Ring canals are stable intercellular junctions that form cytoplasmic bridges between cells. They are present between developing germ line cells in both ovaries and testes in most animals, including humans, where they facilitate the synchronized development of gametes. Ring canals originate from arrested cytokinesis during germline proliferation, followed by stabilization of the stalled cleavage furrows with cytoskeletal proteins. Thus, ring canal development begins as a modified mitosis. They are best characterized so far in Drosophila females where ring canals allow the flow of cytoplasm from nurse cells to oocytes throughout oogenesis. By studying female sterile mutants in which cytoplasm transport is defective, several genes have been discovered that encode ring canal structural proteins or regulators. Work on these genes has revealed that the actin cytoskeleton of female ring canals is highly dynamic to accommodate ring canal growth. In addition, the initial formation of ring canals is tightly coordinated with another germline structure, the fusome. The goal of this project is to continue the study of ring canals in Drosophila.
The specific aims are: 1) to characterize the roles of proteins encoded by the hts gene in fusome and ring canal biogenesis; 2) to further define the kinetics of ring canal growth including the determination of F-actin turnover rates during different stages of egg chamber development; and 3) to begin characterizing ring canals in somatic cells. Work on the hts gene is likely to shed important light on how cytokinesis is modified in cells that form stable junctions with their sisters. Ring canal diameter expands dramatically during oogenesis in a biphasic pattern. The more rapid second phase is Arp2/3-dependent.
Aim two will explore ring canal protein dynamics in during the first phase of Apr2/3-independent growth using genetic and cellular analyses of cytoskeletal proteins tagged with fluorescent proteins. Although ring canals are recognized as a common feature of germline cells, they are not restricted to the germline. However, there is scant information on the prevalence, function or molecular makeup of ring canals in somatic cells.
Aim three begins to address this dearth of information with the analysis of ring canals connecting somatic follicle cells in egg chambers. Genetic analysis will be carried out on a follicle cell ring canal protein identified in a protein-trapping screen. A phenotype associated with loss of follicle cells ring canals will likely provide the first insight into their function in epithelial cells.
