The full cycle of germline development in vitro


Cristina Eguizabal, Co-ordinator of ESHRE's SIGStem Cells, remembers her time as a post-doc in Cambridge with Katsuhiko Hayashi, presenter of this year's Keynote Lecture in Barcelona.

Professor Katsuhiko Hayashi's presentation of an opening Keynote Lecture in Barcelona was a great honour for ESHRE and for me personally an opportunity to recollect experience from 12 years ago. It was during my first post-doc appointment in Dr Anne McLaren´s laboratory at the Gurdon Institute in Cambridge that I meet him for the first time.

At that time, the laboratories of Professor McLaren and Azim Surani were working together and all the post-docs were helping each other. So that was how Professor Hayashi was the one who showed me how to perform the chromosome spread technique from mouse fetal ovaries and how to perform immunofluorescence, and later providing with me Scp3 antibody from his previous lab in Japan in order to detect meiotic figures. So it gave great pleasure to me and the SIG Stem Cells to propose him to ESHRE a year or two ago for this year's Keynote Lecture.

Katsuhiko Hayashi is now a widely acclaimed Japanese group leader and his scientific career is quite simply admirable. In 2011 while at Kyoto University he succeeded in differentiating in vitro primordial germ cells from male mouse ES and iPS cells and induced sperm from these cells following a 2-step protocol to produce healthy pups by in vitro fertilisation.(1) The following year, with a similar approach of differentiating primordial germ cells in vitro from female mouse ES and iPS cells, he grew them in culture with fetal ovary somatic cells to transplant back into ovaries of other mice to obtain inmature oocytes. These oocytes were matured in vitro and went on create pups by IVF.(2)

In their last relevant publication in 2016, Hayashi´s group was able to generate fully in vitro functional oocytes after co-culture with fetal gonads.(3)

In his lecture in Barcelona he highlighted the difference in efficiency for creating pups depending on the source of pluripotent stem cells used (3.5% from ES cells or 0.9% from iPS cells). He also noted that maturation is critical in oogenesis in vitro; many of the in vitro oocytes generated are immature, have low mitochondria copy number and are more frequenty aneuploid than found in vivo oocytes. Moreover, he added that the extracellular matrix (ECM) plays an important role in the dormant state of primordial follicles, which can also be produced in culture.

Putting his experiments together, these studies on the differentiation of mouse ES or iPS cells into reproductive cells will contribute greatly to human reproductive medicine in the future. So it's not fanciful to wonder when we will generate functional human oocytes from pluripotent stem cells in vitro. This big question still remains open, but an answer now seems a little nearer than before.
I must confess that during his lecture I kept thinking of the past 12 years and realising how fast the science of stem cells science has developed - and how far my former colleague Katsuhiko Katsuhiko has come! I am so proud of him.

1. Hayashi K, Ohta H, Kurimoto K, et al. Reconstitution of the mouse germ cell specification pathway in culture by pluripotent stem cells. Cell 2011; 14: 519-32.
2. Hayashi K, Ogushi S, Kurimoto K, et al. Offspring from oocytes derived from in vitro primordial germ cell-like cells in mice. Science 2012; 338: 971-975.
3. Hikabe O, Hamazaki N, Nagamatsu G, et al. Reconstitution in vitro of the entire cycle of the mouse female germ line. Nature 2016; 539: 299-303.