| From the point of view of evolution, all living organisms on this planet are descended from an ancestor cell by continuous cell division. This chain of division leads to the formation of different species and different types of cells within one organism. Thus, understanding the cell division process is a matter of great interest to studies in both evolution and development.; For faithful transmission of genetic information, both timing and coordination of various molecular events are critical during cell division. During the cell cycle, both microfilament and microtubule networks undergo extensive rearrangement to facilitate chromosomal movement and cytokinesis. However, little is known about how Cdk1-CycB, the key regulator of cell cycle progression, regulates the timing of cell cycle progression and cytoskeletal dynamics. In Drosophila melanogaster, the first 14 embryonic cycles are maternally controlled, occur in syncytium and exhibit only S phase and M phase. These features make the syncytial embryo an ideal system to investigate the timing mechanism of the cell cycle as well as how cell cycle machinery regulates cytoskeletal dynamics.; Here I describe the effect of CycB levels in regulating both the timing and cytoskeletal dynamics in these early embryonic cycles. The embryonic mitoses prior to cycle 10 has long been viewed as synchronous and having equal duration. However, based on both live and fixed embryos, I demonstrate that uneven distribution of CycB result in longer metaphase and shorter anaphase in the middle of the embryo compared to the two polar regions. I then present data to show that Cdk1-CycB negatively affects microtubule stability in vivo. In the second half of this thesis, I present our results from a genetic screen for genetic modifiers of Cdk1-CycB. Surprisingly, many suppressor genes encode factors that regulate cytoskeletal stability. This provides an entry point to further investigate the effects of Cdk1-CycB on cytoskeletal dynamics. Interestingly, a few enhancer and suppressors identified from the genetic screen encodes several key players that regulate metaphase-anaphase transition, indicating that Cdk1-CycB may be directly involved in regulating this process. These studies provide a better understanding of early embryonic mitoses in wild-type Drosophila embryos and illustrate the importance of Cdk1-CycB function at this developmental stage. |
