RHODAMINE-PHALLOIDIN AND ANTITUBULIN ANTIBODY STAINING OF SPINDLE FIBERS THAT WERE IRRADIATED WITH AN ULTRAVIOLET MICROBEAM

We irradiated chromosomal spindle fibres in crane-fly spermatocytes wi th an ultraviolet microbeam of 270 nm wavelength light with total ener gies near those that cause actin filaments in myofibrils to depolymeri ze; after irradiation we stained the cells with rhodamine-labelled pha lloidin and with anti-tubulin antibodies. In some cells, the irradiati on reduced both phalloidin and tubulin staining of the chromosomal spi ndle fibres; in other cells, the irradiations reduced phalloidin stain ing but not tubulin staining; in yet other cells, the irradiations red uced tubulin staining but not phalloidin staining. In all irradiated c ells in which phalloidin staining was reduced in the irradiated areas phalloidin staining also was reduced poleward from the irradiated area s. These results show that phalloidin staining of chromosomal spindle fibres is not dependent on the presence of kinetochore microtubules, a nd, therefore, that actin filaments are present in the spindle fibres in vivo. We suggest that actin filaments present in spindle fibres in vivo may be involved in causing chromosome movements during anaphase.