Microtubule dynamics and distribution of γ-tubulin in male germ cells of Bombyx mori (Lepidoptera)

Male germ cells of Bombyx mori (Lepidoptera) have three cell kinds such as spermatogonia, eupyrene spermatocytes and apyrene spermatocytes. We observed spindle structure and the distribution of γ-tubulin in spermatogenesis. The microtubules (MTs) of mitotic apparatus in Bombyx spermatogonia were similar to that of general mammalian cells. In eupyrene spermatocytes, the asters were separated from the spindle pole, and then the spindle was transformed into a barrel shape at metaphase. In apyrene spermatocytes, the feeble-looking spindle body was formed, and asters were not separated at metaphase. The barrel-shaped spindle was not formed in apyrene metaphase cells. The chromosome arrangements on the equatorial plate were quite rough at metaphase and the movements toward the poles during anaphase were not synchronous. In all the three kinds of cells, spots of γ-tubulin were observed at centrosomes during cell division. Only in eupyrene spermatocytes, however, γ-tubulin was also disclosed in the spindle region from metaphase to anaphase. Many newly formed non-kinetochore-MTs appeared in the spindle interzonal region when the kinetochore-MTs disappeared and chromosomes reached the flat edge of spindle pole. It is indicated that non-kinetochore-MTs are built up by the action of spindle γ-tubulin. On the other hand, the distribution of γ-tubulin in apyrene spermatocytes appeared similar to the spermatogonia that performed regular chromosome separation. Therefore, we consider that the feeble spindle and the missegregation of chromosomes in apyrene meiosis are not caused by the γ-tubulin in the centrosomes