Pluripotent Stem Cells Can Differentiate into Functional Sperm

A new study led by researchers at Kyoto University shows that mouse pluripotent stem cells can differentiate into functional sperm. These sperm were successfully used to produce healthy, fertile offspring and provide the most comprehensive model yet for generating male germ cells in a test tube. The findings were published in Cell Stem Cell. 

Beginning with mouse pluripotent stem cells, the scientists prepared primordial germ cells and examined over 10000 of them in 8 different conditions using what they call a new reconstituted testis method. To validate the best conditions for manufacturing spermatogonia stem cells, they confirmed that the cells shared several properties with those in mouse testis, including the expression of key genes, epigenetics, and the transient upregulation of retrotransposons. 

“Retrotransposon control was recaptured. Retrotransposon regulation is a mechanism to control the effects of retrotransposons on key genes by randomly repeating their regulation,” said lead researcher Mitinori Saitou. The identical epigenetics was also crucial, he added. 

To confirm the spermatogonia stem cells behaved just as those produced in the body, the researchers injected their laboratory-made spermatogonia stem cells into mouse testes, where the cells were allowed to develop into spermatids. These spermatids were harvested and injected into eggs to grow embryos. The embryos were then used to impregnate mice, which went on to give birth to healthy offspring that were also fertile.