Fsp27 promotes lipid droplet growth by lipid exchange and transfer at lipid droplet contact sites

Lipid droplets (LDs) are dynamic cellular organelles that control many biological processes. However, molecular components determining LD growth are poorly understood. Genetic analysis has indicated that Fsp27, an LD-associated protein, is important in controlling LD size and lipid storage in adipocytes. In this paper, we demonstrate that Fsp27 is focally enriched at the LD-LD contacting site (LDCS). Photobleaching revealed the occurrence of lipid exchange between contacted LDs in wild-type adipocytes and Fsp27-overexpressing cells but not Fsp27-deficient adipocytes. Furthermore, live-cell imaging revealed a unique Fsp27-mediated LD growth process involving a directional net lipid transfer from the smaller to larger LDs at LDCSs, which is in accordance with the biophysical analysis of the internal pressure difference between the contacting LD pair. Thus, we have uncovered a novel molecular mechanism of LD growth mediated by Fsp27.     

The Lerhamn drill core and its bearing for the graptolite biostratigraphy of the Ordovician Tøyen Shale in Scania,southern Sweden

Maletz, J. & Ahlberg, P. 2011: The Lerhamn drill core and its bearing for the graptolite biostratigraphy of the Ordovician Tøyen Shale in Scania, southern Sweden. Lethaia, Vol. 44, pp. 350–368. A drill core through the Lower Ordovician Tøyen Shale Formation at Lerhamn, NW Scania, southern Sweden, provides important new information for the precise biostratigraphic resolution of the Floian to lower Darriwilian time interval in southern Scandinavia. The Hunnegraptus copiosus, Tetragraptus phyllograptoides, Cymatograptus protobalticus (new), Baltograptus vacillans (new), Baltograptus sp. cf. Baltograptus deflexus (new), Baltograptus minutus (new), Isograptus victoriae, Undulograptus austrodentatus (Arienigraptus zhejiangensis and Undulograptus sinicus Subzones) and the (?)Corymbograptus retroflexus (new) biozones are differentiated in the core and their correlation in Scania is discussed. The Lerhamn drill core provides the most detailed graptolite record of the Floian Stage in Scandinavia. The interval is dominated by a number of species of the genus Baltograptus, endemic to the Atlantic Faunal realm and highly useful for regional biostratigraphic correlation. The biostratigraphic framework is based on endemic and pandemic faunal elements. The mixture of both elements in the drill core allows a more precise inter‐continental correlation of Lower to Middle Ordovician graptolite faunas and may – in the future – provide information as to the climatic history of regions dominated by Baltograptus faunas in the Floian. The (?)C. retroflexus Biozone is based on species originally described from Bohemia, but the record of the zone in the Lerhamn drill core indicates a wider distribution of its fauna. □Biostratigraphy, graptolites, Ordovician, Scania, Sweden.     

New snakeflies (Insecta: Raphidioptera) from the Lower Cretaceous of the UK,Spain and Brazil

Abstract: Several new taxa of snakeflies (Raphidioptera) are described from the Lower Cretaceous deposits of the Wealden, UK (Barremian), Montsec, Spain (Barremian) and the Crato Formation, Brazil (Aptian). Mesoraphidia ednae sp. nov. and M. hilli sp. nov. are described from the Wealden; Nanoraphidia lithographica sp. nov. and Iberoraphidia dividua gen. et sp. nov. are described from Montsec, and Baissoptera lisae sp. nov. is described from the Crato Formation. The geographical range of Nanoraphidia has potentially been extended.     

The identity of the Ordovician (Darriwilian) graptolite Fucoides dentatus Brongniart, 1828

Abstract: The biostratigraphically important Middle Ordovician (Darriwilian) biserial graptolite Fucoides dentatus Brongniart, 1828 is redescribed and illustrated from its type material and from additional specimens collected at the type locality – Lévis, Quebec, Canada. It is referred to Levisograptus gen. nov., which includes also the austrodentatus group of early axonophoran graptolites. The species has previously been confused with a younger, mid‐Darriwilian species, now referred to as Eoglyptograptus gerhardi sp. nov., and recognized as the type species of the genus Eoglyptograptus Mitchell. Both species can be differentiated easily by their respective proximal development types and show nonoverlapping biostratigraphical ranges. Levisograptus dentatus (Brongniart) is an important biostratigraphical index species in the early Darriwilian. Eoglyptograptus species are found in the higher Darriwilian and are biogeographically restricted to the Atlantic Faunal Realm.     

Caveolae: The FAQs

Caveolae are an abundant, but enigmatic, plasma membrane feature of vertebrate cells. In this brief commentary, the authors attempt to answer some key questions related to the formation and function of caveolae based on round‐table discussions at the first EMBO Workshop on Caveolae held in France in May 2019.     

Beyond the Levant: First Evidence of a Pre-Pottery Neolithic Incursion into the Nefud Desert,Saudi Arabia

Pre-Pottery Neolithic assemblages are best known from the fertile areas of the Mediterranean Levant. The archaeological site of Jebel Qattar 101 (JQ-101), at Jubbah in the southern part of the Nefud Desert of northern Saudi Arabia, contains a large collection of stone tools, adjacent to an Early Holocene palaeolake. The stone tool assemblage contains lithic types, including El-Khiam and Helwan projectile points, which are similar to those recorded in Pre-Pottery Neolithic A and Pre-Pottery Neolithic B assemblages in the Fertile Crescent. Jebel Qattar lies ∼500 kilometres outside the previously identified geographic range of Pre-Pottery Neolithic cultures. Technological analysis of the typologically diagnostic Jebel Qattar 101 projectile points indicates a unique strategy to manufacture the final forms, thereby raising the possibility of either direct migration of Levantine groups or the acculturation of mobile communities in Arabia. The discovery of the Early Holocene site of Jebel Qattar suggests that our view of the geographic distribution and character of Pre-Pottery Neolithic cultures may be in need of revision.     

Building a Better Dynasore: The Dyngo Compounds Potently Inhibit Dynamin and Endocytosis

Dynamin GTPase activity increases when it oligomerizes either into helices in the presence of lipid templates or into rings in the presence of SH3 domain proteins. Dynasore is a dynamin inhibitor of moderate potency (IC₅₀ ? 15 μM in vitro). We show that dynasore binds stoichiometrically to detergents used for in vitro drug screening, drastically reducing its potency (IC₅₀ = 479 μM) and research tool utility. We synthesized a focused set of dihydroxyl and trihydroxyl dynasore analogs called the Dyngo? compounds, five of which had improved potency, reduced detergent binding and reduced cytotoxicity, conferred by changes in the position and/or number of hydroxyl substituents. The Dyngo compound 4a was the most potent compound, exhibiting a 37‐fold improvement in potency over dynasore for liposome‐stimulated helical dynamin activity. In contrast, while dynasore about equally inhibited dynamin assembled in its helical or ring states, 4a and 6a exhibited >36‐fold reduced activity against rings, suggesting that they can discriminate between helical or ring oligomerization states. 4a and 6a inhibited dynamin‐dependent endocytosis of transferrin in multiple cell types (IC₅₀ of 5.7 and 5.8 μM, respectively), at least sixfold more potently than dynasore, but had no effect on dynamin‐independent endocytosis of cholera toxin. 4a also reduced synaptic vesicle endocytosis and activity‐dependent bulk endocytosis in cultured neurons and synaptosomes. Overall, 4a and 6a are improved and versatile helical dynamin and endocytosis inhibitors in terms of potency, non‐specific binding and cytotoxicity. The data further suggest that the ring oligomerization state of dynamin is not required for clathrin‐mediated endocytosis .     

Formation of Raft-Like Assemblies within Clusters of Influenza Hemagglutinin Observed by MD Simulations

The association of hemagglutinin (HA) with lipid rafts in the plasma membrane is an important feature of the assembly process of influenza virus A. Lipid rafts are thought to be small, fluctuating patches of membrane enriched in saturated phospholipids, sphingolipids, cholesterol and certain types of protein. However, raft-associating transmembrane (TM) proteins generally partition into Ld domains in model membranes, which are enriched in unsaturated lipids and depleted in saturated lipids and cholesterol. The reason for this apparent disparity in behavior is unclear, but model membranes differ from the plasma membrane in a number of ways. In particular, the higher protein concentration in the plasma membrane may influence the partitioning of membrane proteins for rafts. To investigate the effect of high local protein concentration, we have conducted coarse-grained molecular dynamics (CG MD) simulations of HA clusters in domain-forming bilayers. During the simulations, we observed a continuous increase in the proportion of raft-type lipids (saturated phospholipids and cholesterol) within the area of membrane spanned by the protein cluster. Lateral diffusion of unsaturated lipids was significantly attenuated within the cluster, while saturated lipids were relatively unaffected. On this basis, we suggest a possible explanation for the change in lipid distribution, namely that steric crowding by the slow-diffusing proteins increases the chemical potential for unsaturated lipids within the cluster region. We therefore suggest that a local aggregation of HA can be sufficient to drive association of the protein with raft-type lipids. This may also represent a general mechanism for the targeting of TM proteins to rafts in the plasma membrane, which is of functional importance in a wide range of cellular processes.     

Quantitative proteomic analysis of the adipocyte plasma membrane

The adipocyte is a key regulator of mammalian metabolism. To advance our understanding of this important cell, we have used quantitative proteomics to define the protein composition of the adipocyte plasma membrane (PM) in the presence and absence of insulin. Using this approach, we have identified a high confidence list of 486 PM proteins, 52 of which potentially represent novel cell surface proteins, including a member of the adiponectin receptor family and an unusually high number of hydrolases with no known function. Several novel insulin-responsive proteins including the sodium/hydrogen exchanger, NHE6 and the collagens III and VI were also identified, and we provide evidence of PM-ER association suggestive of a unique functional association between these two organelles in the adipocyte. Together these studies provide a wealth of potential therapeutic targets for the manipulation of adipocyte function and a valuable resource for metabolic research and PM biology.     

Phytoplankton patchiness in Winam Gulf,Lake Victoria: a study using principal component analysis of in situ fluorescent excitation spectra

1. In order to characterise phytoplankton patchiness at fine scales, a profiling multiwavelength fluorometer was cast at numerous locations throughout Winam Gulf in Lake Victoria to measure fluorescent excitation spectra, which are indicators of both phytoplankton diversity and coloured dissolved organic matter (CDOM). 2. Processing the spectral data with principal component analysis (PCA) revealed that linear combinations of four fundamental ‘base’ spectra could explain almost all of the variation in spectral measurements. Three of the base spectra were associated with spatially distinct patches of phytoplankton containing different species assemblages, while the fourth base spectrum was due to CDOM fluorescence. 3. The locations of the phytoplankton patches were traced to the south‐east of Winam Gulf, the western end of the Rusinga Channel and the open waters of Lake Victoria adjacent to Winam Gulf, respectively. The high CDOM fluorescence was traced mainly to relatively deep water in the Rusinga Channel. 4. The phytoplankton and CDOM patchiness were interpreted in the context of physical and chemical gradients that were measured at the site at the same scale as the spectral data. Strong relationships were found between the gradients in spectral data and other environmental variables, which suggested several underlying explanations for the phytoplankton and CDOM patchiness.