Chapter 1
Introduction to the Detection
of DNA Strand Breaks
T AKEHIKO KOJI
Introduction
DNA strand breaks, especially single-stranded breaks (SSB), are
very commonly found through the life cycle of cells. In fact, SSB
have been implicated to play important roles in the regulation of
cell proliferation (Stewart et a1.1990), cell differentiation (Appleby and Modak 1977; Farzaneh et a1.1982; Dawson and Lough
1988) and cell death (Gold et al. 1993; Peitsch et al. 1993; Bortner
et al. 1995; Hashimoto et al. 1995). Also, in the course of replicative DNA synthesis (Ogawa and Okazaki 1980), DNA repair
(Ma et al. 1995) and genetic recombination in meiosis, SSB occur
transiently. On the other hand, DNA double-stranded breaks
(DSB) were often the results of DNA damages induced by irradiation of ionizing radial rays or by some antitumor drugs. Recently, however, DSB have been highlighted as a biochemical
marker (Wyllie 1980) of apoptosis, the notion of which was introduced by Kerr et al. (1972). Currently, cell death is categorized
into two groups; apoptosis and necrosis. Apoptosis, in contrast
to necrosis, is morphologically characterized by the special features of chromatin condensation to the nuclear periphery and
the fragmentation of the cell into apoptotic bodies. More importantly, apoptosis requires the de novo expression of specific
genes and so implies that the death can be manipulated artificially.
To demonstrate the presence ofSSB, the nucleoid sedimentation technique was previously undertaken as a biochemical
method, where the nucleoids consisting of DNA in a supercoiled
Correspondence to Takehiko Koji, Nagasaki University, Dept. of Histology
and Cell Biology, 1-12-4, Sakamoto, Nagasaki, 852-8523, Japan (phone +81095-849-7025; fax +81-095-849-7028; e-mail tkoji@net.nagasaki-u.ac.jp)
Introduction to the Detection
of DNA Strand Breaks
T AKEHIKO KOJI
Introduction
DNA strand breaks, especially single-stranded breaks (SSB), are
very commonly found through the life cycle of cells. In fact, SSB
have been implicated to play important roles in the regulation of
cell proliferation (Stewart et a1.1990), cell differentiation (Appleby and Modak 1977; Farzaneh et a1.1982; Dawson and Lough
1988) and cell death (Gold et al. 1993; Peitsch et al. 1993; Bortner
et al. 1995; Hashimoto et al. 1995). Also, in the course of replicative DNA synthesis (Ogawa and Okazaki 1980), DNA repair
(Ma et al. 1995) and genetic recombination in meiosis, SSB occur
transiently. On the other hand, DNA double-stranded breaks
(DSB) were often the results of DNA damages induced by irradiation of ionizing radial rays or by some antitumor drugs. Recently, however, DSB have been highlighted as a biochemical
marker (Wyllie 1980) of apoptosis, the notion of which was introduced by Kerr et al. (1972). Currently, cell death is categorized
into two groups; apoptosis and necrosis. Apoptosis, in contrast
to necrosis, is morphologically characterized by the special features of chromatin condensation to the nuclear periphery and
the fragmentation of the cell into apoptotic bodies. More importantly, apoptosis requires the de novo expression of specific
genes and so implies that the death can be manipulated artificially.
To demonstrate the presence ofSSB, the nucleoid sedimentation technique was previously undertaken as a biochemical
method, where the nucleoids consisting of DNA in a supercoiled
Correspondence to Takehiko Koji, Nagasaki University, Dept. of Histology
and Cell Biology, 1-12-4, Sakamoto, Nagasaki, 852-8523, Japan (phone +81095-849-7025; fax +81-095-849-7028; e-mail tkoji@net.nagasaki-u.ac.jp)