The K2: Open-source simultaneous triple-color TIRF microscope for live-cell and single-molecule imaging

Imaging the dynamics and interactions of biomolecules at the single-molecule level in live cells and reconstituted systems has generated unprecedented knowledge about the biomolecular processes underlying many cellular functions. To achieve the speed and sensitivity needed to detect and follow individual molecules, these experiments typically require custom-built microscopes or custom modifications of commercial systems. The costs of such single-molecule microscopes, their technical complexity and the lack of open-source documentation on how to build custom setups therefore limit the accessibility of single-molecule imaging techniques. To advance the adaptation of dynamic single-molecule imaging by a wider community, we present the "K2": an open-source, simultaneous triple-color total internal reflection fluorescence (TIRF) microscope specifically designed for live-cell and single-molecule imaging. We explain our design considerations and provide step-by-step building instructions, parts list and full CAD models. The modular design of this TIRF microscope allows users to customize it to their scientific and financial needs, or to re-use parts of our design to improve the capabilities of their existing setups without necessarily having to build a full copy of the K2 microscope.

The NEDD8 inhibitor MLN4924 increases the size of the nucleolus and activates p53 through the ribosomal-Mdm2 pathway

The ubiquitin-like molecule NEDD8 is essential for viability, growth and development, and is a potential target for therapeutic intervention. We found that the small molecule inhibitor of NEDDylation, MLN4924, alters the morphology and increases the surface size of the nucleolus in human and germline cells of Caenorhabditis elegans in the absence of nucleolar fragmentation. SILAC proteomics and monitoring of rRNA production, processing and ribosome profiling shows that MLN4924 changes the composition of the nucleolar proteome but does not inhibit RNA Pol I transcription. Further analysis demonstrates that MLN4924 activates the p53 tumour suppressor through the RPL11/RPL5-Mdm2 pathway, with characteristics of nucleolar stress. The study identifies the nucleolus as a target of inhibitors of NEDDylation and provides a mechanism for p53 activation upon NEDD8 inhibition. It also indicates that targeting the nucleolar proteome without affecting nucleolar transcription initiates the required signalling events for the control of cell cycle regulators.

Subnuclear localization of the active variant surface glycoprotein gene expression site in Trypanosoma brucei

In Trypanosoma brucei, transcription by RNA polymerase II and 5' capping of messenger RNA are uncoupled: a capped spliced leader is trans spliced to every RNA. This decoupling makes it possible to have protein-coding gene transcription driven by RNA polymerase I. Indeed, indirect evidence suggests that the genes for the major surface glycoproteins, variant surface glycoproteins (VSGs) in bloodstream-form trypanosomes, are transcribed by RNA polymerase I. In a single trypanosome, only one VSG expression site is maximally transcribed at any one time, and it has been speculated that transcription takes place at a unique site within the nucleus, perhaps in the nucleolus. We tested this by using fluorescence in situ hybridization. With probes that cover about 50 kb of the active 221 expression site, we detected nuclear transcripts of this site in a single fluorescent spot, which did not colocalize with the nucleolus. Analysis of marker gene-tagged active expression site DNA by fluorescent DNA in situ hybridization confirmed the absence of association with the nucleolus. Even an active expression site in which the promoter had been replaced by an rDNA promoter did not colocalize with the nulceolus. As expected, marker genes inserted in the rDNA array predominantly colocalize with the nucleolus, whereas the tubulin gene arrays do not. We conclude that transcription of the active VSG expression site does not take place in the nucleolus.

Reduction of migrainous headaches during the use of acenocoumarol

Disappearance of migraine during the use of warfarin and of phenprocoumon has been described in sporadic case reports. Treatment with heparin has also been associated with a reduction of migranous headaches. Recently, the Netherlands Pharmacovigilance Foundation LAREB received a case report concerning the diminution of migrainous headaches associated with the use of the vitamin K antagonist, acenocoumarol.