Biology subjects

Frölich, S.

Publications and source records attributed to Frölich, S..

3 recordsLinked to original sources

bioRxiv2024

The Regulatory Logic of Planarian Stem Cell Differentiation

Cell type identity is determined by gene regulatory networks (GRNs), comprising the expression of specific transcription factors (TFs) regulating target genes (TGs) via binding to open chromatin regions (OCRs). The regulatory logic of differentiation includes factors specific to one or multiple cell types, functioning in a combinatorial fashion. Classic approaches of GRN discovery used perturbational data to elucidate TF-TG links, but are laborious and not scalable across the tree of life. Single cell transcriptomics has emerged as a revolutionary approach to study gene expression with cell type resolution, but incorporating perturbational data is challenging. Planarians, with their pluripotent neoblast stem cells continuously giving rise to all cell types, offer an ideal model to attempt this integration. Despite extensive single cell transcriptomic studies, the transcriptional and chromatin regulation at the cell type level remains unexplored. Here, we investigate the regulatory logic of planarian stem cell differentiation by obtaining an organism-level integration of single cell transcriptomics and single cell accessibility data. We identify specific open chromatin profiles for major differentiated cell types and analyse their transcriptomic landscape, revealing distinct gene modules expressed in individual types and combinations of them. Integrated analysis unveils gene networks reflecting known TF interactions in each type and identifies TFs potentially driving differentiation across multiple cell types. To validate our predictions, we combined TF knockdown RNAi experiments with single cell transcriptomics. We focus on hnf4, a TF known to be expressed in gut phagocytes, and confirm its influence on other types, including parenchymal cells. Our results demonstrate high overlap between predicted targets and experimentally-validated differentially-regulated genes. Overall, our study integrates TFs, TGs and OCRs to reveal the regulatory logic of planarian stem cell differentiation, showcasing that the combination of single cell methods and perturbational studies will be key for characterising GRNs widely.

systems biology↗

bioRxiv2019

PfCERLI1, a conserved rhoptry associated protein essential for invasion by Plasmodium falciparum merozoites.

The disease-causing blood stage of the Plasmodium falciparum lifecycle begins with invasion of human erythrocytes by merozoites. Many vaccine candidates with key roles in binding to the erythrocyte surface and entry are secreted from the large bulb-like rhoptry organelles at the apical tip of the merozoite. Here we identify an essential role for the conserved protein P. falciparum Cytosolically Exposed Rhoptry Leaflet Interacting protein 1 (PfCERLI1) in rhoptry function. We show that PfCERLI1 localises to the cytosolic face of the rhoptry bulb membrane and knockdown of PfCERLI1 inhibits merozoite invasion. While schizogony and merozoite organelle biogenesis appear normal, biochemical techniques and semi-quantitative super-resolution microscopy show that PfCERLI1 knockdown prevents secretion of key rhoptry antigens that coordinate merozoite invasion. PfCERLI1 is the first rhoptry associated protein identified to have a direct role in function of this essential malaria invasion organelle which has broader implications for understanding apicomplexan invasion biology.

microbiology↗

bioRxiv2018

Telomere-loop dynamics in chromosome end protection

We used super-resolution microscopy to investigate the role of macromolecular telomere structure in chromosome end protection. In murine and human cells with reduced TRF2, we find that ATM-activation at chromosome ends occurs with a structural change from t-loops to linearized chromosome ends through t-loop unfolding. Comparably, we find Aurora B kinase regulates telomere linearity concurrent with ATM activation at telomeres during mitotic arrest. Using a separation of function allele, we find that the TRFH domain of TRF2 regulates t-loop formation while suppressing ATM activity. Notably, we demonstrate that telomere linearity and ATM activation occur separately from telomere fusion via non-homologous end-joining (NHEJ). Further, we show that linear DDR-positive telomeres can remain resistant to fusion, even during an extended G1-arrest when NHEJ is most active. Collectively, these results suggest t-loops act as conformational switches that regulate ATM activation at chromosome ends independent of mechanisms to suppress chromosome end fusion.

molecular biology↗