Possible mechanism of life span extension by the <i>miro-1(tm1966)</i> mutation.

<p>On one hand (upper branch), the defect in <i>miro-1</i> may cause a neurosecretory defect which activates the <i>daf-16</i>-dependent stress resistance pathway. At the same time <i>miro-1(tm1966)</i> contains less mitochondria than the wild type (bottom branch). This may contribute to the phenotype through reduced ROS production or activation of a mitochondria stress resistance pathway.</p

Reduced amount of mitochondria of <i>miro-1(tm1966)</i> mutants.

<p>A. qPCR was performed on RNA extracted from individual L3 animals to determine the mtDNA copy number. Average and standard deviation from 20 animals are shown. B. Percentage of muscle area covered by mitochondria, calculated from images similar to those shown in panel C. C. Fluorescence images of body wall muscle mitochondria in animal carrying <i>zcIs14[myo-3</i>::<i>mtGFP]</i>. Rhomboid shapes are individual muscle cells, and bright spots within are mitochondria. D. Hypodermal mitochondria. From images similar to those in panel E, the width of the band containing mitochondria (yellow arrows in E), and the density of mitochondria within this band were measured. Six wild-type and nine mutant animals were assayed. E. Hypodermal mitochondria stained with MitoTracker Red CMXRos. Original fluorescence images and thresholded image representing mitochondria are shown.</p

<i>daf-16/FOXO</i> dependent life span extension of <i>miro-1(tm1966)</i>.

<p>A. Life span of <i>miro-1</i> double mutants are shown (average +/- standard deviation). This assay was terminated after all <i>miro-1(tm1966)</i> animals had died, since <i>daf-2</i> mutants live very long time. The average life span was calculated for worms which died before the assay was terminated. Therefore, life spans for long lived <i>daf-2</i> and <i>miro-1; daf-2</i> double mutants are minimal possible values. B. Level of <i>sod-3</i>::<i>gfp</i> was quantified by taking fluorescence images and measuring mean brightness. C. Aldicarb resistance of <i>miro-1</i> and mutants with weak synaptic defects. D. Representative survival curve of double mutants.</p

<i>C</i>. <i>elegans miro-1</i> Mutation Reduces the Amount of Mitochondria and Extends Life Span

<div><p>Mitochondria play a critical role in aging, however, the underlying mechanism is not well understood. We found that a mutation disrupting the <i>C</i>. <i>elegans</i> homolog of Miro GTPase (<i>miro-1</i>) extends life span. This phenotype requires simultaneous loss of <i>miro-1</i> from multiple tissues including muscles and neurons, and is dependent on <i>daf-16/FOXO</i>. Notably, the amount of mitochondria in the <i>miro-1</i> mutant is reduced to approximately 50% of the wild-type. Despite this reduction, oxygen consumption is only weakly reduced, suggesting that mitochondria of <i>miro-1</i> mutants are more active than wild-type mitochondria. The ROS damage is slightly reduced and the mitochondrial unfolded protein response pathway is weakly activated in <i>miro-1</i> mutants. Unlike previously described long-lived mitochondrial electron transport chain mutants, <i>miro-1</i> mutants have normal growth rate. These results suggest that the reduction in the amount of mitochondria can affect the life span of an organism through activation of stress pathways.</p></div