What we generally take away from classes in basic biology is that our DNA calls the shots when it comes to the developmental stages of human life. But a team led by Dr. Miguel Ramalho-Santos, Senior Investigator at the Lunenfeld-Tanenbaum Research Institute (LTRI), has fundamentally shifted our understanding of how we develop at the embryonic stage.
The research explored the role of transposons — DNA elements often referred to as “selfish DNA” due to their ability to prioritize their own replication during early development, sometimes at the expense of other genes or the organism’s overall well-being.
For years, scientists believed transposons were mostly harmful, occasionally wreaking havoc in the genome and contributing to a variety of diseases, including hemophilia, neurological disorders and cancer.
“But here we have discovered that these elements are not mere genomic parasites but are essential for early development.“
— Dr. Miguel Ramalho-Santos, who holds the Canada 150 Research Chair in Developmental Epigenetics
The study, published in the January 2025 issue of Developmental Cell, indicates that transposons are in fact critical to ensuring human embryonic cells proceed normally through early development. In fact, when these DNA elements are inhibited, or prevented from behaving normally, embryonic cells regress back to a more primitive stage.
The research team focused their investigation on a particular type of transposon called LINE-1. Dr. Juan Zhang, a senior co-author and post-doctoral fellow who spearheaded the research, initially found it intriguing that LINE-1 was abundant in early embryos.
“We show that LINE-1 regulates gene expression at a crucial turning point where the embryo starts to specialize its cells for various functions. Our results indicate that this is not an accidental occurrence but a vital evolutionary mechanism,” says Dr. Zhang.
This fundamental research has important implications for fertility treatments and the use of stem cells in regenerative medicine. Moreover, this work unveils novel roles for LINE-1 that can now be explored in the disease contexts where it has been implicated, from neurological disorders to cancer.
Dr. Anne-Claude Gingras, Director of LTRI and Vice-President of Research for Sinai Health, says, “This research underscores just how much more there is to learn, not only about human development but also about these enigmatic genome elements whose roles are only beginning to emerge. I congratulate my colleagues on breaking new ground with this fascinating insight into human biology, and I eagerly anticipate further discoveries as they continue their work.”