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In 1931, Hermann J. Muller's postdoctoral student, George D. Snell (Nobel Prize recipient––1980) initiated research to replicate with mice Muller's X-ray-induced mutational findings with fruit flies. Snell failed to induce the two types of mutations of interest, based on fly data (sex-linked lethals/recessive visible mutations) even though the study was well designed, used large doses of X-rays, and was published in Genetics. These findings were never cited by Muller, and the Snell paper (Snell, Genetics 20:545–567, 1935) did not cite the 1927 Muller paper (Muller, Science 66:84, 1927). This situation raises questions concerning how Snell wrote the paper (e.g., ignoring the significance of not providing support for Muller's findings in a mammal). The question may be raised whether professional pressures were placed upon Snell to downplay the significance of his findings, which could have negatively impacted the career of Muller and the LNT theory. While Muller would receive worldwide attention, and receive the Nobel Prize in 1946 "for the discovery that mutations can be induced by X-rays," Snell's negative mutation data were almost entirely ignored by his contemporary and subsequent radiation genetics/mutation researchers. This raises questions concerning how the apparent lack of interest in Snell's negative findings helped Muller professionally, including his success in using his fruit fly data to influence hereditary and cancer risk assessment and to obtain the Nobel Prize. [ABSTRACT FROM AUTHOR]

This paper assesses the judgments of leading radiation geneticists and cancer risk assessment scientists from the mid-1950s to mid-1970s that background radiation has a significant effect on human genetic disease and cancer incidence. This assumption was adopted by the National Academy of Sciences (NAS) Biological Effects of Atomic Radiation (BEAR) I Genetics Panel for genetic diseases and subsequently applied to cancer risk assessment by other leading individuals/advisory groups (e.g., International Commission on Radiation Protection-ICRP). These recommendations assumed that a sizeable proportion of human mutations originated from background radiation due to cumulative exposure over prolonged reproductive periods and the linear nature of the dose-response. This paper shows that the assumption that background radiation is a significant cause of spontaneous mutation, genetic diseases, and cancer incidence is not supported by experimental and epidemiological findings, and discredits erroneous risk assessments that improperly influenced the recommendations of national and international advisory committees, risk assessment policies, and beliefs worldwide. [ABSTRACT FROM AUTHOR]

Germinal mosaicism is a well-established mechanism by which new spontaneous mutations enter the human population, but it is only rather recently that clusters of mutations arising in that way have been acknowledged and dealt with in specific-locus experiments on male mice. This paper reports the first cluster of germinal mosaic mutations to have been identified in experiments on the induction of dominant skeletal mutations. The mutation was detected in six offspring of a control male from the radiation part of an Assessment-of-Dominant-Damage (ADD) experiment. Reasons are provided to explain why this one litter of six mutants was excluded from the analysis of induction of dominant mutations causing the more common skeletal anomalies, which is reported in another paper. The effects of excluding this litter from that analysis are fully described. There is discussion of why such clusters should be included in some analyses but omitted in others. They should certainly always be reported because, in some cases, they can have a major impact on conclusions. Details on this one cluster of FCGM mutations provide numerous examples of how a dominant skeletal mutation that causes rare effects can also cause many of the more common anomalies. [Copyright &y& Elsevier]

Assessment-of-Dominant-Damage (ADD) experiments explored induction by proven specific-locus mutagens of dominant mutations that cause skeletal anomalies, cataracts, and stunted growth in offspring of mutagenized male mice. The data set reported here includes 6134 offspring. Mutagenic treatments included 600 R (i.e., approximately 6 Gy) of X-rays delivered in about 7 min, 600 R of gamma rays delivered over about 110 days, and four weekly intraperitoneal (i.p.) injections of 77.5 mg/kg of ethylnitrosourea (ENU). The results reported in this paper are restricted to mutations induced in stem-cell spermatogonia and to the 34 more common skeletal anomalies (i.e., those found in 0.5% or more of the control offspring). Mutation induction was demonstrated for eight anomalies in the acute X-ray experiment and for 17 anomalies (including those same eight anomalies) in the ENU experiment. In spite of the surprisingly high mutation rates found for these treatments, there was no hint of any induction of such dominant mutations by 600 R of chronic gamma radiation. Our results suggest that several anomalies related to variation in the sacralization pattern may be particularly useful for revealing induction of dominant mutations. [Copyright &y& Elsevier]

Short digits (Dsh) is a radiation-induced mouse mutant. Homozygous mice are characterized by multiple defects strongly resembling those resulting from Sonic hedgehog (Shh) inactivation. Heterozygous mice show a limb reduction phenotype with fusion and shortening of the proximal and middle phalanges in all digits, similar to human brachydactyly type Al, a condition caused by mutations in Indian hedgehog (IHH). We mapped Dsh to chromosome S in a region containing Shh and were able to demonstrate an inversion comprising 11.7 Mb. The distal breakpoint is 13.2 98 kb upstream of Shh, separating the coding sequence from several putative regulatory elements identified by interspecies comparison. The inversion results in almost complete down regulation of Shh expression during E9.S-E12.S, explaining the homozygous phenotype. At E13.S and E14.S, however, Shh is upregulated in the phalangeal anlagen of Dsh/+ mice, at a time point and in a region where WT Shh is never expressed. The dysregulation of Shh expression causes the local upregulation of hedgehog target genes such as Gli1-3, patched, and Pthlh, as well as the downregulation of IHH and Gdf5. This results in shortening of the digits through an arrest of chondrocyte differentiation and the disruption of joint development. [ABSTRACT FROM AUTHOR]