Without rings, chromosome arms get broken
Protein ring ensures daughter-cells inherit complete genetic information
You hop on the train, turn around to say goodbye, and the announcement sounds: ‘doors closing’. If you ignore the warning for the sake of one last wave to a friend on the platform, the doors may bruise you, but they won’t cut off your arm. Dividing yeast cells, it seems, are more ruthless. In a study published online in Developmental Cell, Christian Haering and his lab at EMBL Heidelberg have discovered that when these cells divide, chromosome arms which don’t move away in time get broken.
The work confirms the group’s idea that a protein called condensin keeps chromosome arms coiled up, to allow them to be safely moved to opposite ends of the cell before it divides. “We knew from our previous work that condensin forms rings around chromosomes,” says Haering. “In this study, we cut those rings open, and what we saw was that chromosome arms trailed behind – they didn’t make it away from the area where the cell splits in two. And most surprisingly, the cell just divided anyway.”
The results highlight the importance of condensin in ensuring that daughter-cells inherit the genetic material they need to survive. Without condensin rings to keep them coiled up, chromosome arms can get broken by the ‘closing door’ that separates the cells. What’s more, cells with broken chromosomes are left with no way to repair the damage, since the severed genetic material is out of reach in their sister, which leaves them unable to divide again.
By contrast, human cells come closer to safety-conscious trains: faced with chromosome arms trailing across the cutting plane, they stop the door from closing, halting cell division – most of the time. “But some cancer cells show signs that bits of chromosomes have broken and been attached to other chromosomes instead,” Haering points out. “It’s easy to imagine how that could have happened in a context where condensin failed to do its job.”
Sara Cuylen, Jutta Metz, Andrea Hruby, and Christian H Haering. Entrapment of Chromosomes by Condensin Rings Prevents Their Breakage during Cytokinesis. Developmental Cell, Volume 27, Issue 4, 469-478, 25 November 2013. DOI: 10.1016/j.devcel.2013.10.018.
The Haering lab's previous discovery that condensin forms rings around chromosomes