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SIG STEM CELLS

In vitro modelling explored - and more news of how in vitro gametogenesis may transform reproductive medicine

Published 11 October 2018

SIG Co-ordinator Cristina Eguizabal reports from a well attended Campus meeting in Bilbao - and describes further developments in the differentiation of stem cells to mature germ cells.

With close to 100 in attendance, our Campus course on 'In vitro modelling: from embryos to gametes' held in Bilbao in September 2018 was very well received. Current trending research topics in the field of ART and stem cells were tackled and led to a lively debate and discussion. Feedback received was overwhelmingly positive from both our audience and speakers.

The course started rather fittingly with an interesting discussion on reproductive tissue engineering, the new up-and-coming topic in ART. Advances in ovarian tissue engineering were described by Christiani Amorim, while novel approaches in 3D testis modelling were also addressed by Ellen Goossens, who showed that complete spermatogenesis in vitro could be achieved using organoids cultured within porous 3D cell-free or cell-laden scaffolds in mice. Applying human testicular cells in this system certainly holds great promise for the future.
Jan-Bernd Stukenborg demonstrated further potential of 3D culture systems by presenting the reorganisation of rat primary testicular cells into organoids and the establishment of germ cells. Nuria Montserrat highlighted the vast potential of organoids obtained from pluripotent stem cells for future applications in regenerative medicine. Specifically, she demonstrated the assembly of embryonic stem cells and induced pluripotent stem cells into kidney organoids, and the application of microfluidics and 3D bioprinting for studying human nephrogenesis and kidney disease.

Shankar Srinivas shifted the meeting's focus to peri-implantation embryos, demonstrating the application of the latest automated imaging technology for studying cell migration patterns during mouse embryo development. The course also included a clinical component, with Amelia Rodriguez-Aranda giving an interesting presentation on the value of endometrial parameters, assessed through ultrasound imaging, for predicting IVF success rates. To further shed light on the crosstalk between the embryo and endometrium, Hugo Vankelecom illustrated the potential of endometrial organoids generated from human endometrial cells to mimic the menstrual cycle and suitable for studying endometrial cancers and endometriosis.
Idse Heemskerk highlighted the important role of morphogen dynamics in cell fate decisions associated with mammalian gastrulation using human pluripotent stem cells as a model. His work showed that some cell fates depend on a rapid concentration increase rather than absolute levels of signalling molecules.

Shifting to preimplantation development, Nicolas Rivron demonstrated that mouse trophoblast stem cells and embryonic stem cells can cooperate in vitro to form structures that morphologically and transcriptionally resemble blastocysts, termed blastoids. One very relevant subject for understanding germline development is uncovering the epigenetic dynamics of germ cells, and Susana Chuva de Sousa Lopes, a SIG Deputy, demonstrated the cell-to-cell heterogeneity of transcriptional and epigenetic remodeling in female human germ cells. She also emphasised that epigenetic reprogramming in the female germline is a long process. Petra Hajkova showed that germline reprogramming is required to license the meiotic program in both males and females. Meiotic genes are silenced by a combination of epigenetic mechanisms. Finally, Bernhard Payer discussed the role of PRDM14 in epigenetic reprogramming and specifically X-chromosome reactivation in migrating mouse primordial germ cells.

Overall, this proved a very insightful and fascinating meeting, with a very active audience and captivating speakers. The topics discussed were certainly relevant for ART, particularly for the future multidisciplinary direction in which the field is heading. We once again thank all participants and are excited for the promising research to come.

Future events
Our next Campus Course will be held in Lisbon, in May 2019. It is our pleasure to have teamed up with the SIG Reproductive Genetics to present the latest developments in ‘Gene editing techniques in reproductive medicine’. This is currently a very hot topic in reproductive medicine, both of clinical importance and with more fundamental applications involving the study of early development processes in vitro.

We are also pleased to announce that the SIG Stem Cells precongress course for ESHRE 2019 in Vienna will focus on '20 years of human embryonic stem cells. Marking the 20th anniversary of the derivation of the first human embryonic stem cells, we will review the history of human pluripotent stem cells, progress and developments in the field of stem cell research, and more recent clinical applications and the future of regenerative medicine. This anniversary offers an ideal opportunity to look back over the past 20 years in the field, hear from its pioneers, and look forward to what the future may hold. Researchers and embryologists keen on learning more about the field of stem cells will find this course of great interest - advances in ART have been crucial for the development of stem cell technologies, which now themselves hold great promise for the future of ART.

Finally, we would like to invite all ESHRE members to join our SIG Stem Cells social media pages on Facebook and Twitter. Here you can stay up to date with the latest news on our SIG activities, as well as novel research in the field of stem cells.

Advances in the field
In 2016 the Japanese group headed by Katsuhiko Hayashi generated fully-matured oocytes starting from mouse pluripotent stem cells. Remarkably, these oocytes could also be fertilized and led to the birth of fertile pups. Using an innovative 3-step in vitro culture system, involving co-culture with female fetal gonads, both mouse embryonic stem cells and induced pluripotent stem cells could give rise to functional mouse oocytes. Human pluripotent stem cells (hPSCs) have been induced into primordial germ cell-like cells (hPGCLCs), but further differentiation to mature germ cells has not yet been achieved.

Now, in a new development Mitinori Saitou´s group in Japan has described the generation of human oogonia-like cells from human pluripotent stem cells.(1) They showed that primordial germ cell-like cells (hPGCLCs) differentiate progressively into oogonia-like cells during a long-term in vitro culture (~four months) in xenogeneic reconstituted ovaries with mouse embryonic ovarian somatic cells. The hPGCLC-derived oogonia display hallmarks of epigenetic reprogramming, ie, genome-wide DNA demethylation, imprint erasure, removal of aberrant DNA methylation marks, and also acquire an immediate precursory state for meiotic recombination.

Furthermore, the inactive X-chromosome showed progressive demethylation and reactivation, albeit partially. Although the data is very encouraging, the oogonia were not completely normal and would still need to undergo a number of processes to give rise to functional oocytes, namely epigenetic reprogramming and X-chromosome reactivation, which were clearly incomplete and will need to take place before meiosis entry. It will be interesting to know if this is because the mouse somatic cells cannot support human germ cell development or if there are other aspects to the culture system that need improvement. Further work will be essential to improve the efficiency of human germ cell development and further maturation in culture. Nevertheless, these findings establish the germline competence of hPSCs and provide a critical step toward human in vitro gametogenesis.

1. Yamashiro C, Sasaki K, Yabuta Y, et al. Generation of human oogonia from induced pluripotent stem cells in vitro. Science 2018; doi: 10.1126/science.aat1674.

Cristina Eguizabal
Co-ordinator SIG Stem Cells