Journal Article

<i>In vivo</i> and <i>in vitro</i> effects of two novel gamma-actin (<i>ACTG1</i>) mutations that cause DFNA20/26 hearing impairment

Matías Morín, Keith E. Bryan, Fernando Mayo-Merino, Richard Goodyear, Ángeles Mencía, Silvia Modamio-Høybjør, Ignacio del Castillo, Jessica M. Cabalka, Guy Richardson, Felipe Moreno, Peter A. Rubenstein and Miguel Ángel Moreno-Pelayo

in Human Molecular Genetics

Volume 18, issue 16, pages 3075-3089
Published in print August 2009 | ISSN: 0964-6906
Published online May 2009 | e-ISSN: 1460-2083 | DOI: http://dx.doi.org/10.1093/hmg/ddp249
In vivo and in vitro effects of two novel gamma-actin (ACTG1) mutations that cause DFNA20/26 hearing impairment

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Here we report the functional assessment of two novel deafness-associated γ-actin mutants, K118N and E241K, in a spectrum of different situations with increasing biological complexity by combining biochemical and cell biological analysis in yeast and mammalian cells. Our in vivo experiments showed that while the K118N had a very mild effect on yeast behaviour, the phenotype caused by the E241K mutation was very severe and characterized by a highly compromised ability to grow on glycerol as a carbon source, an aberrant multi-vacuolar pattern and the deposition of thick F-actin bundles randomly in the cell. The latter feature is consistent with the highly unusual spontaneous tendency of the E241K mutant to form bundles in vitro, although this propensity to bundle was neutralized by tropomyosin and the E241K filament bundles were hypersensitive to severing in the presence of cofilin. In transiently transfected NIH3T3 cells both mutant actins were normally incorporated into cytoskeleton structures, although cytoplasmic aggregates were also observed indicating an element of abnormality caused by the mutations in vivo. Interestingly, gene-gun mediated expression of these mutants in cochlear hair cells results in no gross alteration in cytoskeletal structures or the morphology of stereocilia. Our results provide a more complete picture of the biological consequences of deafness-associated γ-actin mutants and support the hypothesis that the post-lingual and progressive nature of the DFNA20/26 hearing loss is the result of a progressive deterioration of the hair cell cytoskeleton over time.

Journal Article.  9443 words.  Illustrated.

Subjects: Genetics and Genomics

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