The aprt heterozygote/hemizygote system for screening mutagenic agents allows detection of large deletions

Frequencies of mutation at the hprt and aprt loci in various CHO cell lines were measured after exposure of the cells to ionizing radiation. In D423 and AA8-16, which are aprt+/- heterozygotes, the ratio of hprt- mutants to aprt- mutants ranged from 0.11 to 0.36. In D422 and AA8-5, which are aprt+/0 cell lines in which only one copy of the gene and its flanking sequences is present these ratios were greater than 5. In contrast, chemical mutagenesis generated mutations at both loci, in all cell lines, at equal frequencies. Southern blot analysis of DNA from hprt- and aprt- mutants of one of the aprt+/- heterozygous lines showed some apparently unaltered genes, some rearrangements and some complete deletions of hprt among hprt- mutants, but only complete deletions of aprt-linked sequences among aprt- mutants. These results strongly suggest that X-ray-induced mutational events are frequently larger than 40 kb (the length of the hprt gene) and that the difference among the frequencies observed at the two loci in the two types of cell lines were due to the presence of essential sequences close the respective target genes. The combined use of these cell lines in screening environmental mutagens should allow qualitative as well as quantitative analysis of the mutagenic potential of environmental agents.     

Molecular characterization of 15 rearrangements among 90 human in vivo somatic mutants shows that deletions predominate.

Ninety hypoxanthine phosphoribosyltransferase-deficient mutants were isolated from lymphocytes of 31 individuals drawn from both control populations and populations exposed to low doses of ionizing radiation. Southern analysis of the DNA revealed altered hybridization patterns in 15 mutants. Of these, 14 changes consisted of deletions of 2 to 40 kilobases or more.     

Genetic analysis of opaque2 modifier loci in quality protein maize

Quality protein maize (QPM) was created by selecting genetic modifiers that convert the starchy endosperm of an opaque2 (o2) mutant to a hard, vitreous phenotype. Genetic analysis has shown that there are multiple, unlinked o2 modifiers (Opm), but their identity and mode of action are unknown. Using two independently developed QPM lines, we mapped several major Opm QTLs to chromosomes 1, 7 and 9. A microarray hybridization performed with RNA obtained from true breeding o2 progeny with vitreous and opaque kernel phenotypes identified a small group of differentially expressed genes, some of which map at or near the Opm QTLs. Several of the genes are associated with ethylene and ABA signaling and suggest a potential linkage of o2 endosperm modification with programmed cell death.