Ornithologisches aus Norwegen

Ohne Zusammenfassung     

Structural and functional insights into the fly microRNA biogenesis factor Loquacious

In the microRNA (miRNA) pathway, Dicer processes precursors to mature miRNAs. For efficient processing, double-stranded RNA-binding proteins support Dicer proteins. In flies, Loquacious (Loqs) interacts with Dicer1 (dmDcr1) to facilitate miRNA processing. Here, we have solved the structure of the third double-stranded RNA-binding domain (dsRBD) of Loqs and define specific structural elements that interact with dmDcr1. In addition, we show that the linker preceding dsRBD3 contributes significantly to dmDcr1 binding. Furthermore, our structural work demonstrates that the third dsRBD of Loqs forms homodimers. Mutations in the dimerization interface abrogate dmDcr1 interaction. Loqs, however, binds to dmDcr1 as a monomer using the identified dimerization surface, which suggests that Loqs might form dimers under conditions where dmDcr1 is absent or not accessible. Since critical sequence elements are conserved, we suggest that dimerization might be a general feature of dsRBD proteins in gene silencing.     

Mother rotor anchoring in branching tissue with heterogeneous membrane properties.

Abstract Current understanding of atrial fibrillation is based on the co-existence of multiple re-entrant waves propagating randomly throughout the tissue. However, recent experimental results indicate that in many cases one or a small number of periodic, high-frequency re-entrant sources (mother rotors) can drive the arrhythmia. Owing to the high activation rate, mother rotors seem to be located in regions of shortened action potential duration. In this study a computer model of cardiac propagation was applied to investigate mechanisms leading to the formation and maintenance of such mother rotors. For this purpose, a region of short action potential duration was generated by varying the acetylcholine concentration across the tissue. A mother rotor initiated in the center of this region drifts away, and the activation terminates. If an additional heterogeneity such as a bundle is included into the model, a further drift mechanism directed to the bundle is observed and the rotor can be stabilized. Therefore, bundle insertions may play an important role in the maintenance of mother rotors. The influence of the driving rotor on the activation pattern was studied in a three-dimensional model of rectangular shape and a monolayer model of anatomically correct atrial geometry.