"Jumping Genes," also known as transposons, are being studied by researches at the Carnegie Institution of Science to better understand their influence on the genome.
Transposons make up almost half of our DNA sequences, Carnegie scientists say, and they play a key role in evolution. But their "jumping" can also cause mutations that lead to diseases. Transposons occur in developing sperm and egg cells, but scientists know little about their movements and how they influence future biological developments.
The scientists at Carnegie began studying the jumping genes and found that during a certain period of time of egg cell development, a group of jumping genes hijack a group of cells called "nurse cells" that nurture the developing eggs. The jumping genes use the nurse cells to produce invasive material, similar to how viruses behave, that move into nearby egg cells and and duplicate, affecting other egg cells.
Through evolution, animals have developed a system to suppress the jumping genes using RNA, another form of genetic material, called piRNA. The piRNA suppresses the jumping genes, though some of the jumping genes manage to still move, showing they may have a way to recognize and avoid the piRNA, scientists said.
Conducting research utilizing fruit flies, scientists attempted to track the movements of jumping genes by disrupting the piRNA suppression. Scientists discovered the jumping genes behave as parasitic genetic elements.
“We were very surprised that the these jumping genes barely moved in stem cells that produce developing egg cells, possibly because the stem cells would only have two copies of the genome for these jumping genes to use," said Zhao Zhang, Staff Associate at Carnegie who co-authored the study. "Instead, these moving elements used the supporting nurse cells, which could provide up to thousands copies of the genome per cell, as factories to massively manufacture virus-like particles capable of integration. However, they didn’t integrate into nurse cells where they were produced. Rather, they waited while they were transported into an interconnected egg cell, and then added hundreds, if not thousands, of new copies of themselves into the egg DNA. Our research shows how parasitic genetic elements can time their activity and distinguish between different cell types to robustly propagate to drive evolutionary change and cause disease.”