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High Frequency of Mosaic Mutants Produced by N-ethyl-N-nitrosourea Exposure of Mouse Zygotes
L. B. Russell, J. W. Bangham, K. F. Stelzner and P. R. Hunsicker
Proceedings of the National Academy of Sciences of the United States of America
Vol. 85, No. 23 (Dec. 1, 1988), pp. 9167-9170
Published by: National Academy of Sciences
Stable URL: http://www.jstor.org/stable/32909
Page Count: 4
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Mouse zygotes containing one multiplerecessive parental genome (a, b; p cch; d se; s) and the corresponding wild-type alleles in the other were exposed to N-ethyl-N-nitrosourea (ENU) at various stages in vivo. At weaning age, the resulting mice were examined for mutations at the marked loci as well as at others producing externally visible phenotypes. Because of viability problems in one of two reciprocal crosses, the bulk of the mutagenesis data are derived from the cross that detects recessive mutations in the maternal genome. The mutation rate was ≈ 8 times higher in groups treated 2.5-3 hr postmating (sperm entry, completion of second meiotic division) than in those injected 5-6 hr postmating (pronuclear formation). In the former more sensitive zygote population, the mutation rate is about an order of magnitude greater than that induced by the same ENU exposure (50 mg/kg) to spermatogonial stem cells. Of 11 mutants recovered, 8 were mosaics. Progeny tests have demonstrated germ-line involvement for most of the mosaics, and the average fraction of the germ line carrying the mutation is close to 50%. The nature of the mutations indicates (i) that the mosaicism results not from misassortment at the first cleavage but from mutation affecting one DNA strand of the maternal chromosome, and (ii) that the mutations are intragenic lesions rather then multilocus deletions, thus resembling ENU-induced mutations in spermatogonia. The finding that mosaicism for presumed point mutations is readily inducible by ENU treatment of zygotes may provide a means of generating genetic materials that can be of use for developmental studies.
Proceedings of the National Academy of Sciences of the United States of America © 1988 National Academy of Sciences