Noncoding regions of the gamma-actin gene influence the impact of the gene on myoblast morphology.

Abstract

Abstract. We have addressed the question of whether two highly conserved noncoding regions of the y-actin gene are of functional importance. Human y-actin gene constructs deleted for either the entire 3' untranslated region (UTR) and 3' flank or intron III sequences were transfected into mouse myoblasts and the resulting clones were analyzed for cell morphology and actin protein expression. Transfectants carrying the y-actin gene deleted for the 3' end (y22) exhibited numerous long pseudopods and increased surface area. In contrast, transfectants expressing the y-actin gene deleted for intron III (~/156) were rounded with blebs over the cell surface and showed decreased surface area. The relative expression of/3-to 3,-actin protein decreased for both transfectant types. The total actin protein levels remained constant for the y22 cells but decreased for the 3,156 cells. The results indicate that alterations to transfectant cell morphology can be influenced by the presence or absence of different noncoding regions in the transfected 3,-actin gene. The mechanisms by which noncoding regions of the y-actin gene influence the impact of the gene are unknown. Nevertheless, these noncoding regions are isoform specific and highly conserved in evolution. We propose that the functional significance of the different actin isoforms may involve the properties of these noncoding regions in addition to the differences in protein sequence.

Sequences responsible for intracellular localization of beta-actin messenger RNA also affect cell phenotype.

“…Cell morphology may result from the differences in where each isoform is synthesized. For instance, deletion of the 3'UTR of -y-actin results in changes in myoblast morphology (Lloyd and Gunning, 1993). Our data suggest a relationship between fl-actin mRNA localization and the disposition of actin filaments in these motile cells.…”

Actin expression in germinating seeds of Phaseolus vulgaris L.

“…High levels of regulation of actin have now been encountered at the transcriptional (Lloyd and Gunning 1993), translational and post-translational (Aktories and Wegner 1992;Howard et al 1993) levels. It remains to be determined if one or both of the main actin isoforms that increase during germination in common bean are products arising from a homolog of the ACT7 gene (McDowell et al 1996).…”

“…One of its components, actin is a ubiquitous protein that is highly regulated at various levels, including transcriptionally (Lloyd and Gunning 1993) and post-translationally (Aktories and Wegner 1992;Howard et al 1993;Jungbluth et al 1995). In addition, actin can self-assemble into micro®laments, and the equilibrium between polymeric and monomeric actin is also under tight cellular control by pH, salts, and a subset of proteins that can interact with both the polymer and the monomer (Pollard and Cooper 1986;Sheterline and Sparrow 1994).…”

Vertebrates have conserved capping protein α isoforms with specific expression patterns

“…Elements of RNA transcripts other than the coding region can contribute to the function of a gene, through effects on transcription, translation, and mRNA localization [Lloyd and Gunning, 1993]. To determine if the 3Ј untranslated region of the ␣ subunit transcripts are subject to evolutionary pressure similar to that observed for the coding region, we examined the nucleotide sequences of the 3Ј untranslated region of the ␣ subunit isoforms from chicken, mouse and human.…”