Nevertheless, regulated DNA breakage (and subsequent repair) is necessary for normal development of germ cells. This process must therefore be precisely and strictly controlled by the cell. One way to protect important regions of germ cell DNA is to direct DNA breaks from genes into less important regions. In both mice and humans, the Prdm9 gene is important for directing DNA breaks. The Prdm9-deficient mice examined thus far could not produce offspring. However, the Prdm9 gene is not indispensable for fertility in canids, birds, and likely in human. It was therefore unclear whether and how the results of mouse research can contribute to the knowledge of the mechanisms of development of human germ cells.

The scientific team lead by Zdenek Trachtulec from the Institute of Molecular Genetics of the Czech Academy of Sciences (in the BIOCEV center) has discovered male mice that do not require a functional Prdm9 gene to produce sperm or offspring. Wild-derived mice from the Czech Republic and the tradition of Czech genetics played a major role in this project. In collaboration with colleagues from the United States, Czech scientists have identified a possible cause for the difference in fertility of Prdm9-deficient mice: fertile males repair the DNA breaks in male germ cells more effectively than sterile males. Thus, Czech mice have become an excellent tool to study the development of human sperm and male fertility.

Image of developing male germ cell, where DNA breaks under repair are immunolabeled in orange; chromosomes in green and their ends in magenta.