Skip to Main Content
 

Global Search Box

 
 
 
 

ETD Abstract Container

Abstract Header

New insights into the functions of the two mitotic kinases, NIMA and CDK1, through the cell cycle

Govindaraghavan, Meera

Abstract Details

2013, Doctor of Philosophy, Ohio State University, Molecular, Cellular and Developmental Biology.
In Aspergillus nidulans, the Never in Mitosis A (NIMA) kinase plays an essential role along with the Cdk1 kinase in initiating mitosis. NIMA is the founding member of a family of NIMA related kinases (Neks) that are conserved in all eukaryotic cells. Therefore, to better understand the conserved aspects of mitotic regulation, it is of fundamental importance to study the mechanism of NIMA function through the cell cycle. nimA is an essential gene in A. nidulans, hence the non-essential S. cerevisiae nimA ortholog, KIN3, was used by our collaborators to perform a synthetic lethal screen to identify novel genetic interactors of KIN3 (SL Anglin et al. unpublished). Since KIN3 does not have an essential mitotic role, we hypothesized that extending this genetic analysis to A. nidulans might help us examine potential non-mitotic roles of nimA. Consistent with this expectation, we identified a conserved genetic interaction between nimA and the trafficking pathway involved in the turn-over of cell membrane proteins, the ESCRT (Endosomal Sorting Complex Required for Transport) pathway. Analysis of cells that lack ESCRT function in combination with having partial NIMA function revealed that NIMA has a role in regulating cell tip growth. From parallel microscopy experiments we found that in addition to mitotic nuclear structures, NIMA locates to the tips of growing hyphal cells. Ectopically expressed NIMA also locates to the plus ends of interphase microtubules (Mts) in a manner dependent on the well-studied plus end binding protein, Eb1. Perturbation of NIMA function modifies Eb1 behavior, Mt dynamics and polarized cell growth. Our results contend that NIMA has a cytoplasmic function in cell tip growth during interphase involving the regulation of microtubule dynamics in concert with the ESCRT pathway. Using our genetic approach, we also identified a conserved genetic interaction of nimA with the Set1 methyl transferase complex. Unlike the genetic interaction between NIMA and the ESCRT pathway, we find that the methylation of the histone H3K4 by the Set1 complex is essential in cells that have partial function of either the NIMA or Cdk1 mitotic kinases. We find that the function of the Set1 complex is required along with Cdk1 activation by Cdc25 phosphatase to regulate the successful transition from G2 into mitosis. The Set1 complex is also required for normal mitotic progression, since the absence of Set1 in combination with partially impaired NIMA function causes mitotic defects monitored by the spindle assembly checkpoint. We detected that in contrast to cells with partially active Cdk1 that exhibit a G2 delay (but complete the subsequent mitosis successfully), cells with partial NIMA activity exhibit mitotic defects. A systematic exploration of these mitotic defects allowed us to identify multiple functions for NIMA in specific aspects of mitosis post G2-M transition, that correlate with the dynamic mitotic localization of NIMA. Thus our data support functions for NIMA both in the cytoplasm to regulate microtubule dynamics and cell growth during interphase and also in the nucleus during mitosis. We suggest NIMA might help integrate these two key aspects of cell growth and development.
Stephen Osmani (Advisor)
Anita Hopper (Committee Member)
Harold Fisk (Committee Member)
Iris Meier (Committee Member)
355 p.

Recommended Citations

Citations

  • Govindaraghavan, M. (2013). New insights into the functions of the two mitotic kinases, NIMA and CDK1, through the cell cycle [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1366289368

    APA Style (7th edition)

  • Govindaraghavan, Meera. New insights into the functions of the two mitotic kinases, NIMA and CDK1, through the cell cycle. 2013. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1366289368.

    MLA Style (8th edition)

  • Govindaraghavan, Meera. "New insights into the functions of the two mitotic kinases, NIMA and CDK1, through the cell cycle." Doctoral dissertation, Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1366289368

    Chicago Manual of Style (17th edition)