Abstract
Mitotic cyclin-dependent kinase with their cyclin partners (cyclin:Cdks) are the master regulators of cell cycle progression responsible for regulating a host of activities during mitosis. Nuclear mitotic events, including chromosome condensation and segregation have been directly linked to Cdk activity. However, the regulation and timing of cytoplasmic mitotic events by cyclin:Cdks is poorly understood. In order to examine these mitotic cytoplasmic events, we looked at the dramatic changes in the endoplasmic reticulum (ER) during mitosis in the early Drosophila embryo. The dynamic changes of the ER can be arrested in an interphase state by inhibition of either DNA or protein synthesis. Here we show that this block can be alleviated by micro-injection of Cyclin A (CycA) in which defined mitotic ER clusters gathered at the spindle poles. Conversely, micro-injection of Cyclin B (CycB) did not affect spatial reorganization of the ER, suggesting CycA possesses the ability to initiate mitotic ER events in the cytoplasm. Additionally, RNAi-mediated simultaneous inhibition of all 3 mitotic cyclins (A, B and B3) blocked spatial reorganization of the ER. Our results suggest that mitotic ER reorganization events rely on CycA and that control and timing of nuclear and cytoplasmic events during mitosis may be defined by release of CycA from the nucleus as a consequence of breakdown of the nuclear envelope.
Highlights
Entry into mitosis displays a dramatic remodeling of cellular structure and organization
The Drosophila syncytial blastoderm is well established for the study of mitosis and has led to several discoveries surrounding mitotic events that correlate with vertebrate systems [26,27,28]
The behavior of the Endoplasmic Reticulum (ER) during these syncytial divisions was originally described by Bobinnec and colleagues [16], wherein they followed the ER-lumenal protein Protein Disulfide Isomerase (Pdi) fused to GFP as the embryo cycled through these mitoses
Summary
Entry into mitosis displays a dramatic remodeling of cellular structure and organization. These activities include nuclear events such as chromosome condensation and nuclear envelope breakdown (NEB) and cytoplasmic events including spindle assembly, Golgi apparatus breakdown, and changes in Endoplasmic Reticulum (ER) structure and localization [1]. Essential in this process is the timing and stepwise coordination of both nuclear and cytoplasmic events for proper cell division and distribution of their contents to the newly formed daughter cells. PLOS ONE | DOI:10.1371/journal.pone.0117859 February 17, 2015
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