Masters Theses

Keywords and Phrases

actin; Actomyosin Ring; Cdc14; Cell Cycle; Cytokinesis; Iqg1


"Cytokinesis is the final step in cell division when the cell separates the cytoplasm by contracting a ring composed of filamentous actin (F-actin) and type II myosin. Iqg1, an IQGAP family member, is an essential scaffolding protein in budding yeast (S. cerevisiae) required for actin recruitment to, and contraction of, the actomyosin ring. Actin is recruited by the calponin homology domain (CHD) in anaphase after Iqg1 is localized to the bud neck. Consensus sites for the cyclin-dependent kinase (CDK) Cdc28 were identified flanking the CHD. This led us to the hypothesis that phosphorylation of Iqg1 by Cdc28 negatively regulates actin ring formation prior to anaphase, and that dephosphorylation of Iqg1 by the phosphatase Cdc14 promotes actin ring formation. To test this hypothesis the four perfect consensus CDK phosphorylation sites were mutated to alanine to prevent phosphorylation ( iqg1-4A). Morphological analysis of cells expressing mutant protein indicated cytokinetic failure at more than double the rate of controls. This data indicates that phosphorylation of Iqg1 by CDK is important for cytokinesis. Using immunofluorescence we observed that cells expressing iqg1-4A form both Iqg1 and actin rings prior to anaphase. These data support the hypothesis that the dephosphorylation of the 4 CDK sites in Iqg1 promotes actomyosin ring formation. We also provide evidence that Cdc14 is the key regulator of actin ring formation. Overexpression of Cdc14 resulted in formation of the actin ring prior to anaphase similar to iqg1-4A. Inhibition of Cdc14 prevented actin ring formation even in the presence of an inhibitor of Cdc28 that bypasses the mitotic arrest typically seen in CDC14 mutants. The iqg1-4A mutant can rescue the ability of cdc14-1 cells to form actin rings. These results prove that Iqg1 is the sole target of Cdc14 temporal regulation of actin ring formation."--Abstract, page iii.


Shannon, Katie

Committee Member(s)

Westenberg, David J.
Ercal, Nuran


Biological Sciences

Degree Name

M.S. in Applied and Environmental Biology


Missouri University of Science and Technology

Publication Date

Summer 2014


viii, 63 pages

Note about bibliography

Includes bibliographical references (pages 54-62).


© 2014 Daniel Patrick Miller, All rights reserved.

Document Type

Thesis - Open Access

File Type




Subject Headings


Thesis Number

T 10518

Electronic OCLC #