Intragenic recombination within the p^un allele of the pink-eyed dilution locus in pre-melanocytes and primordial germ cells of embryonic mice treated with N-ethyl-N-nitrosourea

The forward or reverse processes of intragenic recombination (IGR), which occur through the addition or deletion of duplicated homologous exons of the p^un allele in Pun mice, was observed in vivo, after introducing an homozygous p^un allele in a C57BL/6 background. We assessed the frequency of IGR upon N-ethyl-N-nitrosourea (ENU) treatment of pre-melanocytes (PMCs: somatic cells) and primordial germ cells (PGCs: germ cells) of embryonic mice at 10.5 days of development (E10.5). We simultaneously examined IGR and other mutations at the p locus of PMCs responsible for coat color in the offspring obtained by crossing p^un/p^un with p^un/P mice. The frequencies of both spontaneous and ENU-induced IGR were markedly higher than that of the recessive mutation (RM) in PMCs obtained from crossing C57BL/6 and PW strains (Shibuya et al., 1982). ENU also induces IGR at a higher frequency in PGCs at E10.5, which was observed in the next generation. These results indicate that ENU, which preferentially induces gene mutations through base substitution, also induces IGR at a high frequency in the p^un allele in both somatic and germ cells of embryonic mice at the E10.5 developmental stage.