Köhler

Adaptors at the Nuclear Pore

The function of NPCs in nucleocytoplasmic transport is well studied. However, NPCs carry out additional, unconventional duties. In particular, they impact on chromatin architecture and gene activity by physically interacting with the genome.

A key question is how NPCs ‘communicate’ with the gene expression machinery. We recently discovered that the NPC basket employs dedicated Adaptors such as TREX-2 and Mediator to regulate RNA Polymerase II (Schneider et al., Cell 2015). These findings are stepping stones for further mechanistic analyses on how NPCs participate in decoding the genome.

Ubiquitin Signaling on Chromatin

Related to our interest in gene expression, we are studying the modification of chromatin by ubiquitin. When appended to histones, ubiquitin functions as an important epigenetic switch to regulate multiple steps of transcription. Histone H2B monoubiquitination is mediated by the E2 and E3 enzymes Rad6 and Bre1 (Gallego et al., PNAS 2016). Their activity is counteracted by a deubiquitinase of the SAGA complex (Köhler et al., Cell 2010). We are dissecting the structure and function of this intricate molecular machinery to understand its biology in health and disease.

Shaping the Nuclear Membrane

The nuclear envelope encloses and protects the genome. NPCs need to promote the controlled exchange of molecules between nucleus and cytoplasm without disrupting this membrane barrier. Thus, the assembly and insertion of new NPCs is tightly controlled. NPCs are embedded in holes formed by the fusion of the outer and inner nuclear membranes. We have discovered a new function for the NPC basket in remodelling the nuclear membrane to promote NPC and nuclear envelope integrity (Mészáros et al., Dev Cell, 2015). Future studies aim at understanding how various NPC proteins cooperate to sculpt their membrane environment.

We use biochemical, structural, genome-wide and cell biological methods to address these questions. Functional reconstitution is central to our approach, as the ability to reconstruct systems from scratch offers key insights into what is minimally needed and how mechanisms emerge from component parts.

Decrypting Cryptobiosis in Tardigrades

Tardigrades (also known as water bears or moss piglets) are one of the most resilient and fascinating animals known: they withstand conditions that would fatal to nearly all other life forms on earth. This includes temperatures from close to absolute zero to about 150°C, pressures six times greater than those found in the deepest ocean trenches, ionizing radiation at doses lethal for a human, and even the vacuum of outer space. Tardigrades can go without food or water for decades, only to rehydrate, forage, and reproduce. They survive this by falling into an enigmatic state called cryptobiosis (hidden life), in which they are neither dead nor alive.

We have recently started to investigate selected aspects of Tardigrade biology with the generous support of the Swiss NOMIS Foundation (http://nomisfoundation.ch). Our aim is to unravel the molecular secrets behind their outstanding robustness, specifically, how nuclear architecture and function is preserved under extreme conditions.