Essential nucleotide- and protein-dependent functions of <i>Actb</i>/β-actin.

Abstract

The highly similar cytoplasmic β- and γ-actins differ by only four functionally similar amino acids, yet previous in vitro and in vivo data suggest that they support unique functions due to striking phenotypic differences between <i>Actb</i> and <i>Actg1</i> null mouse and cell models. To determine whether the four amino acid variances were responsible for the functional differences between cytoplasmic actins, we gene edited the endogenous mouse <i>Actb</i> locus to translate γ-actin protein. The resulting mice and primary embryonic fibroblasts completely lacked β-actin protein, but were viable and did not present with the most overt and severe cell and organismal phenotypes observed with gene knockout. Nonetheless, the edited mice exhibited progressive high-frequency hearing loss and degeneration of actin-based stereocilia as previously reported for hair cell-specific <i>Actb</i> knockout mice. Thus, β-actin protein is not required for general cellular functions, but is necessary to maintain auditory stereocilia.