Mitochondrial genomes on a string of pearls.

Mitochondria are small, dynamic subcellular structures involved in many physiological functions, including energy production. They stand out among eukaryotic organelles because they have their own genome, a souvenir of their bacterial origin that remains essential for cellular energy metabolism. Mitochondrial DNA (mtDNA) is present in hundreds to thousands of copies per cell, assembled into nucleoprotein complexes called nucleoids. Nucleoids undergo continuous replication and turnover, are distributed regularly along the mitochondrial network, and usually contain only one or two mtDNA molecules (1). This ordered arrangement is unlikely to be random, as spatial organization of nucleoids is critical for mtDNA maintenance and function (2). However, the biophysical principles governing nucleoid positioning have remained poorly defined. On page 102 of this issue, Landoni et al. (3) describe how dynamic and reversible mitochondrial membrane constrictions, called "pearling," spatially organize mtDNA molecules. The findings reveal a mechanistic link between mitochondrial membrane remodeling and mtDNA biology. [ABSTRACT FROM AUTHOR]