The growth of the germline ring canals during Drosophila melanogaster oogenesis

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Project Summary Infertility and impaired fecundity affect millions of people each year; therefore, understanding the pathways and mechanisms that regulate normal gamete formation are necessary. Intercellular bridges are essential structures found in developing sperm and eggs across the animal kingdom; they connect neighboring cells and allow the sharing of materials and coordination of behaviors. The long-term goal of this project is to understand how intercellular bridges are formed, stabilized, and undergo expansion. The germline intercellular bridges, or ring canals, found in the developing fruit fly egg chamber have emerged as the premier model system. Formed after incomplete cytokinesis, the germline ring canals undergo a 20-fold expansion to facilitate the transfer of materials from the supporting nurse cells to the developing oocyte. Mutations that affect ring canal formation, stability, or expansion lead to infertility. Many structural and regulatory proteins localize to the ring canals and/or regulate aspects of their structure; however, an integrated model connecting the proteins and pathways is lacking. The PI’s lab characterized a role for the Ste20 kinase, Misshapen (Msn), the SH2/SH3 adaptor protein, Dreadlocks (Dock), and the coordinated activity of two actin nucleators, the Arp2/3 complex and the formin, Diaphanous (Dia), in the regulation of ring canal size and stability; however the precise mechanisms underlying their contribution and the connections between these regulators is not known. The objective of this proposal is to determine how these proteins contribute to ring canal formation, stability, and expansion, and how their activity is integrated with each other and with other known ring canal proteins. The central hypothesis is that Msn, Dock, Dia, and the Arp2/3 complex spatially and temporally coordinate endocytosis of adherens junction proteins, myosin activity, and changes to the actin cytoskeleton to promote ring canal expansion and maintain stability. Aim 1 will test the hypothesis that regulated endocytosis of the adherens junction protein, E-Cadherin, regulates ring canals size and stability. Aim 2 will determine whether the Arp2/3 complex and/or Dia indirectly regulate ring canal expansion through effects on adherens junctions or myosin activity. Aim 3 will use a candidate-based approach to identify Dock-interacting proteins that coordinate changes in the actin cytoskeleton and cell adhesion in the germline. A combination of undergraduate-appropriate techniques will be used, including fluorescence imaging of live and fixed samples, quantitative image analysis, epistasis experiments, and basic biochemistry. The PI’s strong track record of mentoring 25 undergraduate student researchers, her expertise in cell and developmental biology, and the power and accessibility of the fruit fly model system make her well-positioned to complete the proposed aims. Through their involvement in these aims, students will gain valuable training and experience that will increase their interest in STEM fields. The proteins, structures, and processes being studied are also utilized during normal morphogenesis and can be mis-regulated in disease; therefore, insight from this work will improve our understanding of both normal development and disease in humans.