News | Penn Biologists First Reveal a Two-Way Genetic Arms Race Between Repetitive DNA and Binding Proteins
Deep within the genetic code, a largely overlooked molecular conflict is unfolding. A University of Pennsylvania team reported in Current Biology the first experimental evidence that repetitive genomic sequences called satellite DNA and the proteins that bind them are engaged in an ongoing, two-way evolutionary arms race. The finding challenges traditional views of so-called junk DNA and may offer new explanations for health problems including cancer and infertility.
The study was led by Mia Levine, assistant professor of biology in Penn's School of Arts & Sciences, with postdoctoral researcher Cara Brand as first author.
Not junk DNA, but a possible source of danger?
Satellite DNA does not encode proteins and was long considered genomic noise or an evolutionary remnant. Levine noted that growing evidence shows these repetitive sequences play important roles in chromosome structure, cell division, and other essential processes. Loss of regulation may cause serious consequences, including genomic instability, cancer, and reproductive disorders.
“We usually view the genome as a cooperative system in which every part works to sustain life. But some elements are selfish: they do not cooperate and may even disrupt the whole system,” Levine said.
Cross-species experiment reveals reproductive damage from mismatch
To test whether satellite DNA and binding proteins counterbalance each other during evolution, the team studied two closely related fruit flies: Drosophila melanogaster and Drosophila simulans. The first has an enormous satellite sequence spanning 11 million base pairs, while the second completely lacks it.
Using CRISPR/Cas9, scientists transferred the Drosophila simulans gene for the satellite-binding protein MH (Maternal Haploid) into Drosophila melanogaster. The modified flies could still produce some embryos, but their ovaries developed poorly, egg production fell sharply, and fertility was greatly reduced. When the MH gene was entirely absent, the flies could not reproduce and embryos died.
Crucially, when the gene transfer was performed in a Drosophila melanogaster mutant lacking the satellite DNA sequence, all adverse effects disappeared and ovarian development returned to normal. This showed that the key problem was a mismatch between MH and unfamiliar satellite DNA.
Molecular mechanism identified: DNA repair pathway mistakenly disrupted
The team examined Spartan, the human relative of the MH protein. Spartan breaks down proteins that obstruct DNA packaging, and MH has a similar role. When MH mismatched with Drosophila melanogaster satellite DNA, it may have mistakenly degraded the essential repair enzyme Topoisomerase II (Top2), causing DNA damage and reproductive dysfunction.
Genetically increasing Top2 expression restored fertility, while lowering Top2 worsened the damage. This confirmed that the interaction between MH and satellite DNA involves a DNA repair pathway.
“This repair mechanism exists from yeast to humans and is highly conserved through evolution. Yet its proteins are still evolving rapidly, meaning even core molecular mechanisms continually update to maintain basic function,” Brand said.
Implications beyond fruit flies: The human genome may face a similar internal conflict
“This evolutionary competition is certainly not unique to fruit flies,” Levine said. “Similar rapid evolution occurs in humans and primates. We believe these genetic conflicts are highly important to human health.”
Spartan mutations are associated with cancer, while dysregulated satellite DNA may cause chromosome segregation errors and embryonic aneuploidy, leading to miscarriage and infertility. Levine noted that many miscarriages remain unexplained and satellite DNA is an underexplored source of genomic instability.
The team will next investigate whether other genomic regions participate in this hidden conflict and attempt to reproduce similar mechanisms in mammals.
News | Penn Biologists First Reveal a Two-Way Genetic Arms Race Between Repetitive DNA and Binding Proteins
News | Penn Biologists First Reveal a Two-Way Genetic Arms Race Between Repetitive DNA and Binding Proteins
Deep within the genetic code, a largely overlooked molecular conflict is unfolding. A University of Pennsylvania team reported in Current Biology the first experimental evidence that repetitive genomic sequences called satellite DNA and the proteins that bind them are engaged in an ongoing, two-way evolutionary arms race. The finding challenges traditional views of so-called junk DNA and may offer new explanations for health problems including cancer and infertility.
The study was led by Mia Levine, assistant professor of biology in Penn's School of Arts & Sciences, with postdoctoral researcher Cara Brand as first author.
Not junk DNA, but a possible source of danger?
Satellite DNA does not encode proteins and was long considered genomic noise or an evolutionary remnant. Levine noted that growing evidence shows these repetitive sequences play important roles in chromosome structure, cell division, and other essential processes. Loss of regulation may cause serious consequences, including genomic instability, cancer, and reproductive disorders.
“We usually view the genome as a cooperative system in which every part works to sustain life. But some elements are selfish: they do not cooperate and may even disrupt the whole system,” Levine said.
Cross-species experiment reveals reproductive damage from mismatch
To test whether satellite DNA and binding proteins counterbalance each other during evolution, the team studied two closely related fruit flies: Drosophila melanogaster and Drosophila simulans. The first has an enormous satellite sequence spanning 11 million base pairs, while the second completely lacks it.
Using CRISPR/Cas9, scientists transferred the Drosophila simulans gene for the satellite-binding protein MH (Maternal Haploid) into Drosophila melanogaster. The modified flies could still produce some embryos, but their ovaries developed poorly, egg production fell sharply, and fertility was greatly reduced. When the MH gene was entirely absent, the flies could not reproduce and embryos died.
Crucially, when the gene transfer was performed in a Drosophila melanogaster mutant lacking the satellite DNA sequence, all adverse effects disappeared and ovarian development returned to normal. This showed that the key problem was a mismatch between MH and unfamiliar satellite DNA.
Molecular mechanism identified: DNA repair pathway mistakenly disrupted
The team examined Spartan, the human relative of the MH protein. Spartan breaks down proteins that obstruct DNA packaging, and MH has a similar role. When MH mismatched with Drosophila melanogaster satellite DNA, it may have mistakenly degraded the essential repair enzyme Topoisomerase II (Top2), causing DNA damage and reproductive dysfunction.
Genetically increasing Top2 expression restored fertility, while lowering Top2 worsened the damage. This confirmed that the interaction between MH and satellite DNA involves a DNA repair pathway.
“This repair mechanism exists from yeast to humans and is highly conserved through evolution. Yet its proteins are still evolving rapidly, meaning even core molecular mechanisms continually update to maintain basic function,” Brand said.
Implications beyond fruit flies: The human genome may face a similar internal conflict
“This evolutionary competition is certainly not unique to fruit flies,” Levine said. “Similar rapid evolution occurs in humans and primates. We believe these genetic conflicts are highly important to human health.”
Spartan mutations are associated with cancer, while dysregulated satellite DNA may cause chromosome segregation errors and embryonic aneuploidy, leading to miscarriage and infertility. Levine noted that many miscarriages remain unexplained and satellite DNA is an underexplored source of genomic instability.
The team will next investigate whether other genomic regions participate in this hidden conflict and attempt to reproduce similar mechanisms in mammals.
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