A method for the selective irradiation of part of a genome

Abstract

We developed a method for partial irradiation of cell nuclei and for highlighting the irradiated chromatin domain(s) in both interphase nuclei and metaphase chromosomes. The method involves the use of the replication program of chromosomes and consists of three major steps: I) selection of a suitable chromatin domain, II) damage induction by ¹²⁵I, and III) visualization of the domain. Here, the first step of the method, applied to Chinese hamster HA-1 cells, is described. Using pulse labelling with the replication marker IUdR, it was shown that X_q does not replicate at early S-phase and that the replication timing of X_q can be highly effectively synchronized with hydroxyurea in a whole cell population. Thus, the replication timing of X_q may be used to exclude or to incorporate ¹²⁵I into the X_q. Other chromatin can be selected and targeted with ¹²⁵I in a similar way. Examples of possible applications of the method are given.