Determining the Roles of Homozygous Lethal Mutants Sec24CDJV91 and JN58 in Oocyte Determination and Maintenance in Drosophila melanogaster

Abstract

The process of oogenesis is crucial for female fertility and proper embryonic development of progeny, and a key question in biology is how viable gametes are formed from germline stem cells. However, the process of oocyte determination is not well understood in Drosophila melanogaster. To better characterize the process of oogenesis, the roles of two ethyl methanesulfonate (EMS) mutants, JV91 and JN58, were studied. Both mutant lines produce egg chambers with 16 nurse cells, no oocyte, and clustering of the stable actin rings between germline cells, called “ring canals,” at the center of the egg chamber. The gene in JN58 responsible for these mutant phenotypes has been narrowed down to the cytological region 21D1-21E2 on chromosome 2L. JV91 is an allele of Sec24CD, a secretory protein in the COPII complex that mediates vesicle trafficking from the ER to the Golgi. Sec24CDJV91 mutant cysts initially select an oocyte in the germarium, but oocyte identity is lost by stage 4. As oocyte identity is lost, the ring canals form a cluster at the center of the egg chamber. Oocyte-specific proteins such as Orb, Bicaudal-D (Bic-D), and Gurken (Grk) also accumulate abnormally at the ring canal cluster. Further work is necessary to determine the mechanism by which Sec24CD affects oocyte maintenance and whether it involves members of the Par protein complexes. A better understanding of the roles of Sec24CD and JN58 will help to clarify the process of oocyte determination in Drosophila melanogaster. Discerning the mechanisms of cell identity selection and maintenance may contribute to the comprehension of conserved pathways in humans that are important in disease and in stem cells.