Why this Project?

While mutations in genes such as Atm and Brca1 lead to an increase in radiosensitivity to the individual, nothing is yet known as to whether such mutations also result in increased genetic damage, which can be passed on to offspring.

Project Goals:

1. To investigate whether mice that are heterozygous for genes that confer somatic radio sensitivity also show an increased low-dose radiosensitivity for germline mutations.
   
2. To determine whether the heterozygosity at these genes can result in germline instability in the offspring of irradiated males.
   
3. To measure the spectra and dose response for mutations at expanded simple tandem repeat (ESTR) loci in the germline of ATM and BRCA1 heterozygote male mice acutely exposed to low doses of low-LET radiation, at pre-meiotic stages of spermatogenesis.

Experimental Approach

1. A new sensitive single-molecule PCR system is being used to score mutations at a mouse expanded simple tandem repeat (ESTR) loci to assess germline mutation rates at very low doses.
   
2. As an initial study, the mutation yield at an ESTR locus in the germline of five different wild-type mouse strains will be acutely exposed to low-LET radiation at pre-meiotic stages of spermatogenesis and the mutation yield compared.
   
3. Male Atm +/- and Brca1 +/- mice (and wild-type controls) will be irradiated with γ-ray doses of 0, 0.1 and 0.5 Gy, and germline mutations will be scored in the irradiated animals and in their unirradiated offspring.
   
4. ATM knock-out mice will be experimented with on several different backgrounds in order to find the best model. The most reliable mice in terms of ESTR amplification will be used in our studies.

Expected Outcomes

Most mutational events that were observed involved the gain or loss of a small number of repeat units. The highest values of doubling dose were obtained for two genetically related strains, BALB/c and CB17, while the other strains (CBA/H, C57BL/6 × CBA/H F1 and 129SVJ × C57BL/6) were more sensitive. The research will determine the reasons for these different radiation sensitivities.