TEM TOMOGRAPHY OF A DROSOPHILA ATP6 MUTATION

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. ABSTRACT Our studies of mutations that cause shortened lifespan and neurodegeneration have led us to identify a maternally inherited mutation in the mitochondrial gene ATP6 (ortholog of ATPa). This gene encodes the H+ channel component of the F1F0 ATP synthase, which couples ion gradient dissipation with ATP production via rotary catalysis. In humans, impairment of ATP6 generally manifests in diseases when the mutation is nearly homoplastic. For example, humans bearing the best-characterized mutation in the mitochondrial ATP6 gene (L156R) have MILS, NARP, or are normal depending upon the heteroplasmy of the mutation (>~85%, ~70-85% or <~70% mutant, respectively). In our mutant, ATP6[1] the mutation in nearly homoplastic (98¿4 % mutant). TEM analysis revealed aberrant cristae in mitochondria from ATP6[1] mutants (Figure 1). We have acquired the micrographs using stereological protocols and have discovered the density of mitochondria in ATP6[1] (31 ¿ 3 per 100mM2) does not appear to be significantly different than wild type (35 ¿ 2 per 100mM2, p=0.4). We would like to better understand this morphological aberration to complement our ongoing functional studies of these mitochondria. Specifically, is the internal mitochondiral membrane vesiciular (as it appears in 2D TEM) or is it tubular? Does the internal membrane remain separate from the outer mitochondrial membrane? TEM tomography with a 5nm resolution is extremely well-suited to directly address both of these questions, which have profound consequences on the function of mitochondria. The quality of our 2D TEM and the high frequency with which we see aberrant mitochondria in our mutants suggests the proposed project will not be overly burdensome and will yield instructive results. Figure 1: TEM analysis of aged brains reveals aberrant mitochondrial morphology in ATP6[1] mutants (B). N > 3 each genotype. Quantification demonstrates a high frequency of abnormal mitochondria (>60% of total mitochondria, C). Comparison to wild type (* p<0.01, T-test). In the previous reporting period, blocks from wild-type and ATP6 mutant were received. A double-tilt reconstruction made from each. Dr. Renken collected an additional single-tilt reconstruction from the mutant, using the Tecnai F20. Surface-rendered models, using both tracing and thresholding techniques, were made. In mitochondria from the mutant, there appears to be a radial progression from peripheral tubes to central vesicles.