Biology subjects

Langschied, F.

Publications and source records attributed to Langschied, F..

4 recordsLinked to original sources

bioRxiv2026

Cell-envelope conduits enable transfer of megabase-sized double-stranded DNA between cells of the nosocomial pathogen Acinetobacter baumannii

Horizontal gene transfer in Acinetobacter baumannii has been attributed to conjugative pili, transduction, and natural transformation. Here, we describe a previously unrecognized type of chromosomal DNA exchange mediated by cell-envelope conduits that establish direct cytoplasmic continuity between neighboring A. baumannii cells. Cryo-electron tomography reveals that these conduits, which were found in multiple clinical isolates, comprise an outer membrane, a peptidoglycan layer, and an inner membrane. The ~65 nm-thick conduits contain two ~2 nm-thick filaments, which super-resolution microscopy identifies as DNA. Interstrain horizontal gene transfer assays coupled with whole-genome sequencing demonstrate the transfer and homologous recombination of chromosomal segments up to 1.1 Mbp, corresponding to as much as 27% of the A. baumannii genome. Together, these findings provide direct structural and functional evidence for a conduit-mediated large-scale chromosomal DNA exchange, thus expanding the known repertoire of horizontal gene transfer strategies that may contribute to the remarkable genomic plasticity of A. baumannii.

microbiology↗

bioRxiv2024

Concerted loss of micro-RNAs uncovers multi-level restructuring of gene regulation in rodents

BackgroundThe regulatory network that coordinates gene expression ultimately determines the phenotype of an organism. Micro-RNAs (miRNAs) are post-transcriptional regulators involved in key biological processes. Lineage-specific losses of multiple miRNA families are rare, and reported cases of multiple miRNA losses coincide with significant changes in gene regulation resulting in body plan modifications. Recently, 15 mammalian miRNA families were found to be missing in the Eumuroidea, the rodent lineage that includes the model organisms mouse and rat. However, the impact of their absence on the gene regulatory networks in this lineage remains unknown. ResultsThe in silico characterization of all 15 miRNAs revealed that their absence is best explained by multiple independent losses. Analyzing their target genes in humans reveals a significant enrichment of GO- terms linked to cellular and developmental processes. Overexpressing two of the co-absent miRNAs, Mir-197 and Mir-769, in human and mouse inducible pluripotent stem cells (iPSCs) resulted in significantly perturbed expression patterns in both species. In silico target site prediction revealed a significant enrichment of direct targets exclusively in the down-regulated genes. Four genes were down-regulated in both mouse and human and maximum parsimony suggests that the corresponding miRNA target sites were already present in the last common ancestor of mammals. The response of these genes to miRNA overexpression in mice, therefore, unveils remnants of the ancient gene regulatory network that have persisted until today. The evolutionary age of these regulatory connections provides initial evidence that the miRNA losses in Eumuroidea must have had consequences for the regulation of gene expression. Notably, we show that the miRNA loss in the Eumuroidea coincides with the largest lineage-specific loss of transcription factors within the mammals. ConclusionsThe impact of miRNA losses has thus far been investigated on a gene-by-gene basis. Our findings indicate that cooperative effects between miRNAs should be considered when assessing the impact of miRNA loss. We provide evidence that the Eumuroidea have modified their gene regulatory networks on two levels, transcriptionally and post-transcriptionally. It will now be interesting to precisely chart the differences in gene regulation and assess their combined impact on the suitability of mice and rats as model systems for human disease.

genetics↗

bioRxiv2024

Tracing the taxonomic distribution of plant cell wall degrading enzymes across the tree of life using feature architecture aware orthology assignments

The decomposition of plant material is a key driver of the global carbon cycle, traditionally attributed to fungi and bacteria. However, some invertebrates also possess orthologs to bacterial or fungal cellulolytic enzymes, likely acquired via horizontal gene transfer. This reticulated mode of evolution necessitates ortholog searches in large taxon sets to comprehensively map the repertoire of plant cell wall degrading enzymes (PCDs) across the tree of life, a task surpassing capacities of current software. Here, we use fDOG, a novel profile-based ortholog search tool to trace 235 potential PCDs across more than 18,000 taxa. fDOG allows to start the ortholog search from a single protein sequence as a seed, it performs on par with state-of-the-art software that require the comparison of entire proteomes, and it is unique in routinely scoring protein feature architecture differences between the seed protein and its orthologs. Visualizing the presence-absence patterns of PCD orthologs using a UMAP highlights taxa where recent changes in the enzyme repertoire indicate a change in lifestyle. Three invertebrates have a particularly rich set of PCD orthologs encoded in their genome. Only few of the orthologs show differing protein feature architectures relative to the seed that suggest functional modifications. Thus, the corresponding species represent lineages within the invertebrates that may contribute to the global carbon cycle. This study shows how fDOG can be used to create a multi-scale view on the taxonomic distribution of a metabolic capacity that ranges from tree of life-wide surveys to individual feature architecture changes within a species.

bioinformatics↗

bioRxiv2020

Combinatorial CRISPR screening reveals functional buffering in autophagy

Functional genomics studies in model organisms and human cell lines provided important insights into gene functions and their context-dependent role in genetic circuits. However, our functional understanding of many of these genes and how they combinatorically regulate key biological processes, remains limited. To enable the SpCas9-dependent mapping of gene-gene interactions in human cells, we established 3Cs multiplexing for the generation of combinatorial gRNA libraries in a distribution-unbiased manner and demonstrate its robust performance. The optimal number for combinatorial hit calling was 16 gRNA pairs and the skew of a librarys distribution was identified as a critical parameter dictating experimental scale and data quality. Our approach enabled us to investigate 247,032 gRNA-pairs targeting 12,736 gene-interactions in human autophagy. We identified novel genes essential for autophagy and provide experimental evidence that gene-associated categories of phenotypic strengths exist in autophagy. Furthermore, circuits of autophagy gene interactions reveal redundant nodes driven by paralog genes. Our combinatorial 3Cs approach is broadly suitable to investigate unexpected gene-interaction phenotypes in unperturbed and diseased cell contexts.

cell biology↗