Professor Ueli Aebi passed away at the age of 79 on November 28, 2025. Born on May 31, 1946, in Bern, Switzerland, he was a longstanding member and Fellow of the ASCB. Ueli studied physics, mathematics, and molecular biology at the University of Bern and received his PhD in biophysics and structural biology at the University of Basel in 1977 in the laboratory of Eduard Kellenberger. There, he pioneered the use of antigen display to produce specific antibodies against bacteriophage coat proteins and developed electron microscopy methods to analyze their structural organization.

After completing his PhD in 1977, Ueli moved to the U.S. with his wife Janine and three young children. Following a brief postdoctoral stay with David Eisenberg at UCLA, he joined Johns Hopkins University in 1978 as a faculty member in Tom Pollard’s Department of Cell Biology and Anatomy. During his time at Hopkins, he developed a technique to assemble actin sheets, enabling high resolution insights into F-actin structure. He also initiated studies on the structure of both cytoskeletal intermediate filament proteins and nuclear lamins. In collaboration with Larry Gerace he published a landmark Nature paper titled “The nuclear lamina is a meshwork of intermediate-type filaments”. This work helped to define nuclear architecture and nuclear envelope biology, and it underpins the mechanobiology of the cell nucleus.

In 1986 Ueli returned to Switzerland as Professor of Structural Biology at the Biozentrum, University of Basel. Together with Andreas Engel, he co-founded the Maurice E. Müller Institute for Structural Biology which he directed until 2011. During his time at the Müller Institute he championed the use of quantitative scanning transmission electron microscopy (STEM) for direct mass measurements and atomic force microscopy (AFM) to probe the structure and function of biological nanomachines. His credo, “simplicity is the key to success”, profoundly shaped the institute’s scientific culture, establishing it as an internationally renowned center for structural biology. Ueli also played a key role in the Swiss Nanoscience Institute and the National Centre of Competence in Research (NCCR) Nanoscale Science, where he fostered close links between structural biology, nanoscience and medicine. Moreover, from 2004 until 2008 Ueli served as the President of the European Microscopic Society (EMS).

Throughout his career in Basel, Ueli worked closely with Harald Herrmann to elucidate IF structure and assembly. They identified unit-length filaments (ULF) as the rate-limiting structures in intermediate filament (IF) assembly. This led his group to adopt a “divide and conquer” approach to determine the structure of highly conserved coiled coil regions of IFs, a hallmark of all members of the IF superfamily of proteins. This led to an atomic model of the vimentin tetramer, the minimal structural and functional unit of IFs. His group was also among the first to demonstrate the remarkable mechanical properties of IFs using AFM.

Ueli’s other seminal contributions included studies of the nuclear pore complex (NPC), the gatekeepers of the cell nucleus. His group performed the first direct mass measurements of native NPCs using STEM and generated the first tomographic reconstructions of the complex, which helped define the NPC’s canonical organization. They further mapped nucleoporins within the NPC by immuno-EM and showed by AFM that intrinsically disordered FG-repeat nucleoporins exhibit polymer brush-like behavior, providing key insights into how NPCs mediate nucleocytoplasmic transport.

Beyond fundamental cell biology, Ueli advanced AFM into a biomedical tool to probe tissue mechanics at nanoscale, from detecting disease-related changes in cartilage to identifying nanomechanical signatures that distinguish healthy, benign, and malignant breast tissue. For him, such work embodied the principle that fundamental insights should translate into clinical impact.

Over four decades, Ueli was an inspiring mentor, trusted collaborator, and a most generous colleague. He will be remembered by many and missed by all who knew him. When not doing science, Ueli always felt at home in the Swiss alps where he and his wife Janine and his children Corinne, Monique and Roman all enjoyed hiking, mountain climbing, and skiing.