Role of the centrosome in mitosis: UV micro-irradiation study

Abstract

Ultraviolet micro-irradiation (UV-MI) of the PK (pig kidney embryo) cell centrosome ( λ max=280 nm, spot diameter 1.6 mm, exposure time 5–15 s) at metaphase and anaphase resulted in functional damage of the centrosome. After UV-MI of the centrosome at early metaphase, chromosomes quickly (in 1–3 min) moved away from the irradiated pole and then encircled the non-irradiated pole. Within 10 min after UV-MI spindle disassembled and chromosomes remained unseparated. The minimal dose inducing this effect in 90% of cells was accumulated in 5 s. After the same UV-MI at late metaphase, chromosomes shifted towards the non-irradiated pole; however, anaphase started and chromosome motion towards the non-irradiated pole continued normally. UV-MI of the centrosome at early anaphase for 5–15 s slowed down and then stopped chromosome motion towards the irradiated pole. This was a result of rapid (within 2–3 min) disorganization of the half-spindle. Chromosomes continued to move towards the opposite pole normally, while cytokinesis was significantly retarded. No visible lesion was revealed by electron microscopy after 5 s UV-MI, while 15 s irradiation resulted in the truncation of the microtubule bundles 1.5–2 μm from the centrosome. We concluded that UV-MI inactivates the centrosome and induces disaggregation of microtubule initiation sites. The critical point (checkpoint) in mitosis up to which this damage induces mitotic arrest is mid-metaphase.