The Role of Microtubules in Patterning the Dorsal-ventral Axis of the Drosophila Melanogaster Egg

Jing Jing Feng,  Biology

Faculty Mentor: Dr. Amanda Norvell

This summer I worked in Dr. Norvell’s lab with Carolyn Gray.  Our lab is primarily interested in the asymmetry of cells and how that asymmetry is established, specifically in Drosophila melanogaster oocytes and eggs.  The most recent project I have worked on seeks to investigate how cytoskeletal elements in the oocyte cytoplasm affect the asymmetry of both individual oocytes and eggs. Within the oocyte, a polarized microtubule (MT) network is arrayed with its termini present at opposite ends of the oocyte. Several determinants, including the oocyte nucleus and specific mRNAs, are localized within the oocyte cytoplasm by transport along this MT network. Our lab has studied the localization of a specific mRNA, gurken (grk), during oogenesis.  grk mRNA is localized to the dorsoanterior corner of the oocyte, in a perinuclear position, during the later stages of oogenesis.  Several proteins are required for this localization pattern, including the RNA binding protein Squid (Sqd).  My project set out to test whether Sqd protein localization within the oocyte also requires this properly polarized MT network.  To do this experiment, we used Drosophila stocks carrying a version of Sqd protein that is tagged with Green Fluorescent Protein (GFP).  This Sqd-GFP protein fluoresces and its distribution can be monitored by microscopy.  Female flies expressing Sqd-GFP were fed the MT depolymerizing drug colchicine for varying times, ovaries were isolated, and Sqd protein distribution was monitored.  In untreated ovaries, Sqd-GFP is found in the oocyte nucleus and in a crescent at the posterior pole of the oocyte  cytoplasm.  After treatment with colchicine, Sqd-GFP protein is still localized to the oocyte nucleus, but it is not found at the posterior pole.  This suggests that the nuclear localization of Sqd protein does not require MTs, but the posterior accumulation of Sqd protein does.  Additionally, in these experiments we also observed that the position of the oocyte nucleus in the dorsal anterior corner of the oocyte is dependent on the MT network. In oocytes from colchicine treated females, the oocyte nucleus was detached from the anterior cortex.  We observed that the nucleus became detached from the cortex in many of the colchicine treated flies.  In addition, it was discovered that there may be a direct correlation between time exposed to colchicine and distance in which the nucleus was displaced.  In the future we plan to test how the position of the oocyte nucleus affects grk mRNA localization. 

Personal Statement

This experience has not only taught me to manage an experiment over the course of several weeks, but also to plan and divide work between my partner and me, and to troubleshoot unforeseen problems in the lab.  My participation in research has given me a new found appreciation for the time and effort that goes into producing usable data.  In addition, I now have the confidence to seek other lab positions in the future.  Finally, as a participant for a second time, I really enjoyed the new interdisciplinary aspect of the program.  It was very interesting to listen to the variety of studies each department had in progress, and the lunch discussions were a great opportunity to learn more about the world of research outside of our own laboratory.