Abstract
Cleavage cycles commence and chromosome and centrosome cycles proceed in harmony following fertilization of Drosophila eggs and completion of the meiotic divisions. The sperm-introduced centrioles replicate, separate, and while recruit pericentriolar material centrosomes (CS) form. The CS nucleate asters of microtubules (MT). Spindles form following interaction of some astral MT with kinetochores. In unfertilized eggs, chromosomes do not replicate, and CS and MT asters never form, although their components are present in the egg cytoplasm; unknown mechanisms prevent chromosome replication and CS and MT assembly. In unfertilized Laborc(D) eggs, rudimentary CS assemble spontaneously and instantaneously and nucleate small MT asters. In fertilized Laborc(D) eggs, normal CS form and organize normal asters. However, the CS replicate prior to accomplishment of the first mitosis, and spindles with multiple CS develop. In fertilized Laborc(D) eggs, while the chromosome cycles cease, CS cycles proceed as in wild type. Knowing that Laborc(D) is a dominant-negative mutation and encodes the formation of mutant cytoplasmic dynein heavy chain molecules, we show here that cytoplasmic dynein is involved in prevention of CS assembly in unfertilized eggs and establishing harmony between the chromosome and the CS cycles.
