Meisosomes, folded membrane microdomains between the apical extracellular matrix and epidermis

Apical extracellular matrices (aECMs) form a physical barrier to the environment. In Caenorhabditis elegans, the epidermal aECM, the cuticle, is composed mainly of different types of collagen, associated in circumferential ridges separated by furrows. Here, we show that in mutants lacking furrows, the normal intimate connection between the epidermis and the cuticle is lost, specifically at the lateral epidermis, where, in contrast to the dorsal and ventral epidermis, there are no hemidesmosomes. At the ultrastructural level, there is a profound alteration of structures that we term 'meisosomes,' in reference to eisosomes in yeast. We show that meisosomes are composed of stacked parallel folds of the epidermal plasma membrane, alternately filled with cuticle. We propose that just as hemidesmosomes connect the dorsal and ventral epidermis, above the muscles, to the cuticle, meisosomes connect the lateral epidermis to it. Moreover, furrow mutants present marked modifications of the biomechanical properties of their skin and exhibit a constitutive damage response in the epidermis. As meisosomes co-localise to macrodomains enriched in phosphatidylinositol (4,5) bisphosphate, they could conceivably act, like eisosomes, as signalling platforms, to relay tensile information from the aECM to the underlying epidermis, as part of an integrated stress response to damage

Wolbachia endosymbionts subvert the endoplasmic reticulum to acquire host membranes without triggering ER stress.

The reproductive parasites Wolbachia are the most common endosymbionts on earth, present in a plethora of arthropod species. They have been introduced into mosquitos to successfully prevent the spread of vector-borne diseases, yet the strategies of host cell subversion underlying their obligate intracellular lifestyle remain to be explored in depth in order to gain insights into the mechanisms of pathogen-blocking. Like some other intracellular bacteria, Wolbachia reside in a host-derived vacuole in order to replicate and escape the immune surveillance. Using here the pathogen-blocking Wolbachia strain from Drosophila melanogaster, introduced into two different Drosophila cell lines, we show that Wolbachia subvert the endoplasmic reticulum to acquire their vacuolar membrane and colonize the host cell at high density. Wolbachia redistribute the endoplasmic reticulum, and time lapse experiments reveal tight coupled dynamics suggesting important signalling events or nutrient uptake. Wolbachia infection however does not affect the tubular or cisternal morphologies. A fraction of endoplasmic reticulum becomes clustered, allowing the endosymbionts to reside in between the endoplasmic reticulum and the Golgi apparatus, possibly modulating the traffic between these two organelles. Gene expression analyses and immunostaining studies suggest that Wolbachia achieve persistent infections at very high titers without triggering endoplasmic reticulum stress or enhanced ERAD-driven proteolysis, suggesting that amino acid salvage is achieved through modulation of other signalling pathways

High Susceptibility of Human Dendritic Cells to Invasion by the Intracellular Pathogens Brucella suis, B. abortus, and B. melitensis

Bacteria from the Brucella genus are able to survive and proliferate within macrophages. Because they are phylogenetically closely related to macrophages, myeloid dendritic cells (DCs) constitute potential targets for Brucella bacteria. Here we report that DCs display a great susceptibility to Brucella infection. Therefore, DCs might serve as a reservoir and be important for the development of Brucella bacteria within their host

Nuclear Lipid Droplet Birth during Replicative Stress

International audienceThe nuclear membrane defines the boundaries that confine, protect and shape the genome. As such, its blebbing, ruptures and deformations are known to compromise the integrity of genetic material. Yet, drastic transitions of the nuclear membrane such as its invagination towards the nucleoplasm or its capacity to emit nuclear lipid droplets (nLD) have not been evaluated with respect to their impact on genome dynamics. To begin assessing this, in this work we used Saccharomyces cerevisiae as a model to ask whether a selection of genotoxins can trigger the formation of nLD. We report that nLD formation is not a general feature of all genotoxins, but of those engendering replication stress. Exacerbation of endogenous replication stress by genetic tools also elicited nLD formation. When exploring the lipid features of the nuclear membrane at the base of this emission, we revealed a link with the unsaturation profile of its phospholipids and, for the first time, of its sterol content. We propose that stressed replication forks may stimulate nLD birth by anchoring to the inner nuclear membrane, provided that the lipid context is adequate. Further, we point to a transcriptional feed-back process that counteracts the membrane’s proneness to emit nLD. With nLD representing platforms onto which genome-modifying reactions can occur, our findings highlight them as important players in the response to replication stress

The "acrostyle": a newly described anatomical structure in aphid stylets

UMR BGPI Equipe 2International audienceThe recent demonstration that a plant virus could be retained on protein receptors located exclusively in a small area inside the common duct at the tip of aphid maxillary stylets indicated the possible existence of a distinct anatomical structure at this level. Since no distinct feature within the common duct of any aphid species has ever been reported in the literature, we first carefully re-examined the distal extremity of the maxillary stylets of Acyrthosiphon pisum using transmission- and scanning-electron microscopy. Here, we describe an area of the cuticle surface displaying a different structure that is limited to a “band” paving the bottom of the common duct in each opposing maxillary stylet. This band starts at the very distal extremity, adopts a “comma-like” shape as it continues up towards the salivary canal, reducing in width and disappearing before actually reaching it. Investigations on several aphid species led to the conclusion that this anatomical feature—which we have tentatively named the “acrostyle”—is highly conserved among aphids. We then produced an antibody recognizing a consensus peptide located in the middle of the RR-2 motif of cuticular proteins from A. pisum and showed that this motif is accessible specifically within the acrostyle, indicating a higher concentration of cuticular proteins. While it is clear that at least some viruses can use the acrostyle to interact with their aphid vectors to ensure plant-to-plant transmission, the role of this new “organ” in aphid biology is unknown and calls for further investigation in the near future

Effect of salting process on the histological structure of salmon flesh

Atlantic Salmon , Salmo Salar, is composed of approximately 70% water, 19% protein, 10% lipid and 1% small nutrients (vitamins, glycogen, pigments ...). Smoked salmon comes from the processing of fresh salmon: the fillets are removed from the fish, salted and then smoked. Salting can be carried out with dry salt or by brine injection. The objective of the study was to compare the evolution of the cell structure and ultrastructure of the salmon muscle subjected to salting with dry salt and salting by brine injection.The experiment was carried out on 6 salmons. For each salmon, 1 fillet was salted with dry salt and the other fillet was additionally injected with brine. The fillets were smoked at low temperature (20-22 ° C). Samples were taken for histological analyzes (cryofixation, preparation of 10 μm thick histological sections, staining and observation by optical microscopy) and ultrastructural analyzes (chemical fixation, dehydration, resin inclusion, ultrathin sections, staining and observation by electron microscopy).The results show a decrease in the size of the extracellular spaces after injection of brine, which is probably related to a swelling of the muscle cells that accumulate water. Dry salt salting, on the other hand, shows no difference in the extracellular size compared to the unsalted muscle.The salting substantially degrades the ultrastructure of the muscle with in particular a significant solubilization of the Z-lines. Salting by injection of brine leads to swelling of the myofibrils and almost complete solubilization of the Z lines