Abstract
During the development of the male germline, spermatogonial stem cells (SSCs) originate from gonocytes that differentiate from primordial germ cells (PGCs). In the developing and regenerating mouse testis, expression of the gene LIM homeobox 1 (Lhx1) marks the most undifferentiated SSCs. However, an enrichment of Lhx1 expression in spermatogonia-like cells generated in vitro has not been reported so far. Previously, it was shown that a chemical intervention in male mouse embryonic stem (ES) cells in serum culture, including a timed combination of the SIRT1 inhibitor Ex-527, the DNA methyltransferase inhibitor RG-108 and the electrophilic redox cycling compound tert-butylhydroquinone (tBHQ), was associated with molecular markers of the PGC to gonocyte differentiation process. Here, we report the in vitro differentiation of male mouse ES cells, cultured under dual chemical inhibition of GSK3β and MEK (termed 2i) with leukemia inhibitory factor (LIF) (termed 2iL) and serum, into cells with spermatogonia-like morphology (CSMs) and population-averaged expression of spermatogonia-specific genes. This was achieved by the removal of 2iL and a specific schedule of 2 partial medium replacements per day with alternating 8-hour and 16-hour intervals over a period of 32 days. Combination of this new cell culture protocol with the previously reported chemical intervention in ES cells changed the population-averaged expression of spermatogonia- and gonocyte-specific genes during the differentiation process and increased the population-averaged gene expression of Lhx1 in the resulting CSMs compared to CSMs without chemical intervention. Furthermore, we detected single CSMs with a strong nuclear LHX1/5 protein signal only in the chemical intervention group. Our results provide the first experimental evidence for the generation of CSMs with an enrichment of Lhx1 expression in vitro. We propose that further investigation of the CSMs generated with this in vitro system may provide new insights into male germline and stem cell development.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
The date on the banner was corrected from 02/12/2022 to 02/12/2021. The only change in this version of the manuscript is that it contains a banner (date corrected) on the title page stating that it is a refereed manuscript via the journal-independent peer review service of PeerRef with the final decision “verified with reservations”. The content was not changed compared to the first version which was used for the peer review process of PeerRef. The review report is posted on the website of PeerRef: https://www.peerref.com/refereed-manuscripts