Keala Watson, M.S. candidate

Department of life sciences

"Mob Family Proteins and Tricornered Kinase are Required to Form Dorsal Appendages of the Drosophila Eggshell"

Committee members:

• Dr. Laurel Raftery, Advisory Committee chair
• Dr. Mo Weng, Advisory Committee member
• Dr. Andrew Andres, Advisory Committee member
• Dr. Hong Sun, Graduate College representative

Abstract

To understand how complex tissues are formed, we need to understand how cells communicate with other cells to build structures. In Drosophila melanogaster, epithelial cells form tubular structures to shape the dorsal appendages on the eggshells. One signaling pathway needed for this event is the Hippo-like kinase intracellular pathway. I focus on two key components in this pathway: the NDR kinase Tricornered (Trc) and Mob proteins. In eukaryotes, Mob proteins are known to interact with NDR kinases to promote their activation. The Hippo-like pathway involves the NDR kinase Trc; however, the specific Mob protein(s) that interact with Trc are unclear. I studied the functions of Trc, Mob1, Mob2, and Mob4 in several aspects of tube formation using RNA interference (RNAi) in all somatic follicle cells of the ovary in vivo. First, I evaluated the dorsal appendages on the eggshells that were formed by females with reduced levels of Trc, Mob1, or Mob2 and found that they were shortened or lengthened compared to controls, and also widened at the base. These phenotypes led me to investigate how the organization of the follicle cell tubes for dorsal appendage formation were affected by RNAi of these gene products. Two types of follicle cells create the dorsal appendages, called roof and floor cells. To visualize the cell organization, I used immunofluorescence and confocal microscopy. I then evaluated the organization of each cell type at the specific stages of oogenesis when the tube structures are formed. I found that floor cell organization was most frequently abnormal. Roof cell organization appeared to be affected rarely. I then evaluated whether components of the STRIPAK complex (an established antagonist of the Hippo pathway) contributed to dorsal appendage formation, using RNAi against core STRIPAK components; Strip, Striatin, and Mob4. I then examined the dorsal appendages laid by the females with reduced levels of these gene products. RNAi against each component led to similar abnormalities in the dorsal appendages. These results indicated that STRIPAK also plays a role in proper dorsal appendage formation. This work reveals key components in the morphogenesis of dorsal appendages.