Plattformbasierte Erwerbsarbeit: Stand der empirischen Forschung

This study summarizes the current state of empirical research in economics and social sciences on contract work mediated or provided by online platforms (online contract work). Based on a systematic literature review, this study discusses results on the diffusion of online platforms, the characteristics of workers as well as the motives for labor supply and the working conditions. The study considers services which can be provided from anywhere via the internet (online labor markets), as well as services which are mediated by online platforms but are provided at a predefined location (mobile labor markets). Besides a summary of existing research findings on the topic, this study also evaluates the quality of the empirical methods. The focus lies on the applied methods for data collection as well as the statistical analyses of the data. As a result, the current state of knowledge on online contract work can be regarded as fragmented. While for the United States several studies already exist on the diffusion of online contract work, there is a paucity of corresponding studies in Europe. A considerably higher number of studies deals with other aspects of online contract work, out of which, however, only a few focus on mobile labor markets. Administrative statistics and largescale representative surveys do not yet contain information on online contract work. Existing research on the topic is therefore based on a variety of data sources and methodological approaches, which makes it difficult to compare empirical findings

Hydrogels Based on Chitosan and Chitosan Derivatives for Biomedical Applications

Chitosan (CS) is a polymer obtained from chitin, being this, after the cellulose, the most abundant polysaccharide. The fact of (i) CS being obtained from renewable sources; (ii) CS to possess capability for doing interactions with different moieties being such capability dependent of pH; (iii) plenty of possibilities for chemical modification of CS; and (iv) tuning the final properties of CS derivatives makes this polymer very interesting in academic and technological points of view. In this way, hydrogels based on CS and on CS derivatives have been widely used for biomedical applications. Other important technological applications can be also cited, such as adsorbent of metals and dyes in wastewater from industrial effluents. In pharmaceutical field, hydrogels based on CS are often used as drugs’ and proteins’ carrier formulations due to the inherent characteristics such as the biocompatibility, nontoxicity, hydrophilicity, etc. This chapter is an attempt for updating and joining the plenty of available information regarding the preparation, characterization, and biomedical application of hydrogels based on chitosan and chitosan derivatives. More than 260 references are provided, being the majority of them published in the last 10 years

Stwl Modifies Chromatin Compaction and Is Required to Maintain DNA Integrity in the Presence of Perturbed DNA Replication

Hydroxyurea, a well-known DNA replication inhibitor, induces cell cycle arrest and intact checkpoint functions are required to survive DNA replication stress induced by this genotoxic agent. Perturbed DNA synthesis also results in elevated levels of DNA damage. It is unclear how organisms prevent accumulation of this type of DNA damage that coincides with hampered DNA synthesis. Here, we report the identification of stonewall ( stwl) as a novel hydroxyurea-hypersensitive mutant. We demonstrate that Stwl is required to prevent accumulation of DNA damage induced by hydroxyurea; yet, Stwl is not involved in S/M checkpoint regulation. We show that Stwl is a heterochromatin-associated protein with transcription-repressing capacities. In stwl mutants, levels of trimethylated H3K27 and H3K9 ( two hallmarks of silent chromatin) are decreased. Our data provide evidence for a Stwl-dependent epigenetic mechanism that is involved in the maintenance of the normal balance between euchromatin and heterochromatin and that is required to prevent accumulation of DNA damage in the presence of DNA replication stress.</p

Grp/DChk1 is required for G(2)-M checkpoint activation in Drosophila S2 cells, whereas Dmnk/DChk2 is dispensable

Cell-cycle checkpoints are signal-transduction pathways required to maintain genomic stability in dividing cells. Previously, it was reported that two kinases essential for checkpoint signalling, Chk1 and Chk2 are structurally conserved. In contrast to yeast, Xenopus and mammals, the Chk1- and Chk2-dependent pathways in Drosophila are not understood in detail. Here, we report the function of these checkpoint kinases, referred to as Grp/DChk1 and Dmnk/DChk2 in Drosophila Schneider's cells, and identify an upstream regulator as well as downstream targets of Grp/DChk1. First, we demonstrate that S2 cells are a suitable model for G(2)/M checkpoint studies. S2 cells display Grp/DChk1-dependent and Dmnk/DChk2-independent cell-cycle-checkpoint activation in response to hydroxyurea and ionizing radiation. S2 cells depleted for Grp/DChk1 using RNA interference enter mitosis in the presence of impaired DNA integrity, resulting in prolonged mitosis and mitotic catastrophe. Grp/DChk1 is phosphorylated in a Mei-41/DATR-dependent manner in response to hydroxyurea and ionizing radiation, indicating that Mei-41/ATR is an upstream component in the Grp/DChk1 DNA replication and DNA-damage-response pathways. The level of Cdc25(Stg) and phosphorylation status of Cdc2 are modulated in a Grp/DChk1-dependent manner in response to hydroxyurea and irradiation, indicating that these cell-cycle regulators are downstream targets of the Grp/DChk1-dependent DNA replication and DNA-damage responses. By contrast, depletion of Dmnk/DChk2 by RNA interference had little effect on checkpoint responses to hydroxyurea and irradiation. We conclude that Grp/DChk1, and not Dmnk/DChk2, is the main effector kinase involved in G2/M checkpoint control in Drosophila cells

Supplementary data for article: Snijder, P. M.; Baratashvili, M.; Grzeschik, N. A.; Leuvenink, H. G. D.; Kuijpers, L.; Huitema, S.; Schaap, O.; Giepmans, B. N. G.; Kuipers, J.; Miljkovic, J. L.; et al. Overexpression of Cystathionine γ-Lyase Suppresses Detrimental Effects of Spinocerebellar Ataxia Type 3. Molecular Medicine 2015, 21, 758–768. https://doi.org/10.2119/molmed.2015.00221

Supplementary material for: [https://doi.org/10.2119/molmed.2015.00221]Related to published version: [http://cherry.chem.bg.ac.rs/handle/123456789/2255