Diverse functions of homologous actin isoforms are defined by their nucleotide, rather than their amino acid sequence

Abstract

β‐ and γ‐cytoplasmic actin are nearly indistinguishable in their amino acid sequence, but are encoded by different genes that play non‐redundant biological roles. The key determinants that drive their functional distinction are unknown. Here, we tested the hypothesis that β- and γ-actin functions are defined by their nucleotide, rather than their amino acid sequence, using targeted editing of the mouse genome. Although previous studies have shown that disruption of β-actin gene critically impacts cell migration and mouse embryogenesis, we demonstrate here that generation of a mouse lacking β-actin protein by editing β-actin gene to encode γ-actin protein, and vice versa, does not affect cell migration and/or organism survival. Our data suggest that the essential in vivo function of β-actin is provided by the gene sequence independent of the encoded protein isoform. We propose that this regulation constitutes a global ‘silent code’ mechanism that controls the functional diversity of protein isoforms.

Modular actin nano-architecture enables podosome protrusion and mechanosensing

“…While the cPM primarily consists of β-actin, the pPM is mostly built up from γ-actin. Understanding the non-redundant function of actin isoforms in cytoskeletal remodeling is an area of steeply emerging interest (46)(47)(48). Although not much is known about the different functions of the two isoforms, it is generally assumed that β-actin is preferentially located to protrusive lamellipodial structures and γ-actin to stress fibers (31), something which we also observed in DCs.…”

Essential nucleotide- and protein-dependent functions ofActb/β-actin

“…We found the resulting mice, despite lacking β-actin protein, were born in Mendelian ratios and that the mice and derived fibroblasts appeared phenotypically normal. These results, together with those of a recent study using a similar approach (12) demonstrate that the nucleotide sequence is a critical determinant of actin isoformspecific function. However, we also found that β-actin protein is required to maintain the shape and function of auditory hair cells, demonstrating that other functions of cytoplasmic actins are defined by their amino acid sequences.…”

“…A recent study using clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 methodology also edited the endogenous Actb locus to express γ-actin protein (12), and the resulting mouse line is nearly identical to the one we independently generated and characterized here. Several of the same phenotypes were assessed, and very similar results were obtained.…”

“…Most notably, the Actb transcript has a 3′-UTR "zipcode" sequence not found in the Actg1 transcript that targets the transcript to subcellular regions and regulates translation (10,11). In addition, the transcripts differ in ribosome density and translation rate (12). On the protein level, purified βand γ-actin have slightly different polymerization rates and differentially interact with a subset of actin binding proteins (13,14).…”

NATure of actin amino-terminal acetylation

“…Nevertheless, experiments with the purified isoforms show these can cause differences in polymerization rates (13), and cells have clearly been able to use these differentially to carry out different functions. Recently, Kashina and coworkers (14) demonstrated that the nucleotide sequence of the two genes may play a significant factor in differential actin utilization. Whereas elimination of beta actin is lethal, these authors found that editing the beta actin gene to produce gamma actin did not cause lethality.…”