Cytoplasmic division cycles without the nucleus and mitotic CDK/cyclin complexes

Cytoplasmic divisions are thought to rely on nuclear divisions and mitotic signals. We demonstrate in Drosophila embryos that cytoplasm can divide repeatedly without nuclei and mitotic CDK/cyclin complexes. Cdk1 normally slows an otherwise faster cytoplasmic division cycle, coupling it with nuclear divisions, and when uncoupled, cytoplasm starts dividing before mitosis. In developing embryos where CDK/cyclin activity can license mitotic microtubule (MT) organizers like the spindle, cytoplasmic divisions can occur without the centrosome, a principal organizer of interphase MTs. However, centrosomes become essential in the absence of CDK/cyclin activity, implying that the cytoplasm can employ either the centrosome-based interphase or CDK/cyclin-dependent mitotic MTs to facilitate its divisions. Finally, we present evidence that autonomous cytoplasmic divisions occur during unperturbed fly embryogenesis and that they may help extrude mitotically stalled nuclei during blastoderm formation. We postulate that cytoplasmic divisions occur in cycles governed by a yet-to-be-uncovered clock mechanism autonomous from CDK/cyclin complexes. [Display omitted] •Cytoplasm can divide autonomously without the nucleus and CDK/cyclin complexes•Cdk1 slows an otherwise faster cytoplasmic division cycle to couple it with mitosis•Cytoplasm can use distinct microtubule organizers to transmit its division cue(s)•Autonomous divisions help extrude mitotically delayed nuclei from the blastoderm Bakshi et al. uncover during embryonic cleavage cycles in Drosophila that the cytoplasm can divide independently of both nuclei and the principal CDK/cyclin cell-cycle oscillator. Evidence suggests that such autonomous cytoplasmic divisions may help facilitate extrusion of mitotically delayed nuclei from the blastoderm before the onset of morphogenesis.