RT Journal Article SR Electronic T1 The SPIRE1 actin nucleator coordinates actin/myosin functions in the regulation of mitochondrial motility JF bioRxiv FD Cold Spring Harbor Laboratory SP 2020.06.19.161109 DO 10.1101/2020.06.19.161109 A1 Felix Straub A1 Tobias Welz A1 Hannah Alberico A1 Rafael Oliveira Brandão A1 Anna Huber A1 Annette Samol-Wolf A1 Cord Brakebusch A1 Dori Woods A1 Martin Kollmar A1 Javier Martin-Gonzalez A1 Eugen Kerkhoff YR 2020 UL http://biorxiv.org/content/early/2020/06/20/2020.06.19.161109.abstract AB Subcellular localisation of mitochondria provides a spatial and temporal organisation for cellular energy demands. Long-range mitochondrial transport is mediated by microtubule tracks and associated dynein and kinesin motor proteins. The actin cytoskeleton has a more versatile role and provides transport, tethering, and anchoring functions. SPIRE actin nucleators organise actin filament networks at vesicle membranes, which serve as tracks for myosin 5 motor protein-driven transport processes. Following alternative splicing, SPIRE1 is targeted to mitochondria. In analogy to vesicular SPIRE functions, we have analysed whether SPIRE1 regulates mitochondrial motility. By tracking mitochondria of living fibroblast cells from SPIRE1 mutant mice and splice-variant specific mitochondrial SPIRE1 knockout mice, we determined that the loss of SPIRE1 function increased mitochondrial motility. The SPIRE1 mutant phenotype was reversed by transient overexpression of mitochondrial SPIRE1, which almost completely inhibited motility. Conserved myosin 5 and formin interaction motifs contributed to this inhibition. Consistently, mitochondrial SPIRE1 targeted myosin 5 motors and formin actin filament generators to mitochondria. Our results indicate that SPIRE1 organises an actin/myosin network at mitochondria, which opposes mitochondrial motility.Summary statement The mitochondrial SPIRE1 protein targets myosin 5 motor proteins and formin actin-filament nucleators/elongators towards mitochondria and negatively regulates mitochondrial motility.