Mutagenesis is elevated in male germ cells obtained from DNA polymerase-beta heterozygous mice.
Gametes carry the DNA that will direct the development of the next generation. By compromising genetic integrity, DNA damage and mutagenesis threaten the ability of gametes to fulfill their biological function. DNA repair pathways function in germ cells and serve to ameliorate much DNA damage and prevent mutagenesis. High base excision repair (BER) activity is documented for spermatogenic cells. DNA polymerase-beta (POLB) is required for the short-patch BER pathway. Because mice homozygous null for the Polb gene die soon after birth, mice heterozygous for Polb were used to examine the extent to which POLB contributes to maintaining spermatogenic genomic integrity in vivo. POLB protein levels were reduced only in mixed spermatogenic cells. In vitro short-patch BER activity assays revealed that spermatogenic cell nuclear extracts obtained from Polb heterozygous mice had one third the BER activity of age-matched control mice. Polb heterozygosity had no effect on the BER activities of somatic tissues tested. The Polb heterozygous mouse line was crossed with the lacI transgenic Big Blue mouse line to assess mutant frequency. The spontaneous mutant frequency for mixed spermatogenic cells prepared from Polb heterozygous mice was 2-fold greater than that of wild-type controls, but no significant effect was found among the somatic tissues tested. These results demonstrate that normal POLB abundance is necessary for normal BER activity, which is critical in maintaining a low germline mutant frequency. Notably, spermatogenic cells respond differently than somatic cells to Polb haploinsufficiency.
Allen
Diwi
D
Departments of Cellular and Structural Biology and Pathology, and The Barshop Center for Longevity and Aging Studies, The University of Texas Health Science Center at San Antonio, San Antonio, Texas 78229, USA.
Herbert
Damon C
DC
McMahan
C Alex
CA
Rotrekl
Vladimir
V
Sobol
Robert W
RW
Wilson
Samuel H
SH
Walter
Christi A
CA
D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D001921:Brain / Q000378:metabolism; D004249:DNA Damage; D000072481:DNA Ligase ATP; D011088:DNA Ligases / Q000378:metabolism; D019951:DNA Polymerase beta / Q000378:metabolism*; D004260:DNA Repair; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D006579:Heterozygote; D008099:Liver / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D016296:Mutagenesis; D000075223:Poly-ADP-Ribose Binding Proteins; D013094:Spermatozoa / Q000378:metabolism*; D000076105:X-ray Repair Cross Complementing Protein 1; D029867:Xenopus Proteins
D004268:DNA-Binding Proteins; D000075223:Poly-ADP-Ribose Binding Proteins; D000076105:X-ray Repair Cross Complementing Protein 1; D029867:Xenopus Proteins; D019951:DNA Polymerase beta; C486216:Apex1 protein, mouse; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase; D011088:DNA Ligases; D000072481:DNA Ligase ATP; C000618816:DNA ligase III alpha protein, Xenopus