Cells must regulate their volume in response to changes in osmolarity and during cell division, migration, apoptosis, and transepithelial transport. Regulated membrane transport of ions and metabolites creates osmotic gradients that secondarily drive water across the membrane. Organic ‘osmolytes’ such as glutamate also serve in extracellular signalling and volume-regulatory ion transporters are often used for other purposes, putting volume regulation into the context of diverse organismal functions. Research on cell volume regulation stagnated because the identity of a key player, the Volume-Regulated Anion Channel VRAC, remained unknown. Very recently we identified LRRC8 heteromers as VRAC components and discovered that VRACs are a heterogeneous group of channels. Their remarkable ability to transport not only Cl-, but also signalling molecules or drugs, depends on their LRRC8 subunit composition. This breakthrough now allows us to search for functionally relevant interactors and to dissect the physiological roles of different VRACs using mouse models. Whereas disruption of Lrrc8a abolishes VRAC function, abrogating other Lrrc8 genes (in total five) will change its transport properties. Conditional KO mice will first focus on epithelia which faces large osmolarity changes, on the brain where VRAC-released signalling molecules are supposed to play important roles in physiology and pathology, and on VRAC’s assumed role in vesicle exocytosis. We expect to discover many surprising novel roles of VRACs. Emboldened by our identification of VRAC, we will use genome-wide siRNA screens to identify two other ‘missing’ ion channels, which have been known physiologically for many years and may have widespread roles in signalling and other physiological processes. Once identified, these channels will be studied at a structural, cellular and organismal level. These projects will break new ground in physiology, cell biology, signalling and pathology.

Brain function crucially depends on chemical neurotransmission at synapses, while, conversely, synaptic dysfunction underlies neurological and psychiatric disorders. Synapses are composed of more than 2,000 distinct proteins, spatially organized into specialized molecular machineries. During decades of efforts, researchers have acquired a wealth of knowledge on individual key components of the synapse. However, the overall picture of the spatial arrangement, molecular architecture and interaction network of the synaptic proteome remains largely uncharted. Furthermore, innovative methods that allow system-wide profiling of these organizational aspects of synaptic proteins are in great demand. I propose to develop a highly sensitive cross-linking mass spectrometry (XL-MS) pipeline to analyze structural and organizational features of the synaptic proteome at an unprecedented depth and comprehensiveness. In parallel, I also plan to establish quantitative XL-MS strategies to reveal global network rearrangements and complex-specific alterations during long-term potentiation, which arguably is the most attractive cellular model for learning and memory. Importantly, it is foreseeable that numerous novel insights can be discovered, for which I will use complementary approaches and tools, such as biochemistry, super-resolution imaging, structural modelling and network analysis to validate and interrogate their molecular details and network principles. These studies will yield groundbreaking insights into the molecular architecture of the synapse and thereby fill a crucial knowledge gap in neuroscience. Furthermore, they will provide a framework to gain a deeper understanding of the dynamic regulation in synaptic plasticity and synaptic dysfunction in neurological disorders.

Laser sources that can operate in the mid-infrared are increasingly used in applications spanning laser precision surgery to the remote detection of chemicals. Currently, we are experiencing a humanitarian crisis, with the illegal transport of suffering refugees affecting every European country. This project aims to develop a compact and efficient laser source that could potentially help the safe passage of refugees by remotely detecting carbon dioxide that is present when humans breathe. During the course of this project, new laser materials based on erbium-doped sesquioxides will be grown and fully characterised, and developed into highly efficient laser sources. In order to increase the efficiency of erbium-doped lasers operating near 3 µm, these lasers will be made to also emit radiation near 1.6 µm, creating a so-called cascade laser. By using this scheme, the 3 µm transition can be made more efficient since emission of 1.6 µm radiation depopulates its lower laser level, and this scheme further reduces limiting thermal effects, since the 1.6 µm radiation would normally cause heating effects in the laser crystal. This erbium cascade laser will generate 3 µm radiation with more than double the output power that has been previously demonstrated, paving the way for enhanced application-driven experiments. These will be investigated by Q-switching the two-colour laser, and further using this output to generate radiation near 4 µm by means of optical parametric amplification. This now three-colour laser output increases the applicability of such a laser source, allowing for the detection of a larger range of chemical species, but also accurate detection of specific chemicals by measuring the differential absorption of, for example, carbon dioxide at each wavelength. As such, a crude proof-of-concept experiment will be carried out to determine the carbon dioxide concentration in a laboratory environment, by measuring the differential absorption of cabon dioxide at each of the three wavelengths.