to genetic manipulation and produces transformants with genetic stability, providing a reliable platform for functional genomic research in this fungus. Using green fluorescent protein tagging, we achieved stable transformants that retained wild-type physiological traits. Crucially, our data indicated that C. reniana utilizes a distinct mycoparasitic mechanism, which differs from the well-established sequential process of adhesion, coiling, and lysis seen in C. rosea. Confocal and scanning electron microscopy revealed that C. reniana, following initial coiling and invasive structure formation, penetrates the host hyphae of Botryosphaeria dothidea. It then grows longitudinally within the hyphal lumen, absorbing nutrients and eliminating the pathogen from the inside. Furthermore, C. reniana hyphae can colonize the intercellular spaces of the stem periderm in 84K poplar (Populus alba × P. glandulosa) while displaying a distinct tissue-specific behavior in the roots by forming a mantle on the root surface resembling that of ectomycorrhizae. These findings establish C. reniana as a highly promising secondary model species within the Clonostachys genus. By uncovering a novel "internal-consumption" mycoparasitic mode, this study expands our understanding of the ecological diversity of biocontrol fungi and provides a powerful genetic toolset for future functional genomic research.

Clonostachys reniana

Interaction of host gene-gut microbiota in male grading of Macrobrachium rosenbergii.

UNLABELLED: The giant freshwater prawn (GFP; Macrobrachium rosenbergii), a crustacean of high nutritional and economic value, is crucial for aquaculture. During the same growth cycle, male GFPs develop into three distinct forms: small males, orange claw males, and blue claw males. These morphotypes display varying social behaviors, which severely constrain their industrial development. To address this, this study collected male GFP samples at critical developmental time points (100, 110, and 120 days post-hatching) for phenotypic trait measurement and analysis to obtain external morphological data. Through gut microbiota diversity analysis, we identified key gut bacteria (Lactococcus garvieae and Lactobacillus taiwanensis) influencing male morphotype differentiation. Transcriptomic analysis revealed host Kyoto Encyclopedia of Gene and Genome pathways and key genes (Wnt-6, CTSB, CTSL, PPAE, and TP53) associated with morphotype differentiation. The interactions among phenotypic traits, gut microbiota, and key genes were systematically studied through association analysis. Weighted gene co-expression network analysis was employed to construct co-expression modules, from which critical gene modules influencing phenotypic variation were identified. Through association network analysis, we established an "Achromobacter-CD-TRINITY_DN93139_c0_g2 (calpain clp-1)" interaction model. Our findings provide novel insights into the genetic enhancement of GFPs and offer guidelines for future research regarding gut symbiotic bacteria and breeding initiatives. IMPORTANCE: Male Macrobrachium rosenbergii (giant freshwater prawn [GFP]) in the same growth cycle will develop into small males, orange claw males, and blue claw males. This individual heterogeneity in growth significantly impacts the benefits of aquaculture. However, the factors influencing the differentiation of male GFP morphotype remain unclear. This study analyzed the phenotypic data of various GFP levels, the structure of the intestinal microbiota, and the differential genes within the gonadal transcriptome at critical time points of male GFP-level type differentiation. The aim was to explore the potential role of intestinal microbiota and differential genes in this phenomenon. This study offers new insights into the research on the phenomenon of male GFP-level type differentiation.

Animals

Aggregation of gel-filtered guinea-pig platelets by lipoproteins.

Very low density lipoproteins (VLDL) and low density lipoproteins (LDL) were isolated from serum of hypercholesterolemic guinea-pigs, and the effect of these lipoproteins on guinea-pig platelets was studied. VLDL (greater than 100 microgram/ml) and LDL (greater than 400 microgram/ml) were found to cause aggregation of gel-filtered platelets (GFP), although the extent of GFP aggregation by LDL was smaller than that by VLDL. In platelet-rich plasma, however, lipoproteins could not induce platelet aggregation. VLDL and LDL even at the low concentrations at which lipoproteins alone could not induce aggregation potentiated ADP-induced aggregation of GFP. VLDL-induced aggregation of GFP was inhibited by apyrase (0.2--1.0 mg/ml) in a concentration-related manner. Prostaglandin E1, dipyridamole, potassium cyanide and ethylenediaminetetraacetic acid inhibited VLDL- and ADP-induced aggregation of GFP in the almost same degree. Inhibitions of VLDL-induced GFP aggregation by acetylsalicylic acid and albumin were slightly stronger than that of ADP-induced aggregation. These findings suggest that lipoproteins modulate platelets so that endogenous ADP can be released from platelets.

Adenosine

Cloning, Transformation, and Reporter Gene Analysis of the SalT Promoter in Barley (Hordeum vulgare).

Constitutive gene expression can lead to pleiotropic effects. Therefore, spatial or temporal restriction of expression via specific promoters provides a more targeted approach. This study aimed to clone the SalT promoter and analyze its activity in transgenic barley using GFP and GUS reporter genes. The T-DNA constructs carrying the SalT promoter were introduced into barley cv. Golden Promise, and transgenic plants were confirmed through PCR, hygromycin selection, and Southern hybridization. Both constructs, SalT-GFP and SalT-GUS, were transformed in barley cv. Golden Promise. Here, we characterized the expression pattern of the SalT promoter in barley and utilized it to drive the expression of reporter genes GFP and GUS. The SalT promoter was isolated from rice genomic DNA, cloned into the pNos-AB-M vector, and confirmed through PCR and restriction analysis. Subsequently, GFP and GUS genes were cloned under the SalT promoter in the same vector. The constructs were then subcloned into the p6U vector for plant expression. Agrobacterium-mediated genetic transformation of barley cultivar "Golden Promise" was conducted, resulting in successful integration of the transgenes. Callus induction, regeneration, and root formation efficiency were assessed, demonstrating the potential of the SalT promoter to drive gene expression during various stages of plant development. Molecular analyses, including PCR and Southern hybridization, confirmed the presence and integration of transgenes in the barley genome. Furthermore, GFP fluorescence and GUS staining analyses revealed strong expression of the respective genes under control of the SalT promoter in different plant tissues. This study provides insights into the application of the SalT promoter for genetic manipulation and functional characterization in barley, offering opportunities for crop improvement and biotechnological applications.

Hordeum

Studies on gel-filtered human platelets: isolation and characterization in a medium containing no added Ca2+, Mg2+, or K+.

We have adapted the gel filtration technique for separation of human platelets from the plasma constituents to permit use of an eluant containing no added Ca2+, Mg2+, and K+, and hence allow direct determination of the intracellular concentrations of these ions in the isolated platelets. The eluant employed is modified Ca2+-free Tyrode's buffer which contains Sr2+ (0.2 mM) as a substitute for Mg2+ and lacks added K+. The functional metabolic, and morphological properties of these isolated platelets have been determined ael-filtered platelets (GFP) to low concentrations of ADP and adrenaline was qualitatively similar to that of platelet-rich plasma (PRP). However, a slower response was observed for the GFP. This rate difference was partially or completely reversed by addition of apyrase to the medium. Analysis of the total adenine nucleotide content and the pattern of 14C incorporation into the metabolic adenine nucleotide pool indicated that isolation in this medium caused to significant change in the ATP and ADP contents or in the adenylate energy change in comparison with the PRP. However, a significant increase in the extent of hypoxanthine production from ATP was noted in GFP isolated in media lacking Mg2+. Inclusion of Mg2+ in the elution media prevented this increased hypoxanthine production. The intracellular concentrations of Ca2+, Mg2+, and K+ of the GFP as determined by atomic absorption analysis were in good agreement with the values obtained for platelets separated from plasma by high-speed centrifugation. Platelet Ca2+ and Mg2+ levels remained stable despite the lack of significant extracellular levels of these ions. However platelet K+ fell to about 30 per cent of its initial value after incubation of 90 minutes at 23 degrees C. and a coincident increase was observed in extracellular K+ concentration. This procedure for platelet isolation may be of particular value for studies on the role of Ca2+, Mg2+, and K+ in platelet physiology and metabolic processes.

Adenine

Functional analysis of stem-loop structures within the SARS-CoV-2 5' untranslated region using a plasmid-based reporter system.

The 5' untranslated region (5'UTR) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) contains highly conserved stem-loop structures that regulate viral gene expression. This study investigated the functional contributions of selected 5'UTR stem-loop elements to reporter gene expression using a plasmid-based mammalian expression system. Five constructs were tested using a non-integrating plasmid: the wild-type (WT) 5'UTR fused to GFP under the CMV promoter, and four deletion variants (&#x394;B, &#x394;C, &#x394;D, and &#x394;E) corresponding to deletions of stem-loop 4 (SL4), SL4.5, SL5, and SL5a, respectively. Following transfection into HEK293 cells, GFP fluorescence was quantified using a fluorescence microplate reader, and relative GFP transcript abundance was assessed by RT-qPCR. Deletion of SL4 (&#x394;B) resulted in marked reduction in both fluorescence and relative transcript abundance compared to WT construct, indicating substantially reduced reporter gene expression. In contrast, deletion of SL4.5, SL5, or SL5a did not produce the pronounced reduction observed for &#x394;B, although descriptive RT-qPCR analysis indicated differences in relative transcript abundance among these variants. Statistical analysis of fluorescence data demonstrated significant differences among constructs (one-way ANOVA, p&#x2009;<&#x2009;0.05). Because the reporter assay was based on plasmid expression, the observed differences likely reflect combined contributions from transcription, transcript abundance, RNA stability, and translation rather than translation alone. These findings demonstrate that the SL4 region contributes substantially to reporter gene expression in this experimental system, whereas the remaining stem-loop regions examined exert comparatively modest effects. This study provides additional insight into the functional organization of the SARS-CoV-2 5'UTR and establishes a framework for future investigations aimed at distinguished the transcriptional, post-transcriptional, and translational contributions of individual RNA structural elements.

5' Untranslated Regions

Retrograde gene delivery to hypoglossal motoneurons using adeno-associated virus serotype 9.

Retrograde viral transport (i.e., muscle to motoneuron) enables targeted gene delivery to specific motor pools. Recombinant adeno-associated virus serotype 9 (AAV9) robustly infects motoneurons, but the retrograde transport capabilities of AAV9 have not been systematically evaluated. Accordingly, we evaluated the retrograde transduction efficiency of AAV9 after direct tongue injection in 129SVE mice as well as a mouse model that displays neuromuscular pathology (Gaa(-/-)). Hypoglossal (XII) motoneurons were histologically evaluated 8 weeks after tongue injection with AAV9 encoding green fluorescent protein (GFP) with expression driven by the chicken &#x3b2;-actin promoter (1 &#xd7; 10(11) vector genomes). On average, GFP expression was detected in 234 &#xb1; 43 XII motoneurons 8 weeks after AAV9-GFP tongue injection. In contrast, tongue injection with a highly efficient retrograde anatomical tracer (cholera toxin &#x3b2; subunit, CT-&#x3b2;) resulted in infection of 818 &#xb1; 88 XII motoneurons per mouse. The retrograde transduction efficiency of AAV9 was similar between the 129SVE mice and those with neuromuscular disease (Gaa(-/-)). Routine hematoxylin and eosin staining and cluster of differentiation (CD) immunostaining for T cells (CD3) indicated no persistent inflammation within the tongue or XII nucleus after AAV9 injection. Additional experiments indicated no adverse effects of AAV9 on the pattern of breathing. We conclude that AAV9 can retrogradely infect a significant portion of a given motoneuron pool in normal and dystrophic mice, and that its transduction efficiency is approximately 30% of what can be achieved with CT-&#x3b2;.

Animals

Effects of ions on ADP-induced aggregation of bovine or human platelets.

Effects of divalent cations on ADP-induced aggregation response were examined. Bovine platelets were transferred by Sepharose 2B gel filtration from citrate-PRP into citrate free buffer (buffer-GFP). Response increases, reaches a maximum and decreases with increasing calcium and/or magnesium concentration. For either calcium or magnesium alone, increasing response is proportional to a rate coefficient and, through an apparent ion-platelet association constant, to the fraction of platelet critical sites bound to cation. With both ions present, bound magnesium appears to inhibit bound calcium in excess of that accounted for by competition and a lower rate coefficient for bound magnesium. With citrate present in buffer-GFP, apparent association constants increase, excess magnesium inhibition is present, but systems are path dependent. Initial conditions appear to establish a response which is thereafter immutable to environmental magnesium alteration. Citrate-PRP resembles buffer-GFP: response is sensitive to the selective removal of calcium and excess magnesium inhibition is present. With heparin-PRP, response is immutable to the selective removal of approximately 90% of initial calcium. The dependency of response inhibition observed at high divalent cation concentrations indicates that aggregation is not due to interplatelet cross linking by ions. Ion effects are similar for bovine and human platelets.

Adenosine Diphosphate

Cellular Inflammation-Induced Cleavage of Phosphorothioate DNA Locker Activates CRISPR/Cas9 Regulator for Gene Editing.

The CRISPR technology is a highly promising strategy for developing a versatile toolbox to engineer genetic circuits. However, achieving precise and specific control over the activity of the CRISPR/Cas9 system in response to intracellular processes remains a challenging endeavor. In this study, we present a cellular inflammation-induced activation of an engineered CRISPR/Cas9 regulator for gene regulation. A phosphorothioate (PS)-modified DNA sequence, referred as the "locker," is employed to deactivate single guide RNA (sgRNA), whose locker sequence complements the spacer region of sgRNA. In the presence of myeloperoxidase during cellular inflammation, a halogenation process is triggered, leading to the generation of HClO, specifically cleaving the PS site of locker and activating CRISPR/Cas9 for gene editing. The target GFP gene has been successfully edited, downregulating the GFP protein expression in HeLa cells. This study provides valuable insights into the CRISPR-based gene regulation through specific endogenous processes.

Humans

The Single Amino Acid Change of R516K Enables Efficient Generation of Vesicular Stomatitis Virus-Based Crimean-Congo Hemorrhagic Fever Reporter Virus.

Crimean-Congo hemorrhagic fever virus (CCHFV) is a medically important tick-borne virus, causing severe hemorrhagic diseases in humans. There are no approved vaccines and therapeutics for CCHFV infection. The study of CCHFV authentic virus requires biosafety level 3 facilities, hindering the research and development of antivirals. Here we report the generation of a recombinant vesicular stomatitis virus (VSV) bearing both CCHFV glycoprotein precursor (GPC) and EGFP reporter (rVSV-CCHFV-GFP). We also find that the acquisition of an unexpected single R516K mutation in the GPC protein enables the packaging of high-titer pseudotyped particles. The replication-competent rVSV-CCHFV-GFP reporter virus resembles the entry properties of the authentic virus and allows for rapid assessment of susceptible cell lines, neutralizing antibodies, and host entry factors such as heparan sulfate in fluorescence-based assays. This study provides a valuable strategy for packaging of high-titer CCHFV pseudovirus, and the tool generated here can be served for the identification and evaluation of countermeasures against the cell entry of CCHFV.

Hemorrhagic Fever Virus, Crimean-Congo

Fluorescence-Based mRNA Translation Reporter.

Herein, we describe a fluorescence reporter assay for investigating regulatory elements in the 5'-UTR of mRNA that modulate translational initiation. The canonical translation initiation process generally begins with the assembly of the eIF4F complex at the cap structure, the formation of the ternary complex, which is loaded with the initiator tRNA, and finally, the preinitiation complex. The preinitiation complex then scans the 5'-UTR to identify the authentic translation start site, which is typically characterized by an AUG codon within a sequence context known as the Kozak sequence. It is well established that the 5'-UTR varies extensively in length and contains regulatory, structural, and sequence elements. To investigate these elements, we use a green fluorescence protein (GFP)- and a luciferase-based mRNA reporter. These reporters can be quickly generated by ordering gBlocks or by PCR-based template generation for in vitro transcription, capping and polyadenylation, to produce synthetic mRNAs. These mRNAs can be transfected into cells, and expression can be monitored via GFP fluorescence or by measuring luciferase activity. In this chapter, we provide a step-by-step protocol for designing gBlocks, generating the reporter mRNA, transfecting the cells, and analyzing the results.

Genes, Reporter

Efficient rDNA-mediated multi-copy integration of gene clusters in Aureobasidium melanogenum.

Aureobasidium melanogenum is a promising non-conventional yeast chassis for synthetic biology. However, techniques recombining large genetic fragments, such as gene clusters, are still unavailable, hindering further metabolic reprogramming in this chassis. To achieve multi-copy integration of genes, we employed highly repetitive ribosomal DNA (rDNA) sequences in A. melanogenum as homologous recombination sites for large genetic fragments. First, integration efficiency of three different regions of A. melanogenum rDNA were investigated: RNA polymerase I promoter region (rDNA1, 1.0&#x202f;kb), partial 26S rDNA region (rDNA2, 1.0&#x202f;kb), and RNA polymerase I terminator region (rDNA3, 1.0&#x202f;kb). Our findings revealed that the highest copy numbers and expression stability were observed for the short heterologous green fluorescent protein gene (gfp, 0.7&#x202f;kb) and the long native polyketide synthase gene (pks, 7.0&#x202f;kb) after rDNA1-mediated integration. Specifically, the copy numbers reached 7.0 and 8.0 for gfp and pks, respectively, and they remained stably expressed in the genome after 120-h subculturing. Furthermore, an 11.0&#x202f;kb gene cluster (comprising the native pks, phosphopantetheinyl transferase (npg1), and scytalone dehydratase genes (scd) responsible for melanin biosynthesis) was integrated at the rDNA1 site, resulting in stable recombination with 15.0 copies and an approximately 12-fold increase in melanin production. Overall, the convenience and efficiency of the proposed rDNA-mediated multi-copy insertion strategy will facilitate superior metabolic engineering of A. melanogenum chassis cells.

Multigene Family

A transcription factor-focused CRISPR screen identifies SKI as a BCL11A-independent repressor of &#x3b6;-globin.

The regulation of &#x3b1;-like globin genes, particularly the embryonic &#x3b6;-globin gene (HBZ), remains incompletely understood. To identify transcriptional regulators of HBZ, we establish a GFP reporter system based on the HBZ-P2A-GFP allele in erythroid cell lines and conduct a CRISPR/Cas9 screen targeting 1639 transcription factors. This screen identifies SKI as a potent HBZ repressor. Functional validation shows that SKI loss increases HBZ expression without impairing erythropoiesis, whereas SKI overexpression suppresses HBZ. Tet-on-inducible SKI overexpression and auxin-inducible SKI degradation indicate that SKI rapidly represses HBZ transcription. Transcriptome profiling further reveals that SKI deletion activates HBZ while minimally affecting other erythroid genes. Mechanistically, genome-wide occupancy analyses show that SKI binds the distal enhancers HS-10 and HS-40, with partial co-occupancy by BCL11A. Despite this overlap, dual knockout of SKI and BCL11A synergistically increases HBZ expression, as does base editing of the SKI-binding site within HS-10. We also identify a naturally occurring variant (chr16:193207G>A) within this enhancer in &#x3b1;-thalassemia patients with elevated &#x3b6;-globin levels. Together, these findings establish SKI as a direct, BCL11A-independent transcriptional repressor of &#x3b6;-globin. This work advances our understanding of globin gene regulation and suggests targeted &#x3b6;-globin reactivation as a potential therapeutic strategy for &#x3b1;-thalassemia.

Enhancer

Intravascular AAV9 preferentially targets neonatal neurons and adult astrocytes.

Delivery of genes to the brain and spinal cord across the blood-brain barrier (BBB) has not yet been achieved. Here we show that adeno-associated virus (AAV) 9 injected intravenously bypasses the BBB and efficiently targets cells of the central nervous system (CNS). Injection of AAV9-GFP into neonatal mice through the facial vein results in extensive transduction of dorsal root ganglia and motor neurons throughout the spinal cord and widespread transduction of neurons throughout the brain, including the neocortex, hippocampus and cerebellum. In adult mice, tail vein injection of AAV9-GFP leads to robust transduction of astrocytes throughout the entire CNS, with limited neuronal transduction. This approach may enable the development of gene therapies for a range of neurodegenerative diseases, such as spinal muscular atrophy, through targeting of motor neurons, and amyotrophic lateral sclerosis, through targeting of astrocytes. It may also be useful for rapid postnatal genetic manipulations in basic neuroscience studies.

Animals

The piRNA pathway mediates transcriptional silencing of LTR retrotransposons in ovaries and somatic tissues of&#xa0;Aedes mosquitoes.

The PIWI-interacting RNA (piRNA) pathway preserves genomic integrity by suppressing transposable elements in animal germlines. Despite its well-established function in the animal germline, piRNAs and PIWI proteins are expressed in somatic tissues across arthropod species, and their functions outside the gonads remain poorly understood.&#xa0;Aedes albopictus mosquitoes express four PIWI genes, Piwi4, Piwi5, Piwi6, and&#xa0;Ago3, in both gonadal and somatic tissues. Here, we generated Piwi6 knockout (KO) Ae. albopictus cell lines and observed a substantial upregulation of long terminal repeat retrotransposons, including a full-length endogenous retrovirus that we named Aedes albopictus Endogenous Retrovirus-1 (AalERV1). Nascent RNA sequencing and Cleavage Under Targets and Tagmentation (CUT&Tag) analyses revealed that Piwi6 silences&#xa0;AalERV1 transcriptionally by guiding the deposition of the repressive H3K9me3 histone mark. Consistently, Piwi6 localized to both the cytoplasm and nucleus, with sequences in the intrinsically disordered region guiding nuclear translocation. Reintroduction of full-length GFP-Piwi6, but not a mutant GFP-Piwi6 defective in nuclear localization, rescued AalERV1 repression in Piwi6 KO cells. Importantly, Piwi6-mediated control of AalERV1 was recapitulated in vivo as Piwi6 knockdown increased AalERV1 expression in both ovaries and somatic tissues of Ae. albopictus mosquitoes. These results establish Aedes mosquitoes as a model to study nuclear PIWI functions and suggest that somatic piRNA-mediated transposon silencing is evolutionarily conserved across arthropod species.

Animals

The dynamics of RAD51 foci formation and elongation in living human cells.

Homologous recombination is a DNA repair process that requires binding of RAD51 to ssDNA at the break site. This facilitates the search for a homologous repair template on the sister chromatid, or on the homologous chromosome. How broken DNA ends loaded with RAD51 filaments are brought toward their repair template in the crowded 3D genome is currently poorly understood. This is largely due to a lack of tools to visualize homology search in living human cells. Here, we show that RAD51 and MND1, two proteins operating in homology search, become visible in long, extended structures several hours after double-stranded break formation. Using GFP-MND1 we capture these elongated foci in living human cells and reveal their highly dynamic nature as they traverse the nuclear space and gradually disassemble. We show that resolution of these structures depends on RAD54L, known for its role in RAD51-driven homology search. In addition, we find that loss of cohesin inhibits their resolution, in accordance with a role for cohesin in homology search. Thus, our data suggest that these elongated foci are visible intermediates of an active DNA repair process, and that GFP-MND1 is a powerful tool to study the dynamics of homology search in living human cells.

Humans