Skip to main content

Non-coding RNA pathways and the mammalian male germline

Final Report Summary - NCRNA (Non-coding RNA pathways and the mammalian male germline)

The germ cells are the cell line that gives rise to the sperm and eggs cells that are responsible for the continuity of life. In this respect they merit special attention and are termed the ‘immortal lineage’ because it is the DNA from these cells that crosses the generation barrier and their integrity is crucial to the long-term health of species or society in a human context. The ncRNA award focused on the biology of the germ cells themselves as well as the molecular processes that support their development and survival. RNA is the molecular perspective that my laboratory researches. RNA is copied (transcribed) from the DNA to make coding and non-coding RNAs. The coding RNAs is used as a template to instruct the construction (translate) of the protein-based molecular machines in the cell, whereas the non-coding RNAs (ncRNAs) constitute part of the molecular machinery or have important regulatory function within the cell. In this award we sought to understand how certain types of regulatory ncRNA contributes to spermatogenesis (the process that produces sperm cells) and the identity of spermatogonial stem cells (the stem cells that ensure continued sperm production and fertility throughout adult life). All of our studies were conducted in mice as they are amenable to genetic manipulation that allows one, in conjunction with other techniques, to precisely understand their contribution to a process.

Mobile elements termed transposons are found in the DNA and if they get transcribed into RNA they have the ability to copy/paste themselves into new locations within the DNA. This can cause DNA damage and/or the introduction of mutations into the DNA that are very detrimental to the health of the germ cell and thus possibly future generations. We sought to understand how a type of regulatory ncRNA termed PIWI-interacting (piRNAs) contributes to spermatogenesis. PIWI proteins are molecular RNA scissors that are guided to their targets by piRNAs. We found that the PIWI:piRNA pathway neutralizes transposon’s ability to jump into new DNA locations by cutting the transcribed transposon RNA intermediates during meiosis, the period when germ cells are mixing maternal and paternal DNA. We also identified an additional chromatin (the proteins that package the DNA)-based mechanism that silences transposons to ensure normal germ cell development and the production of sperm. These mechanisms work sequentially during sperm cell development and together with another transposon defence system are essential for protecting spermatogonial stem cells. In summary, we understood the variety of transposon defence mechanisms and how they integrate to protect the immortal lineage from mutation.

Another large achievement of the award was the identification a novel spermatogonial population that is critically required for the efficient regenerative capacity of the testis after injury in mice. These findings have important consequences for experimental and regenerative medicine. There is large and growing unmet clinical demand for fertility preservation of pre-pubescent male cancer patients who are rendered sterile by chemotherapy. While adolescent and adult cancer patients can freeze sperm for future fertility needs, no such fertility strategy is available for pre-pubescent boys. Our study identifies a novel population of potential target stem cells for cryopreservation as future donor cells for transplantation for the restoration of fertility. This objective is one of the ultimate goals of the field and our research merits an important milestone. We plan in the future to explore human spermatogonial stem cell populations and methods from their cryopreservation.