Developmentally-regulated packaging of mitochondrial DNA by the HMG-box protein mtTFA during Xenopus oogenesis.

Mature Xenopus oocytes are highly enriched for mitochondria. The organelles are stored and partitioned to newly-arising cells during embryogenesis, when there is little mitochondrial DNA (mtDNA) replication or transcription. A previously described member of the high mobility group (HMG) family of proteins, mtTFA, has been suggested to play a role in control of mtDNA copy number. mtTFA serves as a mitochondrial transcription factor in humans and Xenopus and as an abundant mtDNA packaging protein in yeast, like its prokaryotic histone-like counterpart, HU protein. Northern blot analysis demonstrated that expression of the gene was regulated during Xenopus oogenesis and specifically peaked at stage II. Western and Southern blotting were used to quantify amounts of the protein and mtDNA, respectively, in each stage of oogenesis. mtTFA:mtDNA ratios were found to be relatively low in previtellogenic oocytes while the ratios increased markedly in mature oocytes.