Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA 94158, USA.
Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA 94158, USA; Biophysics Graduate Program, University of California, San Francisco, San Francisco, CA 94158, USA.
Cell. 2023 Oct 12;186(21):4694-4709.e16. doi: 10.1016/j.cell.2023.09.010.
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.
细胞质分裂被认为依赖于核分裂和有丝分裂信号。我们在果蝇胚胎中证明，细胞质可以在没有核和有丝分裂 CDK/周期蛋白复合物的情况下反复分裂。Cdk1 通常会减缓否则更快的细胞质分裂周期，将其与核分裂偶联，当解偶联时，细胞质在有丝分裂之前开始分裂。在 CDK/周期蛋白活性可以许可有丝分裂微管 (MT) 组织者（如纺锤体）的发育胚胎中，没有中心体，即间期中 MT 的主要组织者，细胞质分裂也可以发生。然而，在缺乏 CDK/周期蛋白活性的情况下，中心体变得必不可少，这意味着细胞质可以利用基于中心体的间期或 CDK/周期蛋白依赖性有丝分裂 MT 来促进其分裂。最后，我们提供的证据表明，在未受干扰的果蝇胚胎发生过程中会发生自主的细胞质分裂，它们可能有助于在胚胎形成期间挤出有丝分裂停滞的核。我们假设细胞质分裂是在一个尚未被发现的时钟机制的控制下发生的，这个时钟机制与 CDK/周期蛋白复合物是自主的。
