Biology subjects

Stelzer, E.

Publications and source records attributed to Stelzer, E..

6 recordsLinked to original sources

bioRxiv2024

mTOR controls growth and internal architecture of human breast cancer spheroids

mTOR is a serine/threonine kinase participating in two distinct functional complexes: mTORC1 and mTORC2. mTORC1 regulates protein translation, cell cycle progression and autophagy. mTORC2 controls cell survival, proliferation and actin cytoskeleton reorganization. mTOR signaling is often deregulated during breast cancer. We investigated how mTOR and its downstream process autophagy determine the inner architecture of solid tumor aggregates at multiple levels. We focused on structures, which are morphologically altered during progression of cancer, including: nuclei number and volume, cell density, number, shape and volume of polarized structures. We developed a breast cancer spheroid model, in which the effects of mTOR and autophagy modulation were investigated by pharmacological inhibition mTOR signaling and induction autophagy, as well as using ATG7 KO spheroids. Spheroids were imaged with light sheet-based fluorescence microscopy and data were quantitatively analyzed. Our data suggest that mTORC1 regulates the spheroid volume, cell number and size. mTORC2 controls nuclei volume and determines growth and elongation of polarized acini inside a spheroid.

cell biology↗

bioRxiv2023

Laser patterning bioprinting using a light sheet-based system equipped with light sheet imaging produces long-term viable skin constructs

This research introduces a new 3D bioprinter that incorporates live imaging of the bioprinted tissue with high resolution and high-speed capabilities. The printer employs a light sheet-based system to photocrosslink polymers into hydrogels at a printing speed of up to 0.66 mm3/s with a resolution of 15.7 {micro}m. A significant advancement of this bioprinter is its ability to track cells and bioink during crosslinking, which enables real- time evaluation of the 3D-bioprinted structures quality. Fibroblast cells were encapsulated using this method, and the viability was evaluated directly after bioprinting and seven days after encapsulation, which was found to be high (83% {+/-} 4.34%). Furthermore, a full- thickness skin construct was bioprinted and maintained in culture for 6 weeks, demonstrating the long-term viability and physiological relevance of the bioprinted tissue. The usage of solid-state laser beam scanning devices could enhance bioprintings speed and precision. This fast and accurate light-based bioprinter offers a promising platform for generating customizable 3D-printed structures with viable long-term cultures. TeaserA novel bioprinter with live imaging capability using light sheet microscopy produces viable long-term cultures with high-resolution structures. Graphical abstractGeneral workflow of bioprinting skin constructs using light sheet bioprinting. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=62 SRC="FIGDIR/small/539793v1_ufig1.gif" ALT="Figure 1"> View larger version (16K): org.highwire.dtl.DTLVardef@550133org.highwire.dtl.DTLVardef@c1cce0org.highwire.dtl.DTLVardef@171c516org.highwire.dtl.DTLVardef@424d05_HPS_FORMAT_FIGEXP M_FIG C_FIG

bioengineering↗

bioRxiv2022

How enhancers regulate wavelike gene expression patterns: A novel enhancer prediction and live reporter system identifies an enhancer associated with the arrest of pair-rule waves in Tribolium

A key problem in development is to understand how genes turn on or off at the right place and right time during embryogenesis. Such decisions are made by non-coding sequences called enhancers. Much of our models of how enhancers work rely on the assumption that genes are activated de novo as stable domains across embryonic tissues. Such view has been strengthened by the intensive landmark studies of the early patterning of the anterior-posterior (AP) axis of the Drosophila embryo, where indeed gene expression domains seem to arise more or less stably. However, careful analysis of gene expressions in other model systems (including the AP patterning in vertebrates and short-germ insects like the beetle Tribolium castaneum) painted a different, very dynamic view of gene regulation, where genes are oftentimes expressed in a wavelike fashion. How such gene expression waves are mediated at the enhancer level is so far unclear. Here we establish the AP patterning of the short-germ beetle Tribolium as a model system to study dynamic and temporal pattern formation at the enhancer level. To that end, we established an enhancer prediction system in Tribolium based on time- and tissue-specific ATAC-seq and an enhancer live reporter system based on MS2 tagging. Using this experimental framework, we discovered several Tribolium enhancers, and assessed the spatiotemporal activities of some of them in live embryos. We found our data consistent with a model in which the timing of gene expression during embryonic pattern formation is mediated by a balancing act between enhancers that induce rapid changes in gene expressions (that we call dynamic enhancers) and enhancers that stabilizes gene expressions (that we call static enhancers).

developmental biology↗

bioRxiv2019

Cell Fate Clusters in ICM Organoids Arise from Cell Fate Heredity & Division - a Modeling Approach

During the mammalian preimplantation phase, cells undergo two subsequent cell fate decisions. During the first cell fate decision, cells become either part of an outer trophectoderm or part of the inner cell mass. Subsequently, the inner cell mass (ICM) segregates into an embryonic and an extraembryonic lineage, giving rise to the epiblast and the primitive endoderm, respectively. Inner cell mass organoids represent an experimental model system for preimplantation development, mimicking the second cell fate decision taking place in in vivo mouse embryos. In a previous study, the spatial pattern of the different cell lineage types was investigated. The study revealed that cells of the same fate tend to cluster stronger than expected for purely random cell fate decisions. Three major processes are hypothesised to contribute to the final cell fate arrangements at the mid and late blastocysts or 24 h old and 48 h old ICM organoids, respectively: 1) intra- and intercellular chemical signalling; 2) a cell sorting process; 3) cell proliferation. In order to quantify the influence of cell proliferation on the emergence of the observed cell lineage type clustering behaviour, we developed an agent-based model. Hereby, cells are mechanically interacting with direct neighbours, and exert adhesion and repulsion forces. The model was applied to compare several current assumptions of how inner cell mass neighbourhood structures are generated. We tested how different assumptions regarding cell fate switches affect the observed neighbourhood relationships. The model supports the hypothesis that initial cell fate acquisition is a stochastically driven process, taking place in the early development of inner cell mass organoids. The model further shows that the observed neighbourhood structures can emerge due to cell fate heredity during cell division and allows the inference of a time point for the cell fate decision. STATEMENT OF SIGNIFICANCECell fate decisions in early embryogenesis have been considered random events, causing a random cell fate distribution. Using an agent-based mathematical model, fitted to ICM organoid data, we show that the assumed random distribution of cell fates occurs only for a short time interval, as cell fate heredity and cell division quickly lead to spatial cell fate clustering. Our results show that neighbourhood clustering can emerge without specific neighbourhood interactions affecting the cell fate decision. The approach indicates four consecutive phases of early development: 1) co-expression of cell fate markers, 2) cell fate decision, 3) division and local cell fate clustering, and 4) phase separation, whereby only the phases 1-3 occur in ICM organoids during the first 24h of growth.

systems biology↗

bioRxiv2019

An ancestral apical brain region contributes to the central complex under the control of foxQ2 in the beetle Tribolium castaneum

The genetic control of anterior brain development is highly conserved throughout animals. For instance, a conserved anterior gene regulatory network specifies the ancestral neuroendocrine center of animals and the apical organ of marine organisms. However, its contribution to the brain in non-marine animals has remained elusive. Here, we study the function of the Tc-foxQ2 forkhead transcription factor, a key regulator of the anterior gene regulatory network of insects. We characterized four distinct types of Tc-foxQ2 positive neural progenitor cells based on differential co-expression with Tc-six3/optix, Tc-six4, Tc-chx/vsx, Tc-nkx2.1/scro, Tc-ey, Tc-rx and Tc-fez1. An enhancer trap line built by genome editing marked Tc-foxQ2 positive neurons, which projected through the primary brain commissure and later through a subset of commissural fascicles. Eventually, they contributed to the central complex. Strikingly, in Tc-foxQ2 RNAi knock-down embryos the primary brain commissure did not split and subsequent development of midline brain structures stalled. Our work establishes foxQ2 as a key regulator of brain midline structures, which distinguish the protocerebrum from segmental ganglia. Unexpectedly, our data suggest that the central complex evolved by integrating neural cells from an ancestral anterior neuroendocrine center.\n\nSummary statementAn ancestral neuroendocrine center contributes to the evolution of the central complex. foxQ2 is a gene required for the development of midline structures of the insect brain, which distinguish protocerebrum from segmental ganglia.

developmental biology↗

bioRxiv2018

The molecular recognition of phosphatidic acid by an amphipathic helix in Opi1

A key event in cellular physiology is the decision between membrane biogenesis and fat storage. Phosphatidic acid (PA) is an important lipid intermediate and signaling lipid at the branch point of these pathways and constantly monitored by the transcriptional repressor Opi1 to orchestrate lipid metabolism. Here, we report on the mechanism of membrane recognition by Opi1 and identify an amphipathic helix (AH) for the selective binding to membranes containing PA over phosphatidylserine (PS). The insertion of the AH into the hydrophobic core of the membrane renders Opi1 sensitive to the lipid acyl chain composition as an important factor contributing to the regulation of membrane biogenesis. Based on these findings, we rationally designed the membrane binding properties of Opi1 to control its responsiveness in the physiological context. Using extensive molecular dynamics (MD) simulations, we identified two PA-selective three-finger grips that tightly bind the phosphate headgroup, while interacting less intimately and more transiently with PS. This work establishes lipid headgroup selectivity as a new feature in the family of AH-containing membrane property sensors.

biochemistry↗