NDP52 acts as a redox sensor in PINK1/Parkin‐mediated mitophagy

Mitophagy, the elimination of mitochondria via the autophagy‐lysosome pathway, is essential for the maintenance of cellular homeostasis. The best characterised mitophagy pathway is mediated by stabilisation of the protein kinase PINK1 and recruitment of the ubiquitin ligase Parkin to damaged mitochondria. Ubiquitinated mitochondrial surface proteins are recognised by autophagy receptors including NDP52 which initiate the formation of an autophagic vesicle around the mitochondria. Damaged mitochondria also generate reactive oxygen species (ROS) which have been proposed to act as a signal for mitophagy, however the mechanism of ROS sensing is unknown. Here we found that oxidation of NDP52 is essential for the efficient PINK1/Parkin‐dependent mitophagy. We identified redox‐sensitive cysteine residues involved in disulphide bond formation and oligomerisation of NDP52 on damaged mitochondria. Oligomerisation of NDP52 facilitates the recruitment of autophagy machinery for rapid mitochondrial degradation. We propose that redox sensing by NDP52 allows mitophagy to function as a mechanism of oxidative stress response.     

Light and electron microscope observations of the type species of Syracosphaera,s. pulchra (Prymnesiophyceae)

Syracosphaera pulchra, the type species of the genus was isolated into unialgal culture and studied with both the light and electron microscope. A conspicuous coiling haptonema is present containing seven microtubules in the shaft and eight in the basal region; features shared with many taxa in the order Prymnesiales. The proximal and distal coccoliths differ in shape but resemble each other structurally: the outer elements alternate to make the rim. The proximal coccoliths possess an organic base-plate scale which is absent in the distal coccoliths. The uncalcified organic scales are ornamented by a radial, more or less concentric, fibrillar pattern and are arranged in several layers between the proximal coccoliths and the plasmalemma. The ultrastructure of the cell is typical of prymnesiophycean algae. The flagellar apparatus is characterized by the absence of secondary microtubular bundles which are usually well developed in other coccolithophorids with two microtubular roots. This feature is also rather similar to that found in members of the Prymnesiales.

This investigation has indicated that S. pulchra has, in some respects, a closer affinity with members of the Prymnesiales than with the coccolithophorids.     

Intrinsic curvature: a marker of millimeter-scale tangential cortico-cortical connectivity?

In this paper, we draw a link between cortical intrinsic curvature and the distributions of tangential connection lengths. We suggest that differential rates of surface expansion not only lead to intrinsic curvature of the cortical sheet, but also to differential inter-neuronal spacing. We propose that there follows a consequential change in the profile of neuronal connections: specifically an enhancement of the tendency towards proportionately more short connections. Thus, the degree of cortical intrinsic curvature may have implications for short-range connectivity.     

Cell division in Hymenomonas carterae (Braarud et Fagerland) Braarud (Prymnesiophyceae)

The cell division cycle of Hymenomonas carterae (Braarud et Fagerland) Braarud was investigated at the ultrastructural level. DNA synthesis and cytokinesis occurred during the 8-hour dark period. All organelles, including the flagellar bases were replicated prior to nuclear division. Prophase consisted of a clustering of the chromosomes into distinct groups and the disappearance of the nucleolus. During metaphase there was complete dissociation of the nuclear envelope resulting in the formation of an open spindle containing no major organelles. The metaphase plate formed at right angles to an imaginary line joining the two pairs of flagellar bases. Elongation of the cell and separation of the chromosomes occurred at anaphase. During early telophase the nuclear envelope veformed and was closely associated with the chromosome masses, resulting in the nuclear possessing convoluted profiles. Telophase was characterized by complete break down of spindle fibres, rounding off of the nuclear profiles, reappearance of the nucleolus, emergence of the flagella and the final separation of the two daughter cells.     

Ultrastructure and ontogeny of a new type of eyespot in dinoflagellates

Summary Ultrastructure and ontogeny of a new type of eyespot in dinoflagellates is described. A marine tidal poolGymnodinium natalense is found to possess a highly organized eyespot whose structure is unique among dinoflagellates. The eyespot is rectangular in ventral view, C-shaped in apical view, and is located posterior to the sulcus. The eyespot is independent of the chloroplast and consists of several (typically six) layers of hemi-cylindrical walls which are concentrically arranged with narrow spacing between them. Each hemicylindrical wall is enclosed by a single unit membrane and is composed of many regularly arranged rectangular crystalline bricks. These crystalline bricks are produced in small vesicles which are formed in the invaginations of the chloroplast. The vesicles containing newly formed crystalline bricks are then transported to the sulcal area to assemble the eyespot. The crystalline bricks are arranged in a neat row within the vesicle termed “eyespot forming vesicle” (EFV), which is located near the sulcus. The hemi-cylindrical wall is constructed within the EFV. Based on the structure of the eyespot, viz. consisting of concentric multi-layered walls, the eyespot is thought to act as a quarter-wave stack antenna.     

BTKbase, mutation database for X-linked agammaglobulinemia (XLA).

X-linked agammaglobulinemia (XLA) is an immunodeficiency caused by mutations in the gene coding for Bruton's agammaglobulinemia tyrosine kinase (BTK). A database (BTKbase) of BTK mutations has been compiled and the recent update lists 463 mutation entries from 406 unrelated families showing 303 unique molecular events. In addition to mutations, the database also lists variants or polymorphisms. Each patient is given a unique patient identity number (PIN). Information is included regarding the phenotype including symptoms. Mutations in all the five domains of BTK have been noticed to cause the disease, the most common event being missense mutations. The mutations appear almost uniformly throughout the molecule and frequently affect CpG sites that code for arginine residues. The putative structural implications of all the missense mutations are given in the database. The improved version of the registry having a number of new features is available at http://www. helsinki.fi/science/signal/btkbase.html     

Phosphatidylserine clustering by the Ebola virus matrix protein is a critical step in viral budding

Phosphatidylserine (PS) is a critical lipid factor in the assembly and spread of numerous lipid‐enveloped viruses. Here, we describe the ability of the Ebola virus (EBOV) matrix protein eVP40 to induce clustering of PS and promote viral budding in vitro, as well as the ability of an FDA‐approved drug, fendiline, to reduce PS clustering and subsequent virus budding and entry. To gain mechanistic insight into fendiline inhibition of EBOV replication, multiple in vitro assays were run including imaging, viral budding and viral entry assays. Fendiline lowers PS content in mammalian cells and PS in the plasma membrane, where the ability of VP40 to form new virus particles is greatly lower. Further, particles that form from fendiline‐treated cells have altered particle morphology and cannot significantly infect/enter cells. These complementary studies reveal the mechanism by which EBOV matrix protein clusters PS to enhance viral assembly, budding, and spread from the host cell while also laying the groundwork for fundamental drug targeting strategies.     

The predominant role of the pith in the Growth and development of internodes in Liquidambar styraciflua (Hamamelidaceae). I. Histological basis of compressive and tensile stresses in developing primary tissues

Quantitative changes in cell pattern in the pith, cortex, cortical collenchyma, and epidermis were followed in developing internodes of Liquidambar to examine the cellular basis of compressive and tensile stresses in organized shoot growth. Initially, the highest rates of cell multiplication occur in the pith, followed successively by the epidermis, cortex, and cortical collenchyma. As internodes enter the phase of maximum elongation growth, mitotic activity begins to shift acropetally, accompanied by pronounced changes in cell pattern. The highest rates of cell multiplication now occur in the pith and cortex and continue until the cessation of internode growth. Concomitantly, reduced rates of cell division in peripheral tissues result in rapid increases in rates of cell elongation in the cortical collenchyma and epidermis. Attention is focused on the role of continued cell division in developing internodes with emphasis on differences in rates of cell multiplication between inner and outer tissues affecting patterns of tissue stress. For example, rapid and sustained increases in cell number in the pith, accompanied by growth of readily extensible pith cells, result in the development of compressive forces driving the growth of internodes. Conversely, continuing divisions in less extensible collenchyma and epidermal cells can relieve threshold tensile stresses resulting from the continuous stretching of these tissues by the developing pith. The concept that the passive extension of peripheral tissues, especially the epidermis, control the rate of internode elongation is viewed as an oversimplification of the interacting role of compressive and tensile forces in organized growth and development.     

Hippos alter their aggregations to mitigate density-dependent drought effects

Megaherbivores play a critical role in the ecology of African savannas and grasslands. In addition, these systems are forecast to experience more frequent and severe droughts as a product of changes in the global climate. Thus, the continued conservation of megaherbivores and their associated ecosystems will require a better understanding of how megaherbivores respond to drought by shifting their movement, diet and social behaviour. We address this need by investigating the factors affecting changes in the abundance of common hippopotamus (Hippopotamus amphibius; hereafter: ‘hippos’) throughout the six major rivers of Kruger National Park, South Africa, during and following the severe drought of 2015/2016. Specifically, we aimed to understand the role of two environmental characteristics that have relevance to hippos and that changed in response to drought: vegetation condition and the extent of pooled surface water. In addition, we investigated the extent to which pre-drought density affected changes in hippo abundance. Although vegetation and daytime refugia both appeared to influence pre-drought hippo abundance, these factors were less important to the change in hippo abundance related to the drought. Instead, the response to drought was most strongly related to the pre-drought abundance of hippos, where river segments supporting more than 50 individuals prior to the drought in 2015 decreased by more than half on average. Furthermore, we show that the degree of aggregation decreased from 2015 to 2016 because of the drought, but then began to increase again as the rains returned in 2017. Our results suggest that in addition to the large pools that support large aggregations of hippos in typical years, additional smaller pools are likely important for accommodating this drought-induced dispersion. However, maintaining this distribution of pools will likely become more challenging as southern Africa's population and water demands increase.