Mitochondrial dynamics and inheritance during Drosophila oogenesis. R.T. Cox 1, A.C. Spradling 1,2. 1) Dept Embryology, Carnegie Inst of Washington, Baltimore, MD; 2) HHMI.
Mitochondria are inherited exclusively from the mother and are organized during oogenesis as a large membrane rich aggregate called the Balbiani body. However, mechanisms regulating mitochondrial localization, transport, and inheritance during oogenesis remain poorly understood. By labeling individual mitochondria with antibodies or GFP-tagged proteins, we have characterized the number, morphology and behavior of mitochondria during the early stages of Drosophila oogenesis. There is a highly organized and dynamic relationship between the fusome, a germline specific organelle, and mitochondria in germline stem cells, forming, and maturing 16-cell cysts. Mitochondria cluster around the fusome in germline stem cells, but not in forming cysts. Once the 16-cell cyst is completed, however, mitochondria re-associate with the fusome, creating a tight halo of organelles. Mitochondria from the fifteen nurse cells subsequently move along the fusome and into the oocyte in parallel with the polarization of microtubule ends and migration of centrioles. Finally, a large clump of mitochondria moves into the oocyte anterior forming a structure reminiscent of the Balbiani body. In hts mutants, which lack fusomes, these events fail to occur and mitochondria remain dispersed. Using our increased knowledge of mitochondrial dynamics, we have begun to search for genes that mediate mitochondrial behavior during oogenesis. clueless, a member of a novel family of TPR containing proteins, appears to be one such gene. During germ cell mitosis in clueless mutants, mitochondria are tightly clumped at the ends of the fusome instead of evenly dispersed. While the biochemical function of Clueless is still unknown, the Dictyostelium discoideum homolog has a similar mutant phenotype. When cluA is removed in D. discoideum, the normally dispersed mitochondria clump together at the middle of the cell (Zhu et al, 1997). Clueless may be involved in normal mitochondrial transport and/or positioning.