Date Approved


Graduate Degree Type


Degree Name

Cell and Molecular Biology (M.S.)

Degree Program

Cell and Molecular Biology

First Advisor

Dawn Clifford Hart

Second Advisor

Bradley Wallar

Third Advisor

Merritt Taylor


Cancer is a disease of uncontrolled cell division. Cell division in eukaryotic cells occurs by the formation of a contractile ring, predominantly composed of filamentous actin (F-actin). During mitosis, actin filaments polymerize to form rings at the medial plane of the cell that constrict causing the cell membrane to pinch and divide. Proteins that regulate this process are essential because dysregulation can lead to uninhibited cell growth and division. In fission yeast, the protein Mid1 functions as a scaffold to recruit regulatory proteins required for actin filament formation and simultaneously anchors the contractile ring at the cell division site. The Mid1 Pleckstrin Homology (PH) domain can bind lipids in the membrane, but direct binding of the PH domain to other contractile ring proteins has not been described. The GTPase Rho1 is an important activator of proteins that regulate actin filaments, and has been shown to localize to the contractile ring during cell division. Since Factin, Mid1, and Rho1 are important components for contractile ring formation and proper cytokinesis, it is important to clarify their interactions. Co-sedimentation experiments indicated that the Mid1 PH domain specifically binds F-actin. The PH domain also inhibits F-actin filaments from elongating by actin polymerization assays. Low speed actin cosedimentation showed that the PH domain also bundles actin filaments. Creation of a Rho1- GFP yeast strain was attempted to perform co-immunoprecipitation of Rho1 and Mid1 in vivo. The confirmation and importance of the interaction of Rho1 and Mid1 will be explored in future studies. The interaction of Mid1 with F-actin and Rho1GTPase may reveal important regulatory events for contractile ring assembly during cell division.