Network of protein interactions within the Drosophila inner kinetochore

The kinetochore provides a physical connection between microtubules and the centromeric regions of chromosomes that is critical for their equitable segregation. The trimeric Mis12 sub-complex of the Drosophila kinetochore binds to the mitotic centromere using CENP-C as a platform. However, knowledge of the precise connections between Mis12 complex components and CENP-C has remained elusive despite the fundamental importance of this part of the cell division machinery. Here, we employ hydrogen–deuterium exchange coupled with mass spectrometry to reveal that Mis12 and Nnf1 form a dimer maintained by interacting coiled-coil (CC) domains within the carboxy-terminal parts of both proteins. Adjacent to these interacting CCs is a carboxy-terminal domain that also interacts with Nsl1. The amino-terminal parts of Mis12 and Nnf1 form a CENP-C-binding surface, which docks the complex and thus the entire kinetochore to mitotic centromeres. Mutational analysis confirms these precise interactions are critical for both structure and function of the complex. Thus, we conclude the organization of the Mis12–Nnf1 dimer confers upon the Mis12 complex a bipolar, elongated structure that is critical for kinetochore function.     

Molecular organization of 2-(2,4-dihydroxylphenyl)-5,6-dichlor 1,3-benzothiazole in monomolecular layers formed with diphytanoylphosphatidylcholine: A linear dichroism-FTIR study

2-(2,4-Dihydroxylphenyl)-5,6-dichlor 1,3-benzothiazole (dHBBT) has very strong antifungal and antitumoral properties in relation to human cancer cells. The aim of this research was to analyze the binding process of dHBBT molecules to the lipid membrane formed from DPhPC at the air-water interface. The effect of dHBBT on the organization of lipid membranes formed with diphytanoylphosphatidylcholine (DPhPC) was studied with the application of monomolecular layer technique, FTIR spectroscopy and linear dichroism-FTIR. On the basis of linear dichroism experiments the mean orientation angle θ between the molecular axis and the normal to monolayer surface was determined. Mean value was calculated at θ = 72° and indicates a horizontal orientation of dHBBT molecules in the lipid membrane formed from DPhPC. dHBBT molecules have considerable influence on the orientation of DPhPC acyl chains. The mean value of the angle between normal to monolayer surface and the main axis of the acyl chain is approximately 45° for DPhPC, while for the lipid monolayer containing dHBBT it is approximately 18°. Such extreme changes in orientation of acyl chains indicate a clear influence of the relationship on the dynamic and structural properties of the monolayer formed from DPhPC. Biological activity of dHBBT molecules is tightly associated with its molecular organization. The results of the research presented in this work are potentially valuable in respect of the development of pharmacologically active preparations of dHBBT.     

Malaria infection status predicts extra‐pair paternity in the blue tit

Extra‐pair matings comprise a common reproductive strategy among socially monogamous bird species. However, it remains unclear why females decide to mate with extra‐pair males. Indirect benefits in terms of improving offspring genetic quality are usually invoked to explain this phenomenon. Parasite resistance genes are often considered as a female target of seeking extra‐pair matings, but the direct test of this hypothesis is generally lacking. Here, we report on a relationship between the status of infection with malaria parasites (Plasmodium and Haemoproteus) and occurrence of extra‐pair paternity in a wild population of the blue tit Cyanistes caeruleus inhabiting Gotland (Sweden). We found that the probability of extra‐pair paternity is significantly related to the infection status of social parents. Infected males showed higher probability of being cuckolded than uninfected ones. However, this was observed only among males mated to uninfected females. Thus, avian malaria may potentially contribute to explanation of extra‐pair mating behaviour.     

Deviating the level of proliferating cell nuclear antigen in Trypanosoma brucei elicits distinct mechanisms for inhibiting proliferation and cell cycle progression

The DNA replication machinery is spatially and temporally coordinated in all cells to reproduce a single exact copy of the genome per division, but its regulation in the protozoan parasite Trypanosoma brucei is not well characterized. We characterized the effects of altering the levels of proliferating cell nuclear antigen, a key component of the DNA replication machinery, in bloodstream form T. brucei. This study demonstrated that tight regulation of TbPCNA levels was critical for normal proliferation and DNA replication in the parasite. Depleting TbPCNA mRNA reduced proliferation, severely diminished DNA replication, arrested the synthesis of new DNA and caused the parasites to accumulated in G2/M. Attenuating the parasite by downregulating TbPCNA caused it to become hypersensitive to hydroxyurea. Overexpressing TbPCNA in T. brucei arrested proliferation, inhibited DNA replication and prevented the parasite from exiting G2/M. These results indicate that distinct mechanisms of cell cycle arrest are associated with upregulating or downregulating TbPCNA. The findings of this study validate deregulating intra-parasite levels of TbPCNA as a potential strategy for therapeutically exploiting this target in bloodstream form T. brucei.