A major focus of research in my laboratory concerns the regulation of interactions between the plasma membrane and the actin cytoskeleton, particularly in epithelial cells. The attachment of membrane proteins to actin filaments just underneath the membrane is a dynamic process controlled by a variety of accessory proteins and certain signal transduction pathways. Actin filaments organize as parallel bundles or branching networks. The types of arrangements are fundamental to the microscopic architecture of cells and tissues because they influence cell shape, cell-cell and cell-substrate adhesions, cell division, cell motility, and cell surface topography. Specifically, we are interested in understanding molecular mechanisms required for formation of distinct actin-based cell surface protrusions such as lamellipodia, filopodia, microvilli, and sensory stereocilia.

CLIC5: a cytoskeletal protein required for proper hearing and balance

CLIC5 (chloride intracellular channel 5) was originally purified from isolated human placental microvilli, where it was found in a protein complex containing actin and several actin-binding proteins. One such protein was Ezrin, a member of the ERM (Ezrin/Radixin/Moesin) family of membrane-cytoskeletal crosslinking proteins. Gene mutations that disrupt expression of CLIC5 cause deafness and vertigo in both mice and humans. In the jitterbug mouse mutant, loss of CLIC5 leads to severe morphological defects on the surface of auditory and vestibular hair cells in the inner ear. A similar defect occurs in Radixin-deficient mice. These defects are likely the result of unstable membrane-cytoskeletal attachments within the pencil-shaped mechanosensory stereocilia that project from the apical surface of hair cells. Our overall hypothesis (see Figure, right) is that CLIC5 and Radixin are part of a protein complex that contains several other known deafness-associated proteins, and that this complex is essential to maintain the structural integrity of stereocilia over the course of a lifetime.

A CLIC gene in Drosophila, the fruit fly

Humans and rodents have 6 CLIC-related genes (CLIC1-6) that have been implicated in a variety of cellular processes, including ion transport, signal transduction, cell differentiation, epithelial tube formation, cell division, apoptosis, response to cellular stress, membrane trafficking, and cytoskeletal organization. Inherent to the study of multi-gene families is the potential for functional redundancy, which can complicate interpretation of experiments in organisms or individual cells expressing multiple family members. Invertebrate organisms, such as the fruit fly (Drosophila melanogaster) and worm (Caenorhabditis elegans), have proven to be extremely powerful deciphering the functional significance of many human gene families. In collaboration with Dr. Soichi Tanda in the Department of Biological Sciences at Ohio University, we are taking advantage of Drosophila as a model system to investigate the biological significance and cellular functions of CLICs. In addition to the many practical advantages and its battery of sophisticated genetic tools, another reason for using Drosophila is that it has only a single CLIC gene, thereby minimizing functional redundancies.