Synergistic decrease of DNA single-strand break repair rates in mouse neural cells lacking both Tdp1 and aprataxin

DNA Repair (Amst). 2009 Jun 4;8(6):760-6. doi: 10.1016/j.dnarep.2009.02.002. Epub 2009 Mar 19.


Ataxia oculomotor apraxia-1 (AOA1) is an autosomal recessive neurodegenerative disease that results from mutations of aprataxin (APTX). APTX associates with the DNA single- and double-strand break repair machinery and is able to remove AMP from 5'-termini at DNA strand breaks in vitro. However, attempts to establish a DNA strand break repair defect in APTX-defective cells have proved conflicting and unclear. We reasoned that this may reflect that DNA strand breaks with 5'-AMP represent only a minor subset of breaks induced in cells, and/or the availability of alternative mechanisms for removing AMP from 5'-termini. Here, we have attempted to increase the dependency of chromosomal single- and double-strand break repair on aprataxin activity by slowing the rate of repair of 3'-termini in aprataxin-defective neural cells, thereby increasing the likelihood that the 5'-termini at such breaks become adenylated and/or block alternative repair mechanisms. To do this, we generated a mouse model in which APTX is deleted together with tyrosyl DNA phosphodiesterase (TDP1), an enzyme that repairs 3'-termini at a subset of single-strand breaks (SSBs), including those with 3'-topoisomerase-1 (Top1) peptide. Notably, the global rate of repair of oxidative and alkylation-induced SSBs was significantly slower in Tdp1(-/-)/Aptx(-/-) double knockout quiescent mouse astrocytes compared with Tdp1(-/-) or Aptx(-/-) single knockouts. In contrast, camptothecin-induced Top1-SSBs accumulated to similar levels in Tdp1(-/-) and Tdp1(-/-)/Aptx(-/-) double knockout astrocytes. Finally, we failed to identify a measurable defect in double-strand break repair in Tdp1(-/-), Aptx(-/-) or Tdp1(-/-)/Aptx(-/-) astrocytes. These data provide direct evidence for a requirement for aprataxin during chromosomal single-strand break repair in primary neural cells lacking Tdp1.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antineoplastic Agents, Phytogenic / pharmacology
  • Astrocytes / drug effects
  • Astrocytes / metabolism*
  • Camptothecin / pharmacology
  • Cells, Cultured
  • DNA Breaks, Single-Stranded / drug effects*
  • DNA Repair / genetics*
  • DNA Topoisomerases, Type I / metabolism
  • DNA-Binding Proteins / physiology*
  • Fibroblasts / cytology
  • Fibroblasts / drug effects
  • Humans
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Neurons / drug effects
  • Neurons / metabolism*
  • Nuclear Proteins / physiology*
  • Phosphoric Diester Hydrolases / physiology*


  • Antineoplastic Agents, Phytogenic
  • Aptx protein, mouse
  • DNA-Binding Proteins
  • Nuclear Proteins
  • Phosphoric Diester Hydrolases
  • Tdp1 protein, mouse
  • DNA Topoisomerases, Type I
  • Camptothecin