A comparison of the dominant cataract and recessive specific-locus mutation rates induced by treatment of male mice with ethylnitrosourea.
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Animals↗
Biomedical subjects
J Favor
Publications and source records attributed to J Favor.
Response to M.A. Dalebroux, testing for the presence of a partially penetrant dominant gene.
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Animals↗
Dominant cataract mutations and specific-locus mutations in mice induced by radiation or ethylnitrosourea.
In a combined experiment, dominant cataract mutations and specific-locus mutations were scored in the same offspring. In radiation experiments, a total of 15 dominant cataract and 38 specific-locus mutations was scored in 29396 offspring. In experiments with ethylnitrosourea (ENU), a total of 12 dominant cataracts and 54 specific-locus mutations was observed in 12712 offspring. The control frequency for dominant cataracts was 0 in 9954 offspring and for specific-locus mutations 11 in 169955 offspring. The ratio of radiation-induced recessive visible to dominant mutations was about 2.5:1. The difference was even more pronounced for ENU-induced mutations. The ratio of recessive visibles to dominant cataracts for chemically induced mutations in spermatogonia was about 5.4:1. The two characteristic features of radiation-induced specific-locus mutations--the augmenting effect of dose fractionation and the quantitative differences in the mutation rates between spermatogonial and post-spermatogonial stages--can also be demonstrated for the induction of dominant cataracts. The dominant cataract mutations recovered can be categorized into 7 phenotypic classes: total opacity, nuclear and zonular cataract, nuclear cataract, anterior pyramidal cataract, anterior polar cataract, anterior capsular cataract, and vacuolated lens. The largest class of mutations, a total of 11, affected the anterior polar region, while the number of total opacities in both experiments was 5. The only noteworthy difference observed between the radiation- and ENU-induced mutations recovered was that, of the 2 radiation-induced total lens opacities, both were associated with an iris anomaly and microphthalmia whereas the ENU-induced total opacities were not.
Animals↗
Chemical and radiation induced late dominant lethal effects in mice.
Although theoretically expected, experimental data to date have not shown dominant lethal expression to occur throughout the developmental period. Specifically, late post-implantation effects have not been demonstrated. We routinely use an experimental technique in which parental females mated to mutagenically treated males are allowed to give birth and wean their litter, and their uterine horns are then inspected for uterine scars indicative of live and dead embryos. In a number of experiments in which males were mutagenically treated with either chemicals or X-irradiation, a discrepancy was observed between the number of live embryos as determined by the scar technique and the number of live observed at birth, suggesting the possibility of embryonic losses at a late stage in development. Initial analyses showed that mutagenic treatment increased the percentage of these late losses. These differences were statistically significant in 2 of 3 analyses. Factors affecting statistical significance and an understanding of dominant lethal mutations are discussed.
Animals↗
EMS-induced dominant lethal dose response curve in DBA/1J male mice.
An ethyl methanesulfonate (EMS) induced dominant lethal dose response experiment was conducted in strain DBA/1J male mice. Two methods of scoring for dominant lethals, the classic method (dissecting females at mid-pregnancy) and an alternative method (inspection of uterine scars after litters were weaned) were compared. Results indicate that strain DBA/1J has a similar sensitivity to EMS-induced dominant lethals as has been previously reported for other mouse genotypes. Of the two methods used to score dominant lethals, the classic method is more sensitive.
Animals↗
Induction of gene mutations in mice: the multiple endpoint approach.
The multiple endpoint mammalian mutagenesis approach developed in our institute screens in the same animal for recessive specific-locus alleles at 7 loci, approximately 30 loci coding for dominant-cataract mutations, 23 loci controlling protein-charge changes and 12 loci for enzyme-activity alterations. Experiments to screen for the approximately 70 loci in the same offspring of treated male mice were performed with ethylnitrosourea (ENU), procarbazine and X-ray exposure. Mutations were recovered for each genetic endpoint in all treatment groups where a sufficient number of offspring was scored. ENU treatment is highly effective in inducing mutations to all genetic endpoints. The mutations were confirmed by breeding tests. The mutation rates to specific-locus and enzyme-activity alleles were both higher than the mutation rates to either dominant-cataract or protein-charge alleles. The advantages and possibilities of the multiple endpoint approach are discussed in detail.
Animals↗
Dominant cataract and recessive specific locus mutations in offspring of X-irradiated male mice.
Male mice were X-irradiated with 3.0 + 3.0 Gy or 5.1 + 5.1 Gy (fractionation interval 24 h). The offspring were screened for dominant cataract and recessive specific locus mutations. In the 3.0 + 3.0-Gy spermatogonial treatment group, 3 dominant cataract mutations were confirmed in 15 551 offspring examined and 29 specific locus mutations were recovered in 18 139 offspring. In the post-spermatogonial treatment group, 1 dominant cataract mutation was obtained in 1120 offspring and 1 recessive specific locus mutation was recovered in 1127 offspring. The induced mutation rate per locus, per gamete, per Gy calculated for recessive specific locus mutations is 2.0 X 10(-5) in post-spermatogonial stages and 3.7 X 10(-5) in spermatogonia. For dominant cataract mutations, assuming 30 loci, the induced mutation rate is 5.0 X 10(-6) in the post-spermatogonial stages and 1.1 X 10(-6) in spermatogonia. In the 5.1 + 5.1-Gy spermatogonial treatment group, 3 dominant cataract mutations were obtained in 11 205 offspring, whereas in 13 201 offspring 27 recessive specific locus mutations were detected in the spermatogonial group. In the post-spermatogonial treatment group no dominant cataract mutation was observed in 425 offspring and 2 recessive specific locus mutations were detected in 445 offspring. The induced mutation rate per locus, gamete and Gy in spermatogonia for recessive specific locus mutations is 2.8 X 10(-5) and for dominant cataract mutations 0.9 X 10(-6). In post-spermatogonial stages, the mutation rate for recessive specific locus alleles is 6.2 X 10(-5). In the concurrent untreated control group, in 11 036 offspring no dominant cataract mutation and in 23 518 offspring no recessive specific locus mutation was observed. Litter size and the number of carriers at weaning have been determined in the confirmation crosses of the obtained dominant cataract mutants as indicators of viability and penetrance effects. Two mutants had a statistically significantly reduced litter size and one mutant had a statistically significantly reduced penetrance.
Animals↗
Genetic localization and phenotypic expression of X-linked cataract (Xcat) in Mus musculus.
Linkage data relative to the markers tabby and glucose-6-phosphate dehydrogenase are presented to locate X-linked cataract (Xcat) in the distal portion of the mouse X-chromosome between jimpy and hypophosphatemia. The human X-linked cataract-dental syndrome, Nance-Horan Syndrome, also maps closely to human hypophosphatemia and would suggest homology between mouse Xcat and human Nance-Horan Syndrome genes. In hemizygous males and homozygous females penetrance is complete with only slight variation in the degree of expression. Phenotypic expression in Xcat heterozygous females ranges from totally clear to totally opaque lenses. The phenotypic expression between the two lenses of a heterozygous individual could also vary between totally clear and totally opaque lenses. However, a correlation in the degree of expression between the eyes of an individual was observed. A variegated pattern of lens opacity was evident in female heterozygotes. Based on these observations, the site of gene action for the Xcat locus is suggested to be endogenous to the lens cells and the precursor cell population of the lens is concluded to be small. The identification of an X-linked cataract locus is an important contribution to the estimate of the number of mutable loci resulting in cataract, an estimate required so that dominant cataract mutagenesis results may be expressed on a per locus basis. The Xcat mutation may be a useful marker for a distal region of the mouse X-chromosome which is relatively sparsely marked and the X-linked cataract mutation may be employed in gene expression and lens development studies.
Animals↗
Mouse small eye results from mutations in a paired-like homeobox-containing gene.
Small eye (Sey) in mouse is a semidominant mutation which in the homozygous condition results in the complete lack of eyes and nasal primordia. On the basis of comparative mapping studies and on phenotypic similarities, Sey has been suggested to be homologous to congenital aniridia (lack of iris) in human. A candidate gene for the aniridia (AN) locus at 11p13 has been isolated by positional cloning and its sequence and that of the mouse homologue has been established (C.T., manuscript in preparation). This gene belongs to the paired-like class of developmental genes first described in Drosophila which contain two highly conserved motifs, the paired box and the homeobox. In vertebrates, genes which encode the single paired domain as well as those which express both motifs have been described as the Pax multigene family. A Pax gene recently described as Pax-6 is identical to the mouse homologue of the candidate aniridia gene. Here we report the analysis of three independent Sey alleles and show that indeed this gene is mutated and that the mutations would predictably interrupt gene function.
Alleles↗