Biology subjects

Zbinden, A.

Publications and source records attributed to Zbinden, A..

4 recordsLinked to original sources

bioRxiv2026

A qualitative and quantitative framework for the characterization of protein-RNA interactions by cross-linking mass spectrometry (XL-MS)

Protein-RNA interactions regulate nearly all levels of gene expression. Their characterization at the molecular basis is critical for understanding the function of protein-RNA complexes, both in cell homeostasis and pathology. Yet, molecular interactions underlying the formation of these complexes remain understudied. UV cross-linking mass spectrometry (XL-MS) is one of the leading approaches for in vitro identification of protein-RNA contact sites, and for providing structural information in the form of distance constraints crucial for the refinement of structural models. Our previously published CLIR-MS method enables qualitative characterization of protein-RNA interactions at residue-specific resolution but was not designed for highly accurate quantitative interpretation. Here, we present a XL-MS workflow based on irradiation with UV light that combines data-dependent acquisition (DDA) and parallel reaction monitoring (PRM) for simultaneous detection and characterization of protein-RNA interaction sites at residue-specific resolution, followed by label-free quantification of cross-linked products. We successfully apply our combined workflow to in vitro reconstituted protein-RNA complexes formed by the proteins TDP-43 and FOX1. We report on novel RNA interaction sites located in the oligomerization interface of the N-terminal domain (NTD) of TDP-43, and characterize quantitatively the process of RNA-induced monomerization of the NTD in an RNA titration experiment. We also investigate temperature-dependent differences in the efficiency of cross-link formation in the FOX1 complex. Our framework offers a unique and novel approach to comparative quantification of protein-RNA cross-links, overcoming the limitations imposed by conventional UV XL-MS methods.

biophysics↗

bioRxiv2026

Monomeric TDP-43 binds GU-rich RNA via its NTD but only its oligomers block cryptic exon inclusion

TDP-43 aggregation is a pathological feature of several neurodegenerative diseases, resulting in nuclear loss of function and RNA dysregulation, including cryptic exon derepression. TDP-43 comprises two RNA recognition motifs required for canonical RNA binding, a low-complexity domain implicated in phase separation, and an N-terminal domain (NTD) that mediates oligomerization. While NTD-driven oligomerization is critical for TDP-43 splicing function, some studies suggest a direct interaction of NTD with RNA. Here, we investigated RNA binding by the NTD and its functional interplay with oligomerization. We show that the NTD preferentially binds UG-rich RNA via residues located at the oligomerization interface. The NTD engaged RNA only on monomeric TDP-43, as RNA binding and oligomerization compete for the same interface and rely on similar interaction modes. By disentangling these competing activities, we demonstrated that oligomerization, but not NTD-RNA interaction, is essential for TDP-43-dependent alternative splicing and repression of cryptic exons. Our findings uncover a previously unappreciated RNA-binding activity within the TDP-43 NTD that directly competes with oligomerization and establish oligomerization as a key determinant of TDP-43 cryptic exon repression.

molecular biology↗

bioRxiv2026

Multi-omic profiling of human thymic B cells reveals intrathymic Ig-class switching and differentiation into multiple memory B cell subsets

Primarily recognized as the site for T cell development, the thymus supports a complex interplay between thymic stromal cells and developing thymocytes, which is essential for T cell maturation and the establishment of central tolerance. Emerging evidence indicates that thymic B cells contribute to tolerance induction by functioning as antigen-presenting cells. However, their developmental pathways and functional roles remain poorly understood. Using tissue mass cytometry, we localized B cells in the thymus and their orientation towards other cells in the medulla. We characterized the heterogeneity of thymic B cells using single-cell RNA sequencing of cells isolated from human thymi, identifying naive, germinal center-like, plasma cell, and multiple memory B cell populations. We identified a distinct pre-B cell subset with local thymic B cell development potential, that can develop due to the inhibition of Notch signaling by Deltex1, a Notch antagonist. Using BCR repertoire analysis, we explored clonal diversity, somatic hypermutation patterns and class switch recombination of thymic B cells. Spectral flow cytometry further validated the surface phenotype of thymic B cell populations and confirmed the presence of distinct CD21-CD27- memory compartments with heterogeneous surface immunoglobulin isotype usage. In doing so we provide novel insights into the unique biology of human thymic B cells, their development, and their differentiation in the human thymus. We conclude that the human thymus supports local B cell development and differentiation into medullary memory-like populations that undergo class switching with limited somatic hypermutation, suggesting secondary lymphoid-like B cell programs adapted to central tolerance induction. One Sentence SummaryThe human thymus is not only a primary lymphoid organ for T cell development, but also a secondary site for the development and maturation of unique populations of B cells.

immunology↗

bioRxiv2022

TDP-43 oligomerization and RNA binding are codependent but their loss elicits distinct pathologies

Aggregation of the RNA-binding protein TDP-43 is the main common neuropathological feature of TDP-43 proteinopathies. In physiological conditions, TDP-43 is predominantly nuclear and contained in biomolecular condensates formed via liquid-liquid phase separation (LLPS). However, in disease, TDP-43 is depleted from these compartments and forms cytoplasmic or, sometimes, intranuclear inclusions. How TDP-43 transitions from physiological to pathological states remains poorly understood. Here, we show that self-oligomerization and RNA binding cooperatively govern TDP-43 stability, functionality, LLPS and cellular localization. Importantly, our data reveal that TDP-43 oligomerization is connected to, and conformationally modulated by, RNA binding. Mimicking the impaired proteasomal activity observed in patients, we found that TDP-43 forms nuclear aggregates via LLPS and cytoplasmic aggregates via aggresome formation. The favored aggregation pathway depended on the TDP-43 state -monomeric/oligomeric, RNA-bound/-unbound- and the subcellular environment -nucleus/cytoplasm. Our work unravels the origins of heterogeneous pathological species occurring in TDP-43 proteinopathies.

cell biology↗