Building the Human Amniotic Sac - Mechanics and Growth Control of Human Post-Gastrulation Amnioids

Please note: to apply to this project, candidates must be eligible for home tuition fee status.

Project background and description

Background

The amnion provides essential signalling, structural, and nutritional support throughout pregnancy, yet the mechanisms governing its formation and growth in humans remain remarkably poorly understood. Silvia Santos’ lab has developed a three-dimensional embryonic stem cell–derived model of the amnion, termed Post-Gastrulation Amnioid (PGA), in which a fluid-filled lumen is enclosed by a surface composed of two cellular layers separated by extracellular matrix. Over ~4 weeks, PGAs grow steadily before reaching a reproducible size plateau of ~2 cm - an intrinsic and unexplained limit to expansion. How do two distinct cell types interplay with extracellular matrix and amniotic fluid over periods of weeks to yield reproducible PGA size?

Central aims and questions

Our goal is to decipher the molecular and biophysical regulation of the size of PGAs. We will use an interdisciplinary approach to explore how form, force, and growth interact in a previously inaccessible human tissue.

We will pursue two objectives:

1. Define the mechanical and geometric evolution of PGAs during size acquisition
2. Identify fluid-transport, cytoskeletal, and matrix deposition mechanisms controlling lumen expansion and amniotic membrane growth

By uncovering how molecular, cellular and mechanical processes collectively determine tissue size, our research will establish PGAs as a model for investigating fundamental principles of growth regulation and morphogenesis, advancing our understanding of how living tissues self-organise, scale and maintain structural integrity.

These insights will also provide a mechanistic framework for understanding disorders associated with abnormal amniotic sac growth and membrane fragility, including complications such as preterm premature rupture of membranes (PPROM).

Methodology

WP 1: Define the temporal evolution of PGA size and mechanics

Despite its small thickness, the amnion represents a crucial barrier protecting the developing foetus within the maternal environment. Amnion strength is vital for proper foetal development and must be tightly regulated. Yet, we know nothing about amnion growth and mechanics.

We will:

• Measure PGA growth quantitatively by combining 3D lightsheet imaging with morphometric analyses to measure lumen expansion, membrane thickness, and matrix deposition across developmental stages.
• Characterise amniotic membrane mechanical properties and lumen pressure across developmental stages to determine if these stay constant over time, indicating homeostatic regulation during growth.

This quantitative description of amniotic sac growth and mechanics across timescales will provide a foundation for understanding mechanisms controlling growth.

WP 2: Identify molecular, cellular, and matrix mechanisms involved in growth control

Amnion growth necessitates coordination of cell growth, matrix deposition, and luminal volume increase. A mechanistic understanding of this interplay is still missing because it cannot be studied in vivo.

We hypothesise that directional fluid transport increases PGA luminal volume. This exerts tension on cells and the matrix, which induces cell proliferation. Increased cell numbers and new matrix deposition reduce amniotic membrane tension. But, over time, the increased number of cells also leads to more fluid transport, restarting the feedback loop.

We will investigate the contributions of the cytoskeleton, cell proliferation and epithelial barrier function to PGA growth using targeted pharmacological and genetic perturbations. The combination of perturbation approaches and multi-omics analyses will identify candidate signalling pathways underlying growth control.

This will uncover the feedback principles that couple fluid transport, epithelial growth, and matrix deposition to volumetric expansion of the amniotic sac.

Candidate background

This project represents an excellent opportunity for interdisciplinary training in experimental and computational skills. It will suit candidates with training in physics, engineering, quantitative cell and developmental biology, or biomedical engineering, and an interest in how forces, growth and matrix dynamics shape tissues. The ideal candidate is likely to be an energetic, organised individual who thrives working on interesting biological problems in a highly collegial and collaborative work environment.

Experience in one or more of the following is desirable: cell culture and differentiation; advanced fluorescence microscopy (light‑sheet or confocal); image analysis and morphometrics; mechanical measurements on cells/tissues; programming; CRISPR‑based genetic perturbations; and transcriptomic or proteomic profiling.

Strong quantitative skills, careful experimental design and collaborative working across labs will be essential. Comprehensive training will be provided in hESC culture and 3D organoid formation, mechanical testing of epithelia and data‑analysis pipelines.

This post provides the successful candidate with mentorship from two experienced PIs, a great wider support network at the Francis Crick Institute and UCL.

Lab-specific question

How have your studies and research experience prepared you to work on interdisciplinary projects?

Funding Notes

Successful applicants will be awarded a non-taxable annual stipend of £27,715 plus payment of university tuition fees. Students of all nationalities are eligible to apply.

References

1. Gharibi, B., Inge, O.C.K., Rodriguez-Hernandez, I., Driscoll, P.C., Dubois, C., Jiang, M., . . . Santos, S.D.M. (2025) Post-gastrulation amnioids as a stem cell-derived model of human extra-embryonic development. Cell 188: 3757–3774 .e3720. PubMed abstract
2. Inge, O.C.K., Copin, E., Cornwall-Scoones, J., Gharibi, B., Rodriguez-Hernandez, I., Soro-Barrio, P., . . . Santos, S.D.M. (2025) Combinatorial BMP4 and activin direct the choice between alternate routes to endoderm in a stem cell model of human gastrulation. Developmental Cell 60: 3304–3320 .e3309. PubMed abstract
3. Harris, A.R., Peter, L., Bellis, J., Baum, B., Kabla, A.J. and Charras, G.T. (2012) Characterizing the mechanics of cultured cell monolayers. Proceedings of the National Academy of Sciences U S A 109: 16449–16454. PubMed abstract
4. Khalilgharibi, N., Fouchard, J., Asadipour, N., Barrientos, R., Duda, M., Bonfanti, A., . . . Charras, G. (2019) Stress relaxation in epithelial monolayers is controlled by the actomyosin cortex. Nature Physics 15: 839–847. PubMed abstract
5. Duque, J., Bonfanti, A., Fouchard, J., Baldauf, L., Azenha, S.R., Ferber, E., . . . Charras, G. (2024) Rupture strength of living cell monolayers. Nature Materials 23: 1563–1574. PubMed abstract