Mason J M, Champion L E, Hook G
Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709-2233, USA.
Genetics. 1997 Aug;146(4):1381-97. doi: 10.1093/genetics/146.4.1381.
A mutator, mu2a, in Drosophila melanogaster potentiates terminal deficiencies. In the female germ line the gamma mutant frequency induced by irradiation of mature oocytes with 5 Gy increases approximately twofold in heterozygotes and 20-fold in homozygotes compared with wild type. The recovery of terminal deficiencies is not limited to breaks close to chromosome ends; high frequencies of deficiencies can be recovered with breakpoints located in centric heterochromatin or near the middle of a chromosome arm. Lesions induced by gamma-rays are repaired slowly in mu2a oocytes, but become "fixed" as terminal deficiencies upon fertilization. A few lesions induced in wild-type females also produce terminal deficiencies. Mutator males do not exhibit an increase in terminal deletions, regardless of the germ cell stage irradiated. In addition, there is no increase in the mutant frequency when mature sperm are irradiated and fertilize eggs produced by mu2a females. The data are consistent with the hypothesis that lesions induced in sperm chromosomes are repaired after fertilization, while lesions induced in oocyte chromosomes are shunted instead to a mechanism that stabilizes broken chromosome ends. We propose that mu2 affects chromosomal structure during oogenesis, thereby modulating DNA repair.
果蝇中的一种突变体mu2a会增强末端缺失。在雌性生殖系中，用5 Gy照射成熟卵母细胞诱导产生的γ突变频率，与野生型相比，杂合子中增加约两倍，纯合子中增加20倍。末端缺失的恢复并不局限于靠近染色体末端的断裂；位于着丝粒异染色质或染色体臂中部附近的断点也能以高频率恢复缺失。γ射线诱导的损伤在mu2a卵母细胞中修复缓慢，但在受精后会作为末端缺失“固定”下来。野生型雌性中诱导产生的一些损伤也会产生末端缺失。无论照射的生殖细胞处于哪个阶段，突变体雄性的末端缺失都不会增加。此外，当照射成熟精子并使其使mu2a雌性产生的卵子受精时，突变频率也不会增加。这些数据与以下假设一致：精子染色体中诱导产生的损伤在受精后会被修复，而卵母细胞染色体中诱导产生的损伤则会转而进入一种稳定断裂染色体末端的机制。我们提出，mu2在卵子发生过程中影响染色体结构，从而调节DNA修复。
