Giant nebenkern produced by colcemid treatment of the spermatocysts of thesilkworm, Bombyx mori

The silkworm spermatocysts isolated from testes were cultured for 24 h in a medium containing 1 mu g of colcemid per mi, which is an inhibitor of tubu lin association to microtubules. In the present experiment, the suppression of meiotic division I by this treatment resulted in the formation of a "gi ant nebenkern" in the primary spermatocyte. Normally, the nebenkern, an org anelle in which all the cell's mitochondria aggregate, is formed in the spe rmatids of insects and changes into elongated mitochondrial derivatives. Af ter washing with the culture medium without colcemid, the cell bearing the giant nebenkern grew to be a sperm with four flagella. When meiotic divisio n II was blocked, the secondary spermatocytes with a nebenkern appeared and the further culture resulted in sperm with two flagella. These results sug gest that the formation of a nebenkern is a necessary step toward the final stages of spermiogenesis.