124 research outputs found
The Carnian/Norian boundary interval at Pizzo Mondello (Sicani Mountains, Sicily) and its bearing for the definition of the GSSP of the Norian Stage
No full textWe present the magnetostratigraphy and stable isotope stratigraphy from an expanded (~430-m-thick) Upper Triassic marine limestone section at Pizzo Mondello, Sicily, and review published biostratigraphic information that can be used to defi ne the location of the conodont Carnian-Norian and Norian-Rhaetian boundaries in this section. Pizzo Mondello offers good potential for magneto-stratigraphic correlation of marine biostrati-graphic and chemostratigraphic data with the continental Newark astrochronological polarity time scale (APTS) for development
of an integrated Late Triassic time scale.
The relatively stable average values of δ18O centered on 0‰ are a strong indication that the Cherty Limestone at Pizzo Mondello suffered very little diagenetic overprinting. The conodont Carnian-Norian boundary is located 12.5 m above a positive shift of δ13C. A statistical approach was applied to evaluate various Pizzo Mondello to Newark magnetostratigraphic correlations. Two correlation options have the highest correlation coefficients. In option #1, the base of Pizzo Mondello correlates with the middle part of the Newark APTS, whereas in option #2, the base of Pizzo Mondello starts toward the early part of the Newark APTS. We prefer option #2 in which the Carnian-Norian boundary based on conodonts, as well as its closely associated positive δ13C shift, correspond to Newark magnetozone E7 at ca. 228–227 Ma (adopting Newark astrochronology), implying a long Norian with a duration of ~20 m.y., and a Rhaetian of ~6 m.y. duration. These ages are in fact not inconsistent with the few high-quality radiometric dates that are available for Late Triassic time scale calibration. Based on its good exposure, accessibility, stratigraphic thickness and continuity, and multiple chronostratigraphic correlation possibilities, we propose Pizzo Mondello as global stratigraphic section and point for the base of the Norian
Integrated stratigraphy of the Norian GSSP Candidate Pizzo Mondello Section (Sicani Mountains, Sicily)
No full text
The fossil record from Pizzo Mondello (Sicani Mountains, Sicily) Norian GSSP candidate
No full textPizzo Mondello (Sicani Mountains, western Sicily, Italy) is one of the best localities in the world for the definition of the Carnian/Norian (C/N) boundary. This boundary is recorded within a succession of about 400 m thick Late Carnian-Late Norian “Calcari
con selce”, well known for the good primary magnetostratigraphic record and stable carbon isotope variations (Muttoni et al, 2001, 2004). This succession has become de facto the standard Tethyan marine reference for the Newark astrochronological polarity time scale (Kent et al., 1999; Muttoni et al., 2004) but it is also extremely interesting for the rich fossil record, consisting of ammonoids, conodonts, pelagic bivalves and radiolarians (Balini et al., 2008). Ammonoids are rather sparse but they provided accurate age constraints for the conodont and pelagic bivalve bioevents, that have been identified through very detailed bedby- bed samplings. Some radiolarian bearing levels also provide additional information for correlations.
The collected ammonoid faunas are very similar to the rich faunas described from western Sicily by Gemmellaro in his famous monograph (1904), but the new collection is bed-by-bed sampled. The most important ammonoid taxa so far identified document very well the Upper Carnian Discotropites plinii Zone and the Lower Norian Guembelites jandianus Zone, while in between the faunas are dominated by the group of Anatomites sensu Gemmellaro and by Gonionotites.
Conodont populations are very rich. The large number of specimens recovered in each sample allows statistical analyses of absolute abundances, the analysis of the different morphologies and the study of the relationships among genera and species, that are described in detail in separate contributions (Mazza et al., 2009; Rigo et al. 2009 in the present abstract volume). Currently 29 established conodont species, 5 new species and several transitional forms have been recognized. The classified species belong to 8 genera, among which the five most widespread Upper Carnian/Lower Norian genera have been recognized: Paragondolella,
Carnepigondolella, Metapolygnathus, Epigondolella and Norigondolella. Conodonts are the most abundant and promising fossil group, then possibly the selection of the Norian GSSP marker event will be chosen within this taxon. Two possible bioevents
for the definition of the Carnian/Norian boundary have been identified: the FAD of Epigondolella quadrata Orchard and the FAD of Metapolygnathus communisti Hayashi. The halobiids are undoubtedly the most common megafossil group recorded in the “Calcari con selce”. Some 1100 specimens coming from about 230 beds were collected. Nine halobiid species and two sub-species have been recognized, grouped in seven assemblages spanning from the Upper Carnian to the Lower
Norian. Of special interest is the occurrence in the C/N boundary interval of the sequence of species Halobia areata, H. superba and H. styriaca, which is typical of the Lower Norian in the North American (Stikinoceras kerri Zone; McRoberts, pers. comm., Krystyn et al., 2002) and Thetyan successions (lower to upper G. jandianus Zone; Krystyn and Gallet, 2002). The abundance of halobiids and the great similarity of the faunas from Sicily with
the faunas from North America suggest the possible selection of secondary C/N marker events within this group.
An additional tool for global correlations is represented by radiolarians, which were found in some samples with high diversity
assemblages. In the 30 m-thick boundary interval there is an overlap between species previously considered Late Carnian with species usually regarded as Early Norian. The first Early Norian radiolarian assemblage occurs above the FAD of E. quadrata. This fauna consists of Braginastrum curvatus Tekin, Capnuchosphaera
deweveri Kozur and Mostler, Capnuchosphaera tricornis De Wever, Kahlerosphaera norica Kozur and Mock, Mostlericyrtium sitepesiforme Tekin, Podobursa akayi Tekin and Xiphothecaella longa (Kozur and Mock)
Tax Progression in Imperfect Labour Markets : A Survey
No full textWe look at the effect of tax progression in imperfect labour markets. The models considered are union models, an equilibrium search model with wage bargaining, an equilibrium search model with wage posting by firms and efficiency wage models. We find that in all basic models, an increase in tax progression leads to lower wages and higher employment. Extensions of the models can however change these results.Tax progression; Redistribution; Labour Market Imperfections
The fossil record from Pizzo Mondello (Sicani Mountains, Sicily) Norian GSSP candidate.
No full textInternational Conodont Symposium ICOS 2009, 13-17 July, Calgary (Canada
Asynchronous nuclear division cycles in multinucleated cells
No full textSynchronous mitosis is common in multinucleated cells. We analyzed a unique asynchronous nuclear division cycle in a multinucleated filamentous fungus, Ashbya gossypii. Nuclear pedigree analysis and observation of GFP-labeled spindle pole bodies demonstrated that neighboring nuclei in A. gossypii cells are in different cell cycle stages despite close physical proximity. Neighboring nuclei did not differ significantly in their patterns of cyclin protein localization such that both G1 and mitotic cyclins were present regardless of cell cycle stage, suggesting that the complete destruction of cyclins is not occurring in this system. Indeed, the expression of mitotic cyclin lacking NH(2)-terminal destruction box sequences did not block cell cycle progression. Cells lacking AgSic1p, a predicted cyclin-dependent kinase (CDK) inhibitor, however, showed aberrant multipolar spindles and fragmented nuclei that are indicative of flawed mitoses. We hypothesize that the continuous cytoplasm in these cells promoted the evolution of a nuclear division cycle in which CDK inhibitors primarily control CDK activity rather than oscillating mitotic cyclin proteins
The impact of Union Power on the Optimal Income Tax Schedule
No full textWe explain the positive correlation between union power and tax progressivity from a normative point of view by integrating labour market frictions and union power in an optimal taxation framework. We find that unions and redistributive taxation are complementary in the sense that they both create inefficiencies that weaken each other. We find that strong unions incease welfare and efficiency when the government faces in adverse selection problem when redistributing income.Optimal Income Taxation; Unions; Matching
Limited functional redundancy and oscillation of cyclins in multinucleated Ashbya gossypii fungal cells
No full textCyclin protein behavior has not been systematically investigated in multinucleated cells with asynchronous mitoses. Cyclins are canonical oscillating cell cycle proteins, but it is unclear how fluctuating protein gradients can be established in multinucleated cells where nuclei in different stages of the division cycle share the cytoplasm. Previous work in A. gossypii, a filamentous fungus in which nuclei divide asynchronously in a common cytoplasm, demonstrated that one G1 and one B-type cyclin do not fluctuate in abundance across the division cycle. We have undertaken a comprehensive analysis of all G1 and B-type cyclins in A. gossypii to determine whether any of the cyclins show periodic abundance across the cell cycle and to examine whether cyclins exhibit functional redundancy in such a cellular environment. We localized all G1 and B-type cyclins and notably found that only AgClb5/6p varies in subcellular localization during the division cycle. AgClb5/6p is lost from nuclei at the meta-anaphase transition in a D-box-dependent manner. These data demonstrate that efficient nuclear autonomous protein degradation can occur within multinucleated cells residing in a common cytoplasm. We have shown that three of the five cyclins in A. gossypii are essential genes, indicating that there is minimal functional redundancy in this multinucleated system. In addition, we have identified a cyclin, AgClb3/4p, that is essential only for sporulation. We propose that the cohabitation of different cyclins in nuclei has led to enhanced substrate specificity and limited functional redundancy within classes of cyclins in multinucleated cells
Abstract 1889: Formation and merger of H69 and H69AR small cell lung cancer (SCLC) tumor cell clusters (TCCs) in vitro
No full textAbstract
A novel manifestation of tumor cell invasiveness, termed mutual cellular pervasion (MCP), was observed in vitro. It involved TCCs formed by SCLC cells.
Suspension cultures of H69 and H69AR cells were grown in flavin-free RPMI 1640 medium with 10% fetal bovine serum as the only source of flavins. Experiments and subcultivations were performed under light with wavelengths above 520 nm. TCC morphology was studied by confocal microscopy and transmission and scanning electron microscopy. Interactions of TCCs were followed by video microscopy in phase contrast and fluorescence modes. Data were analyzed using the Definiens software suite. The interaction of H69AR TCCs with confluent monolayers of human umbilical vascular endothelial cells (HUVEC) was visualized.
Freshly subcultivated, singularized tumor cells rapidly formed aggregates. After two days, solid TCCs prevailed whose surface cells were connected by desmosome-like junctions. Apoptosis but not necrosis became obvious in central parts of clusters with diameters above 100 to 150 μm. TCCs enlarged through both cell proliferation and serial cluster mergers. In the course of TCC merger, four stages were distinguishable: (1) directed cluster movement leading to contact of clusters, (2) formation of a near circular, symmetric structure termed contact disc. It consists of planar surface areas to which both TCCs involved contribute equally. (3) Merger of TCCs took place in the contact disc, and was accompanied by active movement of adjacent cells. (4) Starting from the merger zone, major surface areas of newly formed clusters were mutually pervaded by cells from both participating cell clusters. After numerous merger events, only low numbers of TCCs reaching sizes of up to 2 to 3 mm were present at subcultivation.
No spontaneous bursting, shrinkage, degeneration, or decay of TCCs has been observed. However, when TCCs of H69AR cells were confronted with confluent layers of HUVEC, drastic changes occurred in both formations. First, intense oscillatory cellular movements were triggered on TCC surfaces, preceding the release of cell aggregates which moved away from TCCs to the HUVEC layer. At the same time, HUVEC were disconnected from each other and started moving either randomly or in an oscillatory fashion. Individual tumor cells attached to the much larger HUVEC and spread on their surface, resulting in full covering which secluded HUVEC from the medium.
To our knowledge, neither formation nor merger of malignant TCCs in vitro have been described so far. TCC merger involves mutual cellular penetration of the involved TCC surfaces, i. e. MCP. Contrary to the invasion of tumor cells into non-tumor tissue, pervasion does not lead to destruction but results in TCC growth. However, key features of tumor cell invasion in vivo, such as chemotaxis, spreading and TCC formation as well as disruption of endothelial layers, manifest under conditions in vitro, thus facilitating related experimental studies.
Citation Format: Nico O. Ruprecht, Martin Hungerbuehler, Philipp Kellmann, Nathalie Harder, Günter Schmidt, Carlos Wotzkow, Beat Haenni, Fabian Blank, Hendrik Von Tengg-Kobligk, Christof Granzow. Formation and merger of H69 and H69AR small cell lung cancer (SCLC) tumor cell clusters (TCCs) in vitro [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1889. doi:10.1158/1538-7445.AM2017-1889</jats:p
- …
