ROLE OF THE CENTROSOME IN MITOSIS - UV MICRO-IRRADIATION STUDY

Ultraviolet micro-irradiation (UV-MI) of the PK (pig kidney embryo) ce ll centrosome (lambda(max) = 280 nm, spot diameter 1.6 mm, exposure ti me 5-15 s) at metaphase and anaphase resulted in functional damage of the centrosome. After UV-MI of the centrosome at early metaphase, chro mosomes quickly (in 1-3 min) moved away from the irradiated pole and t hen encircled the non-irradiated pole. Within 10 min after UV-MI the s pindle disassembled and chromosomes remained unseparated. The minimal dose inducing this effect in 90% of cells was accumulated in 5 s. Afte r the same UV-MI at late metaphase, chromosomes shifted towards the no n-irradiated pole; however, anaphase started and chromosome motion tow ards the non-irradiated pole continued normally. UV-MI of the centroso me at early anaphase for 5-15 s slowed down and then stopped chromosom e motion towards the irradiated pole. This was a result of rapid (with in 2-3 min) disorganization of the half-spindle. Chromosomes continued to move towards the opposite pole normally, while cytokinesis was sig nificantly retarded. No visible lesion was revealed by electron micros copy after 5 s UV-MI, while 15 s irradiation resulted in the truncatio n of the microtubule bundles 1.5-2 mu m from the centrosome. We conclu ded that UV-MI inactivates the centrosome and induces disaggregation o f microtubule initiation sites. The critical point (checkpoint) in mit osis up to which this damage induces mitotic arrest is mid-metaphase.