Opening for PhD Student .

We have an opening for a
PhD candidate on “Raman Sensing of Cell Differentiation”

Project description
The project addresses a challenge in the development of stem-cell based therapies and personalized medicine: fast and non-disruptive quality control of cell cultures. It has been shown that Raman spectroscopy is uniquely able to resolve various cell states with minimal impact on cell physiology. The drawback of classical Raman microscopy though is its low signal rendering data acquisition extremely slow. In this project Raman spectroscopy will be supplemented by a compressed-sensing scheme which alleviates this major disadvantage, ultimately permitting to use the technique even for high-throughput applications, such as drug screening.

You will develop a novel microscopy setup that optically implements a programmable compressed sensing scheme. Simultaneously you will develop a machine-learning platform to determine the optimal parameters of the optical elements. You will characterize the setup quantitatively and apply the methodology to a variety of cell models including immune cells and stem cells. In your endeavour you will be supported by a team of biophysicists with ample experience in imaging, from individual molecules to organoids, all in the context of cells and tissue. Our group is embedded in the Cell Observatory, whichn facilitates our collaborative research with groups from biology and drug development.

Key responsibilities

  • Design, build, optimize and characterize the compressed-sensing Raman microscope;
  • Realize a deep-learning platform for optimization of the compressed-sensing scheme;
  • Publish academic papers and present your findings at academic conferences;
  • Communicate closely with the team members and collaborators in biology;
  • Assist with teaching and student supervision;
  • Complete a PhD thesis within four years (1.0 FTE).

The PhD candidate will work closely together with the two PIs (prof T. Schmidt, www.schmidtlab.nl; and prof S. Semrau, www.semraulab.com) driving the project, and the other team members of the group. The candidate will carry responsibility for the research goals within the project.

Selection Criteria

  • Research Master in Physics, Engineering or equivalent;
  • Knowledge in optics and optical techniques is a plus;
  • Excellent command of the English language, and excellent communication skills;
  • Well-developed analytic and organisational skills;
  • Excellent social skills in order to be able to work in a team of varied background.

Applications
To apply for this vacancy, please send an email to Thomas Schmidt (schmidt@physics.leidenuniv.nl), with ‘Application PhD’ in the subject line. Please ensure that you attach the following:

  • A short motivation (max one page) on why you would like to join our group and about your research interests;
  • A Curriculum Vitae, including information about the grades you had as an undergraduate;
  • Contact details of a university teacher or previous/current supervisors who can be contacted for a reference.

Applications will be reviewed starting 1st of November until the position is filled. The starting date of the PhD program is at the beginning of 2024.

Download the full ad HERE.

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Paper on hexanematic order appeared in Nature Comm.

“Hexanematic crossover in epithelial monolayers depends on cell adhesion and cell density”

Julia Eckert, Benoît Ladoux, René-Marc Mège, Luca Giomi & Thomas Schmidt

Changes in tissue geometry during developmental processes are associated with collective migration of cells. Recent experimental and numerical results suggest that these changes could leverage on the coexistence of nematic and hexatic orientational order at different length scales. How this multiscale organization is affected by the material properties of the cells and their sub- strate is presently unknown. In this study, we address these questions in monolayers of Madin-Darby canine kidney cells having various cell densities and molecular repertoires. At small length scales, confluent monolayers are characterized by a prominent hexatic order, independent of the presence of E- cadherin, monolayer density, and underlying substrate stiffness. However, all three properties affect the meso-scale tissue organization. The length scale at which hexatic order transits to nematic order, the “hexanematic” crossover scale, strongly depends on cell-cell adhesions and correlates with monolayer density. Our study demonstrates how epithelial organization is affected by mechanical properties, and provides a robust description of tissue organiza- tion during developmental processes.

To be read in: Nat Comm 14, 5762

Congrats to Julia!

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Rick won LION image award

 

With his high-res image of two interacting tumor spheroids, Rick won the 2022 LION image award. We will see his image on one of the next official documents of the institute.

Read the news item here.

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Integrin as prognostic marker

Integrin alpha-2 popped up in a screen of aggressive and chemoresistant PDAC cancers. In this study of Alessandro and Cecilia we validated the results we obtained in the RNA screen with various methods. Again we find a correlation between cell mechanics, aggressiveness, and chemoresistance. More to come …

Prognostic Significance of Integrin Subunit Alpha 2 (ITGA2) and Role of Mechanical Cues in Resistance to Gemcitabine in Pancreatic Ductal Adenocarcinoma (PDAC).

Gregori, A.; Bergonzini, C.; Capula, M.; Mantini, G.; Khojasteh-Leylakoohi, F.; Comandatore, A.; Khalili-Tanha, G.; Khooei, A.; Morelli, L.; Avan, A.; Danen, E.H.; Schmidt, T.; Giovannetti, E.

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive and chemoresistant cancer, with a poor overall survival. The stiff stroma surrounding PDAC is known to be involved in chemoresistance via mechanical cues, although the mechanisms behind it are poorly understood. Here, we investigated whether integrin alpha 2 (ITGA2), a mechanical sensor of stiffness, correlated with poor prognosis and whether matrix stiffness could trigger chemoresistance to gemcitabine. By assessing two cohorts of patients, we observed a poorer prognosis for the high ITGA2 expression group. An increase in matrix stiffness prompted cancer cells to express more ITGA2 and become chemoresistant. ITGA2 might therefore be an interesting therapeutic target to overcome resistance to gemcitabine.

Cancers (2023) 15:628 (doi:10.3390/cancers15030628)

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Molecule counting in STORM

We developed a novel methodology to count the number of molecules in a STORM image. That allowed us to address the stoichiometry of adhesion proteins in focal adhesions. It appeared that the stoichiometry in FAK is independent on the force exerted by the cell.

Substrate rigidity modulates traction forces and stoichiometry of cell–matrix adhesions.

Hayri E. Balcioglu, Rolf Harkes, Erik H. J. Danen, and Thomas Schmidt.

In cell–matrix adhesions, integrin receptors and associated proteins provide a dynamic coupling of the extracellular matrix (ECM) to the cytoskeleton. This allows bidirectional transmission of forces between the ECM and the cytoskeleton, which tunes intracellular signaling cascades that control survival, proliferation, differentiation, and motility. The quantitative relationships between recruitment of distinct cell–matrix adhesion proteins and local cellular traction forces are not known. Here, we applied quantitative super-resolution microscopy to cell–matrix adhesions formed on fibronectin-stamped elastomeric pillars and developed an approach to relate the number of talin, vinculin, paxillin, and focal adhesion kinase (FAK) molecules to the local cellular traction force. We find that FAK recruitment does not show an association with traction-force application, whereas a ∼60 pN force increase is associated with the recruitment of one talin, two vinculin, and two paxillin molecules on a substrate with an effective stiffness of 47 kPa. On a substrate with a fourfold lower effective stiffness, the stoichiometry of talin:vinculin:paxillin changes to 2:12:6 for the same ∼60 pN traction force. The relative change in force-related vinculin recruitment indicates a stiffness-dependent switch in vinculin function in cell–matrix adhesions. Our results reveal a substrate-stiffness-dependent modulation of the relationship between cellular traction-force and the molecular stoichiometry of cell–matrix adhesions.

doi: 10.1063/5.0077004

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