Scientists track impact of DNA damage in the develo...(DNA. Single-strand DNA damage is far mor...)

But the last decade brought evidence linking single-strand DNA damage with human diseases, including ataxia with oculomotor apraxia (AOA1) and spinocerebellar ataxia with axonal neuropathy (SCAN1). Both disorders are inherited and are characterized by progressive difficulty with walking and other movement. AOA1 is among the most common form of certain inherited movement disorders in Japan and Portugal. McKinnon said those reports sparked new interest in single-strand DNA repair.

This study focused on Xrcc1, a protein long recognized as the master regulator of a pathway essential for single-strand DNA repair in the nervous system. The brain is thought to be particularly susceptible to such damage because neurons consume large amounts of oxygen, which can result in excessive production of free radicals and leave them vulnerable to single-strand DNA damage. Because brain cells do not divide, they cannot use the backup repair systems found in other tissues.

Investigators developed a way to switch off Xrcc1 production in the mouse brain and nervous system as development began. The system meant Xrcc1 still worked normally in the rest of the body.

The strategy used mice developed to make a particular enzyme, known as cre recombinase, in just the nervous system. St. Jude researchers then developed a mouse that carried an Xrcc1 gene outfitted with biochemical tags targeting the gene for inactivation by the enzyme. The result was a mouse whose nervous system lacked Xrcc1 and so was unable to efficiently repair the single-strand DNA damage.

The shutdown triggered a dramatic decline of interneurons throughout the cerebellum. In a subgroup of those cells, the damage triggered apoptosis, or programmed cell death. But the findings suggested the greatest loss occurred as the immature cerebellar interneurons, or progenitor cell
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