DNA damage at Lamina-Associated Domains triggers nuclear envelope reorganization and chromatin detachment to prevent nuclear envelope blebbing and genome instability

Why it matters

Large stretches of our DNA that are switched off are anchored to the inside of the nuclear envelope, on a protein mesh called the nuclear lamina. These stretches are called lamina-associated domains, or LADs. The nuclear edge is known to matter for genome stability and repair, and changes in the lamina are a well-known feature of ageing and of senescent cells. Yet it has been unclear what happens when DNA inside these anchored domains breaks. Because damaged nuclei and a fragile nuclear envelope are linked to ageing, understanding how cells handle breaks at this location could explain one route by which genome damage turns into broken nuclear structure.

What they did

The authors used systems that let them cut both DNA strands at chosen times and at precise places inside LADs. They then watched what happened to the nuclear lamina, to the position of the damaged DNA and to the repair process. They tested which damage-signalling proteins were needed, including ATM, a master kinase that senses breaks, and the chain of proteins it activates. They also tested the role of the LINC complex, which links the inside of the nucleus to the cytoskeleton outside it, and of cytoskeletal components. Finally they forced damaged LADs to stay tethered to the nuclear edge to see the consequences. The abstract does not give the cell types used.

What they found

Breaks inside LADs set off remodelling of the nuclear lamina, and the damaged domains came loose from the envelope and moved into the interior of the nucleus. This movement was controlled by the ATM, gamma-H2AX, MDC1, RNF168 and 53BP1 signalling chain and needed the LINC complex and the cytoskeleton. It did not change which repair pathway the cell chose. When damaged LADs were kept tethered at the periphery, the damage response and repair were delayed, genomic instability rose, and chromatin was pushed out of the nucleus through blebs, small bulges in the nuclear envelope. The authors argue that this links failed repair directly to loss of nuclear integrity, and that moving damaged LADs may relieve mechanical stress and help repair.

Limits

This is a preprint and has not been peer reviewed, so its results may change. The synopsis is based on the abstract only. The abstract mentions ageing and senescence as the reason the question matters, but the experiments it describes are in cells with engineered breaks, not in aged tissue or animals, so a direct role in ageing is not shown. The protective role of the movement is stated as something that 'might' happen, which is a proposal rather than a demonstrated result.

Key terms

Lamina-associated domains (LADs)

Large, mostly silent regions of DNA anchored to the nuclear lamina at the inner edge of the nucleus.

Nuclear lamina

A mesh of lamin proteins lining the inside of the nuclear envelope that gives the nucleus its shape and strength.

ATM

A kinase enzyme that senses DNA double-strand breaks and switches on the damage response.

53BP1

A protein that gathers at double-strand breaks and helps steer and protect the repair process.

LINC complex

A set of proteins spanning the nuclear envelope that connects the nucleus to the cell's cytoskeleton.

Nuclear bleb

A bulge in the nuclear envelope where chromatin can spill out; a sign of a weakened nucleus.