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Vol. 15, Issue 10, 4369-4381, October 2004
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Department of Biology, University of Utah, Salt Lake City, UT 84112
Submitted December 8, 2003;
Revised July 2, 2004;
Accepted July 6, 2004
Monitoring Editor: Thomas Fox
Opposing fission and fusion events maintain the yeast mitochondrial network. Six proteins regulate these membrane dynamics during mitotic growthDnm1p, Mdv1p, and Fis1p mediate fission; Fzo1p, Mgm1p, and Ugo1p mediate fusion. Previous studies established that mitochondria fragment and rejoin at distinct stages during meiosis and sporulation, suggesting that mitochondrial fission and fusion are required during this process. Here we report that strains defective for mitochondrial fission alone, or both fission and fusion, complete meiosis and sporulation. However, visualization of mitochondria in sporulating cultures reveals morphological defects associated with the loss of fusion and/or fission proteins. Specifically, mitochondria collapse to one side of the cell and fail to fragment during presporulation. In addition, mitochondria are not inherited equally by newly formed spores, and mitochondrial DNA nucleoid segregation defects give rise to spores lacking nucleoids. This nucleoid inheritance defect is correlated with an increase in petite spore colonies. Unexpectedly, mitochondria fragment in mature tetrads lacking fission proteins. The latter finding suggests either that novel fission machinery operates during sporulation or that mechanical forces generate the mitochondrial fragments observed in mature spores. These results provide evidence of fitness defects caused by fission mutations and reveal new phenotypes associated with fission and fusion mutations.
Abbreviations used: DIC, differential interference contrast; GFP, green fluorescent protein; mtDNA, mitochondrial DNA.
* Present address: United States Department of Agriculture, Agricultural Research Service, Peoria, IL 61604.
Corresponding author. E-mail address: shaw{at}bioscience.utah.edu.
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