Chromosome movement during meiotic prophase in crane-fly spermatocytes: IV. Actin and the effects of cytochalasin D

Cytochalasin D (CD) was applied to crane-fly spermatocytes at late diakines is with the aim of perturbing actin structure and actin function, thereby t esting the hypothesis that intranuclear chromosome movement during late dia kinesis is actin-based. Isolated testes were incubated in a range of CD con centrations (2-100 mu M) for 1 or 2 h. None of those treatments resulted in cessation of prophase movements in living cells. An immediate effect of 10 -100 mu M CD at late diakinesis was the formation of highly refractile, act in-containing cables within the nonchromosomal nucleoplasm. No such cables were observed in vehicle-treated control cells. CD treatments caused autoso mal bivalents in unusually large numbers of spermatocytes to become aggrega ted into densely-packed clusters; for example, with 40 mu M CD about 80% of late diakinesis spermatocytes had clustered autosomes, vs. about 25% clust ering in untreated cells. We conclude from these data that the mechanism of chromosome positioning at the nuclear envelope is CD-sensitive. Rhodamine- conjugates of phalloidin and DNase I were used to assess the status of acti n in untreated cells as well as the effect of CD on actin distribution. Dif ferences in nucleoplasmic staining with phalloidin and DNase I conjugates s uggest that nucleoplasm at late diakinesis contains actin in a nonfilamento us form. Cell Motil. Cytoskeleton 43:199-212, 1999. (C) 1999 Wiley-Liss, In c.