Publikationen

The thymus is the primary site of T cell development, central to the establishment of self-tolerance and adaptive immune function. In mammals, the thymus undergoes age-related involution, resulting in a global decline in immune function. The thymus has some regenerative ability that relies on pre-existing thymic remnants but is insufficient to prevent involution. Here, we show that the juvenile axolotl (Ambystoma mexicanum) is able to regenerate its thymus de novo after complete removal, constituting an exception among vertebrates. Using single-cell transcriptomics and genetic and transplantation approaches, we demonstrate that de novo thymus regeneration results in the restoration of morphology, cell-type diversity, and function. FOXN1, although it has a conserved role in thymus organogenesis, is dispensable for the initiation of thymic regeneration. In contrast, we identify midkine signaling as a possible early driver of de novo thymus regeneration. This study demonstrates an instance of organ-level regeneration of the lymphoid system, which could guide future clinical strategies seeking to promote thymus regrowth.

The trophectoderm (TE), the first lineage specified during mammalian development, initiates implantation and gives rise to placental trophoblasts. While animal models have elucidated key conserved signaling pathways involved in early TE specification, including bone morphogenetic protein (BMP), WNT, and HIPPO, species-specific differences during early development emphasize the need for human-specific models. We previously identified VGLL1, a coactivator of TEAD transcription factors, as a human-specific placental marker. In this study, we employed a pluripotent stem cell (PSC)-based model of TE induction by BMP4 to investigate chromatin remodeling and transcriptional dynamics during TE formation. BMP4-induced chromatin accessibility changes promoted a trophoblast gene expression program, while mesoderm lineage markers were only transiently expressed upon canonical WNT activation. We found that VGLL1 was expressed downstream of key TE transcription factors (GATA2/3, TFAP2A/C) but was essential for establishment of full trophoblast identity by up-regulating the epidermal growth factor receptor (EGFR) and reinforcing GATA3 expression through positive feedback. Notably, VGLL1 enhanced canonical WNT signaling via direct regulation of WNT receptors and effectors. We also identified KDM6B, a histone demethylase that removes H3K27me3 repressive marks, as a direct VGLL1 target. KDM6B facilitated activation of bivalent promoters associated with TE markers, linking epigenetic regulation to lineage identity. Our findings establish a mechanistic framework positioning VGLL1 as a central regulator that integrates HIPPO, BMP, and WNT signaling pathways to drive establishment of human TE.

Biomolecular condensates have been implicated in key cellular processes such as gene regulation, stress response, and signaling, and dysregulation of condensates has been linked to neurodegeneration and other diseases. Computational algorithms that predict protein condensation can aid systematic characterization of biomolecular condensates at the proteome scale. However, many experimental labs may lack the computational background or resources to run sophisticated prediction tools locally.

Many subcellular compartments are biomolecular condensates made of multiple components, often including several distinct proteins and nucleic acids. However, current tools to measure condensate composition are limited and cannot capture this complexity quantitatively because they either require fluorescent labels, which can perturb composition, or can distinguish only one or two components. Here we describe a label-free method based on quantitative phase imaging and analysis of tie-lines and refractive index to measure the composition of reconstituted condensates with multiple components. We first validate the method empirically in binary mixtures, revealing sequence-encoded density variation and complex ageing dynamics for condensates composed of full-length proteins. We then use analysis of tie-lines and refractive index to simultaneously resolve the concentrations of five macromolecular solutes in multicomponent condensates containing RNA and constructs of multiple RNA-binding proteins. Our measurements reveal an unexpected decoupling of density and composition, highlighting the need to determine molecular stoichiometry in multicomponent condensates. We foresee this approach enabling the study of compositional regulation of condensate properties and function.

Mammalian brain development involves coordinated progenitor amplification, migration, and differentiation. Apical progenitors (APs) establish the ventricular zone (VZ) and are key determinants of brain size and complexity. Rho-family guanosine triphosphatases (Rho-GTPases) regulate cytoskeletal dynamics and AP behavior, but how specific Rho GTPase-activating proteins (Rho-GAPs) influence progenitor identity and VZ architecture remains unclear. Using human forebrain organoids, we investigate the function of the Rho GAP ARHGAP11A in human corticogenesis. CRISPR-Cas9-mediated ARHGAP11A knockout reveals its essential role in maintaining VZ integrity. Loss of ARHGAP11A impairs neuroepithelial organization and randomizes mitotic cleavage-plane orientation via the RHOA-ROCK-actin axis. This leads to premature AP delamination, AP depletion, and reduced cell density and glial numbers. Pharmacological inhibition of RHOA or ROCK rescues these defects, highlighting ARHGAP11A's role in cytoskeletal remodeling to maintain cortical progenitors. Our findings establish ARHGAP11A as a critical regulator of AP identity and VZ integrity, with broad implications for human corticogenesis.

Ether glycerophospholipids bear a long chain alcohol attached via an alkyl or vinyl ether bond at the sn1 position of the glycerol backbone. Ether lipids play a significant role in physiology and human health. However, their cellular functions remain largely unknown due to a lack of tools for identifying their subcellular localization and interacting proteins. Here, we address this methodological gap by synthesizing minimally modified bifunctional ether lipid probes by introducing diazirine and alkyne groups. To interrogate the subcellular kinetics of intracellular ether lipid transport in mammalian cells, we used a combination of fluorescence imaging, machine learning-assisted image analysis, and mathematical modelling. We find that alkyl-linked ether lipids are transported up to twofold faster than vinyl-linked species (plasmalogens), pointing to yet undiscovered cellular lipid transport machinery able to distinguish between linkage types differing by as little as two hydrogen atoms. We find that ether lipid transport predominantly occurs via non-vesicular pathways, with varying contributions from vesicular mechanisms between cell types. Altogether, our results suggest that differential recognition of alkyl- and vinyl ether lipids by lipid transfer proteins contributes to their distinct biological functions. In the future, the probes reported here will enable studying ether lipid biology in much greater detail through identification of interacting proteins and in-depth characterization of intracellular ether lipid dynamics.

CD-CODE 2.0 (https://cd-code.org) is an enhanced web application and database of condensates, expanding the utility of version 1.0 for biomedical research. New features include data on nucleic acids condensate components, infectious condensates, condensate modulating drugs, and disease-linked condensates. Enhanced search functions, programmatic access, and relational architecture enable interconnectivity across major biomedical databases (e.g. condensates, proteins, chemistry, and disease), fostering systems-level insights and accelerating hypothesis generation and therapeutic discovery through the lens of condensate biology.

Accurate assignment of whole-genome sequences to clusters in foodborne outbreak investigations remains challenging. Variability in bioinformatics tools and quality metrics significantly impacts clustering outcomes. This study assessed inter-laboratory variance in cluster identification by providing four datasets of 50 raw Illumina paired-end sequences covering Shiga toxin-producing Escherichia coli, Listeria monocytogenes, Salmonella enterica, and Campylobacter jejuni. Following general rules of a specified guideline, participants applied in-house protocols for read quality assessment, 7-gene MLST, cgMLST, and SNP calling, then assigned samples to predefined focus clusters based on allele distance (AD) and mutations. Results revealed that differences in the interpretation of raw sequence and genome assembly quality influenced sample inclusion and finally cluster composition. Here, intra-species contamination was the most significant factor driving variability in decisions on whether to include or exclude samples. With one exception, 7-gene Multilocus-Sequence Typing (MLST) yielded consistent sequence types using different bioinformatics tools. The largest influence on cgMLST-defined clusters was the inclusion or exclusion of samples. Regarding bioinformatics, cgMLST was mainly reproducible. For S. enterica, discrepancies due to different software (Ridom SeqSphere+ vs. ChewieSnake) were larger than discrepancies due to different schemas. For other species, different schemas introduced larger discrepancies than different software. Most notably, C. jejuni cluster assignment was strongly affected by cgMLST schemas differing by a factor of two in the number of loci. SNP calling using Snippy produced concordant results across participants, except for C. jejuni when recombination filtering was used. This study highlights the impact caused by different interpretations of quality values when assessing clusters. Low-resolution cgMLST schemas were unsuitable for Campylobacter jejuni, and clustering near cut-off values was sensitive to bioinformatics tool selection. Standardized protocols are essential for reliable inter-laboratory comparison in foodborne pathogen surveillance.