Interaction studies between human papillomavirus virus-like particles and laminin 332 by affinity capillary electrophoresis assisted by bio-layer interferometry.

Human papillomavirus (HPV) interacts, in vitro, with laminin 332 (LN332), a key component of the extracellular matrix. In this study, we performed bio-layer interferometry (BLI) and affinity capillary electrophoresis (ACE) to investigate the binding properties of this interaction. Virus-like particles (VLPs), composed of the HPV16 L1 major capsid protein, were used as HPV model and LN332 as the VLPs binding partner. Using BLI, we quantitatively determined the kinetics of the interaction, via the measurement of VLP binding and release from LN332 immobilized onto the surface of aminopropylsilane biosensors. We found an averaged kon of 1.74 x 104 M-1s-1 and an averaged koff of 1.50 x 10-4 s-1. Furthermore, an ACE method was developed to study the interaction under physiological conditions, where the interactants are moving freely in solution, without any fluorescence labeling. Specifically, a constant amount of HPV16-VLPs was preincubated with increasing LN332 concentrations and then the samples were injected in the capillary electrophoresis instrument. A shift in the migration time of the HPV16-VLP/LN332 complexes, carrying an increasing number of LN332 molecules bound per VLP, was observed. The mobility of the complexes was found to decrease with increasing LN332 concentrations in the sample. It was used to quantify stability constant. From BLI and ACE approaches, we reported an apparent equilibrium dissociation constant in the nanomolar range (8.89 nM and 17.7 nM, respectively) for the complex between HPV16-VLPs and LN332.

Ultrastructure of sonic muscles of piranhas (Serrasalmidae).

Among piranhas, different species are able to produce sounds but not all of them use the same mechanism. In all species, the sound-producing muscle originates on the second vertebra, but the insertion differs. Pygopristis denticulata can produce two kinds of pulsed sounds emitted in trains. Its sound production mechanism is mainly based on a muscle bundle that inserts between the two first ribs. In Catoprion mento, the anterior part of the sonic muscle inserts directly on the swim bladder. The most derived species (Serrasalmus and Pygocentrus) make all harmonic tonal sounds. Their sonic muscles constitute a single functional unit transversally surrounding the swim bladder. This study aims to study the ultrastructure of sonic muscles in nine species from these four genera. Epaxial muscles were compared with sonic muscles, and the sonic muscles of the different species were compared between them. Results confirmed ultrastructure modifications in the sonic muscles in comparison to epaxial muscles. Fibers of the sonic muscle are thinner and possess a thicker subsarcolemmal ring housing mitochondria. In sonic muscles, myofibrils are also proportionally less abundant, and their sarcomeres are longer and thinner. Some of these differences allows to separate basal species (e.g., P. denticulata) from more derived species (genera Pygocentrus and Serrasalmus) and supposedly support the observed differences in the acoustic abilities.

Visualization of Chromatin in the Yeast Nucleus and Nucleolus Using Hyperosmotic Shock.

Unlike in most eukaryotic cells, the genetic information of budding yeast in the exponential growth phase is only present in the form of decondensed chromatin, a configuration that does not allow its visualization in cell nuclei conventionally prepared for transmission electron microscopy. In this work, we studied the distribution of chromatin and its relationships to the nucleolus using different cytochemical and immunocytological approaches applied to yeast cells subjected to hyperosmotic shock. Our results show that osmotic shock induces the formation of heterochromatin patches in the nucleoplasm and intranucleolar regions of the yeast nucleus. In the nucleolus, we further revealed the presence of osmotic shock-resistant DNA in the fibrillar cords which, in places, take on a pinnate appearance reminiscent of ribosomal genes in active transcription as observed after molecular spreading ("Christmas trees"). We also identified chromatin-associated granules whose size, composition and behaviour after osmotic shock are reminiscent of that of mammalian perichromatin granules. Altogether, these data reveal that it is possible to visualize heterochromatin in yeast and suggest that the yeast nucleus displays a less-effective compartmentalized organization than that of mammals.

Dispensability of Tubulin Acetylation for 15-protofilament Microtubule Formation in the Mammalian Cochlea.

The development of hearing in mammals requires the formation and maturation of a highly organized and specialized epithelium known as the organ of Corti. This epithelium contains two types of cells, the sensory cells, which are the true receptors of auditory information, and the surrounding supporting cells, which are composed of a highly developed cytoskeleton essential to the architecture of the mature organ of Corti. The supporting cells are the only mammalian cells reported to contain the unusual 15-protofilament microtubules. In this paper, we show that 15-protofilament microtubules appear between the second and fourth day after birth in the pillar cells of the organ of Corti in mice. We also show that contrary to what has been described in the nematode worm Caenorhabiditis. elegans, microtubule acetylation is not essential for the formation of 15-protofilament microtubules in mice but is required for fine-tuning of their diameter.Key words: Acetylation, cytoskeleton, microtubule, inner ear, supporting cells.

Production and characterization of virus-like particles of grapevine fanleaf virus presenting L2 epitope of human papillomavirus minor capsid protein.

BACKGROUND: Virus-like particle (VLP) platform represents a promising approach for the generation of efficient and immunogenic subunit vaccines. Here, the feasibility of using grapevine fanleaf virus (GFLV) VLPs as a new carrier for the presentation of human papillomavirus (HPV) L2 epitope was studied. To achieve this goal, a model of the HPV L2 epitope secondary structure was predicted and its insertion within 5 external loops in the GFLV capsid protein (CP) was evaluated. RESULTS: The epitope sequence was genetically inserted in the αB-αB" domain C of the GFLV CP, which was then over-expressed in Pichia pastoris and Escherichia coli. The highest expression yield was obtained in E. coli. Using this system, VLP formation requires a denaturation-refolding step, whereas VLPs with lower production yield were directly formed using P. pastoris, as confirmed by electron microscopy and immunostaining electron microscopy. Since the GFLV L2 VLPs were found to interact with the HPV L2 antibody under native conditions in capillary electrophoresis and in ELISA, it can be assumed that the inserted epitope is located at the VLP surface with its proper ternary structure. CONCLUSIONS: The results demonstrate that GFLV VLPs constitute a potential scaffold for surface display of the epitope of interest.

Relationships between the structural and functional organization of the turtle cell nucleolus.

The nucleolus is a multifunctional structure of the eukaryotic cell nucleus. However, its primary role is ribosome formation. Although the factors and mechanisms involved in ribogenesis are well conserved in eukaryotes, two types of nucleoli have been observed under the electron microscope: a tricompartmentalized nucleolus in amniotes and a bicompartmentalized nucleolus in other species. A recent study has also revealed that turtles, although belonging to amniotes, displayed a nucleolus with bipartite organization, suggesting that this reptile group may have carried out a reversion phenomenon during evolution. In this study, we examine in great detail the functional organization of the turtle nucleolus. In liver and spleen cells cultured in vitro, we confirm that the turtle nucleolus is mainly formed by two components: a fibrillar zone surrounded by a granular zone. We further show that the fibrillar zone includes densely-contrasted strands, which are positive after silver-stained Nucleolar Organizer Region (Ag-NOR) staining and DNA labelling. We also reveal that the dense strands condensed into a very compact mass within the fibrillar zone after a treatment with actinomycin D or 5,6-dichlorobenzimidazole riboside. Finally, by using pulse-chase experiments with BrUTP, three-dimensional image reconstructions of confocal optical sections, and electron microscopy analysis of ultrathin sections, we show that the topological and spatial dynamics of rRNA within the nucleolus extend from upstream binding factor (UBF)-positive sites in the fibrillar zone to the granular zone, without ever releasing the positive sites for the UBF. Together, these results seem to clearly indicate that the compartmentalization of the turtle nucleolus into two main components reflects a less orderly organization of ribosome formation.

Proteostasis is essential during cochlear development for neuron survival and hair cell polarity.

Protein homeostasis is essential to cell function, and a compromised ability to reduce the load of misfolded and aggregated proteins is linked to numerous age-related diseases, including hearing loss. Here, we show that altered proteostasis consequent to Elongator complex deficiency also impacts the proper development of the cochlea and results in deafness. In the absence of the catalytic subunit Elp3, differentiating spiral ganglion neurons display large aggresome-like structures and undergo apoptosis before birth. The cochlear mechanosensory cells are able to survive proteostasis disruption but suffer defects in polarity and stereociliary bundle morphogenesis. We demonstrate that protein aggregates accumulate at the apical surface of hair cells, where they cause a local slowdown of microtubular trafficking, altering the distribution of intrinsic polarity proteins and affecting kinocilium position and length. Alleviation of protein misfolding using the chemical chaperone 4-phenylbutyric acid during embryonic development ameliorates hair cell polarity in Elp3-deficient animals. Our study highlights the importance of developmental proteostasis in the cochlea and unveils an unexpected link between proteome integrity and polarized organization of cellular components.

Actin-independent trafficking of cochlear connexin 26 to non-lipid raft gap junction plaques.

Hereditary hearing loss affects about 1 per 1000 children. Mutations in GJB2, which encodes the connexin 26 protein (Cx26) involved in cochlear homeostasis, are found in about 50% of patients with autosomal recessive non-syndromic hearing loss. Deciphering the trafficking pathway of cochlear Cx26 in situ should represent an advance in understanding the pathogenic significance of many of these mutations. Connexins trafficking and delivery to lipid raft-associated gap junction plaques usually requires successively microtubule and actin networks. Here we show that cochlear Cx26 exhibits an unusual trafficking pathway. We observed that Cx26 assembly occurs in non-lipid raft membrane domains and that junctional plaques are devoid of actin and associated zonula occludens proteins. Using cytoskeleton-disrupting drugs in organotypic culture, we found that cochlear Cx26 gap junction assembly requires microtubules but not actin filaments. Altogether, our data provide an unexpected insight into Cx26 trafficking pathway and gap junction assembly in the cochlea.

Cochlear connexin 30 homomeric and heteromeric channels exhibit distinct assembly mechanisms.

Many of the mutations in GJB2 and GJB6, which encode connexins 26 and 30 (Cx26 and Cx30), impair the formation of membrane channels and cause autosomal syndromic and non-syndromic hearing loss. In cochlear non-sensory supporting cells, Cx26 and Cx30 form two types of homomeric and heteromeric gap junctions. The biogenesis processes of these channels occurring in situ remain largely unknown. Here we show that Cx30 homomeric and Cx26/Cx30 heteromeric gap junctions exhibit distinct assembly mechanisms in the cochlea. When expressed as homomeric channels, Cx30 preferentially interacts with ß-actin in the peripheral non-junctional membrane region, called perinexus, and strongly relies on the actin network for gap junction plaque assembly. In contrast, we found that Cx26/Cx30 heteromeric gap junction plaques are devoid of perinexus and associated actin network, and resist to actin-depolymerizating drug. This supports that Cx26/Cx30 oligomers could be directly delivered from the interior of the cell to the junctional plaque. Altogether, our data provide a novel insight in homomeric and heteromeric gap junction plaque assembly in the cochlea.

A clinical and histopathological study of malformations observed in fetuses infected by the Zika virus.

BACKGROUND: The recent outbreak of Zika virus (ZIKV) infection and the associated increased prevalence of microcephaly in Brazil underline the impact of viral infections on embryo fetal development. The aim of the present study is to provide a detailed clinical and histopathological study of the fetal disruption caused by the ZIKV, with a special focus on the associated neuropathological findings. METHODS: A detailed feto-placental examination, as well as neuropathological and neurobiological studies were performed on three fetuses collected after pregnancy termination between 22 and 25 weeks of gestation (WG), because brain malformations associated with a maternal and fetal ZIKV infection was diagnosed. RESULTS: In all three cases, the maternal infection occurred during the first trimester of pregnancy. A small head was observed on the ultrasound examination of the second trimester of pregnancy and led to the diagnosis of ZIKV fetopathy and pregnancy termination. The fetal histopathological examination was unremarkable on the viscera but showed on the testis an interstitial lymphocytic infiltrate. The placenta contained a Hofbauer cells hyperplasia with signs of inflammation. Neuropathological findings included a meningoencephalitis and an ex vacuo hydrocephalus. Immunohistochemical studies showed the presence of T lymphocytic and histiocytic meningitis associated with an abundant cerebral astroglial and macrophagic reaction. In situ hybridization demonstrated, abundant ZIKV particles within the cerebral parenchyma mainly in the ventricular/subventricular zone and in the cortical plate. In addition massive cells death and endoplasmic reticulum damage were present. CONCLUSION: The present study reports on the clinical and histopathological findings observed in three fetuses infected by the ZIKV. It emphasizes the severity of brain damages and the minimal visceral and placental changes observed upon ZIKV infection. This confirms the selective neurotropism of ZIKV. Finally, it allows us to describe the cascade of multifactorial developmental defects leading to microcephaly.

Varicella-Zoster Virus ORF9p Binding to Cellular Adaptor Protein Complex 1 Is Important for Viral Infectivity.

ORF9p (homologous to herpes simplex virus 1 [HSV-1] VP22) is a varicella-zoster virus (VZV) tegument protein essential for viral replication. Even though its precise functions are far from being fully described, a role in the secondary envelopment of the virus has long been suggested. We performed a yeast two-hybrid screen to identify cellular proteins interacting with ORF9p that might be important for this function. We found 31 ORF9p interaction partners, among which was AP1M1, the µ subunit of the adaptor protein complex 1 (AP-1). AP-1 is a heterotetramer involved in intracellular vesicle-mediated transport and regulates the shuttling of cargo proteins between endosomes and the trans-Golgi network via clathrin-coated vesicles. We confirmed that AP-1 interacts with ORF9p in infected cells and mapped potential interaction motifs within ORF9p. We generated VZV mutants in which each of these motifs was individually impaired and identified leucine 231 in ORF9p to be critical for the interaction with AP-1. Disrupting ORF9p binding to AP-1 by mutating leucine 231 to alanine in ORF9p strongly impaired viral growth, most likely by preventing efficient secondary envelopment of the virus. Leucine 231 is part of a dileucine motif conserved among alphaherpesviruses, and we showed that VP22 of Marek's disease virus and HSV-2 also interacts with AP-1. This indicates that the function of this interaction in secondary envelopment might be conserved as well.IMPORTANCE Herpesviruses are responsible for infections that, especially in immunocompromised patients, can lead to severe complications, including neurological symptoms and strokes. The constant emergence of viral strains resistant to classical antivirals (mainly acyclovir and its derivatives) pleads for the identification of new targets for future antiviral treatments. Cellular adaptor protein (AP) complexes have been implicated in the correct addressing of herpesvirus glycoproteins in infected cells, and the discovery that a major constituent of the varicella-zoster virus tegument interacts with AP-1 reveals a previously unsuspected role of this tegument protein. Unraveling the complex mechanisms leading to virion production will certainly be an important step in the discovery of future therapeutic targets.

Stress-induced unfolded protein response contributes to Zika virus-associated microcephaly.

Accumulating evidence support a causal link between Zika virus (ZIKV) infection during gestation and congenital microcephaly. However, the mechanism of ZIKV-associated microcephaly remains unclear. We combined analyses of ZIKV-infected human fetuses, cultured human neural stem cells and mouse embryos to understand how ZIKV induces microcephaly. We show that ZIKV triggers endoplasmic reticulum stress and unfolded protein response in the cerebral cortex of infected postmortem human fetuses as well as in cultured human neural stem cells. After intracerebral and intraplacental inoculation of ZIKV in mouse embryos, we show that it triggers endoplasmic reticulum stress in embryonic brains in vivo. This perturbs a physiological unfolded protein response within cortical progenitors that controls neurogenesis. Thus, ZIKV-infected progenitors generate fewer projection neurons that eventually settle in the cerebral cortex, whereupon sustained endoplasmic reticulum stress leads to apoptosis. Furthermore, we demonstrate that administration of pharmacological inhibitors of unfolded protein response counteracts these pathophysiological mechanisms and prevents microcephaly in ZIKV-infected mouse embryos. Such defects are specific to ZIKV, as they are not observed upon intraplacental injection of other related flaviviruses in mice.

Quantitation and biospecific identification of virus-like particles of human papillomavirus by capillary electrophoresis.

Capillary electrophoresis (CE) for HPV-VLP quantitation is a very interesting alternative technique compared to those currently used in viral analysis, such as SDS-PAGE, Western blot or protein assay that are destructive and semi-quantitative or non specific. In this study, the quantitative performance of the CE method was evaluated. A main issue in virus quantitation is the absence of reference material. Therefore, the concentration of a HPV16-VLP sample produced in the laboratory was determined using ELISA with Gardasil®, after adjuvant dissolution, as reference material and conformational H16.V5 antibody. HPV16-VLP concentration was found to influence particles electrophoretic mobility until a plateau was reached for concentrations ≤ 50µgml-1. As zeta potential is directly proportional to the electrophoretic mobility, it was measured at different HPV-VLP concentrations and the results were in complete accordance with the measured electrophoretic mobilities. The concentration dependence of the electrophoretic mobility could be explained by an overlap of the electrical double layers of adjacent particles. The HPV16-VLP peak identity was demonstrated unequivocally by the study of HPV16-VLP/H16.V5 antibody complex formation using affinity CE. Finally, the CE method was successfully validated following the ICH Q2R1 guidelines. To overcome the sample heterogeneity issue, a well-designed sample preparation was used. Considering sample complexity, validation results were satisfactory with maximum repeatability and intermediate precision RSD of 12.2% and a maximum relative bias of 1.4%.

DNA Labeling at Electron Microscopy.

Here, we describe a method for locating DNA on ultrathin sections. This technique is compatible with all usual fixation and embedding procedures and can be combined with cytochemical methods. Ultrathin sections are incubated in a medium containing terminal deoxynucleotidyl transferase (TdT) and various non-isotopic nucleotide analogs. The labeled nucleotides bound to the surface of ultrathin sections are then visualized by an indirect immunogold labeling technique. This high-resolution method provides a powerful tool for pinpointing the precise location of DNA within biological material, even where DNA is present in very low amounts.

Study of intact virus-like particles of human papillomavirus by capillary electrophoresis.

Virus-like particles of human papillomavirus (HPV-VLP), resulting from the self-assembly of the capsid proteins (L1 or L1 and L2), have been widely used to study HPV as they are similar to the native virion. Moreover, two prophylactic vaccines, Gardasil(®) and Cervarix(®), are based on HPV-VLP L1. Analytical techniques currently used to characterize HPV-VLP, such as SDS-PAGE, Western blot, ELISA, are time-consuming and semiquantitative. In this study, CE was evaluated for the analysis of intact HPV16-VLP. The usefulness of capillary inner wall coating as well as various BGEs, pH, and detergent additives were investigated. Reproducible HPV-VLP analysis in CE was achieved using poly(ethylene oxide)-coated capillary and a BGE containing high salt concentration and low SDS concentration. The developed method enables HPV-VLP detection in less than 10 min (migration times RSD: 1.6%). The identity of HPV-VLP peak was confirmed by comparison with a sample obtained from a wild-type baculovirus and with VLP-based vaccine, Gardasil(®) , after adjuvant dissolution. Finally, we applied the developed methodology to VLP-based vaccines, demonstrating that CE could be successfully used for vaccine quality control.

A Dynamic Unfolded Protein Response Contributes to the Control of Cortical Neurogenesis.

The cerebral cortex contains layers of neurons sequentially generated by distinct lineage-related progenitors. At the onset of corticogenesis, the first-born progenitors are apical progenitors (APs), whose asymmetric division gives birth directly to neurons. Later, they switch to indirect neurogenesis by generating intermediate progenitors (IPs), which give rise to projection neurons of all cortical layers. While a direct lineage relationship between APs and IPs has been established, the molecular mechanism that controls their transition remains elusive. Here we show that interfering with codon translation speed triggers ER stress and the unfolded protein response (UPR), further impairing the generation of IPs and leading to microcephaly. Moreover, we demonstrate that a progressive downregulation of UPR in cortical progenitors acts as a physiological signal to amplify IPs and promotes indirect neurogenesis. Thus, our findings reveal a contribution of UPR to cell fate acquisition during mammalian brain development.

Hypervulnerability to Sound Exposure through Impaired Adaptive Proliferation of Peroxisomes.

A deficiency in pejvakin, a protein of unknown function, causes a strikingly heterogeneous form of human deafness. Pejvakin-deficient (Pjvk(-/-)) mice also exhibit variable auditory phenotypes. Correlation between their hearing thresholds and the number of pups per cage suggest a possible harmful effect of pup vocalizations. Direct sound or electrical stimulation show that the cochlear sensory hair cells and auditory pathway neurons of Pjvk(-/-) mice and patients are exceptionally vulnerable to sound. Subcellular analysis revealed that pejvakin is associated with peroxisomes and required for their oxidative-stress-induced proliferation. Pjvk(-/-) cochleas display features of marked oxidative stress and impaired antioxidant defenses, and peroxisomes in Pjvk(-/-) hair cells show structural abnormalities after the onset of hearing. Noise exposure rapidly upregulates Pjvk cochlear transcription in wild-type mice and triggers peroxisome proliferation in hair cells and primary auditory neurons. Our results reveal that the antioxidant activity of peroxisomes protects the auditory system against noise-induced damage.

MicroRNA-124 Regulates Cell Specification in the Cochlea through Modulation of Sfrp4/5.

The organ of Corti, the auditory organ of the mammalian inner ear, contains sensory hair cells and supporting cells that arise from a common sensory progenitor. The molecular bases allowing the specification of these progenitors remain elusive. In the present study, by combining microarray analyses with conditional deletion of Dicer in the developing inner ear, we identified that miR-124 controls cell fate in the developing organ of Corti. By targeting secreted frizzled-related protein 4 (Sfrp4) and Sfrp5, two inhibitors of the Wnt pathway, we showed that miR-124 controls the ß-catenin-dependent and also the PCP-related non-canonical Wnt pathways that contribute to HC differentiation and polarization in the organ of Corti. Thus, our work emphasizes the importance of miR-124 as an epigenetic safeguard that fine-tunes the expression of genes critical for cell patterning during cochlear differentiation.

Spatio-temporal dynamics of ß-tubulin isotypes during the development of the sensory auditory organ in rat.

There are different ß-tubulin isoforms in microtubules of vertebrate tissues. However, their functional significance is still largely unknown. In the present study, we investigated the localization of five ß-tubulin isotypes (ß1-5) within the hearing organ during development in rat. By using confocal microscopy, we showed that with the exception of the ß3-tubulin isoform that was specific to nerve fibres, all the different ß-tubulin isoforms were mainly present in the supporting cells. Contrary to ß1-4-tubulins, we also found that the ß5-tubulin isoform appeared only at a key stage of the post-natal development in specific cell types (pillar cells and Deiters' cells). By using transmission electron microscopy, we revealed further that this developmental stage coincided with the formation of two separate bundles of microtubules from a unique one in these supporting cells. Together, these results suggest that the ß5-tubulin isoform might be involved in the generation of new microtubule bundles from a pre-existing one.

Varicella-zoster virus induces the formation of dynamic nuclear capsid aggregates.

The first step of herpesviruses virion assembly occurs in the nucleus. However, the exact site where nucleocapsids are assembled, where the genome and the inner tegument are acquired, remains controversial. We created a recombinant VZV expressing ORF23 (homologous to HSV-1 VP26) fused to the eGFP and dually fluorescent viruses with a tegument protein additionally fused to a red tag (ORF9, ORF21 and ORF22 corresponding to HSV-1 UL49, UL37 and UL36). We identified nuclear dense structures containing the major capsid protein, the scaffold protein and maturing protease, as well as ORF21 and ORF22. Correlative microscopy demonstrated that the structures correspond to capsid aggregates and time-lapse video imaging showed that they appear prior to the accumulation of cytoplasmic capsids, presumably undergoing the secondary egress, and are highly dynamic. Our observations suggest that these structures might represent a nuclear area important for capsid assembly and/or maturation before the budding at the inner nuclear membrane.