Biology subjects

Witte, L.

Publications and source records attributed to Witte, L..

4 recordsLinked to original sources

bioRxiv2026

Integrin-identity shapes and mechanotemporally encodes the fibroblast transcriptome

Fibroblast transcriptomic states reflect physiological and pathological tissue contexts, yet the upstream determinants that stabilize these states remain poorly defined. Integrins mediate extracellular matrix (ECM) adhesion and biochemical signaling, but whether they encode mechanical constraints into stable transcriptomic programs is unclear. Using engineered mouse fibroblasts, bulk and single-cell transcriptomics, and controlled micromechanical confinement, we show that integrins can shape the transcriptomic landscape. The bulk transcriptome of fibroblasts expressing V- and {beta}1-class indicates a shared mechanosensitive baseline, except when these integrin classes are expressed individually. We also found integrin-specific gene clusters, including {beta}1-class integrin-dependent enrichment of Areg, Epha7, Lhpp and Igf2r, which regulate development, regeneration and disease, and altered YAP1 targeted gene expression. At single-cell resolution under confinement, {beta}1-class integrins sustain a progenitor-associated program, whereas their loss or V-class enrichment promotes a constitutively activated state linked to injury repair and wound healing. Mechanical confinement and confinement duration further reshapes these states in an integrin-identity-dependent manner. Our findings establish integrin-identity as a determinant of how fibroblasts transduce mechanotemporal inputs from the cell surface to the nucleus.

Cell Biology↗

bioRxiv2022

Epistasis lowers the genetic barrier to SARS-CoV-2 neutralizing antibody escape

Consecutive waves of SARS-CoV-2 infection have been driven in part by the repeated emergence of variants with mutations that confer resistance to neutralizing antibodies Nevertheless, prolonged or repeated antigen exposure generates diverse memory B-cells that can produce affinity matured receptor binding domain (RBD)-specific antibodies that likely contribute to ongoing protection against severe disease. To determine how SARS-CoV-2 omicron variants might escape these broadly neutralizing antibodies, we subjected chimeric viruses encoding spike proteins from ancestral, BA.1 or BA.2 variants to selection pressure by a collection of 40 broadly neutralizing antibodies from individuals with various SARS-CoV-2 antigen exposures. Notably, pre-existing substitutions in the BA.1 and BA.2 spikes facilitated acquisition of resistance to many broadly neutralizing antibodies. Specifically, selection experiments identified numerous RBD substitutions that did not confer resistance to broadly neutralizing antibodies in the context of the ancestral Wuhan-Hu-1 spike sequence, but did so in the context of BA.1 and BA.2. A subset of these substitutions corresponds to those that have appeared in several BA.2 daughter lineages that have recently emerged, such as BA.5. By including as few as 2 or 3 of these additional changes in the context of BA.5, we generated spike proteins that were resistant to nearly all of the 40 broadly neutralizing antibodies and were poorly neutralized by plasma from most individuals. The emergence of omicron variants has therefore not only allowed SARS-CoV-2 escape from previously elicited neutralizing antibodies but also lowered the genetic barrier to the acquisition of resistance to the subset of antibodies that remained effective against early omicron variants.

microbiology↗

bioRxiv2022

Memory B cell responses to Omicron subvariants after SARS-CoV-2 mRNA breakthrough infection

Individuals that receive a 3rd mRNA vaccine dose show enhanced protection against severe COVID19 but little is known about the impact of breakthrough infections on memory responses. Here, we examine the memory antibodies that develop after a 3rd or 4th antigenic exposure by Delta or Omicron BA.1 infection, respectively. A 3rd exposure to antigen by Delta breakthrough increases the number of memory B cells that produce antibodies with comparable potency and breadth to a 3rd mRNA vaccine dose. A 4th antigenic exposure with Omicron BA.1 infection increased variant specific plasma antibody and memory B cell responses. However, the 4th exposure did not increase the overall frequency of memory B cells or their general potency or breadth compared to a 3rd mRNA vaccine dose. In conclusion, a 3rd antigenic exposure by Delta infection elicits strain-specific memory responses and increases in the overall potency and breadth of the memory B cells. In contrast, the effects of a 4th antigenic exposure with Omicron BA.1 is limited to increased strain specific memory with little effect on the potency or breadth of memory B cell antibodies. The results suggest that the effect of strain-specific boosting on memory B cell compartment may be limited.

immunology↗

bioRxiv2018

Ykt6 membrane-to-cytosol cycling regulates exosomal Wnt secretion

Protein trafficking in the secretory pathway, for example the secretion of Wnt proteins, requires tight regulation. These ligands activate Wnt signaling pathways and are crucially involved in development and disease. Wnt is transported to the plasma membrane by its cargo receptor Evi, where Wnt/Evi complexes are endocytosed and sorted onto exosomes for long-range secretion. However, the trafficking steps within the endosomal compartment are not fully understood. The promiscuous SNARE Ykt6 folds into an auto-inhibiting conformation in the cytosol, but a portion associates with membranes by its farnesylated and palmitoylated C-terminus. Here, we demonstrate that membrane detachment of Ykt6 is essential for exosomal Wnt secretion. We identified conserved phosphorylation sites within the SNARE domain of Ykt6, which block Ykt6 cycling from the membrane to the cytosol. In Drosophila, Ykt6 RNAi-mediated block of Wg secretion is rescued by wildtype but not phosphomimicking Ykt6. We show that phosphomimicking Ykt6 accumulates at membranes, while wildtype Ykt6 regulates Wnt trafficking between the plasma membrane and multivesicular bodies in a dose-dependent manner. Taken together, we show that exosomal sorting of Wnts is fine-tuned by a regulatory switch in Ykt6 shifting it from a membrane-bound to cytosolic state at the level of endosomal maturation.

cell biology↗