Journal Article

<i>LETM1</i>, deleted in Wolf–Hirschhorn syndrome is required for normal mitochondrial morphology and cellular viability

Kai Stefan Dimmer, Francesca Navoni, Alberto Casarin, Eva Trevisson, Sabine Endele, Andreas Winterpacht, Leonardo Salviati and Luca Scorrano

in Human Molecular Genetics

Volume 17, issue 2, pages 201-214
Published in print January 2008 | ISSN: 0964-6906
Published online October 2007 | e-ISSN: 1460-2083 | DOI: http://dx.doi.org/10.1093/hmg/ddm297
LETM1, deleted in Wolf–Hirschhorn syndrome is required for normal mitochondrial morphology and cellular viability

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Wolf–Hirschhorn syndrome (WHS) is a complex congenital syndrome caused by a monoallelic deletion of the short arm of chromosome 4. Seizures in WHS have been associated with deletion of LETM1 gene. LETM1 encodes for the human homologue of yeast Mdm38p, a mitochondria-shaping protein of unclear function. Here we show that human LETM1 is located in the inner membrane, exposed to the matrix and oligomerized in higher molecular weight complexes of unknown composition. Down-regulation of LETM1 did not disrupt these complexes, but led to DRP1-independent fragmentation of the mitochondrial network. Fragmentation was not associated with changes in the levels of respiratory chain complexes, or with obvious or latent mitochondrial dysfunction, but was recovered by nigericin, which catalyzes the electroneutral exchange of K+ against H+. Down-regulation of LETM1 caused ‘necrosis-like’ death, without activation of caspases and not inhibited by overexpression of Bcl-2. Primary fibroblasts from a WHS patient displayed reduced LETM1 mRNA and protein, but mitochondrial morphology was surprisingly unaffected, raising the question of whether and how WHS patients counteract the consequences of monoallelic deletion of LETM1. LETM1 highlights the relationship between mitochondrial ion homeostasis, integrity of the mitochondrial network and cell viability.

Journal Article.  8735 words.  Illustrated.

Subjects: Genetics and Genomics

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