Tiny Dna Junctions Provide Feedback To Control Genetic Crossovers

Every caller life originates aft a familial shuffle. When organisms make eggs aliases sperm, maternal and paternal chromosomes brace up and switch pieces of DNA successful a process called crossing over. This speech is essential: without astatine slightest 1 switch per chromosome pair, fertility and patient chromosome numbers are astatine risk. At nan aforesaid time, excessively galore swaps—or excessively galore DNA breaks that initiate them—can harm nan genome. How do cells make judge nan equilibrium is conscionable right? A squad of researchers astir Joao Matos of nan Max Perutz Labs publishes nan answers successful Nature.

The squad discovered that mini DNA structures called Holliday junctions are not conscionable stepping-stones connected nan measurement to crossovers, arsenic scientists agelong believed. Instead, they besides thief stabilize a zipper-like building known arsenic nan synaptonemal complex, which holds paired chromosomes together. This stability, successful turn, tells nan compartment to extremity making further DNA breaks, protecting nan genome from damage.

Our presumption was that Holliday junctions are much than passive DNA links. They are basal for building and maintaining nan synaptonemal complex, ensuring that chromosomes enactment paired until crossovers are fresh to form."

Joao Matos, group leader

To trial this idea, first writer Adrian Henggeler turned to baker's yeast, a elemental organism that scientists often usage arsenic a stand-in for quality cells because it goes done meiosis successful a akin way. He was capable to "freeze" millions of yeast cells astatine nan nonstop infinitesimal erstwhile nan DNA junctions and nan chromosome zipper were present, but earlier nan swaps had taken place. By past cutting nan DNA junctions utilizing a unsocial molecular instrumentality developed successful nan lab, he could spot correct distant what happened next.

"One of our eureka moments was seeing nan synaptonemal analyzable illness successful existent clip nan instant nan junctions were removed," says Adrian. "It was precisely what we had hypothesized, abruptly unfolding successful beforehand of our eyes." Without Holliday junctions, nan chromosome zipper fell apart, caller DNA breaks re-started forming, and meiosis could nary longer proceed correctly.

"This study uncovers a elemental but elegant feedback loop," says Joao. "Once crossovers and nan chromosome zipper are stabilized, nan compartment 'knows' it tin extremity making breaks and move guardant safely pinch meiosis."

The adjacent situation is to find retired whether nan aforesaid rule holds existent successful mammals. If it does, it could shed ray connected basal mechanisms that safeguard fertility and support genome stableness crossed species.