Mitochondrial Nucleoids: Superresolution microscopy analysis

• Published in: The international journal of biochemistry & cell biology Vol. 106; pp. 21 - 25
• Main Authors: Ježek, Petr, Špaček, Tomáš, Tauber, Jan, Pavluch, Vojtěch
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier Ltd 01.01.2019
• Subjects: 3D superresolution microscopy; mtDNA; Nucleoids; TFAM; Polγ; Nucleoids; mtDNA; STED; mt; IMM; Pol-β; 3D superresolution microscopy; TFB2M; ATAD3B; MRPL12; POLRMT; mtSSB; OMM; FIB-SEM; IBM; MTERF; PALM; dSTORM; LONP1; TFAM; TEFM
• ISSN: 1357-2725; 1878-5875
• DOI: 10.1016/j.biocel.2018.10.012

•Densely packed mtDNA & TFAM complexes (including other gene expression proteins) form ∼100 nm nucleoids within the mitochondrial matrix.•Putative nucleoid division concomitant to mtDNA replication is yet to be observed in detail.•mtDNA transcription may proceed in larger nucleoids, i.e. with unwinded mtDNA with still attached polycistronic RNA.•Nucleoids are located in cristae-free regions and spatially coordinated with RNA granules and mt ribosomes.•Nucleoids may be attached to the inner mitochondrial membrane in fission sites, hence fragments contain always one nucleoid.•Upon mild fission of the mitochondrial network, all nucleoids (typically ∼10 per 10 μm mitochondrial tubule) do cluster in resulting spheroidal fragments. The mitochondrion owns an autonomous genome. Double-stranded circular mitochondrial DNA (mtDNA) is organized in complexes with a packing/stabilizing transcription factor TFAM, having multiple roles, and proteins of gene expression machinery in structures called nucleoids. From hundreds to thousands nucleoids exist distributed in the matrix of mitochondrial reticulum network. A single mtDNA molecule contained within the single nucleoid is a currently preferred but questioned model. Nevertheless, mtDNA replication should lead transiently to its doubling within a nucleoid. However, nucleoid division has not yet been documented in detail. A 3D superresolution microscopy is required to resolve nucleoid biology occurring in ∼100 nm space, having an advantage over electron microscopy tomography in resolving the particular protein components. We discuss stochastic vs. stimulated emission depletion microscopy yielding wide vs. narrow nucleoid size distribution, respectively. Nucleoid clustering into spheroids fragmented from the continuous mitochondrial network, likewise possible nucleoid attachment to the inner membrane is reviewed.