The Sleeping Embryo

Project Information

MORPHEUS

Grant agreement ID: 101043753

DOI

10.3030/101043753

EC signature date 20 July 2022

Start date 1 January 2023

End date 31 December 2027

Funded under

• European Research Council (ERC)

Total cost

€ 2 000 000,00

EU contribution

€ 2 000 000,00

Coordinated by

MAX-PLANCK-GESELLSCHAFT ZUR FORDERUNG DER WISSENSCHAFTEN EV
Germany

Periodic Reporting for period 1 - MORPHEUS (The Sleeping Embryo)

Reporting period: 2023-01-01 to 2025-06-30

Summary of the context and overall objectives of the project

The closest star to our Sun is the red dwarf Proxima Centauri, which has two known planets, Proxima B and C. Although this planetary system is in our cosmic backyard, "only" 4.2 light-years away, it will take millennia to reach it, so visiting Proxima Centauri is still in the realm of fiction. Sci-fi novels foresee human missions to distant planets by putting travellers into a deep sleep, using stasis pods where all physiological processes are slowed down. This state of suspended animation is said to be completely reversible, bypassing the negative effects of the journey and allowing the body's functions to be reactivated to normal physiological rates.
A naturally occurring state of dormancy known as diapause has been described in insects. This hormonally controlled process allows seasonal adaptation to the local environment. For example, seasonal changes in temperature and photoperiod induce diapause in the fertilised eggs of the silk moth and the adult monarch butterfly.
Over the years, embryonic diapause has been found also in more than 300 mammalian species. In some, embryos enter and exit diapause as part of each reproductive cycle, as in the roe deer (obligate diapause). In others, diapause is triggered by environmental cues or lactation (facultative diapause), as in the mouse. Both types allow species to postpone the time of birth, avoid unfavourable conditions and/or adapt to seasonal changes, thereby increasing the chances of survival for their offspring.
While “normal” (transient) mammalian embryogenesis has been intensively studied, embryonic diapause is still an extremely enigmatic state. In the ERC Consolidator project (MORPHEUS) we seek to understand how the embryo maintains its viability over extended periods of time without losing its potential to develop to birth, upon exit of diapause. Understanding the mechanisms of embryo dormancy will shed light on this fascinating biological state. In addition to basic knowledge, this could provide new methods for preserving embryos, thereby improving fertility treatments. It may also provide insights into how dormant cells remain viable and healthy for long periods of time, with potential implications for regenerative medicine, organ preservation and even delaying ageing. In addition, the study of diapause may improve breeding and conservation efforts for critically endangered species. Thus, understanding embryonic dormancy will expand our fundamental knowledge of embryonic development and pave the way for future medical advances.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

A key feature of embryonic dormancy is that gene activity (expression) is substantially reduced. This state is known as transcriptional quiescence. As the embryo consists of different tissues, we used a technique called single-cell RNA sequencing (scRNA-seq) that allowed us to analyse gene activity in individual cells and then group these cells according to the tissue they belong to.
Our analysis showed that most of the genes encoding proteins involved in cellular metabolism and biosynthesis of cellular components significantly decrease their expression upon entry into diapause. The opposite process of gene reactivation takes place when the embryo emerges from dormancy. We also found that genes involved in protein degradation are also downregulated in the dormant embryo. This suggests that while the embryo is making fewer new proteins, it is also slowing down the degradation of existing proteins, which may help to preserve critical factors that keep cells in a healthy state and responsive to a subsequent exit from embryonic dormancy.
Interestingly, our analysis showed that not all genes are downregulated. On the contrary, there are a number of genes that maintain their transcriptional activity and are even upregulated during diapause. Among these, we found factors that prevent cell differentiation, thereby halting the developmental programme of the embryo.
While embryonic development appeared to be arrested, we also found that several signalling pathways that mediate cell-to-cell communication were activated during diapause. At the same time, a small group of cells called epiblast cells, which later give rise to the animal's body, organised themselves into a rosette-like structure. We found that these cells used receptors called integrins to attach to the surrounding network of proteins known as the extracellular matrix and that the interaction between the integrin receptors and the surrounding extracellular matrix is critical for cell survival. This survival signal is mediated by the translocation of a factor called Yap, from the cytoplasm to the nucleus. Similarly, Yap activity has been shown to suppress apoptosis in dormant cancer cells, contributing to cancer chemoresistance. This suggests that cellular dormancy may have physiological (embryonic diapause) and pathological (dormant cancer cells) manifestations with common fundamental principles.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

As mentioned above, the interaction between integrin receptors and the surrounding extracellular matrix is critical for the survival of epiblast cells during embryonic dormancy. This process is mediated by the translocation of Yap from the cytoplasm to the nucleus. Similarly, Yap activity in the nucleus has been shown to suppress apoptosis in dormant cancer cells, thereby contributing to cancer chemoresistance. This helps cancer cells to persist for long periods of time and potentially (re-)activate after chemotherapy, leading to cancer recurrence. This suggests that cellular dormancy may have both physiological (embryonic diapause) and pathological (dormant cancer cells) manifestations. Therefore, increasing our basic knowledge of physiological dormancy may provide valuable insights into pathological conditions and identify key targets for the development of therapeutics.
The knowledge gained about gene activity and cell-cell signalling during embryo dormancy also helped us to formulate an embryo culture medium that induces and maintains embryo dormancy in vitro. We established a chemical composition that mimics the contents of the uterine fluid and thereby induces dormancy in a dish. In addition to basic research into embryonic dormancy, this could pave the way for the development of embryo preservation methods, improving fertility treatments. It may also aid conservation efforts and breeding programmes for endangered species that use diapause as part of their reproductive cycle.
Overall, our work on embryonic dormancy can provide insights into how dormant cells remain viable for long periods of time, with potential implications for developmental and reproductive biology, as well as improving fertility treatments and even cancer research. The discoveries made in this project will increase the fundamental knowledge of embryonic development and pave the way for future research and potential medical advances.

embryonic diapause