A member of the shelterin complex helps moor telomeres at the nuclear periphery in worms, Ferreira et al. reveal.
Telomeres protect the ends of chromosomes, and the shelterin complex protects telomeres, preventing them from triggering the DNA damage response. Yeast cells shove their telomeres to the fringe of the nucleus, and the marginalized structures gather into bunches. Plant cells also place their telomeres at the edge of the nucleus. Whether animal cells follow suit is unclear, because researchers have noted that telomeres only briefly remain at the nuclear periphery in cultured mammalian cells. Ferreira et al. zoomed in on nematode telomeres to address what happens during animal development.
The researchers discovered that worm telomeres also accumulate at the boundary of the nucleus, but, unlike in yeast cells, they don’t cluster unless the worm lacks telomerase activity.
Embryos and larval worms rely on different mechanisms to anchor the telomeres at the rim of the nucleus, the team found. In embryonic worms, the shelterin subunit POT-1 helps position the telomeres. Two other proteins, the nuclear envelope protein SUN-1 and the SUMO ligase GEI-17, are also necessary. In larval worms, by contrast, telomeres remain in position even if one of these three proteins is missing. That discrepancy suggests that a different mechanism anchors telomeres in later developmental stages.
Why cells go to the trouble of arranging their telomeres at the nuclear rim isn’t clear, but the positioning could indicate that genes near the ends of chromosomes have been silenced. Alternatively, the nuclear envelope may help shelterin protect chromosome ends from recombination.
Text by Mitch Leslie