The actin cytoskeleton plays a key role in diverse biological processes and when perturbed cause human disease and suffering. One such example is Usher type 1 syndrome, a condition characterized by congenital deafness and blindness. Myosin VIIA has been identified as a gene responsible for human Usher syndrome 1B and non-syndromic deafness. In Drosophila, Myosin VIIA is coded by the locus crinkled (ck). Severe mutations of ck/MyoVIIA in flies are lethal or "semi-lethal", with only a small fraction of homozygous flies reaching adulthood. These escapers show defects in actin rich structures such as bristles, epidermal hairs, and in the fly's hearing organ. In addition, severe ck mutant allele flies are infertile. To fully understand how ck contributes to biological functions like bristle and hair formation, further investigation is needed on how the forces it produces are transmitted to the appropriate structure or cargo.
Specific Aim 1 will employee two approaches designed to identify proteins interacting with ck/MyoVIIA, yeast 2-hybrid screens and tandem affinity purification from transgenic flies. Interactions between identified proteins and ck/MyoVIIA will be confirmed with in vitro binding assays, in vivo co-localization studies, and genetic manipulation in transgenic flies. With the observation that severe ck mutants that survive to adulthood are infertile, we propose a novel role for ck/MyoVIIA in actin rich structure in oogenesis which is likely distinct from the bristle and hearing phenotypes based on the cell types in the egg chambers.
Specific Aim 1 will explore the role of ck/MyoVIIA in oogenesis and early embryogenesis using germ line clones homozygous for an allelic series of mutant ck/MyoVIIA ranging from truncated protein to single point mutations. The different ck alleles display different severities of phenotypes regarding the number of escapers and the bristle and hair formation. It is expected to see a range of phenotypes here as well. The morphology of egg chambers will be characterized using confocal microscopy, focusing on irregularities in actin rich structures such as ring canals, microvilli, and cell-cell adhesions. Together these aims will provide insight into how protein complexes are contributing to ck/Myosin VIIA function in actin protrusions and oogenesis.
Usher Syndrome, a leading cause of inherited deafness and blindness, is associated with defects in inner-ear hair cells caused by mutations in several proteins, including Myosin VIIA. Myosin VIIA is essential for proper formation of the actin-based hair cells;however the exact molecular mechanism is unknown. This project will examine proteins in complex with Myosin VIIA and their requirement for normal actin-based protrusion formation and function.