Effect of hyperthermia on radiation-induced chromosome loss in female Drosophila melanogaster.

Three-day-old adult females of mutagen sensitive mutants: mus (1)101D1, mus(1)102D2, mus(1)103D1, mus(1)104D1, mus(1)105D1, mus(3)302D2; meiotic mutants: mei-9D2, mei-9D3, mei-218, and controls st, and w, were subjected to 38 degrees C for 1 hour and 1200R of gamma rays, brooded daily, and nondisjunction and the loss of X chromosomes determined. This was done in an attempt to gain more information on the hyperthermia sensitization of radiation-induced damage. In several strains the hyperthermia treatment sensitized immature class-1 oocytes--the most radiation-resistant stage--to radiation-induced chromosome loss. This class of oocytes is believed to have the greatest number of repair enzymes, and supports the hypothesis that hyperthermia increases radiation-induced genetic damage by interference with repair enzymes. The mature oocytes, which are believed to lack repair enzymes (stage 14), were the most sensitive to heat treatment and radiation. Hyperthermia failed to increase radiation-induced chromosome loss in the meiotic mutants. Hyperthermia may affect excision repair. There was no clear-cut correlation between other defective DNA pathways and influence of hyperthermia on radiation-induced chromosome loss in Drosophila females. The failure of hyperthermia to increase radiation-induced chromosome loss in meiotic mutants may indicate that radiation sensitization by hyperthermia also may be due to interference with chromosome segregation.