The Role of the Microtubules in Gurken (grk) mRNA Localization during Drosophila Oogenesis

Carolyn Gray,  Biology

Faculty Mentor: Dr. Amanda Norvell

My summer research focused on oogenesis in the fruit fly, Drosophila melanogaster. We were specifically interested in studying factors leading to normal eggshell asymmetries.  The signaling protein, Gurken (Grk), is critical in establishing the dorsal-ventral axis of the developing Drosophila oocyte.  The restricted distribution of Grk protein is achieved through the localization of its mRNA.  grk mRNA is normally localized in the dorsoanterior corner of the oocyte, just behind the oocyte nucleus. Several factors are required for the correct localization of grk mRNA, including the proteins Squid (Sqd) and fs(1)K10.  In flies carrying mutations in these genes, grk mRNA is mislocalized to a ring at the anterior cortex of oocyte.  To test the role of microtubules and nuclear positioning in grk mRNA localization, we disrupted the microtubules by treatment with colchicine (50µg/mL), a microtubule-depolymerizing drug.  Female flies were fed colchicine for varying times and their ovaries were isolated. grk mRNA localization was measured by in situ hybridization after 18 hours of colchicine treatment.  In colchicine treated ovaries  the position of the oocyte nucleus was affected, with the nucleus falling away  from the anterior cortex of the oocyte. However, despite the incorrect position of the oocyte nucleus, in wild type flies, grk mRNA remained associated with the mispositioned nuclei.  In  contrast, however, we found that in squid1 and fs(1)K10 mutant flies, grk mRNA did not stay with the oocyte nucleus but was spread diffusely throughout the oocyte cytoplasm.  This novel experiment reveals the requirement of Squid and Fs(1)K10 in gurken localization to the nuclear cortex, which thereby properly establishes the dorsoventral axis of developing Drosophila oocytes.  Future studies will examine the presence of a microtubule basket surrounding the nucleus and determine whether or not nuclear attachment to the anterior corner is required for proper translation of grk mRNA into Grk protein; different isoforms of the Squid gene will also be studied for their specific role in the rescue of the mutant phenotype found in this work. 

Personal Statement

              The Summer Undergraduate Research Program at TCNJ has been very rewarding.  It provided a solid introduction to laboratory research in a comfortable environment.  The Biology staff has been amazing and played a key factor in the success of this program.  Student-faculty breakfasts were held once a week, where our progress was discussed; we also had faculty barbeques, which lent an opportunity to personally get to know professors in the department.  Chances to interact with the faculty on various levels and perform independent work under their instruction allowed students to mature as not only scientists, but as individuals as well.  The relationships formed through collaboration with faculty and peers foster a greater understanding of scientific research; this is the hallmark of the summer research program at TCNJ.  I am a rising senior at The College, and this program has inspired me to pursue a graduate degree in Biology.  I am grateful to Dr. Norvell for such an enlightening experience.