Mitochondrial Reshaping Accompanies Neural Differentiation in the Developing Spinal Cord

Mitochondria, long known as the cell powerhouses, also regulate redox signaling and arbitrate cell survival. The organelles are now appreciated to exert additional critical roles in cell state transition from a pluripotent to a differentiated state through balancing glycolytic and respiratory metabolism. These metabolic adaptations were recently shown to be concomitant with mitochondrial morphology changes and are thus possibly regulated by contingencies of mitochondrial dynamics. In this context, we examined, for the first time, mitochondrial network plasticity during the transition from proliferating neural progenitors to post-mitotic differentiating neurons. We found that mitochondria underwent morphological reshaping in the developing neural tube of chick and mouse embryos. In the proliferating population, mitochondria in the mitotic cells lying at the apical side were very small and round, while they appeared thick and short in interphase cells. In differentiating neurons, mitochondria were reorganized into a thin, dense network. This reshaping of the mitochondrial network was not specific of a subtype of progenitors or neurons, suggesting that this is a general event accompanying neurogenesis in the spinal cord. Our data shed new light on the various changes occurring in the mitochondrial network during neurogenesis and suggest that mitochondrial dynamics could play a role in the neurogenic process.     

Molecular requirements for the formation of a kinetochore–microtubule interface by Dam1 and Ndc80 complexes

Kinetochores are large protein complexes that link sister chromatids to the spindle and transduce microtubule dynamics into chromosome movement. In budding yeast, the kinetochore–microtubule interface is formed by the plus end–associated Dam1 complex and the kinetochore-resident Ndc80 complex, but how they work in combination and whether a physical association between them is critical for chromosome segregation is poorly understood. Here, we define structural elements required for the Ndc80–Dam1 interaction and probe their function in vivo. A novel ndc80 allele, selectively impaired in Dam1 binding, displayed growth and chromosome segregation defects. Its combination with an N-terminal truncation resulted in lethality, demonstrating essential but partially redundant roles for the Ndc80 N-tail and Ndc80–Dam1 interface. In contrast, mutations in the calponin homology domain of Ndc80 abrogated kinetochore function and were not compensated by the presence of Dam1. Our experiments shed light on how microtubule couplers cooperate and impose important constraints on structural models for outer kinetochore assembly.     

The Dam1 complex confers microtubule plus end–tracking activity to the Ndc80 kinetochore complex

Kinetochores must remain associated with microtubule ends, as they undergo rapid transitions between growth and shrinkage. The molecular basis for this essential activity that ensures correct chromosome segregation is unclear. In this study, we have used reconstitution of dynamic microtubules and total internal reflection fluorescence microscopy to define the functional relationship between two important budding yeast kinetochore complexes. We find that the Dam1 complex is an autonomous plus end–tracking complex. The Ndc80 complex, despite being structurally related to the general tip tracker EB1, fails to recognize growing ends efficiently. Dam1 oligomers are necessary and sufficient to recruit Ndc80 to dynamic microtubule ends, where both complexes remain continuously associated. The interaction occurs specifically in the presence of microtubules and is subject to regulation by Ipl1 phosphorylation. These findings can explain how the force harvested by Dam1 is transmitted to the rest of the kinetochore via the Ndc80 complex.     

Dexamethasone induces the expression of the mRNA of lipocortin 1 and 2 and the release of lipocortin 1 and 5 in differentiated, but not undifferentiated U-937 cells.

The effect of dexamethasone on mRNA and protein synthesis of lipocortins (LCT) 1, 2 and 5 has been investigated in U-937 cells. A constitutive expression of both mRNAs and proteins was detected in undifferentiated U-937 cells. This constitutive level was increased time- and dose-dependently by incubation with phorbol myristate acetate (PMA). In U-937 cells differentiated by 24 h incubation with 6 ng/ml PMA, dexamethasone (DEX) (1 microM for 16 h) caused an increased synthesis of the mRNA level of LCT-1 and 2, but not of LCT-5, over the level induced by PMA. DEX had no effect in undifferentiated cells. Moreover, DEX stimulated the extracellular release of LCT-1 and 5, but not of LCT-2, and inhibited the release of PGE2 and TXB2 only in the differentiated U-937 cells. These results suggest that the responsiveness of these cells to glucocorticoids is dependent on the phase of cell differentiation. The selective release of lipocortins by differentiated U-937 cells may explain, at least in part, the inhibition by DEX of the prostanoid release.     

Cyclooxygenases and lipoxygenases are used by the fungus Podospora anserina to repel nematodes

Oxylipins are secondary messengers used universally in the living world for communication and defense. The paradigm is that they are produced enzymatically for the eicosanoids and non-enzymatically for the isoprostanoids. They are supposed to be degraded into volatile organic compounds (VOCs) and to participate in aroma production. Some such chemicals composed of eight carbons are also envisoned as alternatives to fossil fuels. In fungi, oxylipins have been mostly studied in Aspergilli and shown to be involved in signalling asexual versus sexual development, mycotoxin production and interaction with the host for pathogenic species. Through targeted gene deletions of genes encoding oxylipin-producing enzymes and chemical analysis of oxylipins and volatile organic compounds, we show that in the distantly-related ascomycete Podospora anserina, isoprostanoids are likely produced enzymatically. We show the disappearance in the mutants lacking lipoxygenases and cyclooxygenases of the production of 10-hydroxy-octadecadienoic acid and that of 1-octen-3-ol, a common volatile compound. Importantly, this was correlated with the inability of the mutants to repel nematodes as efficiently as the wild type. Overall, our data show that in this fungus, oxylipins are not involved in signalling development but may rather be used directly or as precursors in the production of odors against potential agressors.

Impact of priming on global soil carbon stocks

Fresh carbon input (above and belowground) contributes to soil carbon sequestration, but also accelerates decomposition of soil organic matter through biological priming mechanisms. Currently, poor understanding precludes the incorporation of these priming mechanisms into the global carbon models used for future projections. Here, we show that priming can be incorporated based on a simple equation calibrated from incubation and verified against independent litter manipulation experiments in the global land surface model, ORCHIDEE. When incorporated into ORCHIDEE, priming improved the model's representation of global soil carbon stocks and decreased soil carbon sequestration by 51% (12 ± 3 Pg C) during the period 1901–2010. Future projections with the same model across the range of CO₂ and climate changes defined by the IPCC‐RCP scenarios reveal that priming buffers the projected changes in soil carbon stocks — both the increases due to enhanced productivity and new input to the soil, and the decreases due to warming‐induced accelerated decomposition. Including priming in Earth system models leads to different projections of soil carbon changes, which are challenging to verify at large spatial scales.     

Proteinase K Processing of Rabbit Muscle Creatine Kinase

Proteinase K cleaves selectively both cytosolic and mitochondrial isoforms of creatine kinase leading to the appearance of two fragments, a large N-terminal one (K1) and a small C-terminal peptide (K2) which remain associated together. The loss of enzymatic activity correlates with the extent of monomer cleavage. N-terminal sequencing of the K2 fragments from rabbit cytosolic and pig mitochondrial creatine kinase shows that these peptides begin with A₃₂₈ and A₃₂₄, respectively. Electrospray ionization mass spectrometry demonstrates that K2 peptide is composed of 53 residues (A₃₂₈–K₃₈₀). However, the C-terminal end of the K1 fragment is not A₃₂₇ as expected, but D₃₂₅. Thus, the amino acids residues T₃₂₆ and A₃₂₇ have been eliminated by the protease.     

New ribosome-inactivating proteins with polynucleotide:adenosine glycosidase and antiviral activities from Basella rubra L. and Bougainvillea spectabilis Willd.

New single-chain (type 1) ribosome-inactivating proteins (RIPs) were isolated from the seeds of Basella rubra L. (two proteins) and from the leaves of Bougainvillea spectabilis Willd. (one protein). These RIPs inhibit protein synthesis both in a cell-free system, with an IC₅₀ (concentration causing 50% inhibition) in the 10⁻¹⁰ M range, and by various cell lines, with IC₅₀s in the 10⁻⁸–10⁻⁶ M range. All three RIPs released adenine not only from rat liver ribosomes but also from Escherichia coli rRNA, polyadenylic acid, herring sperm DNA, and artichoke mottled crinkle virus (AMCV) genomic RNA, thus being polynucleotide:adenosine glycosidases. The proteins from Basella rubra had toxicity to mice similar to that of most type 1 RIPs (Barbieri et al., 1993, Biochim Biophys Acta 1154: 237–282) with an LD₅₀ (concentration that is 50% lethal) ≤ 8 mg · kg⁻¹ body weight, whilst the RIP from Bougainvillea spectabilis had an LD₅₀ >32 mg · kg⁻¹. The N-terminal sequence of the two RIPs from Basella rubra had 80–93% identity, whereas it differed from the sequence of the RIP from Bougainvillea spectabilis. When tested with antibodies against various RIPs, the RIPs from Basella gave some cross-reactivity with sera against dianthin 32, and weak cross-reactivity with momordin I and momorcochin-S, whilst the RIP from Bougainvillea did not cross-react with any antiserum tested. An RIP from Basella rubra and one from Bougainvillea spectabilis were tested for antiviral activity, and both inhibited infection of Nicotiana benthamiana by AMCV. Received: 5 March 1997 / Accepted: 27 May 1997     

Dasycladales from the Upper Maastrichtian of Salento Peninsula (Puglia, southern Italy)

Summary A rich dasycladalean assemblage, mainly consisting of new taxa, has been discovered in upper Maastrichtian coarse bioclastic limestones of shelf margin facies cropping out along the southeastern coast of Salento peninsula (Puglia, Southern Italy). It consists of 8 species grouped into 6 genera:Cymopolia decastroi Parente 1994;C. barattoloi Parente, 1994;Zittelina fluegeli n.sp;Jodotella koradae (Dieni, Massari & Radoicic, 1983) nov. comb.;Barattoloporella salentina n. gen. n. sp.;Morelletpora dienii n. sp.;Neomeris spp. (two different species). Zittelina fluegeli n. sp. is characterized by an ovoid thallus with calcification made by a calcareous wall enveloping only the proximal part of the branches (except in basal whorls) and by closely packed, and partly coalescent, calcified ampullae arranged all around the median and distal portion of branches. The transferral ofNeomeris (Larvaria) koradae Dieni, Massari & Radoicic, 1983 into the genusJodotella, with the new combinationJodotella koradae, is proposed on the basis of new observations on the number and arrangement of fertile ampullae. The new genusBarattoloporella, type-speciesBarattoloporella salentina n. gen. n. sp., is erected for dasycladalean algae characterized by a segmented thallus. Each segment consists of: a) basal and apical sterile whorls made by primary branches only, b) central fertile whorls made by primary branches bearing in terminal position one fertile ampulla and one or two secondary branches. morelletpora dienii n. sp. is characterized by a segmented thallus with barrel shaped to pear shaped repetitive elements, consisting of simple whorls of first order branches only. Shape of the branches varies from regularly phloiophorous to more or less differentiated in a stalk and a swollen portion, with or without a subterminal constriction. This is by far the most diverse dasycladalean assemblage ever found in the Maastrichtian. Its diversity supports the conclusion that, within the Late Cretaceous, the Maastrichtian represents a maximum in dasycladalean diversity. Its taxonomic composition strenghtens the hypothesis that dasycladaleans were hardly affected by K/T mass extinction.